patch 9.0.0099: scrollback can be wrong after redrawing the command linev9.0.0099

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

1 files changed, 40 insertions, 4 deletions

diff --git a/src/message.c b/src/message.c
index 7ba82fa050..50a174928c 100644
--- a/src/message.c
+++ b/src/message.c
@@ -2535,6 +2535,7 @@ store_sb_text(
 	    || 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;
     }
 
@@ -2579,23 +2580,58 @@ may_clear_sb_text(void)
 }
 
 /*
- * 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)
 {
+    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;
+    }
+}
+
+/*
+ * Redrawing the command line: clear the last unfinished line.
+ */
+    void
+sb_text_restart_cmdline(void)
+{
+    msgchunk_T *tofree;
+
+    // Needed when returning from nested command line.
     do_clear_sb_text = SB_CLEAR_CMDLINE_BUSY;
-    msg_sb_eol();
+
+    if (last_msgchunk == NULL || last_msgchunk->sb_eol)
+	// No unfinished line: don't clear anything.
+	return;
+
+    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;
+
+	vim_free(tofree);
+	tofree = tofree_next;
+    }
 }
 
 /*
- * Ending to edit the command line.  Clear old lines but the last one later.
+ * 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();
 }
 
 /*