// for debugging
// #define CHECK(c, s) do { if (c) emsg(s); } while (0)
#define CHECK(c, s) do {} while (0)

// memline.c: Contains the functions for appending, deleting and changing the
// text lines. The memfile functions are used to store the information in
// blocks of memory, backed up by a file. The structure of the information is
// a tree.  The root of the tree is a pointer block. The leaves of the tree
// are data blocks. In between may be several layers of pointer blocks,
// forming branches.
//
// Three types of blocks are used:
// - Block nr 0 contains information for recovery
// - Pointer blocks contain list of pointers to other blocks.
// - Data blocks contain the actual text.
//
// Block nr 0 contains the block0 structure (see below).
//
// Block nr 1 is the first pointer block. It is the root of the tree.
// Other pointer blocks are branches.
//
//  If a line is too big to fit in a single page, the block containing that
//  line is made big enough to hold the line. It may span several pages.
//  Otherwise all blocks are one page.
//
//  A data block that was filled when starting to edit a file and was not
//  changed since then, can have a negative block number. This means that it
//  has not yet been assigned a place in the file. When recovering, the lines
//  in this data block can be read from the original file. When the block is
//  changed (lines appended/deleted/changed) or when it is flushed it gets a
//  positive number. Use mf_trans_del() to get the new number, before calling
//  mf_get().
//
// "Mom, can we get ropes?"
// "We have ropes at home."
// Ropes at home:

#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdio.h>
#include <string.h>
#include <time.h>
#include <uv.h>

#include "auto/config.h"
#include "klib/kvec.h"
#include "nvim/ascii_defs.h"
#include "nvim/autocmd.h"
#include "nvim/autocmd_defs.h"
#include "nvim/buffer.h"
#include "nvim/buffer_defs.h"
#include "nvim/change.h"
#include "nvim/cursor.h"
#include "nvim/drawscreen.h"
#include "nvim/eval.h"
#include "nvim/eval/typval.h"
#include "nvim/ex_cmds_defs.h"
#include "nvim/fileio.h"
#include "nvim/getchar.h"
#include "nvim/gettext_defs.h"
#include "nvim/globals.h"
#include "nvim/highlight_defs.h"
#include "nvim/input.h"
#include "nvim/macros_defs.h"
#include "nvim/main.h"
#include "nvim/map_defs.h"
#include "nvim/mark.h"
#include "nvim/mbyte.h"
#include "nvim/memfile.h"
#include "nvim/memfile_defs.h"
#include "nvim/memline.h"
#include "nvim/memory.h"
#include "nvim/message.h"
#include "nvim/option.h"
#include "nvim/option_defs.h"
#include "nvim/option_vars.h"
#include "nvim/os/fs.h"
#include "nvim/os/fs_defs.h"
#include "nvim/os/input.h"
#include "nvim/os/os.h"
#include "nvim/os/os_defs.h"
#include "nvim/os/proc.h"
#include "nvim/os/time.h"
#include "nvim/os/time_defs.h"
#include "nvim/path.h"
#include "nvim/pos_defs.h"
#include "nvim/spell.h"
#include "nvim/statusline.h"
#include "nvim/strings.h"
#include "nvim/ui.h"
#include "nvim/undo.h"
#include "nvim/version.h"
#include "nvim/vim_defs.h"

#ifndef UNIX            // it's in os/unix_defs.h for Unix
# include <time.h>
#endif

enum {
  DATA_ID = (('d' << 8) + 'a'),  // data block id
  PTR_ID = (('p' << 8) + 't'),   // pointer block id
  BLOCK0_ID0 = 'b',              // block 0 id 0
  BLOCK0_ID1 = '0',              // block 0 id 1
};

// pointer to a block, used in a pointer block
typedef struct {
  blocknr_T pe_bnum;            // block number
  linenr_T pe_line_count;       // number of lines in this branch
  linenr_T pe_old_lnum;         // lnum for this block (for recovery)
  int pe_page_count;            // number of pages in block pe_bnum
} PointerEntry;

// A pointer block contains a list of branches in the tree.
typedef struct {
  uint16_t pb_id;               // ID for pointer block: PTR_ID
  uint16_t pb_count;            // number of pointers in this block
  uint16_t pb_count_max;        // maximum value for pb_count
  PointerEntry pb_pointer[];    // list of pointers to blocks
                                // followed by empty space until end of page
} PointerBlock;

// Value for pb_count_max.
#define PB_COUNT_MAX(mfp) \
  (uint16_t)((mfp->mf_page_size - offsetof(PointerBlock, pb_pointer)) / sizeof(PointerEntry))

// A data block is a leaf in the tree.
//
// The text of the lines is at the end of the block. The text of the first line
// in the block is put at the end, the text of the second line in front of it,
// etc. Thus the order of the lines is the opposite of the line number.
typedef struct {
  uint16_t db_id;               // ID for data block: DATA_ID
  unsigned db_free;             // free space available
  unsigned db_txt_start;        // byte where text starts
  unsigned db_txt_end;          // byte just after data block
  // linenr_T db_line_count;
  long db_line_count;           // number of lines in this block
  unsigned db_index[];          // index for start of line
                                // followed by empty space up to db_txt_start
                                // followed by the text in the lines until
                                // end of page
} DataBlock;

// The low bits of db_index hold the actual index. The topmost bit is
// used for the global command to be able to mark a line.
// This method is not clean, but otherwise there would be at least one extra
// byte used for each line.
// The mark has to be in this place to keep it with the correct line when other
// lines are inserted or deleted.
#define DB_MARKED       ((unsigned)1 << ((sizeof(unsigned) * 8) - 1))
#define DB_INDEX_MASK   (~DB_MARKED)

#define INDEX_SIZE  (sizeof(unsigned))      // size of one db_index entry
#define HEADER_SIZE (offsetof(DataBlock, db_index))  // size of data block header

enum {
  B0_FNAME_SIZE_ORG = 900,      // what it was in older versions
  B0_FNAME_SIZE_NOCRYPT = 898,  // 2 bytes used for other things
  B0_FNAME_SIZE_CRYPT = 890,    // 10 bytes used for other things
  B0_UNAME_SIZE = 40,
  B0_HNAME_SIZE = 40,
};
// Restrict the numbers to 32 bits, otherwise most compilers will complain.
// This won't detect a 64 bit machine that only swaps a byte in the top 32
// bits, but that is crazy anyway.
enum {
  B0_MAGIC_LONG = 0x30313233,
  B0_MAGIC_INT = 0x20212223,
  B0_MAGIC_SHORT = 0x10111213,
  B0_MAGIC_CHAR = 0x55,
};

/// Block zero holds all info about the swapfile. This is the first block in the file.
///
/// NOTE: DEFINITION OF BLOCK 0 SHOULD NOT CHANGE! It would make all existing swapfiles unusable!
///
/// If size of block0 changes anyway, adjust MIN_SWAP_PAGE_SIZE in memfile.h!!
///
/// This block is built up of single bytes, to make it portable across
/// different machines. b0_magic_* is used to check the byte order and size of
/// variables, because the rest of the swapfile is not portable.
typedef struct {
  char b0_id[2];                     ///< ID for block 0: BLOCK0_ID0 and BLOCK0_ID1.
  char b0_version[10];               ///< Vim version string
  char b0_page_size[4];              ///< number of bytes per page
  char b0_mtime[4];                  ///< last modification time of file
  char b0_ino[4];                    ///< inode of b0_fname
  char b0_pid[4];                    ///< process id of creator (or 0)
  char b0_uname[B0_UNAME_SIZE];      ///< name of user (uid if no name)
  char b0_hname[B0_HNAME_SIZE];      ///< host name (if it has a name)
  char b0_fname[B0_FNAME_SIZE_ORG];  ///< name of file being edited
  long b0_magic_long;                ///< check for byte order of long
  int b0_magic_int;                  ///< check for byte order of int
  int16_t b0_magic_short;            ///< check for byte order of short
  char b0_magic_char;                ///< check for last char
} ZeroBlock;

// Note: b0_dirty and b0_flags are put at the end of the file name.  For very
// long file names in older versions of Vim they are invalid.
// The 'fileencoding' comes before b0_flags, with a NUL in front.  But only
// when there is room, for very long file names it's omitted.
#define B0_DIRTY        0x55
#define b0_dirty        b0_fname[B0_FNAME_SIZE_ORG - 1]

// The b0_flags field is new in Vim 7.0.
#define b0_flags        b0_fname[B0_FNAME_SIZE_ORG - 2]

// The lowest two bits contain the fileformat.  Zero means it's not set
// (compatible with Vim 6.x), otherwise it's EOL_UNIX + 1, EOL_DOS + 1 or
// EOL_MAC + 1.
#define B0_FF_MASK      3

// Swapfile is in directory of edited file.  Used to find the file from different mount points.
#define B0_SAME_DIR     4

// The 'fileencoding' is at the end of b0_fname[], with a NUL in front of it.
// When empty there is only the NUL.
#define B0_HAS_FENC     8

#define STACK_INCR      5       // nr of entries added to ml_stack at a time

// The line number where the first mark may be is remembered.
// If it is 0 there are no marks at all.
// (always used for the current buffer only, no buffer change possible while
// executing a global command).
static linenr_T lowest_marked = 0;

// arguments for ml_find_line()
enum {
  ML_DELETE = 0x11,  // delete line
  ML_INSERT = 0x12,  // insert line
  ML_FIND = 0x13,    // just find the line
  ML_FLUSH = 0x02,   // flush locked block
};
#define ML_SIMPLE(x)    ((x) & 0x10)  // DEL, INS or FIND

// argument for ml_upd_block0()
typedef enum {
  UB_FNAME = 0,         // update timestamp and filename
  UB_SAME_DIR,  // update the B0_SAME_DIR flag
} upd_block0_T;

typedef enum {
  SEA_CHOICE_NONE = 0,
  SEA_CHOICE_READONLY = 1,
  SEA_CHOICE_EDIT = 2,
  SEA_CHOICE_RECOVER = 3,
  SEA_CHOICE_DELETE = 4,
  SEA_CHOICE_QUIT = 5,
  SEA_CHOICE_ABORT = 6,
} sea_choice_T;

#ifdef INCLUDE_GENERATED_DECLARATIONS
# include "memline.c.generated.h"
#endif

static const char e_ml_get_invalid_lnum_nr[]
  = N_("E315: ml_get: Invalid lnum: %" PRId64);
static const char e_ml_get_cannot_find_line_nr_in_buffer_nr_str[]
  = N_("E316: ml_get: Cannot find line %" PRId64 "in buffer %d %s");
static const char e_pointer_block_id_wrong[]
  = N_("E317: Pointer block id wrong");
static const char e_pointer_block_id_wrong_two[]
  = N_("E317: Pointer block id wrong 2");
static const char e_pointer_block_id_wrong_three[]
  = N_("E317: Pointer block id wrong 3");
static const char e_pointer_block_id_wrong_four[]
  = N_("E317: Pointer block id wrong 4");
static const char e_line_number_out_of_range_nr_past_the_end[]
  = N_("E322: Line number out of range: %" PRId64 " past the end");
static const char e_line_count_wrong_in_block_nr[]
  = N_("E323: Line count wrong in block %" PRId64);
static const char e_warning_pointer_block_corrupted[]
  = N_("E1364: Warning: Pointer block corrupted");

#if __has_feature(address_sanitizer)
# define ML_GET_ALLOC_LINES
#endif

/// Open a new memline for "buf".
///
/// @return  FAIL for failure, OK otherwise.
int ml_open(buf_T *buf)
{
  // init fields in memline struct
  buf->b_ml.ml_stack_size = 0;   // no stack yet
  buf->b_ml.ml_stack = NULL;    // no stack yet
  buf->b_ml.ml_stack_top = 0;   // nothing in the stack
  buf->b_ml.ml_locked = NULL;   // no cached block
  buf->b_ml.ml_line_lnum = 0;   // no cached line
  buf->b_ml.ml_line_offset = 0;
  buf->b_ml.ml_chunksize = NULL;
  buf->b_ml.ml_usedchunks = 0;

  if (cmdmod.cmod_flags & CMOD_NOSWAPFILE) {
    buf->b_p_swf = false;
  }

  // When 'updatecount' is non-zero swapfile may be opened later.
  if (!buf->terminal && p_uc && buf->b_p_swf) {
    buf->b_may_swap = true;
  } else {
    buf->b_may_swap = false;
  }

  // Open the memfile.  No swapfile is created yet.
  memfile_T *mfp = mf_open(NULL, 0);
  if (mfp == NULL) {
    goto error;
  }

  buf->b_ml.ml_mfp = mfp;
  buf->b_ml.ml_flags = ML_EMPTY;
  buf->b_ml.ml_line_count = 1;

  // fill block0 struct and write page 0
  bhdr_T *hp = mf_new(mfp, false, 1);
  if (hp->bh_bnum != 0) {
    iemsg(_("E298: Didn't get block nr 0?"));
    goto error;
  }
  ZeroBlock *b0p = hp->bh_data;

  b0p->b0_id[0] = BLOCK0_ID0;
  b0p->b0_id[1] = BLOCK0_ID1;
  b0p->b0_magic_long = B0_MAGIC_LONG;
  b0p->b0_magic_int = B0_MAGIC_INT;
  b0p->b0_magic_short = (int16_t)B0_MAGIC_SHORT;
  b0p->b0_magic_char = B0_MAGIC_CHAR;
  xstrlcpy(xstpcpy(b0p->b0_version, "VIM "), Version, 6);
  long_to_char((long)mfp->mf_page_size, b0p->b0_page_size);

  if (!buf->b_spell) {
    b0p->b0_dirty = buf->b_changed ? B0_DIRTY : 0;
    b0p->b0_flags = (char)(get_fileformat(buf) + 1);
    set_b0_fname(b0p, buf);
    os_get_username(b0p->b0_uname, B0_UNAME_SIZE);
    b0p->b0_uname[B0_UNAME_SIZE - 1] = NUL;
    os_get_hostname(b0p->b0_hname, B0_HNAME_SIZE);
    b0p->b0_hname[B0_HNAME_SIZE - 1] = NUL;
    long_to_char((long)os_get_pid(), b0p->b0_pid);
  }

  // Always sync block number 0 to disk, so we can check the file name in
  // the swapfile in findswapname(). Don't do this for a help files or
  // a spell buffer though.
  // Only works when there's a swapfile, otherwise it's done when the file
  // is created.
  mf_put(mfp, hp, true, false);
  if (!buf->b_help && !buf->b_spell) {
    mf_sync(mfp, 0);
  }

  // Fill in root pointer block and write page 1.
  hp = ml_new_ptr(mfp);
  assert(hp != NULL);
  if (hp->bh_bnum != 1) {
    iemsg(_("E298: Didn't get block nr 1?"));
    goto error;
  }
  PointerBlock *pp = hp->bh_data;
  pp->pb_count = 1;
  pp->pb_pointer[0].pe_bnum = 2;
  pp->pb_pointer[0].pe_page_count = 1;
  pp->pb_pointer[0].pe_old_lnum = 1;
  pp->pb_pointer[0].pe_line_count = 1;      // line count after insertion
  mf_put(mfp, hp, true, false);

  // Allocate first data block and create an empty line 1.
  hp = ml_new_data(mfp, false, 1);
  if (hp->bh_bnum != 2) {
    iemsg(_("E298: Didn't get block nr 2?"));
    goto error;
  }

  DataBlock *dp = hp->bh_data;
  dp->db_index[0] = --dp->db_txt_start;         // at end of block
  dp->db_free -= 1 + (unsigned)INDEX_SIZE;
  dp->db_line_count = 1;
  *((char *)dp + dp->db_txt_start) = NUL;     // empty line

  return OK;

error:
  if (mfp != NULL) {
    if (hp) {
      mf_put(mfp, hp, false, false);
    }
    mf_close(mfp, true);  // will also xfree(mfp->mf_fname)
  }
  buf->b_ml.ml_mfp = NULL;
  return FAIL;
}

/// ml_setname() is called when the file name of "buf" has been changed.
/// It may rename the swapfile.
void ml_setname(buf_T *buf)
{
  bool success = false;

  memfile_T *mfp = buf->b_ml.ml_mfp;
  if (mfp->mf_fd < 0) {             // there is no swapfile yet
    // When 'updatecount' is 0 and 'noswapfile' there is no swapfile.
    // For help files we will make a swapfile now.
    if (p_uc != 0 && (cmdmod.cmod_flags & CMOD_NOSWAPFILE) == 0) {
      ml_open_file(buf);  // create a swapfile
    }
    return;
  }

  // Try all directories in the 'directory' option.
  char *dirp = p_dir;
  bool found_existing_dir = false;
  while (true) {
    if (*dirp == NUL) {             // tried all directories, fail
      break;
    }
    char *fname = findswapname(buf, &dirp, mfp->mf_fname, &found_existing_dir);
    // alloc's fname
    if (dirp == NULL) {             // out of memory
      break;
    }
    if (fname == NULL) {            // no file name found for this dir
      continue;
    }

    // if the file name is the same we don't have to do anything
    if (path_fnamecmp(fname, mfp->mf_fname) == 0) {
      xfree(fname);
      success = true;
      break;
    }
    // need to close the swapfile before renaming
    if (mfp->mf_fd >= 0) {
      close(mfp->mf_fd);
      mfp->mf_fd = -1;
    }

    // try to rename the swapfile
    if (vim_rename(mfp->mf_fname, fname) == 0) {
      success = true;
      mf_free_fnames(mfp);
      mf_set_fnames(mfp, fname);
      ml_upd_block0(buf, UB_SAME_DIR);
      break;
    }
    xfree(fname);                // this fname didn't work, try another
  }

  if (mfp->mf_fd == -1) {           // need to (re)open the swapfile
    mfp->mf_fd = os_open(mfp->mf_fname, O_RDWR, 0);
    if (mfp->mf_fd < 0) {
      // could not (re)open the swapfile, what can we do????
      emsg(_("E301: Oops, lost the swap file!!!"));
      return;
    }
    os_set_cloexec(mfp->mf_fd);
  }
  if (!success) {
    emsg(_("E302: Could not rename swap file"));
  }
}

/// Open a file for the memfile for all buffers that are not readonly or have
/// been modified.
/// Used when 'updatecount' changes from zero to non-zero.
void ml_open_files(void)
{
  FOR_ALL_BUFFERS(buf) {
    if (!buf->b_p_ro || buf->b_changed) {
      ml_open_file(buf);
    }
  }
}

/// Open a swapfile for an existing memfile, if there is no swapfile yet.
/// If we are unable to find a file name, mf_fname will be NULL
/// and the memfile will be in memory only (no recovery possible).
void ml_open_file(buf_T *buf)
{
  memfile_T *mfp = buf->b_ml.ml_mfp;
  if (mfp == NULL || mfp->mf_fd >= 0 || !buf->b_p_swf
      || (cmdmod.cmod_flags & CMOD_NOSWAPFILE)
      || buf->terminal) {
    return;  // nothing to do
  }

  // For a spell buffer use a temp file name.
  if (buf->b_spell) {
    char *fname = vim_tempname();
    if (fname != NULL) {
      mf_open_file(mfp, fname);           // consumes fname!
    }
    buf->b_may_swap = false;
    return;
  }

  // Try all directories in 'directory' option.
  char *dirp = p_dir;
  bool found_existing_dir = false;
  while (true) {
    if (*dirp == NUL) {
      break;
    }
    // There is a small chance that between choosing the swapfile name
    // and creating it, another Vim creates the file.  In that case the
    // creation will fail and we will use another directory.
    char *fname = findswapname(buf, &dirp, NULL, &found_existing_dir);
    if (dirp == NULL) {
      break;        // out of memory
    }
    if (fname == NULL) {
      continue;
    }
    if (mf_open_file(mfp, fname) == OK) {       // consumes fname!
      // don't sync yet in ml_sync_all()
      mfp->mf_dirty = MF_DIRTY_YES_NOSYNC;
      ml_upd_block0(buf, UB_SAME_DIR);

