vim-patch:9.1.0049: Make "[Command Line]" a special buffer name

Problem:  E95 is possible if a buffer called "[Command Line]" already
          exists when opening the cmdwin. This can also happen if the
          cmdwin's buffer could not be deleted when closing.

Solution: Un-name the cmdwin buffer, and give it a special name instead,
          similar to what's done for quickfix buffers and for unnamed
          prompt and scratch buffers. As a result, BufFilePre/Post are
          no longer fired when opening the cmdwin. Add a "command" key
          to the dictionary returned by getbufinfo() to differentiate
          the cmdwin buffer instead. (Sean Dewar)

Cherry-pick test_normal changes from v9.0.0954.

https://github.com/vim/vim/commit/1fb41032060df09ca2640dc49541f11062f6dfaa

4 files changed, 13 insertions, 4 deletions

diff --git a/src/nvim/buffer.c b/src/nvim/buffer.c
index da1e27aebf..d597d82ee2 100644
--- a/src/nvim/buffer.c
+++ b/src/nvim/buffer.c
@@ -4012,6 +4012,9 @@ char *buf_spname(buf_T *buf)
     if (buf->b_fname != NULL) {
       return buf->b_fname;
     }
+    if (buf == cmdwin_buf) {
+      return _("[Command Line]");
+    }
     if (bt_prompt(buf)) {
       return _("[Prompt]");
     }
@@ -4129,6 +4132,7 @@ void wipe_buffer(buf_T *buf, bool aucmd)
 ///   - Always considered 'nomodified'
 ///
 /// @param bufnr     Buffer to switch to, or 0 to create a new buffer.
+/// @param bufname   Buffer name, or NULL.
 ///
 /// @see curbufIsChanged()
 ///
@@ -4138,9 +4142,11 @@ int buf_open_scratch(handle_T bufnr, char *bufname)
   if (do_ecmd((int)bufnr, NULL, NULL, NULL, ECMD_ONE, ECMD_HIDE, NULL) == FAIL) {
     return FAIL;
   }
-  apply_autocmds(EVENT_BUFFILEPRE, NULL, NULL, false, curbuf);
-  setfname(curbuf, bufname, NULL, true);
-  apply_autocmds(EVENT_BUFFILEPOST, NULL, NULL, false, curbuf);
+  if (bufname != NULL) {
+    apply_autocmds(EVENT_BUFFILEPRE, NULL, NULL, false, curbuf);
+    setfname(curbuf, bufname, NULL, true);
+    apply_autocmds(EVENT_BUFFILEPOST, NULL, NULL, false, curbuf);
+  }
   set_option_value_give_err(kOptBufhidden, STATIC_CSTR_AS_OPTVAL("hide"), OPT_LOCAL);
   set_option_value_give_err(kOptBuftype, STATIC_CSTR_AS_OPTVAL("nofile"), OPT_LOCAL);
   set_option_value_give_err(kOptSwapfile, BOOLEAN_OPTVAL(false), OPT_LOCAL);
diff --git a/src/nvim/eval.lua b/src/nvim/eval.lua
index 9f50fd1758..bc976eaa58 100644
--- a/src/nvim/eval.lua
+++ b/src/nvim/eval.lua
@@ -3219,6 +3219,8 @@ M.funcs = {
       	bufnr		Buffer number.
       	changed		TRUE if the buffer is modified.
       	changedtick	Number of changes made to the buffer.
+      	command		TRUE if the buffer belongs to the
+      			command-line window |cmdwin|.
       	hidden		TRUE if the buffer is hidden.
       	lastused	Timestamp in seconds, like
       			|localtime()|, when the buffer was
diff --git a/src/nvim/eval/buffer.c b/src/nvim/eval/buffer.c
index c43ef50410..7b8f71ef3f 100644
--- a/src/nvim/eval/buffer.c
+++ b/src/nvim/eval/buffer.c
@@ -494,6 +494,7 @@ static dict_T *get_buffer_info(buf_T *buf)
   tv_dict_add_nr(dict, S_LEN("changed"), bufIsChanged(buf));
   tv_dict_add_nr(dict, S_LEN("changedtick"), buf_get_changedtick(buf));
   tv_dict_add_nr(dict, S_LEN("hidden"), buf->b_ml.ml_mfp != NULL && buf->b_nwindows == 0);
+  tv_dict_add_nr(dict, S_LEN("command"), buf == cmdwin_buf);
 
   // Get a reference to buffer variables
   tv_dict_add_dict(dict, S_LEN("variables"), buf->b_vars);
diff --git a/src/nvim/ex_getln.c b/src/nvim/ex_getln.c
index 9b56fffeda..307fd480cc 100644
--- a/src/nvim/ex_getln.c
+++ b/src/nvim/ex_getln.c
@@ -4345,7 +4345,7 @@ static int open_cmdwin(void)
 
   // Create empty command-line buffer.  Be especially cautious of BufLeave
   // autocommands from do_ecmd(), as cmdwin restrictions do not apply to them!
-  const int newbuf_status = buf_open_scratch(0, _("[Command Line]"));
+  const int newbuf_status = buf_open_scratch(0, NULL);
   const bool cmdwin_valid = win_valid(cmdwin_win);
   if (newbuf_status == FAIL || !cmdwin_valid || curwin != cmdwin_win || !win_valid(old_curwin)
       || !bufref_valid(&old_curbuf) || old_curwin->w_buffer != old_curbuf.br_buf) {