vim-patch:8.0.0468: g< after aborting an Ex command (#7941)

Problem:    After aborting an Ex command g< does not work. (Marcin
            Szamotulski)
Solution:   Postpone clearing scrollback messages to until the command line
            has been entered.  Also fix that the screen isn't redrawn if after
            g< the command line is cancelled.
https://github.com/vim/vim/commit/f2405ed2321da4a879fe0b0703af780fc0432c63

3 files changed, 63 insertions, 31 deletions

diff --git a/src/nvim/ex_getln.c b/src/nvim/ex_getln.c
index 774007c66e..3372edb8fd 100644
--- a/src/nvim/ex_getln.c
+++ b/src/nvim/ex_getln.c
@@ -273,6 +273,7 @@ static uint8_t *command_line_enter(int firstc, long count, int indent)
 
   ccline.last_colors = (ColoredCmdline){ .cmdbuff = NULL,
                                          .colors = KV_INITIAL_VALUE };
+  sb_text_start_cmdline();
 
   // autoindent for :insert and :append
   if (s->firstc <= 0) {
@@ -480,6 +481,8 @@ static uint8_t *command_line_enter(int firstc, long count, int indent)
   xfree(ccline.last_colors.cmdbuff);
   kv_destroy(ccline.last_colors.colors);
 
+  sb_text_end_cmdline();
+
   {
     char_u *p = ccline.cmdbuff;
 
diff --git a/src/nvim/memory.c b/src/nvim/memory.c
index bfc2f208dd..b2aef13946 100644
--- a/src/nvim/memory.c
+++ b/src/nvim/memory.c
@@ -66,7 +66,7 @@ void try_to_free_memory(void)
   trying_to_free = true;
 
   // free any scrollback text
-  clear_sb_text();
+  clear_sb_text(true);
   // Try to save all buffers and release as many blocks as possible
   mf_release_all();
 
@@ -633,7 +633,7 @@ void free_all_mem(void)
   free_signs();
   set_expr_line(NULL);
   diff_clear(curtab);
-  clear_sb_text();            /* free any scrollback text */
+  clear_sb_text(true);            // free any scrollback text
 
   /* Free some global vars. */
   xfree(last_cmdline);
diff --git a/src/nvim/message.c b/src/nvim/message.c
index 2643d644a9..097c8b16e4 100644
--- a/src/nvim/message.c
+++ b/src/nvim/message.c
@@ -1759,12 +1759,11 @@ static void msg_puts_display(const char_u *str, int maxlen, int attr,
       }
 
       inc_msg_scrolled();
-      need_wait_return = TRUE;       /* may need wait_return in main() */
-      if (must_redraw < VALID)
-        must_redraw = VALID;
-      redraw_cmdline = TRUE;
-      if (cmdline_row > 0 && !exmode_active)
-        --cmdline_row;
+      need_wait_return = true;       // may need wait_return in main()
+      redraw_cmdline = true;
+      if (cmdline_row > 0 && !exmode_active) {
+        cmdline_row--;
+      }
 
       /*
        * If screen is completely filled and 'more' is set then wait
@@ -1921,30 +1920,38 @@ static void inc_msg_scrolled(void)
     xfree(tofree);
   }
   msg_scrolled++;
+  if (must_redraw < VALID) {
+    must_redraw = VALID;
+  }
 }
 
-static msgchunk_T *last_msgchunk = NULL; /* last displayed text */
+static msgchunk_T *last_msgchunk = NULL;  // last displayed text
 
+typedef enum {
+  SB_CLEAR_NONE = 0,
+  SB_CLEAR_ALL,
+  SB_CLEAR_CMDLINE_BUSY,
+  SB_CLEAR_CMDLINE_DONE
+} sb_clear_T;
 
-static int do_clear_sb_text = FALSE;    /* clear text on next msg */
+// When to clear text on next msg.
+static sb_clear_T do_clear_sb_text = SB_CLEAR_NONE;
 
-/*
- * Store part of a printed message for displaying when scrolling back.
- */
-static void
-store_sb_text (
-    char_u **sb_str,           /* start of string */
-    char_u *s,                 /* just after string */
+/// Store part of a printed message for displaying when scrolling back.
+static void store_sb_text(
+    char_u **sb_str,           // start of string
+    char_u *s,                 // just after string
     int attr,
     int *sb_col,
-    int finish                     /* line ends */
+    int finish                     // line ends
 )
 {
   msgchunk_T  *mp;
 
-  if (do_clear_sb_text) {
-    clear_sb_text();
-    do_clear_sb_text = FALSE;
+  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);
+    do_clear_sb_text = SB_CLEAR_NONE;
   }
 
   if (s > *sb_str) {
@@ -1976,21 +1983,43 @@ store_sb_text (
  */
 void may_clear_sb_text(void)
 {
-  do_clear_sb_text = TRUE;
+  do_clear_sb_text = SB_CLEAR_ALL;
 }
 
-/*
- * Clear any text remembered for scrolling back.
- * Called when redrawing the screen.
- */
-void clear_sb_text(void)
+/// 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();
+}
+
+/// 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;
+}
+
+/// Clear any text remembered for scrolling back.
+/// When "all" is FALSE keep the last line.
+/// Called when redrawing the screen.
+void clear_sb_text(int all)
 {
   msgchunk_T  *mp;
+  msgchunk_T  **lastp;
+
+  if (all) {
+    lastp = &last_msgchunk;
+  } else {
+    if (last_msgchunk == NULL) {
+      return;
+    }
+    lastp = &last_msgchunk->sb_prev;
+  }
 
-  while (last_msgchunk != NULL) {
-    mp = last_msgchunk->sb_prev;
-    xfree(last_msgchunk);
-    last_msgchunk = mp;
+  while (*lastp != NULL) {
+    mp = (*lastp)->sb_prev;
+    xfree(*lastp);
+    *lastp = mp;
   }
 }