      // Flush block zero, so others can read it
      if (mf_sync(mfp, MFS_ZERO) == OK) {
        // Mark all blocks that should be in the swapfile as dirty.
        // Needed for when the 'swapfile' option was reset, so that
        // the swapfile was deleted, and then on again.
        mf_set_dirty(mfp);
        break;
      }
      // Writing block 0 failed: close the file and try another dir
      mf_close_file(buf, false);
    }
  }

  if (*p_dir != NUL && mfp->mf_fname == NULL) {
    need_wait_return = true;  // call wait_return() later
    no_wait_return++;
    semsg(_("E303: Unable to open swap file for \"%s\", recovery impossible"),
          buf_spname(buf) != NULL ? buf_spname(buf) : buf->b_fname);
    no_wait_return--;
  }

  // don't try to open a swapfile again
  buf->b_may_swap = false;
}

/// If still need to create a swapfile, and starting to edit a not-readonly
/// file, or reading into an existing buffer, create a swapfile now.
///
/// @param newfile reading file into new buffer
void check_need_swap(bool newfile)
{
  int old_msg_silent = msg_silent;  // might be reset by an E325 message
  msg_silent = 0;  // If swap dialog prompts for input, user needs to see it!

  if (curbuf->b_may_swap && (!curbuf->b_p_ro || !newfile)) {
    ml_open_file(curbuf);
  }

  msg_silent = old_msg_silent;
}

/// Close memline for buffer 'buf'.
///
/// @param del_file  if true, delete the swapfile
void ml_close(buf_T *buf, int del_file)
{
  if (buf->b_ml.ml_mfp == NULL) {               // not open
    return;
  }
  mf_close(buf->b_ml.ml_mfp, del_file);       // close the .swp file
  if (buf->b_ml.ml_line_lnum != 0
      && (buf->b_ml.ml_flags & (ML_LINE_DIRTY | ML_ALLOCATED))) {
    xfree(buf->b_ml.ml_line_ptr);
  }
  xfree(buf->b_ml.ml_stack);
  XFREE_CLEAR(buf->b_ml.ml_chunksize);
  buf->b_ml.ml_mfp = NULL;

  // Reset the "recovered" flag, give the ATTENTION prompt the next time
  // this buffer is loaded.
  buf->b_flags &= ~BF_RECOVERED;
}

/// Close all existing memlines and memfiles.
/// Only used when exiting.
///
/// @param del_file  if true, delete the memfiles.
void ml_close_all(bool del_file)
{
  FOR_ALL_BUFFERS(buf) {
    ml_close(buf, del_file);
  }
  spell_delete_wordlist();      // delete the internal wordlist
  vim_deltempdir();             // delete created temp directory
}

/// Close all memfiles for not modified buffers.
/// Only use just before exiting!
void ml_close_notmod(void)
{
  FOR_ALL_BUFFERS(buf) {
    if (!bufIsChanged(buf)) {
      ml_close(buf, true);          // close all not-modified buffers
    }
  }
}

/// Update the timestamp in the .swp file.
/// Used when the file has been written.
void ml_timestamp(buf_T *buf)
{
  ml_upd_block0(buf, UB_FNAME);
}

/// Checks whether the IDs in b0 are valid.
static bool ml_check_b0_id(ZeroBlock *b0p)
  FUNC_ATTR_NONNULL_ALL
{
  return b0p->b0_id[0] == BLOCK0_ID0 && b0p->b0_id[1] == BLOCK0_ID1;
}

/// Checks whether all strings in b0 are valid (i.e. nul-terminated).
static bool ml_check_b0_strings(ZeroBlock *b0p)
  FUNC_ATTR_NONNULL_ALL
{
  return (memchr(b0p->b0_version, NUL, 10)
          && memchr(b0p->b0_uname, NUL, B0_UNAME_SIZE)
          && memchr(b0p->b0_hname, NUL, B0_HNAME_SIZE)
          && memchr(b0p->b0_fname, NUL, B0_FNAME_SIZE_CRYPT));
}

/// Update the timestamp or the B0_SAME_DIR flag of the .swp file.
static void ml_upd_block0(buf_T *buf, upd_block0_T what)
{
  bhdr_T *hp;

  memfile_T *mfp = buf->b_ml.ml_mfp;
  if (mfp == NULL || (hp = mf_get(mfp, 0, 1)) == NULL) {
    return;
  }
  ZeroBlock *b0p = hp->bh_data;
  if (ml_check_b0_id(b0p) == FAIL) {
    iemsg(_("E304: ml_upd_block0(): Didn't get block 0??"));
  } else {
    if (what == UB_FNAME) {
      set_b0_fname(b0p, buf);
    } else {    // what == UB_SAME_DIR
      set_b0_dir_flag(b0p, buf);
    }
  }
  mf_put(mfp, hp, true, false);
}

/// Write file name and timestamp into block 0 of a swapfile.
/// Also set buf->b_mtime.
/// Don't use NameBuff[]!!!
static void set_b0_fname(ZeroBlock *b0p, buf_T *buf)
{
  if (buf->b_ffname == NULL) {
    b0p->b0_fname[0] = NUL;
  } else {
    char uname[B0_UNAME_SIZE];

    // For a file under the home directory of the current user, we try to
    // replace the home directory path with "~user". This helps when
    // editing the same file on different machines over a network.
    // First replace home dir path with "~/" with home_replace().
    // Then insert the user name to get "~user/".
    home_replace(NULL, buf->b_ffname, b0p->b0_fname,
                 B0_FNAME_SIZE_CRYPT, true);
    if (b0p->b0_fname[0] == '~') {
      // If there is no user name or it is too long, don't use "~/"
      int retval = os_get_username(uname, B0_UNAME_SIZE);
      size_t ulen = strlen(uname);
      size_t flen = strlen(b0p->b0_fname);
      if (retval == FAIL || ulen + flen > B0_FNAME_SIZE_CRYPT - 1) {
        xstrlcpy(b0p->b0_fname, buf->b_ffname, B0_FNAME_SIZE_CRYPT);
      } else {
        memmove(b0p->b0_fname + ulen + 1, b0p->b0_fname + 1, flen);
        memmove(b0p->b0_fname + 1, uname, ulen);
      }
    }
    FileInfo file_info;
    if (os_fileinfo(buf->b_ffname, &file_info)) {
      long_to_char(file_info.stat.st_mtim.tv_sec, b0p->b0_mtime);
      long_to_char((long)os_fileinfo_inode(&file_info), b0p->b0_ino);
      buf_store_file_info(buf, &file_info);
      buf->b_mtime_read = buf->b_mtime;
      buf->b_mtime_read_ns = buf->b_mtime_ns;
    } else {
      long_to_char(0, b0p->b0_mtime);
      long_to_char(0, b0p->b0_ino);
      buf->b_mtime = 0;
      buf->b_mtime_ns = 0;
      buf->b_mtime_read = 0;
      buf->b_mtime_read_ns = 0;
      buf->b_orig_size = 0;
      buf->b_orig_mode = 0;
    }
  }

  // Also add the 'fileencoding' if there is room.
  add_b0_fenc(b0p, curbuf);
}

/// Update the B0_SAME_DIR flag of the swapfile.  It's set if the file and the
/// swapfile for "buf" are in the same directory.
/// This is fail safe: if we are not sure the directories are equal the flag is
/// not set.
static void set_b0_dir_flag(ZeroBlock *b0p, buf_T *buf)
{
  if (same_directory(buf->b_ml.ml_mfp->mf_fname, buf->b_ffname)) {
    b0p->b0_flags |= B0_SAME_DIR;
  } else {
    b0p->b0_flags = (char)(b0p->b0_flags & ~B0_SAME_DIR);
  }
}

/// When there is room, add the 'fileencoding' to block zero.
static void add_b0_fenc(ZeroBlock *b0p, buf_T *buf)
{
  const int size = B0_FNAME_SIZE_NOCRYPT;

  int n = (int)strlen(buf->b_p_fenc);
  if ((int)strlen(b0p->b0_fname) + n + 1 > size) {
    b0p->b0_flags = (char)(b0p->b0_flags & ~B0_HAS_FENC);
  } else {
    memmove(b0p->b0_fname + size - n,
            buf->b_p_fenc, (size_t)n);
    *(b0p->b0_fname + size - n - 1) = NUL;
    b0p->b0_flags |= B0_HAS_FENC;
  }
}

/// Returns the PID of the process that owns the swapfile, if it is running.
///
/// @param b0p swapfile data
/// @param swap_fname Name of the swapfile. If it's from before a reboot, the result is 0.
///
/// @return PID, or 0 if process is not running or the swapfile is from before a reboot.
static int swapfile_proc_running(const ZeroBlock *b0p, const char *swap_fname)
{
  FileInfo st;
  double uptime;
  // If the system rebooted after when the swapfile was written then the
  // process can't be running now.
  if (os_fileinfo(swap_fname, &st)
      && uv_uptime(&uptime) == 0
      && (Timestamp)st.stat.st_mtim.tv_sec < os_time() - (Timestamp)uptime) {
    return 0;
  }
  int pid = (int)char_to_long(b0p->b0_pid);
  return os_proc_running(pid) ? pid : 0;
}

/// Try to recover curbuf from the .swp file.
///
/// @param checkext  if true, check the extension and detect whether it is a swapfile.
void ml_recover(bool checkext)
{
  buf_T *buf = NULL;
  memfile_T *mfp = NULL;
  char *fname_used = NULL;
  bhdr_T *hp = NULL;
  char *b0_fenc = NULL;
  infoptr_T *ip;
  bool directly;
  bool serious_error = true;
  int orig_file_status = NOTDONE;

  recoverymode = true;
  int called_from_main = (curbuf->b_ml.ml_mfp == NULL);

  // If the file name ends in ".s[a-w][a-z]" we assume this is the swapfile.
  // Otherwise a search is done to find the swapfile(s).
  char *fname = curbuf->b_fname;
  if (fname == NULL) {              // When there is no file name
    fname = "";
  }
  int len = (int)strlen(fname);
  if (checkext && len >= 4
      && STRNICMP(fname + len - 4, ".s", 2) == 0
      && vim_strchr("abcdefghijklmnopqrstuvw", TOLOWER_ASC((uint8_t)fname[len - 2])) != NULL
      && ASCII_ISALPHA(fname[len - 1])) {
    directly = true;
    fname_used = xstrdup(fname);     // make a copy for mf_open()
  } else {
    directly = false;

    // count the number of matching swapfiles
    len = recover_names(fname, false, NULL, 0, NULL);
    if (len == 0) {                 // no swapfiles found
      semsg(_("E305: No swap file found for %s"), fname);
      goto theend;
    }
    int i;
    if (len == 1) {  // one swapfile found, use it
      i = 1;
    } else {  // several swapfiles found, choose
      // list the names of the swapfiles
      recover_names(fname, true, NULL, 0, NULL);
      msg_putchar('\n');
      i = prompt_for_input(_("Enter number of swap file to use (0 to quit): "), 0, false, NULL);
      if (i < 1 || i > len) {
        goto theend;
      }
    }
    // get the swapfile name that will be used
    recover_names(fname, false, NULL, i, &fname_used);
  }
  if (fname_used == NULL) {
    goto theend;  // user chose invalid number.
  }
  // When called from main() still need to initialize storage structure
  if (called_from_main && ml_open(curbuf) == FAIL) {
    getout(1);
  }

  // Allocate a buffer structure for the swapfile that is used for recovery.
  // Only the memline in it is really used.
  buf = xmalloc(sizeof(buf_T));

  // init fields in memline struct
  buf->b_ml.ml_stack_size = 0;          // no stack yet
  buf->b_ml.ml_stack = NULL;            // no stack yet
  buf->b_ml.ml_stack_top = 0;           // nothing in the stack
  buf->b_ml.ml_line_lnum = 0;           // no cached line
  buf->b_ml.ml_line_offset = 0;
  buf->b_ml.ml_locked = NULL;           // no locked block
  buf->b_ml.ml_flags = 0;

  // open the memfile from the old swapfile
  char *p = xstrdup(fname_used);  // save "fname_used" for the message:
  // mf_open() will consume "fname_used"!
  mfp = mf_open(fname_used, O_RDONLY);
  fname_used = p;
  if (mfp == NULL || mfp->mf_fd < 0) {
    semsg(_("E306: Cannot open %s"), fname_used);
    goto theend;
  }
  buf->b_ml.ml_mfp = mfp;

  // The page size set in mf_open() might be different from the page size
  // used in the swapfile, we must get it from block 0.  But to read block
  // 0 we need a page size.  Use the minimal size for block 0 here, it will
  // be set to the real value below.
  mfp->mf_page_size = MIN_SWAP_PAGE_SIZE;

  int hl_id = HLF_E;
  // try to read block 0
  if ((hp = mf_get(mfp, 0, 1)) == NULL) {
    msg_start();
    msg_puts_hl(_("Unable to read block 0 from "), hl_id, true);
    msg_outtrans(mfp->mf_fname, hl_id, true);
    msg_puts_hl(_("\nMaybe no changes were made or Nvim did not update the swap file."), hl_id,
                true);
    msg_end();
    goto theend;
  }
  ZeroBlock *b0p = hp->bh_data;
  if (strncmp(b0p->b0_version, "VIM 3.0", 7) == 0) {
    msg_start();
    msg_outtrans(mfp->mf_fname, 0, true);
    msg_puts_hl(_(" cannot be used with this version of Nvim.\n"), 0, true);
    msg_puts_hl(_("Use Vim version 3.0.\n"), 0, true);
    msg_end();
    goto theend;
  }
  if (ml_check_b0_id(b0p) == FAIL) {
    semsg(_("E307: %s does not look like a Nvim swap file"), mfp->mf_fname);
    goto theend;
  }
  if (b0_magic_wrong(b0p)) {
    msg_start();
    msg_outtrans(mfp->mf_fname, hl_id, true);
    msg_puts_hl(_(" cannot be used on this computer.\n"), hl_id, true);
    msg_puts_hl(_("The file was created on "), hl_id, true);
    // avoid going past the end of a corrupted hostname
    b0p->b0_fname[0] = NUL;
    msg_puts_hl(b0p->b0_hname, hl_id, true);
    msg_puts_hl(_(",\nor the file has been damaged."), hl_id, true);
    msg_end();
    goto theend;
  }

  // If we guessed the wrong page size, we have to recalculate the
  // highest block number in the file.
  if (mfp->mf_page_size != (unsigned)char_to_long(b0p->b0_page_size)) {
    unsigned previous_page_size = mfp->mf_page_size;

    mf_new_page_size(mfp, (unsigned)char_to_long(b0p->b0_page_size));
    if (mfp->mf_page_size < previous_page_size) {
      msg_start();
      msg_outtrans(mfp->mf_fname, hl_id, true);
      msg_puts_hl(_(" has been damaged (page size is smaller than minimum value).\n"), hl_id, true);
      msg_end();
      goto theend;
    }
    off_T size = vim_lseek(mfp->mf_fd, 0, SEEK_END);
    // 0 means no file or empty file
    mfp->mf_blocknr_max = size <= 0 ? 0 : size / mfp->mf_page_size;
    mfp->mf_infile_count = mfp->mf_blocknr_max;

    // need to reallocate the memory used to store the data
    p = xmalloc(mfp->mf_page_size);
    memmove(p, hp->bh_data, previous_page_size);
    xfree(hp->bh_data);
    hp->bh_data = p;
    b0p = hp->bh_data;
  }

  // If .swp file name given directly, use name from swapfile for buffer.
  if (directly) {
    expand_env(b0p->b0_fname, NameBuff, MAXPATHL);
    if (setfname(curbuf, NameBuff, NULL, true) == FAIL) {
      goto theend;
    }
  }

  home_replace(NULL, mfp->mf_fname, NameBuff, MAXPATHL, true);
  smsg(0, _("Using swap file \"%s\""), NameBuff);

  if (buf_spname(curbuf) != NULL) {
    xstrlcpy(NameBuff, buf_spname(curbuf), MAXPATHL);
  } else {
    home_replace(NULL, curbuf->b_ffname, NameBuff, MAXPATHL, true);
  }
  smsg(0, _("Original file \"%s\""), NameBuff);
  msg_putchar('\n');

  // check date of swapfile and original file
  FileInfo org_file_info;
  FileInfo swp_file_info;
  int mtime = (int)char_to_long(b0p->b0_mtime);
  if (curbuf->b_ffname != NULL
      && os_fileinfo(curbuf->b_ffname, &org_file_info)
      && ((os_fileinfo(mfp->mf_fname, &swp_file_info)
           && org_file_info.stat.st_mtim.tv_sec
           > swp_file_info.stat.st_mtim.tv_sec)
          || org_file_info.stat.st_mtim.tv_sec != mtime)) {
    emsg(_("E308: Warning: Original file may have been changed"));
  }
  ui_flush();

  // Get the 'fileformat' and 'fileencoding' from block zero.
  int b0_ff = (b0p->b0_flags & B0_FF_MASK);
  if (b0p->b0_flags & B0_HAS_FENC) {
    int fnsize = B0_FNAME_SIZE_NOCRYPT;

    for (p = b0p->b0_fname + fnsize; p > b0p->b0_fname && p[-1] != NUL; p--) {}
    b0_fenc = xstrnsave(p, (size_t)(b0p->b0_fname + fnsize - p));
  }

  mf_put(mfp, hp, false, false);        // release block 0
  hp = NULL;

  // Now that we are sure that the file is going to be recovered, clear the
  // contents of the current buffer.
  while (!(curbuf->b_ml.ml_flags & ML_EMPTY)) {
    ml_delete(1);
  }

  // Try reading the original file to obtain the values of 'fileformat',
  // 'fileencoding', etc.  Ignore errors.  The text itself is not used.
  if (curbuf->b_ffname != NULL) {
    orig_file_status = readfile(curbuf->b_ffname, NULL, 0,
                                0, MAXLNUM, NULL, READ_NEW, false);
  }

  // Use the 'fileformat' and 'fileencoding' as stored in the swapfile.
  if (b0_ff != 0) {
    set_fileformat(b0_ff - 1, OPT_LOCAL);
  }
  if (b0_fenc != NULL) {
    set_option_value_give_err(kOptFileencoding, CSTR_AS_OPTVAL(b0_fenc), OPT_LOCAL);
    xfree(b0_fenc);
  }
  unchanged(curbuf, true, true);

  blocknr_T bnum = 1;       // start with block 1
  unsigned page_count = 1;  // which is 1 page
  linenr_T lnum = 0;        // append after line 0 in curbuf
  linenr_T line_count = 0;
  int idx = 0;              // start with first index in block 1
  int error = 0;
  buf->b_ml.ml_stack_top = 0;
  buf->b_ml.ml_stack = NULL;
  buf->b_ml.ml_stack_size = 0;

  bool cannot_open = (curbuf->b_ffname == NULL);

  serious_error = false;
  for (; !got_int; line_breakcheck()) {
    if (hp != NULL) {
      mf_put(mfp, hp, false, false);            // release previous block
    }
    // get block
    if ((hp = mf_get(mfp, bnum, page_count)) == NULL) {
      if (bnum == 1) {
        semsg(_("E309: Unable to read block 1 from %s"), mfp->mf_fname);
        goto theend;
      }
      error++;
      ml_append(lnum++, _("???MANY LINES MISSING"), 0, true);
    } else {          // there is a block
      PointerBlock *pp = hp->bh_data;
      if (pp->pb_id == PTR_ID) {                // it is a pointer block
        bool ptr_block_error = false;
        if (pp->pb_count_max != PB_COUNT_MAX(mfp)) {
          ptr_block_error = true;
          pp->pb_count_max = PB_COUNT_MAX(mfp);
        }
        if (pp->pb_count > pp->pb_count_max) {
          ptr_block_error = true;
          pp->pb_count = pp->pb_count_max;
        }
        if (ptr_block_error) {
          emsg(_(e_warning_pointer_block_corrupted));
        }

