vim-patch:9.2.0985: Multiline messages not visible when mapping starts cmdline (#41405)

Problem:  Multiline messages exceeding 'cmdheight' not visible when a
          mapping starts cmdline immediately after it (after 9.2.0967).
Solution: Revert patch 9.2.0967 and use a different solution (zeertzjq).

fixes:  vim/vim#21098
closes: vim/vim#21101

fb4866a2dd

test/functional/legacy/messages_spec.lua

@@ -889,15 +889,15 @@ describe('messages', function()
     ]])
   end)
 
-  -- oldtest: Test_hit_enter_no_eat_mapped_keys()
-  it('hit-enter prompt does not eat keys from a mapping', function()
+  -- oldtest: Test_hit_enter_during_mapping()
+  it('hit-enter prompt during a mapping', function()
     screen = Screen.new(75, 10)
     exec([[
-      set ruler more
+      set ruler
       call setline(1, range(1, 20))
-      " The 8-line :echo scrolls the screen and would raise a hit-enter prompt;
-      " the mapping then runs "gg" to move the cursor to line 1.
+      " The 8-line :echo leads to a hit-enter prompt.
       nnoremap X :echo "a\nb\nc\nd\ne\nf\ng\nh"<CR>gg
+      nnoremap \b :echo "a\nb\nc\nd\ne\nf\ng\nh"<CR>:b<Space>
       normal! 10G
     ]])
     t.eq({ mode = 'n', blocking = false }, api.nvim_get_mode())
@@ -908,6 +908,22 @@ describe('messages', function()
     -- cursor stays put.  With the fix "gg" runs and moves the cursor to line 1.
     t.eq({ mode = 'n', blocking = false }, api.nvim_get_mode())
     t.eq({ 1, 0 }, api.nvim_win_get_cursor(0))
+
+    -- If a mapping starts cmdline after multiline messages exceeding 'cmdheight',
+    -- the messages should still be visible.
+    feed('\\b')
+    screen:expect([[
+      {3:                                                                           }|
+      a                                                                          |
+      b                                                                          |
+      c                                                                          |
+      d                                                                          |
+      e                                                                          |
+      f                                                                          |
+      g                                                                          |
+      h                                                                          |
+      :b ^                                                                        |
+    ]])
   end)
 
   -- oldtest: Test_fileinfo_after_last_bd()

test/old/testdir/test_messages.vim

@@ -758,29 +758,42 @@ func Test_long_formatprg_no_hit_enter()
   call StopVimInTerminal(buf)
 endfunc
 
-" A message shown while a mapping is still being processed must not raise a
-" hit-enter prompt that eats the mapping's remaining keys.
-func Test_hit_enter_no_eat_mapped_keys()
+" A message shown while a mapping is still being processed must not eat the
+" mapping's remaining keys.
+" If a mapping starts cmdline after multiline messages exceeding 'cmdheight',
+" the messages should still be visible.
+func Test_hit_enter_during_mapping()
   CheckRunVimInTerminal
 
   let lines =<< trim END
     set ruler
     call setline(1, range(1, 20))
-    " The 8-line :echo scrolls the screen and would raise a hit-enter prompt;
-    " the mapping then runs "gg" to move the cursor to line 1.
+    " The 8-line :echo leads to a hit-enter prompt.
     nnoremap X :echo "a\nb\nc\nd\ne\nf\ng\nh"<CR>gg
+    nnoremap \b :echo "a\nb\nc\nd\ne\nf\ng\nh"<CR>:b<Space>
     normal! 10G
   END
   call writefile(lines, 'XtestHitEnterMap', 'D')
   let buf = RunVimInTerminal('-S XtestHitEnterMap', #{rows: 10})
-  call WaitForAssert({-> assert_match('10,1', term_getline(buf, 10))})
+  call WaitForAssert({-> assert_match(' 10,1 ', term_getline(buf, 10))})
 
   call term_sendkeys(buf, "X")
   " Without the fix the hit-enter prompt eats the mapping's "g" keys and the
   " cursor stays put.  With the fix "gg" runs and moves the cursor to line 1.
-  call WaitForAssert({-> assert_match('1,1', term_getline(buf, 10))})
+  call WaitForAssert({-> assert_match(' 1,1 ', term_getline(buf, 10))})
   call assert_notmatch('Press ENTER', term_getline(buf, 10))
 
+  call term_sendkeys(buf, '\b')
+  call WaitForAssert({-> assert_match('^:b ', term_getline(buf, 10))})
+  call assert_match('^a *$', term_getline(buf, 2))
+  call assert_match('^b *$', term_getline(buf, 3))
+  call assert_match('^c *$', term_getline(buf, 4))
+  call assert_match('^d *$', term_getline(buf, 5))
+  call assert_match('^e *$', term_getline(buf, 6))
+  call assert_match('^f *$', term_getline(buf, 7))
+  call assert_match('^g *$', term_getline(buf, 8))
+  call assert_match('^h *$', term_getline(buf, 9))
+
   " clean up
   call StopVimInTerminal(buf)
 endfunc