feat(terminal): include sequence terminator in TermRequest event (#37152)

Problem:
Terminals should respond with the terminator (either BEL or ST) used in
the query so that clients can reliably parse the responses. The
`TermRequest` autocmd used to handle background color requests in the
terminal does not have access to the original sequence terminator, so it
always uses BEL. #37018

Solution:
Update vterm parsing to include the terminator type, then forward this
data into the emitted `TermRequest` events for OSC/DCS/APC sequences.
Update the foreground/background `TermRequest` callback to use the same
terminator as the original request.

Details:
I didn't add the terminator to the `TermResponse` event. However, I
assume the `TermResponse` event doesn't care about the terminator
because the sequence is already parsed. I also didn't update any of the
functions in `src/nvim/vterm/state.c` that write out responses. It
looked like those all pretty much used ST, and it would be a much larger
set of changes. In that same file, there's also logic for 8 bit ST
sequences, but from what I can tell, 8 bit doesn't really work (see `:h
xterm-8bit`), so I didn't use the 8 bit ST at all.

runtime/doc/autocmd.txt

@@ -1081,6 +1081,7 @@ TermRequest			When a |:terminal| child process emits an OSC,
 				fields:
 
 				- sequence: the received sequence
+				- terminator: the received sequence terminator (i.e. BEL or ST)
 				- cursor: (1,0)-indexed, buffer-relative
 				  position of the cursor when the sequence was
 				  received (line number may be <= 0 if the

runtime/doc/news.txt

@@ -231,6 +231,7 @@ EVENTS
 • Creating or updating a progress message with |nvim_echo()| triggers a |Progress| event.
 • |MarkSet| is triggered after a |mark| is set by the user (currently doesn't
   support implicit marks like |'[| or |'<|, …).
+• New `terminator` parameter for |TermRequest| event.
 
 HIGHLIGHTS
 

runtime/lua/vim/_defaults.lua

@@ -567,7 +567,14 @@ do
           red, green, blue = 65535, 65535, 65535
         end
         local command = fg_request and 10 or 11
-        local data = string.format('\027]%d;rgb:%04x/%04x/%04x\007', command, red, green, blue)
+        local data = string.format(
+          '\027]%d;rgb:%04x/%04x/%04x%s',
+          command,
+          red,
+          green,
+          blue,
+          args.data.terminator
+        )
         vim.api.nvim_chan_send(channel, data)
       end
     end,

src/nvim/terminal.c

@@ -202,6 +202,7 @@ struct terminal {
   StringBuilder selection;  ///< Growable array containing full selection data
 
   StringBuilder termrequest_buffer;  ///< Growable array containing unfinished request sequence
+  VTermTerminator termrequest_terminator;  ///< Terminator (BEL or ST) used in the termrequest
 
   size_t refcount;                  // reference count
 };
@@ -234,6 +235,7 @@ static void emit_termrequest(void **argv)
   int row = (int)(intptr_t)argv[4];
   int col = (int)(intptr_t)argv[5];
   size_t sb_deleted = (size_t)(intptr_t)argv[6];
+  VTermTerminator terminator = (VTermTerminator)(intptr_t)argv[7];
 
   if (term->sb_pending > 0) {
     // Don't emit the event while there is pending scrollback because we need
@@ -242,7 +244,7 @@ static void emit_termrequest(void **argv)
     // terminal is refreshed and the pending scrollback is cleared.
     multiqueue_put(term->pending.events, emit_termrequest, term, sequence, (void *)sequence_length,
                    pending_send, (void *)(intptr_t)row, (void *)(intptr_t)col,
-                   (void *)(intptr_t)sb_deleted);
+                   (void *)(intptr_t)sb_deleted, (void *)(intptr_t)terminator);
     return;
   }
 
@@ -252,10 +254,13 @@ static void emit_termrequest(void **argv)
   ADD_C(cursor, INTEGER_OBJ(row - (int64_t)(term->sb_deleted - sb_deleted)));
   ADD_C(cursor, INTEGER_OBJ(col));
 
-  MAXSIZE_TEMP_DICT(data, 2);
+  MAXSIZE_TEMP_DICT(data, 3);
   String termrequest = { .data = sequence, .size = sequence_length };
   PUT_C(data, "sequence", STRING_OBJ(termrequest));
   PUT_C(data, "cursor", ARRAY_OBJ(cursor));
+  PUT_C(data, "terminator",
+        terminator ==
+        VTERM_TERMINATOR_BEL ? STATIC_CSTR_AS_OBJ("\x07") : STATIC_CSTR_AS_OBJ("\x1b\\"));
 
   buf_T *buf = handle_get_buffer(term->buf_handle);
   apply_autocmds_group(EVENT_TERMREQUEST, NULL, NULL, true, AUGROUP_ALL, buf, NULL,
@@ -284,7 +289,8 @@ static void schedule_termrequest(Terminal *term)
                  xmemdup(term->termrequest_buffer.items, term->termrequest_buffer.size),
                  (void *)(intptr_t)term->termrequest_buffer.size, term->pending.send,
                  (void *)(intptr_t)line, (void *)(intptr_t)term->cursor.col,
-                 (void *)(intptr_t)term->sb_deleted);
+                 (void *)(intptr_t)term->sb_deleted,
+                 (void *)(intptr_t)term->termrequest_terminator);
 }
 
