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)

NOTE: This is technically a breaking change... maybe this needs a different
solution? (Or maybe this issue can be ignored...)

A GitHub search reveals some plugins expect the old behaviour. However, many of
those plugins also do not seem to account for the string being translated, so
they are subtly broken anyway (not withstanding the fact that you can call any
old buffer "[Command Line]" too...)

closes: #12819

Signed-off-by: Sean Dewar <seandewar@users.noreply.github.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/doc/builtin.txt

@@ -1,4 +1,4 @@
-*builtin.txt*	For Vim version 9.1.  Last change: 2024 Jan 13
+*builtin.txt*	For Vim version 9.1.  Last change: 2024 Jan 23
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -3244,6 +3244,8 @@ getbufinfo([{dict}])
 			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

src/buffer.c

@@ -5936,6 +5936,8 @@ buf_spname(buf_T *buf)
 #endif
 	if (buf->b_fname != NULL)
 	    return buf->b_fname;
+	if (buf == cmdwin_buf)
+	    return (char_u *)_("[Command Line]");
 #ifdef FEAT_JOB_CHANNEL
 	if (bt_prompt(buf))
 	    return (char_u *)_("[Prompt]");

src/evalbuffer.c

@@ -653,6 +653,7 @@ get_buffer_info(buf_T *buf)
     dict_add_number(dict, "changedtick", CHANGEDTICK(buf));
     dict_add_number(dict, "hidden",
 			    buf->b_ml.ml_mfp != NULL && buf->b_nwindows == 0);
+    dict_add_number(dict, "command", buf == cmdwin_buf);
 
     // Get a reference to buffer variables
     dict_add_dict(dict, "variables", buf->b_vars);

src/ex_getln.c

@@ -4537,9 +4537,6 @@ open_cmdwin(void)
     }
     cmdwin_buf = curbuf;
 
-    apply_autocmds(EVENT_BUFFILEPRE, NULL, NULL, FALSE, curbuf);
-    (void)setfname(curbuf, (char_u *)_("[Command Line]"), NULL, TRUE);
-    apply_autocmds(EVENT_BUFFILEPOST, NULL, NULL, FALSE, curbuf);
     set_option_value_give_err((char_u *)"bt",
 					    0L, (char_u *)"nofile", OPT_LOCAL);
     curbuf->b_p_ma = TRUE;

src/testdir/test_cmdwin.vim

@@ -569,4 +569,18 @@ func Test_cmdwin_interrupted()
   delfunc CheckInterrupted
 endfunc
 
+func Test_cmdwin_existing_bufname()
+  func CheckName()
+    call assert_equal(1, getbufinfo('')[0].command)
+    call assert_equal(0, getbufinfo('[Command Line]')[0].command)
+    call assert_match('#a\s*"\[Command Line\]"', execute('ls'))
+    call assert_match('%a\s*"\[Command Line\]"', execute('ls'))
+  endfunc
+
+  file [Command Line]
+  call feedkeys("q::call CheckName()\<CR>:q\<CR>", 'ntx')
+  0file
+  delfunc CheckName
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/testdir/test_normal.vim

@@ -3158,7 +3158,7 @@ func Test_normal50_commandline()
   CheckFeature cmdline_hist
 
   func! DoTimerWork(id)
-    call assert_equal('[Command Line]', bufname(''))
+    call assert_equal(1, getbufinfo('')[0].command)
 
     " should fail, with E11, but does fail with E23?
     "call feedkeys("\<c-^>", 'tm')

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    49,
 /**/
     48,
 /**/