fix(extui): route interactive messages to more-window (#33885)

Problem:  Extui does not route messages emitted as a result of a typed
          command to the "more" window.
          Command message leading shell messages is missing a kind.
          Messages not routed to 'cmdheight' area after it was 0.
Solution: Route messages that were emitted in the same event loop as an
          entered command to the "more" window. Also append multiple
          messages in an already open more-window.
          Assign it the `shell_cmd` kind.
          Change message position when 'cmdheight' changes from 0.

runtime/doc/ui.txt

@@ -832,6 +832,7 @@ must handle.
 		"quickfix"	Quickfix navigation message
 		"search_cmd"	Entered search command
 		"search_count"	Search count message ("S" flag of 'shortmess')
+		"shell_cmd"	|:!cmd| executed command
 		"shell_err"	|:!cmd| shell stderr output
 		"shell_out"	|:!cmd| shell stdout output
 		"shell_ret"	|:!cmd| shell return code

runtime/lua/vim/_extui.lua

@@ -82,10 +82,14 @@ function M.enable(opts)
   local function check_opt(name, value)
     if name == 'cmdheight' then
       -- 'cmdheight' set; (un)hide cmdline window and set its height.
-      ext.cmdheight = value
+      local cfg = { height = math.max(value, 1), hide = value == 0 }
-      ext.cfg.msg.pos = ext.cmdheight == 0 and 'box' or ext.cfg.msg.pos
-      local cfg = { height = math.max(ext.cmdheight, 1), hide = ext.cmdheight == 0 }
       api.nvim_win_set_config(ext.wins[ext.tab].cmd, cfg)
+      -- Change message position when 'cmdheight' was or becomes 0.
+      if value == 0 or ext.cmdheight == 0 then
+        ext.cfg.msg.pos = value == 0 and 'box' or ext.cmdheight == 0 and 'cmd'
+        ext.msg.prev_msg = ''
+      end
+      ext.cmdheight = value
     elseif name == 'termguicolors' then
       -- 'termguicolors' toggled; add or remove border and set 'winblend' for box windows.
       for _, tab in ipairs(api.nvim_list_tabpages()) do

runtime/lua/vim/_extui/cmdline.lua

@@ -6,7 +6,7 @@ local M = {
   indent = 0, -- Current indent for block event.
   prompt = false, -- Whether a prompt is active; messages are placed in the 'prompt' window.
   row = 0, -- Current row in the cmdline buffer, > 0 for block events.
-  level = 0, -- Current cmdline level, 0 when inactive (otherwise unused).
+  level = -1, -- Current cmdline level, 0 when inactive, -1 one loop iteration after closing.
 }
 
 --- Set the 'cmdheight' and cmdline window height. Reposition message windows.
@@ -121,16 +121,21 @@ function M.cmdline_hide(_, abort)
     api.nvim_buf_set_lines(ext.bufs.cmd, 0, -1, false, {})
   end
 
+  local clear = vim.schedule_wrap(function(was_prompt)
     -- Avoid clearing prompt window when it is re-entered before the next event
     -- loop iteration. E.g. when a non-choice confirm button is pressed.
-  if M.prompt then
+    if was_prompt and not M.prompt then
-    vim.schedule(function()
-      if not M.prompt then
       api.nvim_buf_set_lines(ext.bufs.cmd, 0, -1, false, {})
       api.nvim_win_set_config(ext.wins[ext.tab].prompt, { hide = true })
     end
+    -- Messages emitted as a result of a typed command are treated specially:
+    -- remember if the cmdline was used this event loop iteration.
+    -- NOTE: Message event callbacks are themselves scheduled, so delay two iterations.
+    vim.schedule(function()
+      M.level = -1
     end)
-  end
+  end)
+  clear(M.prompt)
 