        // check line count when using pointer block first time
        if (idx == 0 && line_count != 0) {
          for (int i = 0; i < (int)pp->pb_count; i++) {
            line_count -= pp->pb_pointer[i].pe_line_count;
          }
          if (line_count != 0) {
            error++;
            ml_append(lnum++, _("???LINE COUNT WRONG"), 0, true);
          }
        }

        if (pp->pb_count == 0) {
          ml_append(lnum++, _("???EMPTY BLOCK"), 0, true);
          error++;
        } else if (idx < (int)pp->pb_count) {         // go a block deeper
          if (pp->pb_pointer[idx].pe_bnum < 0) {
            // Data block with negative block number.
            // Try to read lines from the original file.
            // This is slow, but it works.
            if (!cannot_open) {
              line_count = pp->pb_pointer[idx].pe_line_count;
              if (readfile(curbuf->b_ffname, NULL, lnum,
                           pp->pb_pointer[idx].pe_old_lnum - 1, line_count,
                           NULL, 0, false) != OK) {
                cannot_open = true;
              } else {
                lnum += line_count;
              }
            }
            if (cannot_open) {
              error++;
              ml_append(lnum++, _("???LINES MISSING"), 0, true);
            }
            idx++;                  // get same block again for next index
            continue;
          }

          // going one block deeper in the tree
          int top = ml_add_stack(buf);  // new entry in stack
          ip = &(buf->b_ml.ml_stack[top]);
          ip->ip_bnum = bnum;
          ip->ip_index = idx;

          bnum = pp->pb_pointer[idx].pe_bnum;
          line_count = pp->pb_pointer[idx].pe_line_count;
          page_count = (unsigned)pp->pb_pointer[idx].pe_page_count;
          idx = 0;
          continue;
        }
      } else {            // not a pointer block
        DataBlock *dp = hp->bh_data;
        if (dp->db_id != DATA_ID) {             // block id wrong
          if (bnum == 1) {
            semsg(_("E310: Block 1 ID wrong (%s not a .swp file?)"),
                  mfp->mf_fname);
            goto theend;
          }
          error++;
          ml_append(lnum++, _("???BLOCK MISSING"), 0, true);
        } else {
          // It is a data block.
          // Append all the lines in this block.
          bool has_error = false;

          // Check the length of the block.
          // If wrong, use the length given in the pointer block.
          if (page_count * mfp->mf_page_size != dp->db_txt_end) {
            ml_append(lnum++,
                      _("??? from here until ???END lines" " may be messed up"),
                      0, true);
            error++;
            has_error = true;
            dp->db_txt_end = page_count * mfp->mf_page_size;
          }

          // Make sure there is a NUL at the end of the block so we
          // don't go over the end when copying text.
          *((char *)dp + dp->db_txt_end - 1) = NUL;

          // Check the number of lines in the block.
          // If wrong, use the count in the data block.
          if (line_count != dp->db_line_count) {
            ml_append(lnum++,
                      _("??? from here until ???END lines"
                        " may have been inserted/deleted"),
                      0, true);
            error++;
            has_error = true;
          }

          bool did_questions = false;
          for (int i = 0; i < dp->db_line_count; i++) {
            if ((char *)&(dp->db_index[i]) >= (char *)dp + dp->db_txt_start) {
              // line count must be wrong
              error++;
              ml_append(lnum++, _("??? lines may be missing"), 0, true);
              break;
            }

            int txt_start = (dp->db_index[i] & DB_INDEX_MASK);
            if (txt_start <= (int)HEADER_SIZE
                || txt_start >= (int)dp->db_txt_end) {
              error++;
              // avoid lots of lines with "???"
              if (did_questions) {
                continue;
              }
              did_questions = true;
              p = "???";
            } else {
              did_questions = false;
              p = (char *)dp + txt_start;
            }
            ml_append(lnum++, p, 0, true);
          }
          if (has_error) {
            ml_append(lnum++, _("???END"), 0, true);
          }
        }
      }
    }

    if (buf->b_ml.ml_stack_top == 0) {          // finished
      break;
    }

    // go one block up in the tree
    ip = &(buf->b_ml.ml_stack[--(buf->b_ml.ml_stack_top)]);
    bnum = ip->ip_bnum;
    idx = ip->ip_index + 1;         // go to next index
    page_count = 1;
  }

  // Compare the buffer contents with the original file.  When they differ
  // set the 'modified' flag.
  // Lines 1 - lnum are the new contents.
  // Lines lnum + 1 to ml_line_count are the original contents.
  // Line ml_line_count + 1 in the dummy empty line.
  if (orig_file_status != OK || curbuf->b_ml.ml_line_count != lnum * 2 + 1) {
    // Recovering an empty file results in two lines and the first line is
    // empty.  Don't set the modified flag then.
    if (!(curbuf->b_ml.ml_line_count == 2 && *ml_get(1) == NUL)) {
      changed_internal(curbuf);
      buf_inc_changedtick(curbuf);
    }
  } else {
    for (idx = 1; idx <= lnum; idx++) {
      // Need to copy one line, fetching the other one may flush it.
      p = xstrnsave(ml_get(idx), (size_t)ml_get_len(idx));
      int i = strcmp(p, ml_get(idx + lnum));
      xfree(p);
      if (i != 0) {
        changed_internal(curbuf);
        buf_inc_changedtick(curbuf);
        break;
      }
    }
  }

  // Delete the lines from the original file and the dummy line from the
  // empty buffer.  These will now be after the last line in the buffer.
  while (curbuf->b_ml.ml_line_count > lnum
         && !(curbuf->b_ml.ml_flags & ML_EMPTY)) {
    ml_delete(curbuf->b_ml.ml_line_count);
  }
  curbuf->b_flags |= BF_RECOVERED;
  check_cursor(curwin);

  recoverymode = false;
  if (got_int) {
    emsg(_("E311: Recovery Interrupted"));
  } else if (error) {
    no_wait_return++;
    msg(">>>>>>>>>>>>>", 0);
    emsg(_("E312: Errors detected while recovering; look for lines starting with ???"));
    no_wait_return--;
    msg(_("See \":help E312\" for more information."), 0);
    msg(">>>>>>>>>>>>>", 0);
  } else {
    if (curbuf->b_changed) {
      msg(_("Recovery completed. You should check if everything is OK."), 0);
      msg_puts(_("\n(You might want to write out this file under another name\n"));
      msg_puts(_("and run diff with the original file to check for changes)"));
    } else {
      msg(_("Recovery completed. Buffer contents equals file contents."), 0);
    }
    msg_puts(_("\nYou may want to delete the .swp file now."));
    if (swapfile_proc_running(b0p, fname_used)) {
      // Warn there could be an active Vim on the same file, the user may
      // want to kill it.
      msg_puts(_("\nNote: process STILL RUNNING: "));
      msg_outnum((int)char_to_long(b0p->b0_pid));
    }
    msg_puts("\n\n");
    cmdline_row = msg_row;
  }
  redraw_curbuf_later(UPD_NOT_VALID);

theend:
  xfree(fname_used);
  recoverymode = false;
  if (mfp != NULL) {
    if (hp != NULL) {
      mf_put(mfp, hp, false, false);
    }
    mf_close(mfp, false);           // will also xfree(mfp->mf_fname)
  }
  if (buf != NULL) {  // may be NULL if swapfile not found.
    xfree(buf->b_ml.ml_stack);
    xfree(buf);
  }
  if (serious_error && called_from_main) {
    ml_close(curbuf, true);
  } else {
    apply_autocmds(EVENT_BUFREADPOST, NULL, curbuf->b_fname, false, curbuf);
    apply_autocmds(EVENT_BUFWINENTER, NULL, curbuf->b_fname, false, curbuf);
  }
}

/// Find the names of swapfiles in current directory and the directory given
/// with the 'directory' option.
///
/// Used to:
/// - list the swapfiles for "nvim -r"
/// - count the number of swapfiles when recovering
/// - list the swapfiles when recovering
/// - list the swapfiles for swapfilelist()
/// - find the name of the n'th swapfile when recovering
///
/// @param fname  base for swapfile name
/// @param do_list  when true, list the swapfile names
/// @param ret_list  when not NULL add file names to it
/// @param nr  when non-zero, return nr'th swapfile name
/// @param fname_out  result when "nr" > 0
int recover_names(char *fname, bool do_list, list_T *ret_list, int nr, char **fname_out)
{
  int num_names;
  char *(names[6]);
  char *tail;
  char *p;
  int file_count = 0;
  char **files;
  char *fname_res = NULL;
#ifdef HAVE_READLINK
  char fname_buf[MAXPATHL];
#endif

  if (fname != NULL) {
#ifdef HAVE_READLINK
    // Expand symlink in the file name, because the swapfile is created
    // with the actual file instead of with the symlink.
    fname_res = (resolve_symlink(fname, fname_buf) == OK) ? fname_buf : fname;
#else
    fname_res = fname;
#endif
  }

  if (do_list) {
    // use msg() to start the scrolling properly
    msg(_("Swap files found:"), 0);
    msg_putchar('\n');
  }

  // Do the loop for every directory in 'directory'.
  // First allocate some memory to put the directory name in.
  char *dir_name = xmalloc(strlen(p_dir) + 1);
  char *dirp = p_dir;
  while (*dirp) {
    // Isolate a directory name from *dirp and put it in dir_name (we know
    // it is large enough, so use 31000 for length).
    // Advance dirp to next directory name.
    copy_option_part(&dirp, dir_name, 31000, ",");

    if (dir_name[0] == '.' && dir_name[1] == NUL) {     // check current dir
      if (fname == NULL) {
        names[0] = xstrdup("*.sw?");
        // For Unix names starting with a dot are special.  MS-Windows
        // supports this too, on some file systems.
        names[1] = xstrdup(".*.sw?");
        names[2] = xstrdup(".sw?");
        num_names = 3;
      } else {
        num_names = recov_file_names(names, fname_res, true);
      }
    } else {                      // check directory dir_name
      if (fname == NULL) {
        names[0] = concat_fnames(dir_name, "*.sw?", true);
        // For Unix names starting with a dot are special.  MS-Windows
        // supports this too, on some file systems.
        names[1] = concat_fnames(dir_name, ".*.sw?", true);
        names[2] = concat_fnames(dir_name, ".sw?", true);
        num_names = 3;
      } else {
        int len = (int)strlen(dir_name);
        p = dir_name + len;
        if (after_pathsep(dir_name, p) && len > 1 && p[-1] == p[-2]) {
          // Ends with '//', Use Full path for swap name
          tail = make_percent_swname(dir_name, p, fname_res);
        } else {
          tail = path_tail(fname_res);
          tail = concat_fnames(dir_name, tail, true);
        }
        num_names = recov_file_names(names, tail, false);
        xfree(tail);
      }
    }

    int num_files;
    if (num_names == 0) {
      num_files = 0;
    } else if (expand_wildcards(num_names, names, &num_files, &files,
                                EW_KEEPALL|EW_FILE|EW_SILENT) == FAIL) {
      num_files = 0;
    }

    // When no swapfile found, wildcard expansion might have failed (e.g.
    // not able to execute the shell).
    // Try finding a swapfile by simply adding ".swp" to the file name.
    if (*dirp == NUL && file_count + num_files == 0 && fname != NULL) {
      char *swapname = modname(fname_res, ".swp", true);
      if (swapname != NULL) {
        if (os_path_exists(swapname)) {
          files = xmalloc(sizeof(char *));
          files[0] = swapname;
          swapname = NULL;
          num_files = 1;
        }
        xfree(swapname);
      }
    }

    // Remove swapfile name of the current buffer, it must be ignored.
    // But keep it for swapfilelist().
    if (curbuf->b_ml.ml_mfp != NULL
        && (p = curbuf->b_ml.ml_mfp->mf_fname) != NULL
        && ret_list == NULL) {
      for (int i = 0; i < num_files; i++) {
        // Do not expand wildcards, on Windows would try to expand
        // "%tmp%" in "%tmp%file"
        if (path_full_compare(p, files[i], true, false) & kEqualFiles) {
          // Remove the name from files[i].  Move further entries
          // down.  When the array becomes empty free it here, since
          // FreeWild() won't be called below.
          xfree(files[i]);
          if (--num_files == 0) {
            xfree(files);
          } else {
            for (; i < num_files; i++) {
              files[i] = files[i + 1];
            }
          }
        }
      }
    }
    if (nr > 0) {
      file_count += num_files;
      if (nr <= file_count) {
        *fname_out = xstrdup(files[nr - 1 + num_files - file_count]);
        dirp = "";                        // stop searching
      }
    } else if (do_list) {
      if (dir_name[0] == '.' && dir_name[1] == NUL) {
        if (fname == NULL) {
          msg_puts(_("   In current directory:\n"));
        } else {
          msg_puts(_("   Using specified name:\n"));
        }
      } else {
        msg_puts(_("   In directory "));
        msg_home_replace(dir_name);
        msg_puts(":\n");
      }

      if (num_files) {
        for (int i = 0; i < num_files; i++) {
          // print the swapfile name
          msg_outnum(++file_count);
          msg_puts(".    ");
          msg_puts(path_tail(files[i]));
          msg_putchar('\n');
          StringBuilder msg = KV_INITIAL_VALUE;
          swapfile_info(files[i], &msg);
          msg_outtrans(msg.items, 0, false);
          kv_destroy(msg);
        }
      } else {
        msg_puts(_("      -- none --\n"));
      }
      ui_flush();
    } else if (ret_list != NULL) {
      for (int i = 0; i < num_files; i++) {
        char *name = concat_fnames(dir_name, files[i], true);
        tv_list_append_allocated_string(ret_list, name);
      }
    } else {
      file_count += num_files;
    }

    for (int i = 0; i < num_names; i++) {
      xfree(names[i]);
    }
    if (num_files > 0) {
      FreeWild(num_files, files);
    }
  }
  xfree(dir_name);
  return file_count;
}

/// Append the full path to name with path separators made into percent
/// signs, to dir. An unnamed buffer is handled as "" (<currentdir>/"")
/// signs, to "dir". An unnamed buffer is handled as "" (<currentdir>/"")
/// The last character in "dir" must be an extra slash or backslash, it is
/// removed.
char *make_percent_swname(char *dir, char *dir_end, const char *name)
  FUNC_ATTR_NONNULL_ARG(1, 2)
{
  char *d = NULL;
  char *f = fix_fname(name != NULL ? name : "");
  if (f == NULL) {
    return NULL;
  }

  char *s = xstrdup(f);
  for (d = s; *d != NUL; MB_PTR_ADV(d)) {
    if (vim_ispathsep(*d)) {
      *d = '%';
    }
  }

  dir_end[-1] = NUL;  // remove one trailing slash
  d = concat_fnames(dir, s, true);
  xfree(s);
  xfree(f);
  return d;
}

// PID of swapfile owner, or zero if not running.
static int proc_running;

/// For Vimscript "swapinfo()".
///
/// @return  information found in swapfile "fname" in dictionary "d".
void swapfile_dict(const char *fname, dict_T *d)
{
  int fd;
  ZeroBlock b0;

  if ((fd = os_open(fname, O_RDONLY, 0)) >= 0) {
    if (read_eintr(fd, &b0, sizeof(b0)) == sizeof(b0)) {
      if (ml_check_b0_id(&b0) == FAIL) {
        tv_dict_add_str(d, S_LEN("error"), "Not a swap file");
      } else if (b0_magic_wrong(&b0)) {
        tv_dict_add_str(d, S_LEN("error"), "Magic number mismatch");
      } else {
        // We have swap information.
        tv_dict_add_str_len(d, S_LEN("version"), b0.b0_version, 10);
        tv_dict_add_str_len(d, S_LEN("user"), b0.b0_uname,
                            B0_UNAME_SIZE);
        tv_dict_add_str_len(d, S_LEN("host"), b0.b0_hname,
                            B0_HNAME_SIZE);
        tv_dict_add_str_len(d, S_LEN("fname"), b0.b0_fname,
                            B0_FNAME_SIZE_ORG);

        tv_dict_add_nr(d, S_LEN("pid"), swapfile_proc_running(&b0, fname));
        tv_dict_add_nr(d, S_LEN("mtime"), char_to_long(b0.b0_mtime));
        tv_dict_add_nr(d, S_LEN("dirty"), b0.b0_dirty ? 1 : 0);
        tv_dict_add_nr(d, S_LEN("inode"), char_to_long(b0.b0_ino));
      }
    } else {
      tv_dict_add_str(d, S_LEN("error"), "Cannot read file");
    }
    close(fd);
  } else {
    tv_dict_add_str(d, S_LEN("error"), "Cannot open file");
  }
}

/// Loads info from swapfile `fname`, and displays it to the user.
///
/// @return  timestamp (0 when unknown).
static time_t swapfile_info(char *fname, StringBuilder *msg)
{
  assert(fname != NULL);
  ZeroBlock b0;
  time_t x = (time_t)0;
#ifdef UNIX
  char uname[B0_UNAME_SIZE];
#endif

  // print the swapfile date
  FileInfo file_info;
  if (os_fileinfo(fname, &file_info)) {
#ifdef UNIX
    // print name of owner of the file
    if (os_get_uname((uv_uid_t)file_info.stat.st_uid, uname, B0_UNAME_SIZE) == OK) {
      kv_printf(*msg, "%s%s", _("          owned by: "), uname);
      kv_printf(*msg, _("   dated: "));
    } else {
      kv_printf(*msg, _("             dated: "));
    }
#else
    msg_puts(_("             dated: "));
#endif
    x = file_info.stat.st_mtim.tv_sec;
    char ctime_buf[100];  // hopefully enough for every language
    kv_printf(*msg, "%s", os_ctime_r(&x, ctime_buf, sizeof(ctime_buf), true));
  }

  // print the original file name
  int fd = os_open(fname, O_RDONLY, 0);
  if (fd >= 0) {
    if (read_eintr(fd, &b0, sizeof(b0)) == sizeof(b0)) {
      if (strncmp(b0.b0_version, "VIM 3.0", 7) == 0) {
        kv_printf(*msg, _("         [from Vim version 3.0]"));
      } else if (ml_check_b0_id(&b0) == FAIL) {
        kv_printf(*msg, _("         [does not look like a Nvim swap file]"));
      } else if (!ml_check_b0_strings(&b0)) {
        kv_printf(*msg, _("         [garbled strings (not nul terminated)]"));
      } else {
        kv_printf(*msg, _("         file name: "));
        if (b0.b0_fname[0] == NUL) {
          kv_printf(*msg, _("[No Name]"));
        } else {
          kv_printf(*msg, "%s", b0.b0_fname);
        }

        kv_printf(*msg, _("\n          modified: "));
        kv_printf(*msg, b0.b0_dirty ? _("YES") : _("no"));

        if (*(b0.b0_uname) != NUL) {
          kv_printf(*msg, _("\n         user name: "));
          kv_printf(*msg, "%s", b0.b0_uname);
        }

        if (*(b0.b0_hname) != NUL) {
          if (*(b0.b0_uname) != NUL) {
            kv_printf(*msg, _("   host name: "));
          } else {
            kv_printf(*msg, _("\n         host name: "));
          }
          kv_printf(*msg, "%s", b0.b0_hname);
        }

        if (char_to_long(b0.b0_pid) != 0) {
          kv_printf(*msg, _("\n        process ID: "));
          kv_printf(*msg, "%d", (int)char_to_long(b0.b0_pid));
          if ((proc_running = swapfile_proc_running(&b0, fname))) {
            kv_printf(*msg, _(" (STILL RUNNING)"));
          }
        }

        if (b0_magic_wrong(&b0)) {
          kv_printf(*msg, _("\n         [not usable on this computer]"));
        }
      }
    } else {
      kv_printf(*msg, _("         [cannot be read]"));
    }
    close(fd);
  } else {
    kv_printf(*msg, _("         [cannot be opened]"));
  }
  kv_printf(*msg, "\n");

  return x;
}

/// @return  true if the swapfile looks OK and there are no changes, thus it can be safely deleted.
static bool swapfile_unchanged(char *fname)
{
  ZeroBlock b0;

