vim-patch:9.0.0099: scrollback can be wrong after redrawing the command line (#19562)

Problem:    Scrollback can be wrong after redrawing the command line.
Solution:   Clear unfinished scrollback when redrawing. (closes vim/vim#10807)
46af7bc08d

src/nvim/ex_getln.c

@@ -3823,6 +3823,7 @@ void redrawcmd(void)
 
   redrawing_cmdline = true;
 
+  sb_text_restart_cmdline();
   msg_start();
   redrawcmdprompt();
 

src/nvim/message.c

@@ -2503,6 +2503,7 @@ static void store_sb_text(char_u **sb_str, char_u *s, int attr, int *sb_col, int
   if (do_clear_sb_text == SB_CLEAR_ALL
       || do_clear_sb_text == SB_CLEAR_CMDLINE_DONE) {
     clear_sb_text(do_clear_sb_text == SB_CLEAR_ALL);
+    msg_sb_eol();  // prevent messages from overlapping
     do_clear_sb_text = SB_CLEAR_NONE;
   }
 
@@ -2537,18 +2538,47 @@ void may_clear_sb_text(void)
   do_clear_sb_text = SB_CLEAR_ALL;
 }
 
-/// Starting to edit the command line, do not clear messages now.
+/// Starting to edit the command line: do not clear messages now.
 void sb_text_start_cmdline(void)
 {
-  do_clear_sb_text = SB_CLEAR_CMDLINE_BUSY;
-  msg_sb_eol();
+  if (do_clear_sb_text == SB_CLEAR_CMDLINE_BUSY) {
+    // Invoking command line recursively: the previous-level command line
+    // doesn't need to be remembered as it will be redrawn when returning
+    // to that level.
+    sb_text_restart_cmdline();
+  } else {
+    msg_sb_eol();
+    do_clear_sb_text = SB_CLEAR_CMDLINE_BUSY;
+  }
 }
 
-/// Ending to edit the command line.  Clear old lines but the last one later.
+/// Redrawing the command line: clear the last unfinished line.
+void sb_text_restart_cmdline(void)
+{
+  // Needed when returning from nested command line.
+  do_clear_sb_text = SB_CLEAR_CMDLINE_BUSY;
+
+  if (last_msgchunk == NULL || last_msgchunk->sb_eol) {
+    // No unfinished line: don't clear anything.
+    return;
+  }
+
+  msgchunk_T *tofree = msg_sb_start(last_msgchunk);
+  last_msgchunk = tofree->sb_prev;
+  if (last_msgchunk != NULL) {
+    last_msgchunk->sb_next = NULL;
+  }
+  while (tofree != NULL) {
+    msgchunk_T *tofree_next = tofree->sb_next;
+    xfree(tofree);
+    tofree = tofree_next;
+  }
+}
+
+/// Ending to edit the command line: clear old lines but the last one later.
 void sb_text_end_cmdline(void)
 {
   do_clear_sb_text = SB_CLEAR_CMDLINE_DONE;
-  msg_sb_eol();
 }
 
 /// Clear any text remembered for scrolling back.

src/nvim/testdir/test_messages.vim

@@ -118,7 +118,9 @@ func Test_message_more()
   let buf = RunVimInTerminal('', {'rows': 6})
   call term_sendkeys(buf, ":call setline(1, range(1, 100))\n")
 
-  call term_sendkeys(buf, ":%p#\n")
+  call term_sendkeys(buf, ":%pfoo\<C-H>\<C-H>\<C-H>#")
+  call WaitForAssert({-> assert_equal(':%p#', term_getline(buf, 6))})
+  call term_sendkeys(buf, "\n")
   call WaitForAssert({-> assert_equal('  5 5', term_getline(buf, 5))})
   call WaitForAssert({-> assert_equal('-- More --', term_getline(buf, 6))})
 
@@ -194,6 +196,13 @@ func Test_message_more()
   call WaitForAssert({-> assert_equal('100 100', term_getline(buf, 5))})
   call WaitForAssert({-> assert_equal('Press ENTER or type command to continue', term_getline(buf, 6))})
 
+  " A command line that doesn't print text is appended to scrollback,
+  " even if it invokes a nested command line.
+  call term_sendkeys(buf, ":\<C-R>=':'\<CR>:\<CR>g<")
+  call WaitForAssert({-> assert_equal('100 100', term_getline(buf, 4))})
+  call WaitForAssert({-> assert_equal(':::', term_getline(buf, 5))})
+  call WaitForAssert({-> assert_equal('Press ENTER or type command to continue', term_getline(buf, 6))})
+
   call term_sendkeys(buf, ":%p#\n")
   call WaitForAssert({-> assert_equal('  5 5', term_getline(buf, 5))})
   call WaitForAssert({-> assert_equal('-- More --', term_getline(buf, 6))})

test/functional/legacy/messages_spec.lua

@@ -27,7 +27,16 @@ describe('messages', function()
     it('works', function()
       command('call setline(1, range(1, 100))')
 
-      feed(':%p#\n')
+      feed(':%pfoo<C-H><C-H><C-H>#')
+      screen:expect([[
+        1                                                                          |
+        2                                                                          |
+        3                                                                          |
+        4                                                                          |
+        5                                                                          |
+        :%p#^                                                                       |
+      ]])
+      feed('\n')
       screen:expect([[
         {2:  1 }1                                                                      |
         {2:  2 }2                                                                      |
@@ -241,6 +250,18 @@ describe('messages', function()
         {1:Press ENTER or type command to continue}^                                    |
       ]])
 
+      -- A command line that doesn't print text is appended to scrollback,
+      -- even if it invokes a nested command line.
+      feed([[:<C-R>=':'<CR>:<CR>g<lt>]])
+      screen:expect([[
+        {2: 97 }97                                                                     |
+        {2: 98 }98                                                                     |
+        {2: 99 }99                                                                     |
+        {2:100 }100                                                                    |
+        :::                                                                        |
+        {1:Press ENTER or type command to continue}^                                    |
+      ]])
+
       feed(':%p#\n')
       screen:expect([[
         {2:  1 }1                                                                      |