 static int parse_osc8(const char *str, int *attr)
@@ -336,6 +342,7 @@ static int on_osc(int command, VTermStringFragment frag, void *user)
   }
   kv_concat_len(term->termrequest_buffer, frag.str, frag.len);
   if (frag.final) {
+    term->termrequest_terminator = frag.terminator;
     if (has_event(EVENT_TERMREQUEST)) {
       schedule_termrequest(term);
     }
@@ -370,6 +377,7 @@ static int on_dcs(const char *command, size_t commandlen, VTermStringFragment fr
   }
   kv_concat_len(term->termrequest_buffer, frag.str, frag.len);
   if (frag.final) {
+    term->termrequest_terminator = frag.terminator;
     schedule_termrequest(term);
   }
   return 1;
@@ -392,6 +400,7 @@ static int on_apc(VTermStringFragment frag, void *user)
   }
   kv_concat_len(term->termrequest_buffer, frag.str, frag.len);
   if (frag.final) {
+    term->termrequest_terminator = frag.terminator;
     schedule_termrequest(term);
   }
   return 1;

src/nvim/vterm/parser.c

@@ -72,13 +72,15 @@ static void do_escape(VTerm *vt, char command)
   DEBUG_LOG("libvterm: Unhandled escape ESC 0x%02x\n", command);
 }
 
-static void string_fragment(VTerm *vt, const char *str, size_t len, bool final)
+static void string_fragment(VTerm *vt, const char *str, size_t len, bool final,
+                            VTermTerminator terminator)
 {
   VTermStringFragment frag = {
     .str = str,
     .len = len,
     .initial = vt->parser.string_initial,
     .final = final,
+    .terminator = terminator,
   };
 
   switch (vt->parser.state) {
@@ -160,7 +162,8 @@ size_t vterm_input_write(VTerm *vt, const char *bytes, size_t len)
 
     if (c == 0x00 || c == 0x7f) {  // NUL, DEL
       if (IS_STRING_STATE()) {
-        string_fragment(vt, string_start, (size_t)(bytes + pos - string_start), false);
+        string_fragment(vt, string_start, (size_t)(bytes + pos - string_start), false,
+                        VTERM_TERMINATOR_ST);
         string_start = bytes + pos + 1;
       }
       if (vt->parser.emit_nul) {
@@ -188,7 +191,8 @@ size_t vterm_input_write(VTerm *vt, const char *bytes, size_t len)
         continue;  // All other C0s permitted in SOS
       }
       if (IS_STRING_STATE()) {
-        string_fragment(vt, string_start, (size_t)(bytes + pos - string_start), false);
+        string_fragment(vt, string_start, (size_t)(bytes + pos - string_start), false,
+                        VTERM_TERMINATOR_ST);
       }
       do_control(vt, c);
       if (IS_STRING_STATE()) {
@@ -316,7 +320,8 @@ string_state:
     case PM:
     case SOS:
       if (c == 0x07 || (c1_allowed && c == 0x9c)) {
-        string_fragment(vt, string_start, string_len, true);
+        string_fragment(vt, string_start, string_len, true,
+                        c == 0x07 ? VTERM_TERMINATOR_BEL : VTERM_TERMINATOR_ST);
         ENTER_NORMAL_STATE();
       }
       break;
@@ -395,7 +400,7 @@ string_state:
       if (vt->parser.in_esc) {
         string_len -= 1;
       }
-      string_fragment(vt, string_start, string_len, false);
+      string_fragment(vt, string_start, string_len, false, VTERM_TERMINATOR_ST);
     }
   }
 

src/nvim/vterm/vterm_defs.h

@@ -91,11 +91,17 @@ typedef enum {
   VTERM_N_PROPS,
 } VTermProp;
 
+typedef enum {
+  VTERM_TERMINATOR_BEL,  // \x07
+  VTERM_TERMINATOR_ST,  // \x1b\x5c
+} VTermTerminator;
+
 typedef struct {
   const char *str;
   size_t len : 30;
   bool initial : 1;
   bool final : 1;
+  VTermTerminator terminator;
 } VTermStringFragment;
 
 typedef union {

test/functional/terminal/parser_spec.lua

@@ -1,11 +1,13 @@
 local n = require('test.functional.testnvim')()
 
-local clear = n.clear
 local api = n.api
 local assert_alive = n.assert_alive
+local clear = n.clear
+local exec_lua = n.exec_lua
 
 local OSC_PREFIX = string.char(0x1b, 0x5d)
 local BEL = string.char(0x07)
+local ST = string.char(0x1b, 0x5c)
 local NUL = string.char(0x00)
 
 describe(':terminal', function()
@@ -60,4 +62,34 @@ describe(':terminal', function()
     api.nvim_chan_send(chan, input)
     assert_alive()
   end)
+
+  it('uses terminator matching query for OSC TermRequest #37018', function()
+    local chan = api.nvim_open_term(0, {})
+    exec_lua([[
+      vim.api.nvim_create_autocmd("TermRequest", {
+        callback = function(args)
+          _G.osc10_response = {sequence = args.data.sequence, terminator = args.data.terminator }
+        end
+      })
+    ]])
+
+    local function send_osc_with_terminator(terminator)
+      local input = OSC_PREFIX .. '10;?' .. terminator
+      api.nvim_chan_send(chan, input)
+    end
+
+    send_osc_with_terminator(BEL)
+    --- @type string
+    assert.same(
+      { sequence = OSC_PREFIX .. '10;?', terminator = BEL },
+      exec_lua([[return _G.osc10_response]])
+    )
+
+    send_osc_with_terminator(ST)
+    --- @type string
+    assert.same(
+      { sequence = OSC_PREFIX .. '10;?', terminator = ST },
+      exec_lua([[return _G.osc10_response]])
+    )
+  end)
 end)