patch 9.2.0997: ch_sendexpr() cannot answer a request named with a string id

Problem:  A request that a server named with a string cannot be
          answered, since ch_sendexpr() rejects an "id" that is not a
          Number.
Solution: Require a Number only when Vim has to match a reply, which
          is with ch_evalexpr() or when a callback is given.  Send the
          message as it is otherwise (Hirohito Higashi).

fixes:  #14091
fixes:  #19003
closes: #21114
closes: #21126

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Signed-off-by: Hirohito Higashi <h.east.727@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/doc/channel.txt

@@ -812,6 +812,13 @@ ch_sendexpr({handle}, {expr} [, {options}])			*ch_sendexpr()*
 		If a response message is not expected for {expr}, then don't
 		specify the "callback" item in {options}.
 
+		In "lsp" mode an "id" item in {expr} is sent as it is when no
+		response is expected, which is how a request from the server
+		is answered; it may be of any type the server used.  When a
+		response is expected, with |ch_evalexpr()| or with the
+		"callback" item, Vim assigns the ID itself and the item must
+		be a |Number|.
+
 		Can also be used as a |method|: >
 			GetChannel()->ch_sendexpr(expr)
 <

runtime/doc/version9.txt

@@ -1,4 +1,4 @@
-*version9.txt*	For Vim version 9.2.  Last change: 2026 Aug 20
+*version9.txt*	For Vim version 9.2.  Last change: 2026 Aug 23
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -52705,7 +52705,8 @@ Changed ~
 - |extend()| and |extendnew()| also accept |Blobs|.
 - events like |CursorMoved| are no longer triggered for what happened while
   they were ignored with 'eventignore'.
-
+- |ch_sendexpr()| accepts a non-Number "id" in "lsp" mode when no response is
+  expected, so a request from the server can be answered.
 
 							*added-9.3*
 Added ~

src/channel.c

@@ -5120,6 +5120,7 @@ ch_expr_common(typval_T *argvars, typval_T *rettv, int eval)
     {
 	dict_T		*d;
 	dictitem_T	*di;
+	char		*key = ch_mode == CH_MODE_LSP ? "id" : "seq";
 
 	// return an empty dict by default
 	if (rettv_dict_alloc(rettv) == FAIL)
@@ -5129,22 +5130,20 @@ ch_expr_common(typval_T *argvars, typval_T *rettv, int eval)
 	    return;
 
 	d = argvars[1].vval.v_dict;
-	if (ch_mode == CH_MODE_LSP)
-	    di = dict_find(d, (char_u *)"id", -1);
-	else
-	    di = dict_find(d, (char_u *)"seq", -1);
-	if (di != NULL && di->di_tv.v_type != VAR_NUMBER)
+	di = dict_find(d, (char_u *)key, -1);
+	if (argvars[2].v_type == VAR_DICT
+		&& dict_has_key(argvars[2].vval.v_dict, "callback"))
+	    callback_present = TRUE;
+
+	// The id is what a reply is matched by, so it must be a number when
+	// one is waited for.
+	if (di != NULL && di->di_tv.v_type != VAR_NUMBER
+		&& (ch_mode == CH_MODE_DAP || eval || callback_present))
 	{
-	    // only number type is supported for the 'id' or 'seq' item
-	    semsg(_(e_invalid_value_for_argument_str),
-		    ch_mode == CH_MODE_LSP ? "id" : "seq");
+	    semsg(_(e_invalid_value_for_argument_str), key);
 	    return;
 	}
 
-	if (argvars[2].v_type == VAR_DICT)
-	    if (dict_has_key(argvars[2].vval.v_dict, "callback"))
-		callback_present = TRUE;
-
 	if (ch_mode == CH_MODE_DAP)
 	{
 	    // DAP message always has a sequence number (id)
@@ -5169,7 +5168,7 @@ ch_expr_common(typval_T *argvars, typval_T *rettv, int eval)
 	    // When sending an expression, if the message has an 'id' item,
 	    // then use it.
 	    id = 0;
-	    if (di != NULL)
+	    if (di != NULL && di->di_tv.v_type == VAR_NUMBER)
 		id = di->di_tv.vval.v_number;
 	}
 	if (ch_mode == CH_MODE_LSP && !dict_has_key(d, "jsonrpc"))

src/testdir/test_channel.vim

@@ -2809,9 +2809,20 @@ func LspTests(port)
   "       \ 'result': {'method': 'echo', 'jsonrpc': '2.0',
   "       \ 'params': {'m': 'raw-message'}}}], g:lspNotif)
 
+  " Test for sending a message with a String id, which is what answering a
+  " request from a server that named it with one takes
+  let g:lspNotif = []
+  call ch_sendexpr(ch, #{method: 'echo', id: 'e8a1-4c2f',
+        \ params: #{s: 'msg-with-string-id'}})
+  " Send a ping to wait for all the notification messages to arrive
+  call assert_equal('alive', ch_evalexpr(ch, #{method: 'ping'}).result)
+  call assert_equal([#{jsonrpc: '2.0', result:
+        \ #{method: 'echo', jsonrpc: '2.0', id: 'e8a1-4c2f',
+        \ params: #{s: 'msg-with-string-id'}}}], g:lspNotif)
+
   " Invalid arguments to ch_evalexpr() and ch_sendexpr()
-  call assert_fails('call ch_sendexpr(ch, #{method: "cookie", id: "cookie"})',
-        \ 'E475:')
+  call assert_fails('call ch_sendexpr(ch, #{method: "cookie", id: "cookie"},'
+        \ .. ' #{callback: "LspOtCb"})', 'E475:')
   call assert_fails('call ch_evalexpr(ch, #{method: "ping", id: [{}]})', 'E475:')
   call assert_fails('call ch_evalexpr(ch, [1, 2, 3])', 'E1206:')
   call assert_fails('call ch_sendexpr(ch, "abc")', 'E1206:')

src/version.c

@@ -763,6 +763,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    997,
 /**/
     996,
 /**/