  // Swapfile must exist.
  if (!os_path_exists(fname)) {
    return false;
  }

  // must be able to read the first block
  int fd = os_open(fname, O_RDONLY, 0);
  if (fd < 0) {
    return false;
  }
  if (read_eintr(fd, &b0, sizeof(b0)) != sizeof(b0)) {
    close(fd);
    return false;
  }

  bool ret = true;

  // the ID and magic number must be correct
  if (ml_check_b0_id(&b0) == FAIL || b0_magic_wrong(&b0)) {
    ret = false;
  }

  // must be unchanged
  if (b0.b0_dirty) {
    ret = false;
  }

  // Host name must be known and must equal the current host name, otherwise
  // comparing pid is meaningless.
  if (*(b0.b0_hname) == NUL) {
    ret = false;
  } else {
    char hostname[B0_HNAME_SIZE];
    os_get_hostname(hostname, B0_HNAME_SIZE);
    hostname[B0_HNAME_SIZE - 1] = NUL;
    b0.b0_hname[B0_HNAME_SIZE - 1] = NUL;  // in case of corruption
    if (STRICMP(b0.b0_hname, hostname) != 0) {
      ret = false;
    }
  }

  // process must be known and not running.
  if (char_to_long(b0.b0_pid) == 0 || swapfile_proc_running(&b0, fname)) {
    ret = false;
  }

  // We do not check the user, it should be irrelevant for whether the swap
  // file is still useful.

  close(fd);
  return ret;
}

static int recov_file_names(char **names, char *path, bool prepend_dot)
  FUNC_ATTR_NONNULL_ALL
{
  int num_names = 0;

  // May also add the file name with a dot prepended, for swapfile in same
  // dir as original file.
  if (prepend_dot) {
    names[num_names] = modname(path, ".sw?", true);
    if (names[num_names] == NULL) {
      return num_names;
    }
    num_names++;
  }

  // Form the normal swapfile name pattern by appending ".sw?".
  names[num_names] = concat_fnames(path, ".sw?", false);
  if (num_names >= 1) {     // check if we have the same name twice
    char *p = names[num_names - 1];
    int i = (int)strlen(names[num_names - 1]) - (int)strlen(names[num_names]);
    if (i > 0) {
      p += i;               // file name has been expanded to full path
    }
    if (strcmp(p, names[num_names]) != 0) {
      num_names++;
    } else {
      xfree(names[num_names]);
    }
  } else {
    num_names++;
  }

  return num_names;
}

/// sync all memlines
///
/// @param check_file  if true, check if original file exists and was not changed.
/// @param check_char  if true, stop syncing when character becomes available, but
///
/// always sync at least one block.
void ml_sync_all(int check_file, int check_char, bool do_fsync)
{
  FOR_ALL_BUFFERS(buf) {
    if (buf->b_ml.ml_mfp == NULL || buf->b_ml.ml_mfp->mf_fname == NULL) {
      continue;                             // no file
    }
    ml_flush_line(buf, false);              // flush buffered line
                                            // flush locked block
    ml_find_line(buf, 0, ML_FLUSH);
    if (bufIsChanged(buf) && check_file && mf_need_trans(buf->b_ml.ml_mfp)
        && buf->b_ffname != NULL) {
      // If the original file does not exist anymore or has been changed
      // call ml_preserve() to get rid of all negative numbered blocks.
      FileInfo file_info;
      if (!os_fileinfo(buf->b_ffname, &file_info)
          || file_info.stat.st_mtim.tv_sec != buf->b_mtime_read
          || file_info.stat.st_mtim.tv_nsec != buf->b_mtime_read_ns
          || os_fileinfo_size(&file_info) != buf->b_orig_size) {
        ml_preserve(buf, false, do_fsync);
        did_check_timestamps = false;
        need_check_timestamps = true;           // give message later
      }
    }
    if (buf->b_ml.ml_mfp->mf_dirty == MF_DIRTY_YES) {
      mf_sync(buf->b_ml.ml_mfp, (check_char ? MFS_STOP : 0)
              | (do_fsync && bufIsChanged(buf) ? MFS_FLUSH : 0));
      if (check_char && os_char_avail()) {      // character available now
        break;
      }
    }
  }
}

/// sync one buffer, including negative blocks
///
/// after this all the blocks are in the swapfile
///
/// Used for the :preserve command and when the original file has been
/// changed or deleted.
///
/// @param message  if true, the success of preserving is reported.
void ml_preserve(buf_T *buf, bool message, bool do_fsync)
{
  memfile_T *mfp = buf->b_ml.ml_mfp;
  int got_int_save = got_int;

  if (mfp == NULL || mfp->mf_fname == NULL) {
    if (message) {
      emsg(_("E313: Cannot preserve, there is no swap file"));
    }
    return;
  }

  // We only want to stop when interrupted here, not when interrupted
  // before.
  got_int = false;

  ml_flush_line(buf, false);        // flush buffered line
  ml_find_line(buf, 0, ML_FLUSH);   // flush locked block
  int status = mf_sync(mfp, MFS_ALL | (do_fsync ? MFS_FLUSH : 0));

  // stack is invalid after mf_sync(.., MFS_ALL)
  buf->b_ml.ml_stack_top = 0;

  // Some of the data blocks may have been changed from negative to
  // positive block number. In that case the pointer blocks need to be
  // updated.
  //
  // We don't know in which pointer block the references are, so we visit
  // all data blocks until there are no more translations to be done (or
  // we hit the end of the file, which can only happen in case a write fails,
  // e.g. when file system if full).
  // ml_find_line() does the work by translating the negative block numbers
  // when getting the first line of each data block.
  if (mf_need_trans(mfp) && !got_int) {
    linenr_T lnum = 1;
    while (mf_need_trans(mfp) && lnum <= buf->b_ml.ml_line_count) {
      bhdr_T *hp = ml_find_line(buf, lnum, ML_FIND);
      if (hp == NULL) {
        status = FAIL;
        goto theend;
      }
      CHECK(buf->b_ml.ml_locked_low != lnum, "low != lnum");
      lnum = buf->b_ml.ml_locked_high + 1;
    }
    ml_find_line(buf, 0, ML_FLUSH);  // flush locked block
    // sync the updated pointer blocks
    if (mf_sync(mfp, MFS_ALL | (do_fsync ? MFS_FLUSH : 0)) == FAIL) {
      status = FAIL;
    }
    buf->b_ml.ml_stack_top = 0;  // stack is invalid now
  }
theend:
  got_int |= got_int_save;

  if (message) {
    if (status == OK) {
      msg(_("File preserved"), 0);
    } else {
      emsg(_("E314: Preserve failed"));
    }
  }
}

// NOTE: The pointer returned by the ml_get_*() functions only remains valid
// until the next call!
//  line1 = ml_get(1);
//  line2 = ml_get(2);  // line1 is now invalid!
// Make a copy of the line if necessary.

/// @return  a pointer to a (read-only copy of a) line in curbuf.
///
/// On failure an error message is given and IObuff is returned (to avoid
/// having to check for error everywhere).
char *ml_get(linenr_T lnum)
{
  return ml_get_buf_impl(curbuf, lnum, false);
}

/// @return  a pointer to a (read-only copy of a) line.
///
/// This is the same as ml_get(), but taking in the buffer
/// as an argument.
char *ml_get_buf(buf_T *buf, linenr_T lnum)
{
  return ml_get_buf_impl(buf, lnum, false);
}

/// Like `ml_get_buf`, but allow the line to be mutated in place.
///
/// This is very limited. Generally ml_replace_buf()
/// should be used to modify a line.
///
/// @return a pointer to a line in the buffer
char *ml_get_buf_mut(buf_T *buf, linenr_T lnum)
{
  return ml_get_buf_impl(buf, lnum, true);
}

/// @return  pointer to position "pos".
char *ml_get_pos(const pos_T *pos)
  FUNC_ATTR_NONNULL_ALL
{
  return ml_get_buf(curbuf, pos->lnum) + pos->col;
}

/// @return  length (excluding the NUL) of the given line.
colnr_T ml_get_len(linenr_T lnum)
{
  return ml_get_buf_len(curbuf, lnum);
}

/// @return  length (excluding the NUL) of the text after position "pos".
colnr_T ml_get_pos_len(pos_T *pos)
{
  return ml_get_buf_len(curbuf, pos->lnum) - pos->col;
}

/// @return  length (excluding the NUL) of the given line in the given buffer.
colnr_T ml_get_buf_len(buf_T *buf, linenr_T lnum)
{
  if (*ml_get_buf(buf, lnum) == NUL) {
    return 0;
  }

  return buf->b_ml.ml_line_len - 1;
}

/// @return  codepoint at pos. pos must be either valid or have col set to MAXCOL!
int gchar_pos(pos_T *pos)
  FUNC_ATTR_NONNULL_ARG(1)
{
  // When searching columns is sometimes put at the end of a line.
  if (pos->col == MAXCOL || pos->col > ml_get_len(pos->lnum)) {
    return NUL;
  }
  return utf_ptr2char(ml_get_pos(pos));
}

/// @param will_change  true mark the buffer dirty (chars in the line will be changed)
///
/// @return  a pointer to a line in a specific buffer
static char *ml_get_buf_impl(buf_T *buf, linenr_T lnum, bool will_change)
  FUNC_ATTR_NONNULL_ALL
{
  static int recursive = 0;
  static char questions[4];

  if (buf->b_ml.ml_mfp == NULL) {       // there are no lines
    buf->b_ml.ml_line_len = 1;
    return "";
  }

  if (lnum > buf->b_ml.ml_line_count) {  // invalid line number
    if (recursive == 0) {
      // Avoid giving this message for a recursive call, may happen when
      // the GUI redraws part of the text.
      recursive++;
      siemsg(_(e_ml_get_invalid_lnum_nr), (int64_t)lnum);
      recursive--;
    }
    ml_flush_line(buf, false);
errorret:
    STRCPY(questions, "???");
    buf->b_ml.ml_line_len = 4;
    buf->b_ml.ml_line_lnum = lnum;
    return questions;
  }
  lnum = MAX(lnum, 1);  // pretend line 0 is line 1

  // See if it is the same line as requested last time.
  // Otherwise may need to flush last used line.
  // Don't use the last used line when 'swapfile' is reset, need to load all
  // blocks.
  if (buf->b_ml.ml_line_lnum != lnum) {
    ml_flush_line(buf, false);

    // Find the data block containing the line.
    // This also fills the stack with the blocks from the root to the data
    // block and releases any locked block.
    bhdr_T *hp;
    if ((hp = ml_find_line(buf, lnum, ML_FIND)) == NULL) {
      if (recursive == 0) {
        // Avoid giving this message for a recursive call, may happen
        // when the GUI redraws part of the text.
        recursive++;
        get_trans_bufname(buf);
        shorten_dir(NameBuff);
        siemsg(_(e_ml_get_cannot_find_line_nr_in_buffer_nr_str),
               (int64_t)lnum, buf->b_fnum, NameBuff);
        recursive--;
      }
      goto errorret;
    }

    DataBlock *dp = hp->bh_data;

    int idx = lnum - buf->b_ml.ml_locked_low;
    unsigned start = (dp->db_index[idx] & DB_INDEX_MASK);
    // The text ends where the previous line starts.  The first line ends
    // at the end of the block.
    unsigned end = idx == 0 ? dp->db_txt_end : (dp->db_index[idx - 1] & DB_INDEX_MASK);

    buf->b_ml.ml_line_ptr = (char *)dp + start;
    buf->b_ml.ml_line_len = (colnr_T)(end - start);
    buf->b_ml.ml_line_lnum = lnum;
    buf->b_ml.ml_flags &= ~(ML_LINE_DIRTY | ML_ALLOCATED);
  }
  if (will_change) {
    buf->b_ml.ml_flags |= (ML_LOCKED_DIRTY | ML_LOCKED_POS);
#ifdef ML_GET_ALLOC_LINES
    if (buf->b_ml.ml_flags & ML_ALLOCATED) {
      // can't make the change in the data block
      buf->b_ml.ml_flags |= ML_LINE_DIRTY;
    }
#endif
    ml_add_deleted_len_buf(buf, buf->b_ml.ml_line_ptr, -1);
  }

#ifdef ML_GET_ALLOC_LINES
  if ((buf->b_ml.ml_flags & (ML_LINE_DIRTY | ML_ALLOCATED)) == 0) {
    // make sure the text is in allocated memory
    buf->b_ml.ml_line_ptr = xmemdup(buf->b_ml.ml_line_ptr,
                                    (size_t)buf->b_ml.ml_line_len);
    buf->b_ml.ml_flags |= ML_ALLOCATED;
    if (will_change) {
      // can't make the change in the data block
      buf->b_ml.ml_flags |= ML_LINE_DIRTY;
    }
  }
#endif
  return buf->b_ml.ml_line_ptr;
}

/// Check if a line that was just obtained by a call to ml_get
/// is in allocated memory.
/// This ignores ML_ALLOCATED to get the same behavior as without ML_GET_ALLOC_LINES.
int ml_line_alloced(void)
{
  return curbuf->b_ml.ml_flags & ML_LINE_DIRTY;
}

/// @param lnum  append after this line (can be 0)
/// @param line  text of the new line
/// @param len  length of line, including NUL, or 0
/// @param flags  ML_APPEND_ flags
///
/// @return  FAIL for failure, OK otherwise
static int ml_append_int(buf_T *buf, linenr_T lnum, char *line, colnr_T len, int flags)
  FUNC_ATTR_NONNULL_ARG(1)
{
  // lnum out of range
  if (lnum > buf->b_ml.ml_line_count || buf->b_ml.ml_mfp == NULL) {
    return FAIL;
  }

  if (lowest_marked && lowest_marked > lnum) {
    lowest_marked = lnum + 1;
  }

  if (len == 0) {
    len = (colnr_T)strlen(line) + 1;            // space needed for the text
  }
  int space_needed = len + (int)INDEX_SIZE;     // space needed for text + index

  memfile_T *mfp = buf->b_ml.ml_mfp;
  int page_size = (int)mfp->mf_page_size;

  // find the data block containing the previous line
  // This also fills the stack with the blocks from the root to the data block
  // This also releases any locked block.
  bhdr_T *hp;
  if ((hp = ml_find_line(buf, lnum == 0 ? 1 : lnum,
                         ML_INSERT)) == NULL) {
    return FAIL;
  }

  buf->b_ml.ml_flags &= ~ML_EMPTY;

  int db_idx;                   // index for lnum in data block
  if (lnum == 0) {              // got line one instead, correct db_idx
    db_idx = -1;                // careful, it is negative!
  } else {
    db_idx = lnum - buf->b_ml.ml_locked_low;
  }
  // get line count (number of indexes in current block) before the insertion
  int line_count = buf->b_ml.ml_locked_high - buf->b_ml.ml_locked_low;

  DataBlock *dp = hp->bh_data;

  // If
  // - there is not enough room in the current block
  // - appending to the last line in the block
  // - not appending to the last line in the file
  // insert in front of the next block.
  if ((int)dp->db_free < space_needed && db_idx == line_count - 1
      && lnum < buf->b_ml.ml_line_count) {
    // Now that the line is not going to be inserted in the block that we
    // expected, the line count has to be adjusted in the pointer blocks
    // by using ml_locked_lineadd.
    (buf->b_ml.ml_locked_lineadd)--;
    (buf->b_ml.ml_locked_high)--;
    if ((hp = ml_find_line(buf, lnum + 1, ML_INSERT)) == NULL) {
      return FAIL;
    }

    db_idx = -1;                    // careful, it is negative!
    // get line count before the insertion
    line_count = buf->b_ml.ml_locked_high - buf->b_ml.ml_locked_low;
    CHECK(buf->b_ml.ml_locked_low != lnum + 1, "locked_low != lnum + 1");

    dp = hp->bh_data;
  }

  if (buf->b_prev_line_count == 0) {
    buf->b_prev_line_count = buf->b_ml.ml_line_count;
  }
  buf->b_ml.ml_line_count++;

  if ((int)dp->db_free >= space_needed) {       // enough room in data block
    // Insert new line in existing data block, or in data block allocated above.
    dp->db_txt_start -= (unsigned)len;
    dp->db_free -= (unsigned)space_needed;
    dp->db_line_count++;

    // move the text of the lines that follow to the front
    // adjust the indexes of the lines that follow
    if (line_count > db_idx + 1) {          // if there are following lines
      // Offset is the start of the previous line.
      // This will become the character just after the new line.
      int offset = db_idx < 0 ? (int)dp->db_txt_end
                              : (int)((dp->db_index[db_idx]) & DB_INDEX_MASK);
      memmove((char *)dp + dp->db_txt_start,
              (char *)dp + dp->db_txt_start + len,
              (size_t)offset - (dp->db_txt_start + (size_t)len));
      for (int i = line_count - 1; i > db_idx; i--) {
        dp->db_index[i + 1] = dp->db_index[i] - (unsigned)len;
      }
      dp->db_index[db_idx + 1] = (unsigned)(offset - len);
    } else {  // add line at the end
      dp->db_index[db_idx + 1] = dp->db_txt_start;
    }

    // copy the text into the block
    memmove((char *)dp + dp->db_index[db_idx + 1], line, (size_t)len);
    if (flags & ML_APPEND_MARK) {
      dp->db_index[db_idx + 1] |= DB_MARKED;
    }

    // Mark the block dirty.
    buf->b_ml.ml_flags |= ML_LOCKED_DIRTY;
    if (!(flags & ML_APPEND_NEW)) {
      buf->b_ml.ml_flags |= ML_LOCKED_POS;
    }
  } else {        // not enough space in data block
    // If there is not enough room we have to create a new data block and copy some
    // lines into it.
    // Then we have to insert an entry in the pointer block.
    // If this pointer block also is full, we go up another block, and so on, up
    // to the root if necessary.
    // The line counts in the pointer blocks have already been adjusted by
    // ml_find_line().
    int line_count_left, line_count_right;
    int page_count_left, page_count_right;
    bhdr_T *hp_left;
    bhdr_T *hp_right;
    bhdr_T *hp_new;
    int lines_moved;
    int data_moved = 0;                     // init to shut up gcc
    int total_moved = 0;                    // init to shut up gcc
    int stack_idx;
    bool in_left;
    linenr_T lnum_left, lnum_right;
    PointerBlock *pp_new;