   M.prompt, M.level, curpos[1], curpos[2] = false, 0, 0, 0
   win_config(ext.wins[ext.tab].cmd, true, ext.cmdheight)

runtime/lua/vim/_extui/messages.lua

@@ -219,8 +219,9 @@ function M.show_msg(tar, content, replace_last, more)
     local srow, scol = row, col
     -- Split at newline and concatenate first and last message chunks.
     for str in (chunk[2] .. '\0'):gmatch('.-[\n%z]') do
-      local idx = i > 1 and row == srow and 0 or 1
+      local idx = #lines + (i > 1 and row == srow and 0 or 1)
-      lines[#lines + idx] = idx > 0 and str:sub(1, -2) or lines[#lines] .. str:sub(1, -2)
+      -- Filter out NL, CRs and appended NUL. TODO: actually handle carriage return?
+      lines[idx] = (lines[idx] or '') .. str:gsub('[\n\r%z]', '')
       col = #lines[#lines]
       row = row + (str:sub(-1) == '\0' and 0 or 1)
       if tar == 'box' then
@@ -279,6 +280,7 @@ function M.show_msg(tar, content, replace_last, more)
   end
 end
 
+local append_more = 0
 local replace_bufwrite = false
 --- Route the message to the appropriate sink.
 ---
@@ -302,7 +304,7 @@ function M.msg_show(kind, content)
   elseif kind == 'return_prompt' then
     -- Bypass hit enter prompt.
     vim.api.nvim_feedkeys(vim.keycode('<CR>'), 'n', false)
-  elseif kind == 'verbose' then
+  elseif kind == 'verbose' and append_more == 0 then
     -- Verbose messages are sent too often to be meaningful in the cmdline:
     -- always route to box regardless of cfg.msg.pos.
     M.show_msg('box', content, false)
@@ -323,7 +325,9 @@ function M.msg_show(kind, content)
       M.virt.last[M.virt.idx.search][1] = nil
     end
 
-    M.show_msg(tar, content, replace_bufwrite, kind == 'list_cmd')
+    -- Messages sent as a result of a typed command should be routed to the more window.
+    local more = ext.cmd.level >= 0 or kind == 'list_cmd'
+    M.show_msg(tar, content, replace_bufwrite, more)
     -- Replace message for every second bufwrite message.
     replace_bufwrite = not replace_bufwrite and kind == 'bufwrite'
   end
@@ -367,9 +371,14 @@ function M.msg_history_show(entries)
     return
   end
 
+  -- Appending messages while 'more' window is open.
+  append_more = entries[1][1] == 'spill' and append_more + 1 or 0
+  if append_more < 2 then
     api.nvim_buf_set_lines(ext.bufs.more, 0, -1, false, {})
+  end
+
   for i, entry in ipairs(entries) do
-    M.show_msg('more', entry[2], i == 1)
+    M.show_msg('more', entry[2], i == 1 and append_more < 2)
   end
 
   M.set_pos('more')
@@ -402,6 +411,7 @@ function M.set_pos(type)
           if api.nvim_win_is_valid(win) then
             api.nvim_win_set_config(win, { hide = true })
           end
+          append_more = 0
         end,
         desc = 'Hide inactive more window.',
       })

src/nvim/ex_cmds.c

@@ -1025,6 +1025,7 @@ void do_bang(int addr_count, exarg_T *eap, bool forceit, bool do_in, bool do_out
   if (addr_count == 0) {                // :!
     // echo the command
     msg_start();
+    msg_ext_set_kind("shell_cmd");
     msg_putchar(':');
     msg_putchar('!');
     msg_outtrans(newcmd, 0, false);

test/functional/ui/messages_spec.lua

@@ -463,7 +463,7 @@ describe('ui/ext_messages', function()
         {
           content = { { (':!%s\r\n[No write since last change]\n'):format(cmd) } },
           history = false,
-          kind = '',
+          kind = 'shell_cmd',
         },
         {
           content = { { ('stdout%s\n'):format(t.is_os('win') and '\r' or '') } },