vim-patch:9.1.2138: win_execute() and 'autochdir' can corrupt buffer name (#37767)

Problem:  With 'autochdir' win_execute() can corrupt the buffer name,
          causing :write to use wrong path.
Solution: Save and restore b_fname when 'autochdir' is active
          (Ingo Karkat).

This is caused by a bad interaction of the 'autochdir' behavior,
overriding of the current directory via :lchdir, and the temporary
window switching done by win_execute(), manifesting when e.g. a custom
completion inspects other buffers:
1. In the initial state after the :lcd .. we have curbuf->b_fname =
   "Xsubdir/file".
2. do_autochdir() is invoked, temporarily undoing the :lcd .., changing
   back into the Xsubdir/ subdirectory.
3. win_execute() switches windows, triggering win_enter_ext() →
   win_fix_current_dir() → shorten_fnames(TRUE)
4. shorten_fnames() processes *all* buffers
5. shorten_buf_fname() makes the filename relative to the current
   (wrong) directory; b_fname becomes "file" instead of "Xsubdir/file"
6. Directory restoration correctly restores working directory via
   mch_chdir() (skipping a second do_autochdir() invocation because
   apply_acd is FALSE), but b_fname remains corrupted, with the
   "Xsubdir/" part missing.
7. expand("%:p") (and commands like :write) continue to use the
   corrupted filename, resolving to a wrong path that's missing the
   "Xsubdir/" part.

To fix the problem the short filename is saved if its in effect (i.e.
pointed to by curbuf->b_fname) and 'autochdir' happened. It's then
restored in case of a local cwd override. The conditions limit this
workaround to when 'autochdir' is active *and* overridden by a :lchdir.

closes: vim/vim#19343

abb4d74033

Co-authored-by: Ingo Karkat <swdev@ingo-karkat.de>

src/nvim/eval/window.c

@@ -509,6 +509,7 @@ bool win_execute_before(win_execute_T *args, win_T *wp, tabpage_T *tp)
   args->curpos = wp->w_cursor;
   args->cwd_status = FAIL;
   args->apply_acd = false;
+  args->save_sfname = NULL;
 
   // Getting and setting directory can be slow on some systems, only do
   // this when the current or target window/tab have a local directory or
@@ -523,6 +524,9 @@ bool win_execute_before(win_execute_T *args, win_T *wp, tabpage_T *tp)
   // If 'acd' is set, check we are using that directory.  If yes, then
   // apply 'acd' afterwards, otherwise restore the current directory.
   if (args->cwd_status == OK && p_acd) {
+    if (curbuf->b_sfname != NULL && curbuf->b_fname == curbuf->b_sfname) {
+      args->save_sfname = xstrdup(curbuf->b_sfname);
+    }
     do_autochdir();
     char autocwd[MAXPATHL];
     if (os_dirname(autocwd, MAXPATHL) == OK) {
@@ -543,9 +547,15 @@ void win_execute_after(win_execute_T *args)
   restore_win_noblock(&args->switchwin, true);
 
   if (args->apply_acd) {
+    xfree(args->save_sfname);
     do_autochdir();
   } else if (args->cwd_status == OK) {
     os_chdir(args->cwd);
+    if (args->save_sfname != NULL) {
+      xfree(curbuf->b_sfname);
+      curbuf->b_sfname = args->save_sfname;
+      curbuf->b_fname = curbuf->b_sfname;
+    }
   }
 
   // Update the status line if the cursor moved.

src/nvim/eval/window.h

@@ -23,6 +23,7 @@ typedef struct {
   char cwd[MAXPATHL];
   int cwd_status;
   bool apply_acd;
+  char *save_sfname;
   switchwin_T switchwin;
 } win_execute_T;
 

test/functional/legacy/autochdir_spec.lua

@@ -32,6 +32,7 @@ describe('autochdir behavior', function()
     eq(dir, eval([[substitute(getcwd(), '.*/\(\k*\)', '\1', '')]]))
   end)
 
+  -- oldtest: Test_set_filename_other_window()
   it(':file in win_execute() does not cause wrong directory', function()
     command('cd ' .. dir)
     source([[
@@ -64,6 +65,7 @@ describe('autochdir behavior', function()
     expected_empty()
   end)
 
+  -- oldtest: Test_acd_win_execute()
   it('win_execute() does not change directory', function()
     local subdir = 'Xfile'
     command('cd ' .. dir)
@@ -78,6 +80,7 @@ describe('autochdir behavior', function()
     matches(dir .. '$', eval('getcwd()'))
   end)
 
+  -- oldtest: Test_verbose_pwd()
   it(':verbose pwd shows whether autochdir is used', function()
     local subdir = 'Xautodir'
     command('cd ' .. dir)
@@ -115,4 +118,28 @@ describe('autochdir behavior', function()
     command('wincmd w')
     matches('%[window%].*' .. dir .. '/' .. subdir .. '$', exec_capture('verbose pwd'))
   end)
+
+  it('overriding via :lcd is not clobbered by win_execute()', function()
+    command('cd ' .. dir)
+    source([[
+      func Test_lcd_win_execute()
+        let startdir = getcwd()
+        call mkdir('Xsubdir', 'R')
+        set autochdir
+        edit Xsubdir/file
+        call assert_match('_autochdir.Xsubdir.file$', expand('%:p'))
+        split
+        lcd ..
+        call assert_match('_autochdir.Xsubdir.file$', expand('%:p'))
+        call win_execute(win_getid(2), "")
+        call assert_match('_autochdir.Xsubdir.file$', expand('%:p'))
+
+        set noautochdir
+        bwipe!
+        call chdir(startdir)
+      endfunc
+    ]])
+    call('Test_lcd_win_execute')
+    expected_empty()
+  end)
 end)

test/old/testdir/test_cd.vim

@@ -192,6 +192,28 @@ func Test_lcd_split()
   quit!
 endfunc
 
+" Test that a temporary override of 'autochdir' via :lcd isn't clobbered by win_execute() in a split window.
+func Test_lcd_win_execute()
+  CheckFunction test_autochdir
+  CheckOption autochdir
+
+  let startdir = getcwd()
+  call mkdir('Xsubdir', 'R')
+  call test_autochdir()
+  set autochdir
+  edit Xsubdir/file
+  call assert_match('testdir.Xsubdir.file$', expand('%:p'))
+  split
+  lcd ..
+  call assert_match('testdir.Xsubdir.file$', expand('%:p'))
+  call win_execute(win_getid(2), "")
+  call assert_match('testdir.Xsubdir.file$', expand('%:p'))
+
+  set noautochdir
+  bwipe!
+  call chdir(startdir)
+endfunc
+
 func Test_cd_from_non_existing_dir()
   CheckNotMSWindows