    // We are going to allocate a new data block. Depending on the
    // situation it will be put to the left or right of the existing
    // block.  If possible we put the new line in the left block and move
    // the lines after it to the right block. Otherwise the new line is
    // also put in the right block. This method is more efficient when
    // inserting a lot of lines at one place.
    if (db_idx < 0) {           // left block is new, right block is existing
      lines_moved = 0;
      in_left = true;
      // space_needed does not change
    } else {                  // left block is existing, right block is new
      lines_moved = line_count - db_idx - 1;
      if (lines_moved == 0) {
        in_left = false;                // put new line in right block
                                        // space_needed does not change
      } else {
        data_moved = (int)(((dp->db_index[db_idx]) & DB_INDEX_MASK) -
                           dp->db_txt_start);
        total_moved = data_moved + lines_moved * (int)INDEX_SIZE;
        if ((int)dp->db_free + total_moved >= space_needed) {
          in_left = true;               // put new line in left block
          space_needed = total_moved;
        } else {
          in_left = false;                  // put new line in right block
          space_needed += total_moved;
        }
      }
    }

    int page_count = ((space_needed + (int)HEADER_SIZE) + page_size - 1) / page_size;
    hp_new = ml_new_data(mfp, flags & ML_APPEND_NEW, page_count);
    if (db_idx < 0) {           // left block is new
      hp_left = hp_new;
      hp_right = hp;
      line_count_left = 0;
      line_count_right = line_count;
    } else {                  // right block is new
      hp_left = hp;
      hp_right = hp_new;
      line_count_left = line_count;
      line_count_right = 0;
    }
    DataBlock *dp_right = hp_right->bh_data;
    DataBlock *dp_left = hp_left->bh_data;
    blocknr_T bnum_left = hp_left->bh_bnum;
    blocknr_T bnum_right = hp_right->bh_bnum;
    page_count_left = (int)hp_left->bh_page_count;
    page_count_right = (int)hp_right->bh_page_count;

    // May move the new line into the right/new block.
    if (!in_left) {
      dp_right->db_txt_start -= (unsigned)len;
      dp_right->db_free -= (unsigned)len + (unsigned)INDEX_SIZE;
      dp_right->db_index[0] = dp_right->db_txt_start;
      if (flags & ML_APPEND_MARK) {
        dp_right->db_index[0] |= DB_MARKED;
      }

      memmove((char *)dp_right + dp_right->db_txt_start,
              line, (size_t)len);
      line_count_right++;
    }
    // may move lines from the left/old block to the right/new one.
    if (lines_moved) {
      dp_right->db_txt_start -= (unsigned)data_moved;
      dp_right->db_free -= (unsigned)total_moved;
      memmove((char *)dp_right + dp_right->db_txt_start,
              (char *)dp_left + dp_left->db_txt_start,
              (size_t)data_moved);
      int offset = (int)(dp_right->db_txt_start - dp_left->db_txt_start);
      dp_left->db_txt_start += (unsigned)data_moved;
      dp_left->db_free += (unsigned)total_moved;

      // update indexes in the new block
      for (int to = line_count_right, from = db_idx + 1;
           from < line_count_left; from++, to++) {
        dp_right->db_index[to] = dp->db_index[from] + (unsigned)offset;
      }
      line_count_right += lines_moved;
      line_count_left -= lines_moved;
    }

    // May move the new line into the left (old or new) block.
    if (in_left) {
      dp_left->db_txt_start -= (unsigned)len;
      dp_left->db_free -= (unsigned)len + (unsigned)INDEX_SIZE;
      dp_left->db_index[line_count_left] = dp_left->db_txt_start;
      if (flags & ML_APPEND_MARK) {
        dp_left->db_index[line_count_left] |= DB_MARKED;
      }
      memmove((char *)dp_left + dp_left->db_txt_start,
              line, (size_t)len);
      line_count_left++;
    }

    if (db_idx < 0) {           // left block is new
      lnum_left = lnum + 1;
      lnum_right = 0;
    } else {                  // right block is new
      lnum_left = 0;
      if (in_left) {
        lnum_right = lnum + 2;
      } else {
        lnum_right = lnum + 1;
      }
    }
    dp_left->db_line_count = line_count_left;
    dp_right->db_line_count = line_count_right;

    // release the two data blocks
    // The new one (hp_new) already has a correct blocknumber.
    // The old one (hp, in ml_locked) gets a positive blocknumber if
    // we changed it and we are not editing a new file.
    if (lines_moved || in_left) {
      buf->b_ml.ml_flags |= ML_LOCKED_DIRTY;
    }
    if (!(flags & ML_APPEND_NEW) && db_idx >= 0 && in_left) {
      buf->b_ml.ml_flags |= ML_LOCKED_POS;
    }
    mf_put(mfp, hp_new, true, false);

    // flush the old data block
    // set ml_locked_lineadd to 0, because the updating of the
    // pointer blocks is done below
    int lineadd = buf->b_ml.ml_locked_lineadd;
    buf->b_ml.ml_locked_lineadd = 0;
    ml_find_line(buf, 0, ML_FLUSH);  // flush data block

    // update pointer blocks for the new data block
    for (stack_idx = buf->b_ml.ml_stack_top - 1; stack_idx >= 0; stack_idx--) {
      infoptr_T *ip = &(buf->b_ml.ml_stack[stack_idx]);
      int pb_idx = ip->ip_index;
      if ((hp = mf_get(mfp, ip->ip_bnum, 1)) == NULL) {
        return FAIL;
      }
      PointerBlock *pp = hp->bh_data;         // must be pointer block
      if (pp->pb_id != PTR_ID) {
        iemsg(_(e_pointer_block_id_wrong_three));
        mf_put(mfp, hp, false, false);
        return FAIL;
      }
      // TODO(vim): If the pointer block is full and we are adding at the end
      // try to insert in front of the next block
      // block not full, add one entry
      if (pp->pb_count < pp->pb_count_max) {
        if (pb_idx + 1 < (int)pp->pb_count) {
          memmove(&pp->pb_pointer[pb_idx + 2],
                  &pp->pb_pointer[pb_idx + 1],
                  (size_t)(pp->pb_count - pb_idx - 1) * sizeof(PointerEntry));
        }
        pp->pb_count++;
        pp->pb_pointer[pb_idx].pe_line_count = line_count_left;
        pp->pb_pointer[pb_idx].pe_bnum = bnum_left;
        pp->pb_pointer[pb_idx].pe_page_count = page_count_left;
        pp->pb_pointer[pb_idx + 1].pe_line_count = line_count_right;
        pp->pb_pointer[pb_idx + 1].pe_bnum = bnum_right;
        pp->pb_pointer[pb_idx + 1].pe_page_count = page_count_right;

        if (lnum_left != 0) {
          pp->pb_pointer[pb_idx].pe_old_lnum = lnum_left;
        }
        if (lnum_right != 0) {
          pp->pb_pointer[pb_idx + 1].pe_old_lnum = lnum_right;
        }

        mf_put(mfp, hp, true, false);
        buf->b_ml.ml_stack_top = stack_idx + 1;             // truncate stack

        if (lineadd) {
          (buf->b_ml.ml_stack_top)--;
          // fix line count for rest of blocks in the stack
          ml_lineadd(buf, lineadd);
          // fix stack itself
          buf->b_ml.ml_stack[buf->b_ml.ml_stack_top].ip_high += lineadd;
          (buf->b_ml.ml_stack_top)++;
        }

        // We are finished, break the loop here.
        break;
      }
      // pointer block full
      //
      // split the pointer block
      // allocate a new pointer block
      // move some of the pointer into the new block
      // prepare for updating the parent block
      while (true) {          // do this twice when splitting block 1
        hp_new = ml_new_ptr(mfp);
        if (hp_new == NULL) {             // TODO(vim): try to fix tree
          return FAIL;
        }
        pp_new = hp_new->bh_data;

        if (hp->bh_bnum != 1) {
          break;
        }

        // if block 1 becomes full the tree is given an extra level
        // The pointers from block 1 are moved into the new block.
        // block 1 is updated to point to the new block
        // then continue to split the new block
        memmove(pp_new, pp, (size_t)page_size);
        pp->pb_count = 1;
        pp->pb_pointer[0].pe_bnum = hp_new->bh_bnum;
        pp->pb_pointer[0].pe_line_count = buf->b_ml.ml_line_count;
        pp->pb_pointer[0].pe_old_lnum = 1;
        pp->pb_pointer[0].pe_page_count = 1;
        mf_put(mfp, hp, true, false);             // release block 1
        hp = hp_new;                          // new block is to be split
        pp = pp_new;
        CHECK(stack_idx != 0, _("stack_idx should be 0"));
        ip->ip_index = 0;
        stack_idx++;                  // do block 1 again later
      }
      // move the pointers after the current one to the new block
      // If there are none, the new entry will be in the new block.
      total_moved = pp->pb_count - pb_idx - 1;
      if (total_moved) {
        memmove(&pp_new->pb_pointer[0],
                &pp->pb_pointer[pb_idx + 1],
                (size_t)(total_moved) * sizeof(PointerEntry));
        pp_new->pb_count = (uint16_t)total_moved;
        pp->pb_count = (uint16_t)(pp->pb_count - (total_moved - 1));
        pp->pb_pointer[pb_idx + 1].pe_bnum = bnum_right;
        pp->pb_pointer[pb_idx + 1].pe_line_count = line_count_right;
        pp->pb_pointer[pb_idx + 1].pe_page_count = page_count_right;
        if (lnum_right) {
          pp->pb_pointer[pb_idx + 1].pe_old_lnum = lnum_right;
        }
      } else {
        pp_new->pb_count = 1;
        pp_new->pb_pointer[0].pe_bnum = bnum_right;
        pp_new->pb_pointer[0].pe_line_count = line_count_right;
        pp_new->pb_pointer[0].pe_page_count = page_count_right;
        pp_new->pb_pointer[0].pe_old_lnum = lnum_right;
      }
      pp->pb_pointer[pb_idx].pe_bnum = bnum_left;
      pp->pb_pointer[pb_idx].pe_line_count = line_count_left;
      pp->pb_pointer[pb_idx].pe_page_count = page_count_left;
      if (lnum_left) {
        pp->pb_pointer[pb_idx].pe_old_lnum = lnum_left;
      }
      lnum_left = 0;
      lnum_right = 0;

      // recompute line counts
      line_count_right = 0;
      for (int i = 0; i < (int)pp_new->pb_count; i++) {
        line_count_right += pp_new->pb_pointer[i].pe_line_count;
      }
      line_count_left = 0;
      for (int i = 0; i < (int)pp->pb_count; i++) {
        line_count_left += pp->pb_pointer[i].pe_line_count;
      }

      bnum_left = hp->bh_bnum;
      bnum_right = hp_new->bh_bnum;
      page_count_left = 1;
      page_count_right = 1;
      mf_put(mfp, hp, true, false);
      mf_put(mfp, hp_new, true, false);
    }

    // Safety check: fallen out of for loop?
    if (stack_idx < 0) {
      iemsg(_("E318: Updated too many blocks?"));
      buf->b_ml.ml_stack_top = 0;       // invalidate stack
    }
  }

  // The line was inserted below 'lnum'
  ml_updatechunk(buf, lnum + 1, len, ML_CHNK_ADDLINE);
  return OK;
}

/// Flush any pending change and call ml_append_int()
///
/// @param buf
/// @param lnum  append after this line (can be 0)
/// @param line  text of the new line
/// @param len  length of line, including NUL, or 0
/// @param flags  ML_APPEND_ flags
///
/// @return  FAIL for failure, OK otherwise
static int ml_append_flush(buf_T *buf, linenr_T lnum, char *line, colnr_T len, int flags)
  FUNC_ATTR_NONNULL_ARG(1)
{
  if (lnum > buf->b_ml.ml_line_count) {
    return FAIL;  // lnum out of range
  }
  if (buf->b_ml.ml_line_lnum != 0) {
    // This may also invoke ml_append_int().
    ml_flush_line(buf, false);
  }

  return ml_append_int(buf, lnum, line, len, flags);
}

/// Append a line after lnum (may be 0 to insert a line in front of the file).
/// "line" does not need to be allocated, but can't be another line in a
/// buffer, unlocking may make it invalid.
///
/// "newfile": true when starting to edit a new file, meaning that pe_old_lnum
///              will be set for recovery
/// Check: The caller of this function should probably also call
/// appended_lines().
///
/// @param lnum  append after this line (can be 0)
/// @param line  text of the new line
/// @param len  length of new line, including NUL, or 0
/// @param newfile  flag, see above
///
/// @return  FAIL for failure, OK otherwise
int ml_append(linenr_T lnum, char *line, colnr_T len, bool newfile)
{
  return ml_append_flags(lnum, line, len, newfile ? ML_APPEND_NEW : 0);
}

/// @param lnum  append after this line (can be 0)
/// @param line  text of the new line
/// @param len  length of new line, including nul, or 0
/// @param flags  ML_APPEND_ values
///
/// @return  FAIL for failure, OK otherwise
int ml_append_flags(linenr_T lnum, char *line, colnr_T len, int flags)
{
  // When starting up, we might still need to create the memfile
  if (curbuf->b_ml.ml_mfp == NULL && open_buffer(false, NULL, 0) == FAIL) {
    return FAIL;
  }

  return ml_append_flush(curbuf, lnum, line, len, flags);
}

/// Like ml_append() but for an arbitrary buffer.  The buffer must already have
/// a memline.
///
/// @param lnum  append after this line (can be 0)
/// @param line  text of the new line
/// @param len  length of new line, including NUL, or 0
/// @param newfile  flag, see above
int ml_append_buf(buf_T *buf, linenr_T lnum, char *line, colnr_T len, bool newfile)
  FUNC_ATTR_NONNULL_ARG(1)
{
  if (buf->b_ml.ml_mfp == NULL) {
    return FAIL;
  }

  return ml_append_flush(buf, lnum, line, len, newfile ? ML_APPEND_NEW : 0);
}

void ml_add_deleted_len(char *ptr, ssize_t len)
{
  ml_add_deleted_len_buf(curbuf, ptr, len);
}

void ml_add_deleted_len_buf(buf_T *buf, char *ptr, ssize_t len)
{
  if (inhibit_delete_count) {
    return;
  }
  ssize_t maxlen = (ssize_t)strlen(ptr);
  if (len == -1 || len > maxlen) {
    len = maxlen;
  }
  buf->deleted_bytes += (size_t)len + 1;
  buf->deleted_bytes2 += (size_t)len + 1;
  if (buf->update_need_codepoints) {
    mb_utflen(ptr, (size_t)len, &buf->deleted_codepoints,
              &buf->deleted_codeunits);
    buf->deleted_codepoints++;  // NL char
    buf->deleted_codeunits++;
  }
}

int ml_replace(linenr_T lnum, char *line, bool copy)
{
  return ml_replace_buf(curbuf, lnum, line, copy, false);
}

/// Replace line "lnum", with buffering, in current buffer.
///
/// @param copy  if true, make a copy of the line, otherwise the line has been
///              copied to allocated memory already.
///              if false, the "line" may be freed to add text properties!
///
/// Do not use it after calling ml_replace().
///
/// Check: The caller of this function should probably also call
/// changed_lines(), unless update_screen(UPD_NOT_VALID) is used.
///
/// @return  FAIL for failure, OK otherwise
int ml_replace_buf(buf_T *buf, linenr_T lnum, char *line, bool copy, bool noalloc)
{
  if (line == NULL) {           // just checking...
    return FAIL;
  }

  // When starting up, we might still need to create the memfile
  if (buf->b_ml.ml_mfp == NULL && open_buffer(false, NULL, 0) == FAIL) {
    return FAIL;
  }

  if (copy) {
    assert(!noalloc);
    line = xstrdup(line);
  }

  if (buf->b_ml.ml_line_lnum != lnum) {
    // another line is buffered, flush it
    ml_flush_line(buf, false);
  }

  if (kv_size(buf->update_callbacks)) {
    ml_add_deleted_len_buf(buf, ml_get_buf(buf, lnum), -1);
  }

  if (buf->b_ml.ml_flags & (ML_LINE_DIRTY | ML_ALLOCATED)) {
    xfree(buf->b_ml.ml_line_ptr);  // free allocated line
  }

  buf->b_ml.ml_line_ptr = line;
  buf->b_ml.ml_line_len = (colnr_T)strlen(line) + 1;
  buf->b_ml.ml_line_lnum = lnum;
  buf->b_ml.ml_flags = (buf->b_ml.ml_flags | ML_LINE_DIRTY) & ~ML_EMPTY;
  if (noalloc) {
    // TODO(bfredl): this is a bit of a hack. but replacing lines in a loop is really common,
    // and allocating a separate scratch buffer for each line which is immediately freed adds
    // a lot of noise. A more general refactor could be to use a _fixed_ scratch buffer for
    // all lines up to $REASONABLE_SIZE .
    ml_flush_line(buf, true);
  }

  return OK;
}

/// Delete line `lnum` in buffer
///
/// @note The caller of this function should probably also call changed_lines() after this.
///
/// @param message  Show "--No lines in buffer--" message.
///
/// @return  FAIL for failure, OK otherwise
int ml_delete_buf(buf_T *buf, linenr_T lnum, bool message)
  FUNC_ATTR_NONNULL_ALL
{
  ml_flush_line(buf, false);
  return ml_delete_int(buf, lnum, message ? ML_DEL_MESSAGE : 0);
}

/// Delete line `lnum` in the current buffer.
///
/// @param flags  ML_DEL_MESSAGE may give a "No lines in buffer" message.
///               ML_DEL_UNDO this is called from undo.
///
/// @return  FAIL for failure, OK otherwise
static int ml_delete_int(buf_T *buf, linenr_T lnum, int flags)
  FUNC_ATTR_NONNULL_ALL
{
  if (lowest_marked && lowest_marked > lnum) {
    lowest_marked--;
  }

  // If the file becomes empty the last line is replaced by an empty line.
  if (buf->b_ml.ml_line_count == 1) {       // file becomes empty
    if (flags & ML_DEL_MESSAGE) {
      set_keep_msg(_(no_lines_msg), 0);
    }

    int i = ml_replace_buf(buf, 1, "", true, false);
    buf->b_ml.ml_flags |= ML_EMPTY;

    return i;
  }

  // find the data block containing the line
  // This also fills the stack with the blocks from the root to the data block
  // This also releases any locked block.
  memfile_T *mfp = buf->b_ml.ml_mfp;
  if (mfp == NULL) {
    return FAIL;
  }

  bhdr_T *hp;
  if ((hp = ml_find_line(buf, lnum, ML_DELETE)) == NULL) {
    return FAIL;
  }

  DataBlock *dp = hp->bh_data;
  // compute line count (number of entries in block) before the delete
  int count = buf->b_ml.ml_locked_high - buf->b_ml.ml_locked_low + 2;
  int idx = lnum - buf->b_ml.ml_locked_low;

  if (buf->b_prev_line_count == 0) {
    buf->b_prev_line_count = buf->b_ml.ml_line_count;
  }
  buf->b_ml.ml_line_count--;

  int line_start = ((dp->db_index[idx]) & DB_INDEX_MASK);
  int line_size;
  if (idx == 0) {               // first line in block, text at the end
    line_size = (int)(dp->db_txt_end - (unsigned)line_start);
  } else {
    line_size = (int)(((dp->db_index[idx - 1]) & DB_INDEX_MASK) - (unsigned)line_start);
  }

  // Line should always have an NL char internally (represented as NUL),
  // even if 'noeol' is set.
  assert(line_size >= 1);
  ml_add_deleted_len_buf(buf, (char *)dp + line_start, line_size - 1);

