patch 8.0.0468: after aborting an Ex command g< does not work

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.

src/ex_getln.c

@@ -258,6 +258,7 @@ getcmdline(
 	return NULL;			    /* out of memory */
     ccline.cmdlen = ccline.cmdpos = 0;
     ccline.cmdbuff[0] = NUL;
+    sb_text_start_cmdline();
 
     /* autoindent for :insert and :append */
     if (firstc <= 0)
@@ -2083,6 +2084,7 @@ returncmd:
 #ifdef CURSOR_SHAPE
     ui_cursor_shape();		/* may show different cursor shape */
 #endif
+    sb_text_end_cmdline();
 
     {
 	char_u *p = ccline.cmdbuff;

src/gui.c

@@ -630,7 +630,7 @@ gui_init(void)
      * where Vim was started. */
     emsg_on_display = FALSE;
     msg_scrolled = 0;
-    clear_sb_text();
+    clear_sb_text(TRUE);
     need_wait_return = FALSE;
     msg_didany = FALSE;
 

src/message.c

@@ -2146,8 +2146,6 @@ msg_puts_display(
 
 	    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;
@@ -2367,6 +2365,8 @@ inc_msg_scrolled(void)
     }
 #endif
     ++msg_scrolled;
+    if (must_redraw < VALID)
+	must_redraw = VALID;
 }
 
 /*
@@ -2389,7 +2389,15 @@ static msgchunk_T *last_msgchunk = NULL; /* last displayed text */
 static msgchunk_T *msg_sb_start(msgchunk_T *mps);
 static msgchunk_T *disp_sb_line(int row, msgchunk_T *smp);
 
-static int do_clear_sb_text = FALSE;	/* clear text on next msg */
+typedef enum {
+    SB_CLEAR_NONE = 0,
+    SB_CLEAR_ALL,
+    SB_CLEAR_CMDLINE_BUSY,
+    SB_CLEAR_CMDLINE_DONE
+} sb_clear_T;
+
+/* 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.
@@ -2404,10 +2412,11 @@ store_sb_text(
 {
     msgchunk_T	*mp;
 
-    if (do_clear_sb_text)
+    if (do_clear_sb_text == SB_CLEAR_ALL
+	    || do_clear_sb_text == SB_CLEAR_CMDLINE_DONE)
     {
-	clear_sb_text();
-	do_clear_sb_text = FALSE;
+	clear_sb_text(do_clear_sb_text == SB_CLEAR_ALL);
+	do_clear_sb_text = SB_CLEAR_NONE;
     }
 
     if (s > *sb_str)
@@ -2447,23 +2456,53 @@ store_sb_text(
     void
 may_clear_sb_text(void)
 {
-    do_clear_sb_text = TRUE;
+    do_clear_sb_text = SB_CLEAR_ALL;
+}
+
+/*
+ * 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(void)
+clear_sb_text(int all)
 {
     msgchunk_T	*mp;
+    msgchunk_T	**lastp;
 
-    while (last_msgchunk != NULL)
+    if (all)
+	lastp = &last_msgchunk;
+    else
     {
-	mp = last_msgchunk->sb_prev;
-	vim_free(last_msgchunk);
-	last_msgchunk = mp;
+	if (last_msgchunk == NULL)
+	    return;
+	lastp = &last_msgchunk->sb_prev;
+    }
+
+    while (*lastp != NULL)
+    {
+	mp = (*lastp)->sb_prev;
+	vim_free(*lastp);
+	*lastp = mp;
     }
 }
 

src/misc2.c

@@ -970,7 +970,7 @@ lalloc(long_u size, int message)
 	    break;
 	releasing = TRUE;
 
-	clear_sb_text();	      /* free any scrollback text */
+	clear_sb_text(TRUE);	      /* free any scrollback text */
 	try_again = mf_release_all(); /* release as many blocks as possible */
 
 	releasing = FALSE;
@@ -1148,7 +1148,7 @@ free_all_mem(void)
 # ifdef FEAT_DIFF
     diff_clear(curtab);
 # endif
-    clear_sb_text();	      /* free any scrollback text */
+    clear_sb_text(TRUE);	      /* free any scrollback text */
 
     /* Free some global vars. */
     vim_free(username);

src/proto/message.pro

@@ -52,7 +52,9 @@ void msg_puts_long_len_attr(char_u *longstr, int len, int attr);
 void msg_puts_attr(char_u *s, int attr);
 int message_filtered(char_u *msg);
 void may_clear_sb_text(void);
-void clear_sb_text(void);
+void sb_text_start_cmdline(void);
+void sb_text_end_cmdline(void);
+void clear_sb_text(int all);
 void show_sb_text(void);
 void msg_sb_eol(void);
 int msg_use_printf(void);

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    468,
 /**/
     467,
 /**/