vim-patch:8.2.0911: crash when opening a buffer for the cmdline window fails

Problem:    Crash when opening a buffer for the cmdline window fails. (Chris
            Barber)
Solution:   Check do_ecmd() succeeds.  Reset got_int if "q" was used at the
            more prompt. (closes vim/vim#6211)
9b7cce28d5

Make code match latest Vim instead.

src/nvim/buffer.c

@@ -4184,9 +4184,13 @@ void wipe_buffer(buf_T *buf, bool aucmd)
 /// @param bufnr     Buffer to switch to, or 0 to create a new buffer.
 ///
 /// @see curbufIsChanged()
-void buf_open_scratch(handle_T bufnr, char *bufname)
+///
+/// @return  FAIL for failure, OK otherwise
+int buf_open_scratch(handle_T bufnr, char *bufname)
 {
-  (void)do_ecmd((int)bufnr, NULL, NULL, NULL, ECMD_ONE, ECMD_HIDE, NULL);
+  if (do_ecmd((int)bufnr, NULL, NULL, NULL, ECMD_ONE, ECMD_HIDE, NULL) == FAIL) {
+    return FAIL;
+  }
   apply_autocmds(EVENT_BUFFILEPRE, NULL, NULL, false, curbuf);
   (void)setfname(curbuf, bufname, NULL, true);
   apply_autocmds(EVENT_BUFFILEPOST, NULL, NULL, false, curbuf);
@@ -4194,4 +4198,5 @@ void buf_open_scratch(handle_T bufnr, char *bufname)
   set_option_value_give_err("bt", 0L, "nofile", OPT_LOCAL);
   set_option_value_give_err("swf", 0L, NULL, OPT_LOCAL);
   RESET_BINDING(curwin);
+  return OK;
 }

src/nvim/ex_getln.c

@@ -4073,17 +4073,27 @@ static int open_cmdwin(void)
     ga_clear(&winsizes);
     return K_IGNORE;
   }
+  // Don't let quitting the More prompt make this fail.
+  got_int = false;
+
+  // Set "cmdwin_type" before any autocommands may mess things up.
   cmdwin_type = get_cmdline_type();
   cmdwin_level = ccline.level;
 
   // Create empty command-line buffer.
-  buf_open_scratch(0, _("[Command Line]"));
+  if (buf_open_scratch(0, _("[Command Line]")) == FAIL) {
+    // Some autocommand messed it up?
+    win_close(curwin, true, false);
+    ga_clear(&winsizes);
+    cmdwin_type = 0;
+    return Ctrl_C;
+  }
   // Command-line buffer has bufhidden=wipe, unlike a true "scratch" buffer.
   set_option_value_give_err("bh", 0L, "wipe", OPT_LOCAL);
-  curwin->w_p_rl = cmdmsg_rl;
-  cmdmsg_rl = false;
   curbuf->b_p_ma = true;
   curwin->w_p_fen = false;
+  curwin->w_p_rl = cmdmsg_rl;
+  cmdmsg_rl = false;
 
   // Don't allow switching to another buffer.
   curbuf->b_ro_locked++;

src/nvim/testdir/test_cmdline.vim

@@ -1453,6 +1453,33 @@ func Test_cmdwin_tabpage()
   tabclose!
 endfunc
 
+func Test_cmdwin_interrupted()
+  CheckScreendump
+
+  " aborting the :smile output caused the cmdline window to use the current
+  " buffer.
+  let lines =<< trim [SCRIPT]
+    au WinNew * smile
+  [SCRIPT]
+  call writefile(lines, 'XTest_cmdwin')
+
+  let buf = RunVimInTerminal('-S XTest_cmdwin', {'rows': 18})
+  call TermWait(buf, 1000)
+  " open cmdwin
+  call term_sendkeys(buf, "q:")
+  call TermWait(buf, 500)
+  " quit more prompt for :smile command
+  call term_sendkeys(buf, "q")
+  call TermWait(buf, 500)
+  " execute a simple command
+  call term_sendkeys(buf, "aecho 'done'\<CR>")
+  call VerifyScreenDump(buf, 'Test_cmdwin_interrupted', {})
+
+  " clean up
+  call StopVimInTerminal(buf)
+  call delete('XTest_cmdwin')
+endfunc
+
 " Test for backtick expression in the command line
 func Test_cmd_backtick()
   CheckNotMSWindows  " FIXME: see #19297

test/functional/legacy/cmdline_spec.lua

@@ -1,6 +1,7 @@
 local helpers = require('test.functional.helpers')(after_each)
 local Screen = require('test.functional.ui.screen')
 local clear = helpers.clear
+local command = helpers.command
 local feed = helpers.feed
 local feed_command = helpers.feed_command
 local exec = helpers.exec
@@ -141,3 +142,81 @@ describe('cmdline', function()
     ]])
   end)
 end)
+
+describe('cmdwin', function()
+  before_each(clear)
+
+  -- oldtest: Test_cmdwin_interrupted()
+  it('still uses a new buffer when interrupting more prompt on open', function()
+    local screen = Screen.new(30, 16)
+    screen:set_default_attr_ids({
+      [0] = {bold = true, foreground = Screen.colors.Blue},  -- NonText
+      [1] = {bold = true, reverse = true},  -- StatusLine
+      [2] = {reverse = true},  -- StatusLineNC
+      [3] = {bold = true, foreground = Screen.colors.SeaGreen},  -- MoreMsg
+      [4] = {bold = true},  -- ModeMsg
+    })
+    screen:attach()
+    command('set more')
+    command('autocmd WinNew * highlight')
+    feed('q:')
+    screen:expect({any = '{3:%-%- More %-%-}^'})
+    feed('q')
+    screen:expect([[
+                                    |
+      {0:~                             }|
+      {0:~                             }|
+      {0:~                             }|
+      {0:~                             }|
+      {0:~                             }|
+      {2:[No Name]                     }|
+      {0::}^                             |
+      {0:~                             }|
+      {0:~                             }|
+      {0:~                             }|
+      {0:~                             }|
+      {0:~                             }|
+      {0:~                             }|
+      {1:[Command Line]                }|
+                                    |
+    ]])
+    feed([[aecho 'done']])
+    screen:expect([[
+                                    |
+      {0:~                             }|
+      {0:~                             }|
+      {0:~                             }|
+      {0:~                             }|
+      {0:~                             }|
+      {2:[No Name]                     }|
+      {0::}echo 'done'^                  |
+      {0:~                             }|
+      {0:~                             }|
+      {0:~                             }|
+      {0:~                             }|
+      {0:~                             }|
+      {0:~                             }|
+      {1:[Command Line]                }|
+      {4:-- INSERT --}                  |
+    ]])
+    feed('<CR>')
+    screen:expect([[
+      ^                              |
+      {0:~                             }|
+      {0:~                             }|
+      {0:~                             }|
+      {0:~                             }|
+      {0:~                             }|
+      {0:~                             }|
+      {0:~                             }|
+      {0:~                             }|
+      {0:~                             }|
+      {0:~                             }|
+      {0:~                             }|
+      {0:~                             }|
+      {0:~                             }|
+      {0:~                             }|
+      done                          |
+    ]])
+  end)
+end)