  // special case: If there is only one line in the data block it becomes empty.
  // Then we have to remove the entry, pointing to this data block, from the
  // pointer block. If this pointer block also becomes empty, we go up another
  // block, and so on, up to the root if necessary.
  // The line counts in the pointer blocks have already been adjusted by
  // ml_find_line().
  if (count == 1) {
    mf_free(mfp, hp);           // free the data block
    buf->b_ml.ml_locked = NULL;

    for (int stack_idx = buf->b_ml.ml_stack_top - 1; stack_idx >= 0; stack_idx--) {
      buf->b_ml.ml_stack_top = 0;           // stack is invalid when failing
      infoptr_T *ip = &(buf->b_ml.ml_stack[stack_idx]);
      idx = ip->ip_index;
      if ((hp = mf_get(mfp, ip->ip_bnum, 1)) == NULL) {
        return FAIL;
      }
      PointerBlock *pp = hp->bh_data;         // must be pointer block
      if (pp->pb_id != PTR_ID) {
        iemsg(_(e_pointer_block_id_wrong_four));
        mf_put(mfp, hp, false, false);
        return FAIL;
      }
      count = --(pp->pb_count);
      if (count == 0) {             // the pointer block becomes empty!
        mf_free(mfp, hp);
      } else {
        if (count != idx) {             // move entries after the deleted one
          memmove(&pp->pb_pointer[idx], &pp->pb_pointer[idx + 1],
                  (size_t)(count - idx) * sizeof(PointerEntry));
        }
        mf_put(mfp, hp, true, false);

        buf->b_ml.ml_stack_top = stack_idx;             // truncate stack
        // fix line count for rest of blocks in the stack
        if (buf->b_ml.ml_locked_lineadd != 0) {
          ml_lineadd(buf, buf->b_ml.ml_locked_lineadd);
          buf->b_ml.ml_stack[buf->b_ml.ml_stack_top].ip_high +=
            buf->b_ml.ml_locked_lineadd;
        }
        (buf->b_ml.ml_stack_top)++;

        break;
      }
    }
    CHECK(stack_idx < 0, _("deleted block 1?"));
  } else {
    // delete the text by moving the next lines forwards
    int text_start = (int)dp->db_txt_start;
    memmove((char *)dp + text_start + line_size,
            (char *)dp + text_start, (size_t)(line_start - text_start));

    // delete the index by moving the next indexes backwards
    // Adjust the indexes for the text movement.
    for (int i = idx; i < count - 1; i++) {
      dp->db_index[i] = dp->db_index[i + 1] + (unsigned)line_size;
    }

    dp->db_free += (unsigned)line_size + (unsigned)INDEX_SIZE;
    dp->db_txt_start += (unsigned)line_size;
    dp->db_line_count--;

    // mark the block dirty and make sure it is in the file (for recovery)
    buf->b_ml.ml_flags |= (ML_LOCKED_DIRTY | ML_LOCKED_POS);
  }

  ml_updatechunk(buf, lnum, line_size, ML_CHNK_DELLINE);
  return OK;
}

/// Delete line "lnum" in the current buffer.
///
/// @note The caller of this function should probably also call
/// deleted_lines() after this.
///
/// @return  FAIL for failure, OK otherwise
int ml_delete(linenr_T lnum)
{
  return ml_delete_flags(lnum, 0);
}

/// Like ml_delete() but using flags (see ml_delete_int()).
///
/// @return  FAIL for failure, OK otherwise
int ml_delete_flags(linenr_T lnum, int flags)
{
  ml_flush_line(curbuf, false);
  if (lnum < 1 || lnum > curbuf->b_ml.ml_line_count) {
    return FAIL;
  }

  return ml_delete_int(curbuf, lnum, flags);
}

/// set the B_MARKED flag for line 'lnum'
void ml_setmarked(linenr_T lnum)
{
  // invalid line number
  if (lnum < 1 || lnum > curbuf->b_ml.ml_line_count
      || curbuf->b_ml.ml_mfp == NULL) {
    return;                         // give error message?
  }
  if (lowest_marked == 0 || lowest_marked > lnum) {
    lowest_marked = lnum;
  }

  // find the data block containing the line
  // This also fills the stack with the blocks from the root to the data block
  // This also releases any locked block.
  bhdr_T *hp;
  if ((hp = ml_find_line(curbuf, lnum, ML_FIND)) == NULL) {
    return;                 // give error message?
  }
  DataBlock *dp = hp->bh_data;
  dp->db_index[lnum - curbuf->b_ml.ml_locked_low] |= DB_MARKED;
  curbuf->b_ml.ml_flags |= ML_LOCKED_DIRTY;
}

/// find the first line with its B_MARKED flag set
linenr_T ml_firstmarked(void)
{
  if (curbuf->b_ml.ml_mfp == NULL) {
    return 0;
  }

  // The search starts with lowest_marked line. This is the last line where
  // a mark was found, adjusted by inserting/deleting lines.
  for (linenr_T lnum = lowest_marked; lnum <= curbuf->b_ml.ml_line_count;) {
    // Find the data block containing the line.
    // This also fills the stack with the blocks from the root to the data
    // block This also releases any locked block.
    bhdr_T *hp;
    if ((hp = ml_find_line(curbuf, lnum, ML_FIND)) == NULL) {
      return 0;                   // give error message?
    }
    DataBlock *dp = hp->bh_data;

    for (int i = lnum - curbuf->b_ml.ml_locked_low;
         lnum <= curbuf->b_ml.ml_locked_high; i++, lnum++) {
      if ((dp->db_index[i]) & DB_MARKED) {
        (dp->db_index[i]) &= DB_INDEX_MASK;
        curbuf->b_ml.ml_flags |= ML_LOCKED_DIRTY;
        lowest_marked = lnum + 1;
        return lnum;
      }
    }
  }

  return 0;
}

/// clear all DB_MARKED flags
void ml_clearmarked(void)
{
  if (curbuf->b_ml.ml_mfp == NULL) {        // nothing to do
    return;
  }

  // The search starts with line lowest_marked.
  for (linenr_T lnum = lowest_marked; lnum <= curbuf->b_ml.ml_line_count;) {
    // Find the data block containing the line.
    // This also fills the stack with the blocks from the root to the data
    // block and releases any locked block.
    bhdr_T *hp;
    if ((hp = ml_find_line(curbuf, lnum, ML_FIND)) == NULL) {
      return;                   // give error message?
    }
    DataBlock *dp = hp->bh_data;

    for (int i = lnum - curbuf->b_ml.ml_locked_low;
         lnum <= curbuf->b_ml.ml_locked_high; i++, lnum++) {
      if ((dp->db_index[i]) & DB_MARKED) {
        (dp->db_index[i]) &= DB_INDEX_MASK;
        curbuf->b_ml.ml_flags |= ML_LOCKED_DIRTY;
      }
    }
  }

  lowest_marked = 0;
}

size_t ml_flush_deleted_bytes(buf_T *buf, size_t *codepoints, size_t *codeunits)
{
  size_t ret = buf->deleted_bytes;
  *codepoints = buf->deleted_codepoints;
  *codeunits = buf->deleted_codeunits;
  buf->deleted_bytes = 0;
  buf->deleted_codepoints = 0;
  buf->deleted_codeunits = 0;
  return ret;
}

/// flush ml_line if necessary
static void ml_flush_line(buf_T *buf, bool noalloc)
{
  static bool entered = false;

  if (buf->b_ml.ml_line_lnum == 0 || buf->b_ml.ml_mfp == NULL) {
    return;             // nothing to do
  }
  if (buf->b_ml.ml_flags & ML_LINE_DIRTY) {
    // This code doesn't work recursively.
    if (entered) {
      return;
    }
    entered = true;

    buf->flush_count++;

    linenr_T lnum = buf->b_ml.ml_line_lnum;
    char *new_line = buf->b_ml.ml_line_ptr;

    bhdr_T *hp = ml_find_line(buf, lnum, ML_FIND);
    if (hp == NULL) {
      siemsg(_("E320: Cannot find line %" PRId64), (int64_t)lnum);
    } else {
      DataBlock *dp = hp->bh_data;
      int idx = lnum - buf->b_ml.ml_locked_low;
      int start = ((dp->db_index[idx]) & DB_INDEX_MASK);
      char *old_line = (char *)dp + start;
      int old_len;
      if (idx == 0) {           // line is last in block
        old_len = (int)dp->db_txt_end - start;
      } else {  // text of previous line follows
        old_len = (int)(dp->db_index[idx - 1] & DB_INDEX_MASK) - start;
      }
      colnr_T new_len = buf->b_ml.ml_line_len;
      int extra = new_len - old_len;            // negative if lines gets smaller

      // if new line fits in data block, replace directly
      if ((int)dp->db_free >= extra) {
        // if the length changes and there are following lines
        int count = buf->b_ml.ml_locked_high - buf->b_ml.ml_locked_low + 1;
        if (extra != 0 && idx < count - 1) {
          // move text of following lines
          memmove((char *)dp + dp->db_txt_start - extra,
                  (char *)dp + dp->db_txt_start,
                  (size_t)(start - (int)dp->db_txt_start));

          // adjust pointers of this and following lines
          for (int i = idx + 1; i < count; i++) {
            dp->db_index[i] -= (unsigned)extra;
          }
        }
        dp->db_index[idx] -= (unsigned)extra;

        // adjust free space
        dp->db_free -= (unsigned)extra;
        dp->db_txt_start -= (unsigned)extra;

        // copy new line into the data block
        memmove(old_line - extra, new_line, (size_t)new_len);
        buf->b_ml.ml_flags |= (ML_LOCKED_DIRTY | ML_LOCKED_POS);
        // The else case is already covered by the insert and delete
        if (extra != 0) {
          ml_updatechunk(buf, lnum, extra, ML_CHNK_UPDLINE);
        }
      } else {
        // Cannot do it in one data block: Delete and append.
        // Append first, because ml_delete_int() cannot delete the
        // last line in a buffer, which causes trouble for a buffer
        // that has only one line.
        // Don't forget to copy the mark!
        // How about handling errors???
        (void)ml_append_int(buf, lnum, new_line, new_len,
                            (dp->db_index[idx] & DB_MARKED) ? ML_APPEND_MARK : 0);
        (void)ml_delete_int(buf, lnum, 0);
      }
    }
    if (!noalloc) {
      xfree(new_line);
    }

    entered = false;
  } else if (buf->b_ml.ml_flags & ML_ALLOCATED) {
    assert(!noalloc);  // caller must set ML_LINE_DIRTY with noalloc, handled above
    xfree(buf->b_ml.ml_line_ptr);
  }

  buf->b_ml.ml_flags &= ~(ML_LINE_DIRTY | ML_ALLOCATED);
  buf->b_ml.ml_line_lnum = 0;
  buf->b_ml.ml_line_offset = 0;
}

/// create a new, empty, data block
static bhdr_T *ml_new_data(memfile_T *mfp, bool negative, int page_count)
{
  assert(page_count >= 0);
  bhdr_T *hp = mf_new(mfp, negative, (unsigned)page_count);
  DataBlock *dp = hp->bh_data;
  dp->db_id = DATA_ID;
  dp->db_txt_start = dp->db_txt_end = (unsigned)page_count * mfp->mf_page_size;
  dp->db_free = dp->db_txt_start - (unsigned)HEADER_SIZE;
  dp->db_line_count = 0;

  return hp;
}

/// create a new, empty, pointer block
static bhdr_T *ml_new_ptr(memfile_T *mfp)
{
  bhdr_T *hp = mf_new(mfp, false, 1);
  PointerBlock *pp = hp->bh_data;
  pp->pb_id = PTR_ID;
  pp->pb_count = 0;
  pp->pb_count_max = PB_COUNT_MAX(mfp);

  return hp;
}

/// lookup line 'lnum' in a memline
///
/// @param action: if ML_DELETE or ML_INSERT the line count is updated while searching
///                if ML_FLUSH only flush a locked block
///                if ML_FIND just find the line
///
/// If the block was found it is locked and put in ml_locked.
/// The stack is updated to lead to the locked block. The ip_high field in
/// the stack is updated to reflect the last line in the block AFTER the
/// insert or delete, also if the pointer block has not been updated yet. But
/// if ml_locked != NULL ml_locked_lineadd must be added to ip_high.
///
/// @return  NULL for failure, pointer to block header otherwise
static bhdr_T *ml_find_line(buf_T *buf, linenr_T lnum, int action)
{
  bhdr_T *hp;
  int top;

  memfile_T *mfp = buf->b_ml.ml_mfp;

  // If there is a locked block check if the wanted line is in it.
  // If not, flush and release the locked block.
  // Don't do this for ML_INSERT_SAME, because the stack need to be updated.
  // Don't do this for ML_FLUSH, because we want to flush the locked block.
  // Don't do this when 'swapfile' is reset, we want to load all the blocks.
  if (buf->b_ml.ml_locked) {
    if (ML_SIMPLE(action)
        && buf->b_ml.ml_locked_low <= lnum
        && buf->b_ml.ml_locked_high >= lnum) {
      // remember to update pointer blocks and stack later
      if (action == ML_INSERT) {
        (buf->b_ml.ml_locked_lineadd)++;
        (buf->b_ml.ml_locked_high)++;
      } else if (action == ML_DELETE) {
        (buf->b_ml.ml_locked_lineadd)--;
        (buf->b_ml.ml_locked_high)--;
      }
      return buf->b_ml.ml_locked;
    }

    mf_put(mfp, buf->b_ml.ml_locked, buf->b_ml.ml_flags & ML_LOCKED_DIRTY,
           buf->b_ml.ml_flags & ML_LOCKED_POS);
    buf->b_ml.ml_locked = NULL;

    // If lines have been added or deleted in the locked block, need to
    // update the line count in pointer blocks.
    if (buf->b_ml.ml_locked_lineadd != 0) {
      ml_lineadd(buf, buf->b_ml.ml_locked_lineadd);
    }
  }

  if (action == ML_FLUSH) {         // nothing else to do
    return NULL;
  }

  blocknr_T bnum = 1;                         // start at the root of the tree
  blocknr_T bnum2;
  int page_count = 1;
  linenr_T low = 1;
  linenr_T high = buf->b_ml.ml_line_count;

  if (action == ML_FIND) {      // first try stack entries
    for (top = buf->b_ml.ml_stack_top - 1; top >= 0; top--) {
      infoptr_T *ip = &(buf->b_ml.ml_stack[top]);
      if (ip->ip_low <= lnum && ip->ip_high >= lnum) {
        bnum = ip->ip_bnum;
        low = ip->ip_low;
        high = ip->ip_high;
        buf->b_ml.ml_stack_top = top;           // truncate stack at prev entry
        break;
      }
    }
    if (top < 0) {
      buf->b_ml.ml_stack_top = 0;               // not found, start at the root
    }
  } else {  // ML_DELETE or ML_INSERT
    buf->b_ml.ml_stack_top = 0;         // start at the root
  }
  // search downwards in the tree until a data block is found
  while (true) {
    if ((hp = mf_get(mfp, bnum, (unsigned)page_count)) == NULL) {
      goto error_noblock;
    }

    // update high for insert/delete
    if (action == ML_INSERT) {
      high++;
    } else if (action == ML_DELETE) {
      high--;
    }

    DataBlock *dp = hp->bh_data;
    if (dp->db_id == DATA_ID) {         // data block
      buf->b_ml.ml_locked = hp;
      buf->b_ml.ml_locked_low = low;
      buf->b_ml.ml_locked_high = high;
      buf->b_ml.ml_locked_lineadd = 0;
      buf->b_ml.ml_flags &= ~(ML_LOCKED_DIRTY | ML_LOCKED_POS);
      return hp;
    }

    PointerBlock *pp = (PointerBlock *)(dp);                // must be pointer block
    if (pp->pb_id != PTR_ID) {
      iemsg(_(e_pointer_block_id_wrong));
      goto error_block;
    }

    top = ml_add_stack(buf);  // add new entry to stack
    infoptr_T *ip = &(buf->b_ml.ml_stack[top]);
    ip->ip_bnum = bnum;
    ip->ip_low = low;
    ip->ip_high = high;
    ip->ip_index = -1;                  // index not known yet

    bool dirty = false;
    int idx;
    for (idx = 0; idx < (int)pp->pb_count; idx++) {
      linenr_T t = pp->pb_pointer[idx].pe_line_count;
      CHECK(t == 0, _("pe_line_count is zero"));
      if ((low += t) > lnum) {
        ip->ip_index = idx;
        bnum = pp->pb_pointer[idx].pe_bnum;
        page_count = pp->pb_pointer[idx].pe_page_count;
        high = low - 1;
        low -= t;

        // a negative block number may have been changed
        if (bnum < 0) {
          bnum2 = mf_trans_del(mfp, bnum);
          if (bnum != bnum2) {
            bnum = bnum2;
            pp->pb_pointer[idx].pe_bnum = bnum;
            dirty = true;
          }
        }

        break;
      }
    }
    if (idx >= (int)pp->pb_count) {         // past the end: something wrong!
      if (lnum > buf->b_ml.ml_line_count) {
        siemsg(_(e_line_number_out_of_range_nr_past_the_end),
               (int64_t)lnum - buf->b_ml.ml_line_count);
      } else {
        siemsg(_(e_line_count_wrong_in_block_nr), bnum);
      }
      goto error_block;
    }
    if (action == ML_DELETE) {
      pp->pb_pointer[idx].pe_line_count--;
      dirty = true;
    } else if (action == ML_INSERT) {
      pp->pb_pointer[idx].pe_line_count++;
      dirty = true;
    }
    mf_put(mfp, hp, dirty, false);
  }

error_block:
  mf_put(mfp, hp, false, false);
error_noblock:
  // If action is ML_DELETE or ML_INSERT we have to correct the tree for
  // the incremented/decremented line counts, because there won't be a line
  // inserted/deleted after all.
  if (action == ML_DELETE) {
    ml_lineadd(buf, 1);
  } else if (action == ML_INSERT) {
    ml_lineadd(buf, -1);
  }
  buf->b_ml.ml_stack_top = 0;
  return NULL;
}

/// add an entry to the info pointer stack
///
/// @return  number of the new entry
static int ml_add_stack(buf_T *buf)
{
  int top = buf->b_ml.ml_stack_top;

  // may have to increase the stack size
  if (top == buf->b_ml.ml_stack_size) {
    CHECK(top > 0, _("Stack size increases"));     // more than 5 levels???

    buf->b_ml.ml_stack_size += STACK_INCR;
    size_t new_size = sizeof(infoptr_T) * (size_t)buf->b_ml.ml_stack_size;
    buf->b_ml.ml_stack = xrealloc(buf->b_ml.ml_stack, new_size);
  }

  buf->b_ml.ml_stack_top++;
  return top;
}

/// Update the pointer blocks on the stack for inserted/deleted lines.
/// The stack itself is also updated.
///
/// When an insert/delete line action fails, the line is not inserted/deleted,
/// but the pointer blocks have already been updated. That is fixed here by
/// walking through the stack.
///
/// Count is the number of lines added, negative if lines have been deleted.
static void ml_lineadd(buf_T *buf, int count)
{
  memfile_T *mfp = buf->b_ml.ml_mfp;

  for (int idx = buf->b_ml.ml_stack_top - 1; idx >= 0; idx--) {
    infoptr_T *ip = &(buf->b_ml.ml_stack[idx]);
    bhdr_T *hp;
    if ((hp = mf_get(mfp, ip->ip_bnum, 1)) == NULL) {
      break;
    }
    PointerBlock *pp = hp->bh_data;       // must be pointer block
    if (pp->pb_id != PTR_ID) {
      mf_put(mfp, hp, false, false);
      iemsg(_(e_pointer_block_id_wrong_two));
      break;
    }
    pp->pb_pointer[ip->ip_index].pe_line_count += count;
    ip->ip_high += count;
    mf_put(mfp, hp, true, false);
  }
}

#if defined(HAVE_READLINK)

/// Resolve a symlink in the last component of a file name.
/// Note that f_resolve() does it for every part of the path, we don't do that
/// here.
///
/// @return  OK if it worked and the resolved link in "buf[MAXPATHL]",
///          FAIL otherwise
int resolve_symlink(const char *fname, char *buf)
{
  char tmp[MAXPATHL];
  int depth = 0;

  if (fname == NULL) {
    return FAIL;
  }

  // Put the result so far in tmp[], starting with the original name.
  xstrlcpy(tmp, fname, MAXPATHL);

  while (true) {
    // Limit symlink depth to 100, catch recursive loops.
    if (++depth == 100) {
      semsg(_("E773: Symlink loop for \"%s\""), fname);
      return FAIL;
    }

    int ret = (int)readlink(tmp, buf, MAXPATHL - 1);
    if (ret <= 0) {
      if (errno == EINVAL || errno == ENOENT) {
        // Found non-symlink or not existing file, stop here.
        // When at the first level use the unmodified name, skip the
        // call to vim_FullName().
        if (depth == 1) {
          return FAIL;
        }

        // Use the resolved name in tmp[].
        break;
      }

      // There must be some error reading links, use original name.
      return FAIL;
    }
    buf[ret] = NUL;

    // Check whether the symlink is relative or absolute.
    // If it's relative, build a new path based on the directory
    // portion of the filename (if any) and the path the symlink
    // points to.
    if (path_is_absolute(buf)) {
      STRCPY(tmp, buf);
    } else {
      char *tail = path_tail(tmp);
      if (strlen(tail) + strlen(buf) >= MAXPATHL) {
        return FAIL;
      }
      STRCPY(tail, buf);
    }
  }

  // Try to resolve the full name of the file so that the swapfile name will
  // be consistent even when opening a relative symlink from different
  // working directories.
  return vim_FullName(tmp, buf, MAXPATHL, true);
}
#endif

/// Make swapfile name out of the file name and a directory name.
///
/// @return  pointer to allocated memory or NULL.
char *makeswapname(char *fname, char *ffname, buf_T *buf, char *dir_name)
{
  char *fname_res = fname;
#ifdef HAVE_READLINK
  char fname_buf[MAXPATHL];

  // Expand symlink in the file name, so that we put the swapfile with the
  // actual file instead of with the symlink.
  if (resolve_symlink(fname, fname_buf) == OK) {
    fname_res = fname_buf;
  }
#endif
  int len = (int)strlen(dir_name);

  char *s = dir_name + len;
  if (after_pathsep(dir_name, s) && len > 1 && s[-1] == s[-2]) {
    // Ends with '//', Use Full path
    char *r = NULL;
    s = make_percent_swname(dir_name, s, fname_res);
    if (s != NULL) {
      r = modname(s, ".swp", false);
      xfree(s);
    }
    return r;
  }

  // Prepend a '.' to the swapfile name for the current directory.
  char *r = modname(fname_res, ".swp",
                    dir_name[0] == '.' && dir_name[1] == NUL);
  if (r == NULL) {          // out of memory
    return NULL;
  }

  s = get_file_in_dir(r, dir_name);
  xfree(r);
  return s;
}

/// Get file name to use for swapfile or backup file.
/// Use the name of the edited file "fname" and an entry in the 'dir' or 'bdir' option "dname".
/// - If "dname" is ".", return "fname" (swapfile in dir of file).
/// - If "dname" starts with "./", insert "dname" in "fname" (swapfile relative to dir of file).
/// - Otherwise, prepend "dname" to the tail of "fname" (swapfile in specific dir).
///
/// The return value is an allocated string and can be NULL.
///
/// @param dname  don't use "dirname", it is a global for Alpha
char *get_file_in_dir(char *fname, char *dname)
{
  char *retval;

  char *tail = path_tail(fname);

  if (dname[0] == '.' && dname[1] == NUL) {
    retval = xstrdup(fname);
  } else if (dname[0] == '.' && vim_ispathsep(dname[1])) {
    if (tail == fname) {            // no path before file name
      retval = concat_fnames(dname + 2, tail, true);
    } else {
      char save_char = *tail;
      *tail = NUL;
      char *t = concat_fnames(fname, dname + 2, true);
      *tail = save_char;
      retval = concat_fnames(t, tail, true);
      xfree(t);
    }
  } else {
    retval = concat_fnames(dname, tail, true);
  }

  return retval;
}

/// Build the ATTENTION message: info about an existing swapfile.
///
/// @param buf  buffer being edited
/// @param fname  swapfile name
/// @param fhname  swapfile name, home replaced
/// @param msg  string buffer, emitted as either a regular or confirm message
static void attention_message(buf_T *buf, char *fname, char *fhname, StringBuilder *msg)
{
  assert(buf->b_fname != NULL);

  emsg(_("E325: ATTENTION"));
  kv_printf(*msg, _("Found a swap file by the name \""));
  kv_printf(*msg, "%s\"\n", fhname);
  const time_t swap_mtime = swapfile_info(fname, msg);
  kv_printf(*msg, (_("While opening file \"")));
  kv_printf(*msg, "%s\"\n", buf->b_fname);
  FileInfo file_info;
  if (!os_fileinfo(buf->b_fname, &file_info)) {
    kv_printf(*msg, _("      CANNOT BE FOUND"));
  } else {
    kv_printf(*msg, _("             dated: "));
    time_t x = file_info.stat.st_mtim.tv_sec;
    char ctime_buf[50];
    kv_printf(*msg, "%s", os_ctime_r(&x, ctime_buf, sizeof(ctime_buf), true));
    if (swap_mtime != 0 && x > swap_mtime) {
      kv_printf(*msg, _("      NEWER than swap file!\n"));
    }
  }
  // Some of these messages are long to allow translation to
  // other languages.
  kv_printf(*msg, _("\n(1) Another program may be editing the same file.  If this is"
                    " the case,\n    be careful not to end up with two different"
                    " instances of the same\n    file when making changes."
                    "  Quit, or continue with caution.\n"));
  kv_printf(*msg, _("(2) An edit session for this file crashed.\n"));
  kv_printf(*msg, _("    If this is the case, use \":recover\" or \"nvim -r "));
  kv_printf(*msg, "%s", buf->b_fname);
  kv_printf(*msg, (_("\"\n    to recover the changes (see \":help recovery\").\n")));
  kv_printf(*msg, _("    If you did this already, delete the swap file \""));
  kv_printf(*msg, "%s", fname);
  kv_printf(*msg, _("\"\n    to avoid this message.\n"));
}

/// Trigger the SwapExists autocommands.
///
/// @return  a value for equivalent to do_dialog().
static sea_choice_T do_swapexists(buf_T *buf, char *fname)
{
  set_vim_var_string(VV_SWAPNAME, fname, -1);
  set_vim_var_string(VV_SWAPCHOICE, NULL, -1);

  // Trigger SwapExists autocommands with <afile> set to the file being
  // edited.  Disallow changing directory here.
  allbuf_lock++;
  apply_autocmds(EVENT_SWAPEXISTS, buf->b_fname, NULL, false, NULL);
  allbuf_lock--;

  set_vim_var_string(VV_SWAPNAME, NULL, -1);

  switch (*get_vim_var_str(VV_SWAPCHOICE)) {
  case 'o':
    return SEA_CHOICE_READONLY;
  case 'e':
    return SEA_CHOICE_EDIT;
  case 'r':
    return SEA_CHOICE_RECOVER;
  case 'd':
    return SEA_CHOICE_DELETE;
  case 'q':
    return SEA_CHOICE_QUIT;
  case 'a':
    return SEA_CHOICE_ABORT;
  }

  return SEA_CHOICE_NONE;
}

/// Find out what name to use for the swapfile for buffer 'buf'.
///
/// Several names are tried to find one that does not exist. Last directory in
/// option is automatically created.
///
/// @note If BASENAMELEN is not correct, you will get error messages for
///   not being able to open the swap or undo file.
/// @note May trigger SwapExists autocmd, pointers may change!
///
/// @param[in]  buf  Buffer for which swapfile names needs to be found.
/// @param[in,out]  dirp  Pointer to a list of directories. When out of memory,
///                       is set to NULL. Is advanced to the next directory in
///                       the list otherwise.
/// @param[in]  old_fname  Allowed existing swapfile name. Except for this
///                        case, name of the non-existing file is used.
/// @param[in,out]  found_existing_dir  If points to true, then new directory
///                                     for swapfile is not created. At first
///                                     findswapname() call this argument must
///                                     point to false. This parameter may only
///                                     be set to true by this function, it is
///                                     never set to false.
///
/// @return [allocated] Name of the swapfile.
static char *findswapname(buf_T *buf, char **dirp, char *old_fname, bool *found_existing_dir)
  FUNC_ATTR_WARN_UNUSED_RESULT FUNC_ATTR_NONNULL_ARG(1, 2, 4)
{
  char *buf_fname = buf->b_fname;

  // Isolate a directory name from *dirp and put it in dir_name.
  // First allocate some memory to put the directory name in.
  const size_t dir_len = strlen(*dirp) + 1;
  char *dir_name = xmalloc(dir_len);
  copy_option_part(dirp, dir_name, dir_len, ",");

  // We try different swapfile names until we find one that does not exist yet.
  char *fname = makeswapname(buf_fname, buf->b_ffname, buf, dir_name);

  while (true) {
    size_t n;
    if (fname == NULL) {        // must be out of memory
      break;
    }
    if ((n = strlen(fname)) == 0) {        // safety check
      XFREE_CLEAR(fname);
      break;
    }
    // check if the swapfile already exists
    // Extra security check: When a swapfile is a symbolic link, this
    // is most likely a symlink attack.
    FileInfo file_info;
    bool file_or_link_found = os_fileinfo_link(fname, &file_info);
    if (!file_or_link_found) {
      break;
    }

    // A file name equal to old_fname is OK to use.
    if (old_fname != NULL && path_fnamecmp(fname, old_fname) == 0) {
      break;
    }

    // get here when file already exists
    if (fname[n - 2] == 'w' && fname[n - 1] == 'p') {   // first try
      // If we get here the ".swp" file really exists.
      // Give an error message, unless recovering, no file name, we are
      // viewing a help file or when the path of the file is different
      // (happens when all .swp files are in one directory).
      if (!recoverymode && buf_fname != NULL && !buf->b_help && !(buf->b_flags & BF_DUMMY)) {
        int fd;
        ZeroBlock b0;
        bool differ = false;

        // Try to read block 0 from the swapfile to get the original file name (and inode number).
        fd = os_open(fname, O_RDONLY, 0);
        if (fd >= 0) {
          if (read_eintr(fd, &b0, sizeof(b0)) == sizeof(b0)) {
            proc_running = swapfile_proc_running(&b0, fname);

            // If the swapfile has the same directory as the
            // buffer don't compare the directory names, they can
            // have a different mountpoint.
            if (b0.b0_flags & B0_SAME_DIR) {
              if (path_fnamecmp(path_tail(buf->b_ffname),
                                path_tail(b0.b0_fname)) != 0
                  || !same_directory(fname, buf->b_ffname)) {
                // Symlinks may point to the same file even
                // when the name differs, need to check the
                // inode too.
                expand_env(b0.b0_fname, NameBuff, MAXPATHL);
                if (fnamecmp_ino(buf->b_ffname, NameBuff,
                                 char_to_long(b0.b0_ino))) {
                  differ = true;
                }
              }
            } else {
              // The name in the swapfile may be "~user/path/file".  Expand it first.
              expand_env(b0.b0_fname, NameBuff, MAXPATHL);
              if (fnamecmp_ino(buf->b_ffname, NameBuff,
                               char_to_long(b0.b0_ino))) {
                differ = true;
              }
            }
          }
          close(fd);
        }

        // Show the ATTENTION message when:
        //  - there is an old swapfile for the current file
        //  - the buffer was not recovered
        if (!differ && !(curbuf->b_flags & BF_RECOVERED)
            && vim_strchr(p_shm, SHM_ATTENTION) == NULL) {
          sea_choice_T choice = SEA_CHOICE_NONE;

          // It's safe to delete the swapfile if all these are true:
          // - the edited file exists
          // - the swapfile has no changes and looks OK
          if (os_path_exists(buf->b_fname) && swapfile_unchanged(fname)) {
            choice = SEA_CHOICE_DELETE;
            if (p_verbose > 0) {
              verb_msg(_("Found a swap file that is not useful, deleting it"));
            }
          }

          // If there is a SwapExists autocommand and we can handle the
          // response, trigger it.  It may return 0 to ask the user anyway.
          if (choice == SEA_CHOICE_NONE
              && swap_exists_action != SEA_NONE
              && has_autocmd(EVENT_SWAPEXISTS, buf_fname, buf)) {
            choice = do_swapexists(buf, fname);
          }

          if (choice == SEA_CHOICE_NONE && swap_exists_action == SEA_READONLY) {
            // always open readonly.
            choice = SEA_CHOICE_READONLY;
          }

          proc_running = 0;  // Set by attention_message..swapfile_info.
          if (choice == SEA_CHOICE_NONE) {
            no_wait_return++;
            // Show info about the existing swapfile.
            StringBuilder msg = KV_INITIAL_VALUE;
            char *fhname = home_replace_save(NULL, fname);
            attention_message(buf, fname, fhname, &msg);

            // We don't want a 'q' typed at the more-prompt
            // interrupt loading a file.
            got_int = false;

            // If vimrc has "simalt ~x" we don't want it to
            // interfere with the prompt here.
            flush_buffers(FLUSH_TYPEAHEAD);

            if (swap_exists_action != SEA_NONE) {
              kv_printf(msg, _("Swap file \""));
              kv_printf(msg, "%s", fhname);
              kv_printf(msg, _("\" already exists!"));
              char *run_but = _("&Open Read-Only\n&Edit anyway\n&Recover\n&Quit\n&Abort");
              char *but = _("&Open Read-Only\n&Edit anyway\n&Recover\n&Delete it\n&Quit\n&Abort");
              choice = (sea_choice_T)do_dialog(VIM_WARNING, _("VIM - ATTENTION"), msg.items,
                                               proc_running ? run_but : but, 1, NULL, false);

              // compensate for missing "Delete it" button
              choice += proc_running && choice >= 4;
              // pretend screen didn't scroll, need redraw anyway
              msg_reset_scroll();
            } else {
              msg_outtrans(msg.items, 0, false);
            }
            no_wait_return--;
            kv_destroy(msg);
            xfree(fhname);
          }

          switch (choice) {
          case SEA_CHOICE_READONLY:  // "Open Read-Only"
            buf->b_p_ro = true;
            break;
          case SEA_CHOICE_EDIT:  // "Edit anyway"
            break;
          case SEA_CHOICE_RECOVER:  // "Recover"
            swap_exists_action = SEA_RECOVER;
            break;
          case SEA_CHOICE_DELETE:  // "Delete it"
            os_remove(fname);
            break;
          case SEA_CHOICE_QUIT:  // "Quit"
            swap_exists_action = SEA_QUIT;
            break;
          case SEA_CHOICE_ABORT:  // "Abort"
            swap_exists_action = SEA_QUIT;
            got_int = true;
            break;
          case SEA_CHOICE_NONE:
            msg_puts("\n");
            if (msg_silent == 0) {
              // call wait_return() later
              need_wait_return = true;
            }
            break;
          }

          // If the swapfile was deleted this `fname` can be used.
          if (choice != SEA_CHOICE_NONE && !os_path_exists(fname)) {
            break;
          }
        }
      }
    }

    // Permute the ".swp" extension to find a unique swapfile name.
    // First decrement the last char: ".swo", ".swn", etc.
    // If that still isn't enough decrement the last but one char: ".svz"
    // Can happen when many Nvim instances are editing the same file (including "No Name" buffers).
    if (fname[n - 1] == 'a') {          // ".s?a"
      if (fname[n - 2] == 'a') {        // ".saa": tried enough, give up
        emsg(_("E326: Too many swap files found"));
        XFREE_CLEAR(fname);
        break;
      }
      fname[n - 2]--;                   // ".svz", ".suz", etc.
      fname[n - 1] = 'z' + 1;
    }
    fname[n - 1]--;                     // ".swo", ".swn", etc.
  }

  if (os_isdir(dir_name)) {
    *found_existing_dir = true;
  } else if (!*found_existing_dir && **dirp == NUL) {
    int ret;
    char *failed_dir;
    if ((ret = os_mkdir_recurse(dir_name, 0755, &failed_dir, NULL)) != 0) {
      semsg(_("E303: Unable to create directory \"%s\" for swap file, "
              "recovery impossible: %s"),
            failed_dir, os_strerror(ret));
      xfree(failed_dir);
    }
  }

  xfree(dir_name);
  return fname;
}

static int b0_magic_wrong(ZeroBlock *b0p)
{
  return b0p->b0_magic_long != B0_MAGIC_LONG
         || b0p->b0_magic_int != B0_MAGIC_INT
         || b0p->b0_magic_short != (int16_t)B0_MAGIC_SHORT
         || b0p->b0_magic_char != B0_MAGIC_CHAR;
}

/// Compare current file name with file name from swapfile.
/// Try to use inode numbers when possible.
/// Return non-zero when files are different.
///
/// When comparing file names a few things have to be taken into consideration:
/// - When working over a network the full path of a file depends on the host.
///   We check the inode number if possible.  It is not 100% reliable though,
///   because the device number cannot be used over a network.
/// - When a file does not exist yet (editing a new file) there is no inode
///   number.
/// - The file name in a swapfile may not be valid on the current host.  The
///   "~user" form is used whenever possible to avoid this.
///
/// This is getting complicated, let's make a table:
///
///              ino_c  ino_s  fname_c  fname_s  differ =
///
/// both files exist -> compare inode numbers:
///              != 0   != 0     X        X      ino_c != ino_s
///
/// inode number(s) unknown, file names available -> compare file names
///              == 0    X       OK       OK     fname_c != fname_s
///               X     == 0     OK       OK     fname_c != fname_s
///
/// current file doesn't exist, file for swapfile exist, file name(s) not
/// available -> probably different
///              == 0   != 0    FAIL      X      true
///              == 0   != 0     X       FAIL    true
///
/// current file exists, inode for swap unknown, file name(s) not
/// available -> probably different
///              != 0   == 0    FAIL      X      true
///              != 0   == 0     X       FAIL    true
///
/// current file doesn't exist, inode for swap unknown, one file name not
/// available -> probably different
///              == 0   == 0    FAIL      OK     true
///              == 0   == 0     OK      FAIL    true
///
/// current file doesn't exist, inode for swap unknown, both file names not
/// available -> compare file names
///              == 0   == 0    FAIL     FAIL    fname_c != fname_s
///
/// Only the last 32 bits of the inode will be used. This can't be changed
/// without making the block 0 incompatible with 32 bit versions.
///
/// @param fname_c  current file name
/// @param fname_s  file name from swapfile
static bool fnamecmp_ino(char *fname_c, char *fname_s, long ino_block0)
{
  uint64_t ino_c = 0;               // ino of current file
  uint64_t ino_s;                   // ino of file from swapfile
  char buf_c[MAXPATHL];             // full path of fname_c
  char buf_s[MAXPATHL];             // full path of fname_s
  int retval_c;                     // flag: buf_c valid
  int retval_s;                     // flag: buf_s valid

  FileInfo file_info;
  if (os_fileinfo(fname_c, &file_info)) {
    ino_c = os_fileinfo_inode(&file_info);
  }

  // First we try to get the inode from the file name, because the inode in
  // the swapfile may be outdated.  If that fails (e.g. this path is not
  // valid on this machine), use the inode from block 0.
  if (os_fileinfo(fname_s, &file_info)) {
    ino_s = os_fileinfo_inode(&file_info);
  } else {
    ino_s = (uint64_t)ino_block0;
  }

  if (ino_c && ino_s) {
    return ino_c != ino_s;
  }

  // One of the inode numbers is unknown, try a forced vim_FullName() and
  // compare the file names.
  retval_c = vim_FullName(fname_c, buf_c, MAXPATHL, true);
  retval_s = vim_FullName(fname_s, buf_s, MAXPATHL, true);
  if (retval_c == OK && retval_s == OK) {
    return strcmp(buf_c, buf_s) != 0;
  }

  // Can't compare inodes or file names, guess that the files are different,
  // unless both appear not to exist at all, then compare with the file name
  // in the swapfile.
  if (ino_s == 0 && ino_c == 0 && retval_c == FAIL && retval_s == FAIL) {
    return strcmp(fname_c, fname_s) != 0;
  }
  return true;
}

/// Move a long integer into a four byte character array.
/// Used for machine independency in block zero.
static void long_to_char(long n, char *s_in)
{
  uint8_t *s = (uint8_t *)s_in;
  s[0] = (uint8_t)(n & 0xff);
  n = (unsigned)n >> 8;
  s[1] = (uint8_t)(n & 0xff);
  n = (unsigned)n >> 8;
  s[2] = (uint8_t)(n & 0xff);
  n = (unsigned)n >> 8;
  s[3] = (uint8_t)(n & 0xff);
}

static long char_to_long(const char *s_in)
{
  const uint8_t *s = (uint8_t *)s_in;

  long retval = s[3];
  retval <<= 8;
  retval |= s[2];
  retval <<= 8;
  retval |= s[1];
  retval <<= 8;
  retval |= s[0];

  return retval;
}

/// Set the flags in the first block of the swapfile:
/// - file is modified or not: buf->b_changed
/// - 'fileformat'
/// - 'fileencoding'
void ml_setflags(buf_T *buf)
{
  if (!buf->b_ml.ml_mfp) {
    return;
  }
  bhdr_T *hp = pmap_get(int64_t)(&buf->b_ml.ml_mfp->mf_hash, 0);
  if (hp) {
    ZeroBlock *b0p = hp->bh_data;
    b0p->b0_dirty = buf->b_changed ? B0_DIRTY : 0;
    b0p->b0_flags = (char)((b0p->b0_flags & ~B0_FF_MASK) | (uint8_t)(get_fileformat(buf) + 1));
    add_b0_fenc(b0p, buf);
    hp->bh_flags |= BH_DIRTY;
    mf_sync(buf->b_ml.ml_mfp, MFS_ZERO);
  }
}

enum {
  MLCS_MAXL = 800,  // max no of lines in chunk
  MLCS_MINL = 400,  // should be half of MLCS_MAXL
};

/// Keep information for finding byte offset of a line
///
/// @param updtype  may be one of:
///                 ML_CHNK_ADDLINE: Add len to parent chunk, possibly splitting it
///                         Careful: ML_CHNK_ADDLINE may cause ml_find_line() to be called.
///                 ML_CHNK_DELLINE: Subtract len from parent chunk, possibly deleting it
///                 ML_CHNK_UPDLINE: Add len to parent chunk, as a signed entity.
static void ml_updatechunk(buf_T *buf, linenr_T line, int len, int updtype)
{
  static buf_T *ml_upd_lastbuf = NULL;
  static linenr_T ml_upd_lastline;
  static linenr_T ml_upd_lastcurline;
  static int ml_upd_lastcurix;

  linenr_T curline = ml_upd_lastcurline;
  int curix = ml_upd_lastcurix;
  bhdr_T *hp;

  if (buf->b_ml.ml_usedchunks == -1 || len == 0) {
    return;
  }
  if (buf->b_ml.ml_chunksize == NULL) {
    buf->b_ml.ml_chunksize = xmalloc(sizeof(chunksize_T) * 100);
    buf->b_ml.ml_numchunks = 100;
    buf->b_ml.ml_usedchunks = 1;
    buf->b_ml.ml_chunksize[0].mlcs_numlines = 1;
    buf->b_ml.ml_chunksize[0].mlcs_totalsize = 1;
  }

  if (updtype == ML_CHNK_UPDLINE && buf->b_ml.ml_line_count == 1) {
    // First line in empty buffer from ml_flush_line() -- reset
    buf->b_ml.ml_usedchunks = 1;
    buf->b_ml.ml_chunksize[0].mlcs_numlines = 1;
    buf->b_ml.ml_chunksize[0].mlcs_totalsize = buf->b_ml.ml_line_len;
    return;
  }

  // Find chunk that our line belongs to, curline will be at start of the
  // chunk.
  if (buf != ml_upd_lastbuf || line != ml_upd_lastline + 1
      || updtype != ML_CHNK_ADDLINE) {
    for (curline = 1, curix = 0;
         curix < buf->b_ml.ml_usedchunks - 1
         && line >= curline +
         buf->b_ml.ml_chunksize[curix].mlcs_numlines;
         curix++) {
      curline += buf->b_ml.ml_chunksize[curix].mlcs_numlines;
    }
  } else if (curix < buf->b_ml.ml_usedchunks - 1
             && line >= curline + buf->b_ml.ml_chunksize[curix].mlcs_numlines) {
    // Adjust cached curix & curline
    curline += buf->b_ml.ml_chunksize[curix].mlcs_numlines;
    curix++;
  }
  chunksize_T *curchnk = buf->b_ml.ml_chunksize + curix;

  if (updtype == ML_CHNK_DELLINE) {
    len = -len;
  }
  curchnk->mlcs_totalsize += len;
  if (updtype == ML_CHNK_ADDLINE) {
    int rest;
    DataBlock *dp;
    curchnk->mlcs_numlines++;

    // May resize here so we don't have to do it in both cases below
    if (buf->b_ml.ml_usedchunks + 1 >= buf->b_ml.ml_numchunks) {
      buf->b_ml.ml_numchunks = buf->b_ml.ml_numchunks * 3 / 2;
      buf->b_ml.ml_chunksize = xrealloc(buf->b_ml.ml_chunksize,
                                        sizeof(chunksize_T) * (size_t)buf->b_ml.ml_numchunks);
    }

    if (buf->b_ml.ml_chunksize[curix].mlcs_numlines >= MLCS_MAXL) {
      int end_idx;
      int text_end;

      memmove(buf->b_ml.ml_chunksize + curix + 1,
              buf->b_ml.ml_chunksize + curix,
              (size_t)(buf->b_ml.ml_usedchunks - curix) * sizeof(chunksize_T));
      // Compute length of first half of lines in the split chunk
      int size = 0;
      int linecnt = 0;
      while (curline < buf->b_ml.ml_line_count
             && linecnt < MLCS_MINL) {
        if ((hp = ml_find_line(buf, curline, ML_FIND)) == NULL) {
          buf->b_ml.ml_usedchunks = -1;
          return;
        }
        dp = hp->bh_data;
        int count
          = buf->b_ml.ml_locked_high - buf->b_ml.ml_locked_low + 1;  // number of entries in block
        int idx = curline - buf->b_ml.ml_locked_low;
        curline = buf->b_ml.ml_locked_high + 1;
        // compute index of last line to use in this MEMLINE
        rest = count - idx;
        if (linecnt + rest > MLCS_MINL) {
          end_idx = idx + MLCS_MINL - linecnt - 1;
          linecnt = MLCS_MINL;
        } else {
          end_idx = count - 1;
          linecnt += rest;
        }
        if (idx == 0) {  // first line in block, text at the end
          text_end = (int)dp->db_txt_end;
        } else {
          text_end = ((dp->db_index[idx - 1]) & DB_INDEX_MASK);
        }
        size += text_end - (int)((dp->db_index[end_idx]) & DB_INDEX_MASK);
      }
      buf->b_ml.ml_chunksize[curix].mlcs_numlines = linecnt;
      buf->b_ml.ml_chunksize[curix + 1].mlcs_numlines -= linecnt;
      buf->b_ml.ml_chunksize[curix].mlcs_totalsize = size;
      buf->b_ml.ml_chunksize[curix + 1].mlcs_totalsize -= size;
      buf->b_ml.ml_usedchunks++;
      ml_upd_lastbuf = NULL;         // Force recalc of curix & curline
      return;
    } else if (buf->b_ml.ml_chunksize[curix].mlcs_numlines >= MLCS_MINL
               && curix == buf->b_ml.ml_usedchunks - 1
               && buf->b_ml.ml_line_count - line <= 1) {
      // We are in the last chunk and it is cheap to create a new one
      // after this. Do it now to avoid the loop above later on
      curchnk = buf->b_ml.ml_chunksize + curix + 1;
      buf->b_ml.ml_usedchunks++;
      if (line == buf->b_ml.ml_line_count) {
        curchnk->mlcs_numlines = 0;
        curchnk->mlcs_totalsize = 0;
      } else {
        // Line is just prior to last, move count for last
        // This is the common case  when loading a new file
        hp = ml_find_line(buf, buf->b_ml.ml_line_count, ML_FIND);
        if (hp == NULL) {
          buf->b_ml.ml_usedchunks = -1;
          return;
        }
        dp = hp->bh_data;
        if (dp->db_line_count == 1) {
          rest = (int)(dp->db_txt_end - dp->db_txt_start);
        } else {
          rest = (int)((dp->db_index[dp->db_line_count - 2]) & DB_INDEX_MASK)
                 - (int)dp->db_txt_start;
        }
        curchnk->mlcs_totalsize = rest;
        curchnk->mlcs_numlines = 1;
        curchnk[-1].mlcs_totalsize -= rest;
        curchnk[-1].mlcs_numlines -= 1;
      }
    }
  } else if (updtype == ML_CHNK_DELLINE) {
    curchnk->mlcs_numlines--;
    ml_upd_lastbuf = NULL;       // Force recalc of curix & curline
    if (curix < (buf->b_ml.ml_usedchunks - 1)
        && (curchnk->mlcs_numlines + curchnk[1].mlcs_numlines)
        <= MLCS_MINL) {
      curix++;
      curchnk = buf->b_ml.ml_chunksize + curix;
    } else if (curix == 0 && curchnk->mlcs_numlines <= 0) {
      buf->b_ml.ml_usedchunks--;
      memmove(buf->b_ml.ml_chunksize, buf->b_ml.ml_chunksize + 1,
              (size_t)buf->b_ml.ml_usedchunks * sizeof(chunksize_T));
      return;
    } else if (curix == 0 || (curchnk->mlcs_numlines > 10
                              && (curchnk->mlcs_numlines +
                                  curchnk[-1].mlcs_numlines)
                              > MLCS_MINL)) {
      return;
    }

    // Collapse chunks
    curchnk[-1].mlcs_numlines += curchnk->mlcs_numlines;
    curchnk[-1].mlcs_totalsize += curchnk->mlcs_totalsize;
    buf->b_ml.ml_usedchunks--;
    if (curix < buf->b_ml.ml_usedchunks) {
      memmove(buf->b_ml.ml_chunksize + curix,
              buf->b_ml.ml_chunksize + curix + 1,
              (size_t)(buf->b_ml.ml_usedchunks - curix) * sizeof(chunksize_T));
    }
    return;
  }
  ml_upd_lastbuf = buf;
  ml_upd_lastline = line;
  ml_upd_lastcurline = curline;
  ml_upd_lastcurix = curix;
}

/// Find offset for line or line with offset.
///
/// @param buf buffer to use
/// @param lnum if > 0, find offset of lnum, return offset
///             if == 0, return line with offset *offp
/// @param offp offset to use to find line, store remaining column offset
///             Should be NULL when getting offset of line
/// @param no_ff ignore 'fileformat' option, always use one byte for NL.
///
/// @return  -1 if information is not available
int ml_find_line_or_offset(buf_T *buf, linenr_T lnum, int *offp, bool no_ff)
{
  bhdr_T *hp;
  int text_end;
  int offset;
  int ffdos = !no_ff && (get_fileformat(buf) == EOL_DOS);
  int extra = 0;

  // take care of cached line first. Only needed if the cached line is before
  // the requested line. Additionally cache the value for the cached line.
  // This is used by the extmark code which needs the byte offset of the edited
  // line. So when doing multiple small edits on the same line the value is
  // only calculated once.
  //
  // NB: caching doesn't work with 'fileformat'. This is not a problem for
  // bytetracking, as bytetracking ignores 'fileformat' option. But calling
  // line2byte() will invalidate the cache for the time being (this function
  // was never cached to start with anyway).
  bool can_cache = (lnum != 0 && !ffdos && buf->b_ml.ml_line_lnum == lnum);
  if (lnum == 0 || buf->b_ml.ml_line_lnum < lnum || !no_ff) {
    ml_flush_line(curbuf, false);
  } else if (can_cache && buf->b_ml.ml_line_offset > 0) {
    return (int)buf->b_ml.ml_line_offset;
  }

  if (buf->b_ml.ml_usedchunks == -1
      || buf->b_ml.ml_chunksize == NULL
      || lnum < 0) {
    // memline is currently empty. Although if it is loaded,
    // it behaves like there is one empty line.
    if (no_ff && buf->b_ml.ml_mfp && (lnum == 1 || lnum == 2)) {
      return lnum - 1;
    }
    return -1;
  }

  if (offp == NULL) {
    offset = 0;
  } else {
    offset = *offp;
  }
  if (lnum == 0 && offset <= 0) {
    return 1;       // Not a "find offset" and offset 0 _must_ be in line 1
  }
  // Find the last chunk before the one containing our line. Last chunk is
  // special because it will never qualify.
  linenr_T curline = 1;
  int curix = 0;
  int size = 0;
  while (curix < buf->b_ml.ml_usedchunks - 1
         && ((lnum != 0
              && lnum >= curline + buf->b_ml.ml_chunksize[curix].mlcs_numlines)
             || (offset != 0
                 && offset > size +
                 buf->b_ml.ml_chunksize[curix].mlcs_totalsize
                 + ffdos * buf->b_ml.ml_chunksize[curix].mlcs_numlines))) {
    curline += buf->b_ml.ml_chunksize[curix].mlcs_numlines;
    size += buf->b_ml.ml_chunksize[curix].mlcs_totalsize;
    if (offset && ffdos) {
      size += buf->b_ml.ml_chunksize[curix].mlcs_numlines;
    }
    curix++;
  }

  while ((lnum != 0 && curline < lnum) || (offset != 0 && size < offset)) {
    if (curline > buf->b_ml.ml_line_count
        || (hp = ml_find_line(buf, curline, ML_FIND)) == NULL) {
      return -1;
    }
    DataBlock *dp = hp->bh_data;
    int count
      = buf->b_ml.ml_locked_high - buf->b_ml.ml_locked_low + 1;  // number of entries in block
    int idx;
    int start_idx = idx = curline - buf->b_ml.ml_locked_low;
    if (idx == 0) {  // first line in block, text at the end
      text_end = (int)dp->db_txt_end;
    } else {
      text_end = ((dp->db_index[idx - 1]) & DB_INDEX_MASK);
    }
    // Compute index of last line to use in this MEMLINE
    if (lnum != 0) {
      if (curline + (count - idx) >= lnum) {
        idx += lnum - curline - 1;
      } else {
        idx = count - 1;
      }
    } else {
      extra = 0;
      while (true) {
        if (!(offset >= size
              + text_end - (int)((dp->db_index[idx]) & DB_INDEX_MASK)
              + ffdos)) {
          break;
        }
        if (ffdos) {
          size++;
        }
        if (idx == count - 1) {
          extra = 1;
          break;
        }
        idx++;
      }
    }
    int len = text_end - (int)((dp->db_index[idx]) & DB_INDEX_MASK);
    size += len;
    if (offset != 0 && size >= offset) {
      if (size + ffdos == offset) {
        *offp = 0;
      } else if (idx == start_idx) {
        *offp = offset - size + len;
      } else {
        *offp = offset - size + len
                - (text_end - (int)((dp->db_index[idx - 1]) & DB_INDEX_MASK));
      }
      curline += idx - start_idx + extra;
      if (curline > buf->b_ml.ml_line_count) {
        return -1;              // exactly one byte beyond the end
      }
      return curline;
    }
    curline = buf->b_ml.ml_locked_high + 1;
  }

  if (lnum != 0) {
    // Count extra CR characters.
    if (ffdos) {
      size += lnum - 1;
    }

    // Don't count the last line break if 'noeol' and ('bin' or
    // 'nofixeol').
    if ((!buf->b_p_fixeol || buf->b_p_bin) && !buf->b_p_eol
        && lnum > buf->b_ml.ml_line_count) {
      size -= ffdos + 1;
    }
  }

  if (can_cache && size > 0) {
    buf->b_ml.ml_line_offset = (size_t)size;
  }

  return size;
}

/// Goto byte in buffer with offset 'cnt'.
void goto_byte(int cnt)
{
  int boff = cnt;

  ml_flush_line(curbuf, false);  // cached line may be dirty
  setpcmark();
  if (boff) {
    boff--;
  }
  linenr_T lnum = (linenr_T)ml_find_line_or_offset(curbuf, 0, &boff, false);
  if (lnum < 1) {         // past the end
    curwin->w_cursor.lnum = curbuf->b_ml.ml_line_count;
    curwin->w_curswant = MAXCOL;
    coladvance(curwin, MAXCOL);
  } else {
    curwin->w_cursor.lnum = lnum;
    curwin->w_cursor.col = (colnr_T)boff;
    curwin->w_cursor.coladd = 0;
    curwin->w_set_curswant = true;
  }
  check_cursor(curwin);

  // Make sure the cursor is on the first byte of a multi-byte char.
  mb_adjust_cursor();
}

/// Increment the line pointer "lp" crossing line boundaries as necessary.
///
/// @return   1 when going to the next line.
///           2 when moving forward onto a NUL at the end of the line).
///          -1 when at the end of file.
///           0 otherwise.
int inc(pos_T *lp)
{
  // when searching position may be set to end of a line
  if (lp->col != MAXCOL) {
    const char *const p = ml_get_pos(lp);
    if (*p != NUL) {  // still within line, move to next char (may be NUL)
      const int l = utfc_ptr2len(p);

      lp->col += l;
      return ((p[l] != NUL) ? 0 : 2);
    }
  }
  if (lp->lnum != curbuf->b_ml.ml_line_count) {     // there is a next line
    lp->col = 0;
    lp->lnum++;
    lp->coladd = 0;
    return 1;
  }
  return -1;
}

/// Same as inc(), but skip NUL at the end of non-empty lines.
int incl(pos_T *lp)
{
  int r;

  if ((r = inc(lp)) >= 1 && lp->col) {
    r = inc(lp);
  }
  return r;
}

int dec(pos_T *lp)
{
  lp->coladd = 0;
  if (lp->col == MAXCOL) {
    // past end of line
    char *p = ml_get(lp->lnum);
    lp->col = ml_get_len(lp->lnum);
    lp->col -= utf_head_off(p, p + lp->col);
    return 0;
  }

  if (lp->col > 0) {
    // still within line
    lp->col--;
    char *p = ml_get(lp->lnum);
    lp->col -= utf_head_off(p, p + lp->col);
    return 0;
  }
  if (lp->lnum > 1) {
    // there is a prior line
    lp->lnum--;
    char *p = ml_get(lp->lnum);
    lp->col = ml_get_len(lp->lnum);
    lp->col -= utf_head_off(p, p + lp->col);
    return 1;
  }

  // at start of file
  return -1;
}

/// Same as dec(), but skip NUL at the end of non-empty lines.
int decl(pos_T *lp)
{
  int r;

  if ((r = dec(lp)) == 1 && lp->col) {
    r = dec(lp);
  }
  return r;
}
