[PATCH 3/3] [gdb/tui] Allow second tui enable if first fails

[Tom de Vries <tdevries@suse.de>]

Commit fb23d7ba4a2 ("[gdb/tui] Handle error in tui_enable") handles a
particular error during tui_enable, but doesn't allow trying to enable TUI
again.

I tried to get this to work, but didn't manage because I didn't understand the
interaction between endwin and the "tui_batch_rendering defer" destructor:
- first endwin restores the shell terminal mode
- then the defer destructor calls doupdate, restoring program shell mode.

Fix this by using reset_shell_mode instead.
---
 gdb/tui/tui.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/gdb/tui/tui.c b/gdb/tui/tui.c
index ea01448f087..ee967e1e38b 100644
--- a/gdb/tui/tui.c
+++ b/gdb/tui/tui.c
@@ -493,7 +493,7 @@ tui_enable (void)
       /* Don't try initialization again.  */
       tui_finish_init = TRIBOOL_UNKNOWN;
 
-      SCREEN *s = init_ncurses ();
+      init_ncurses ();
       w = stdscr;
 
       if (has_colors ())
@@ -530,9 +530,21 @@ tui_enable (void)
 	}
       catch (const gdb_exception &)
 	{
-	  endwin ();
-	  delscreen (s);
+	  /* Clean up screen.  */
+	  clear ();
+	  refresh ();
+
+	  /* Reset terminal to shell terminal mode.  We can't use endwin here,
+	     because afterwards the defer destructor might call doupdate,
+	     restoring program terminal mode.  */
+	  reset_shell_mode ();
+
+	  /* Initialization failed, so TUI is not active.  */
 	  tui_active = false;
+
+	  /* Allow trying to initialize TUI again.  */
+	  tui_finish_init = TRIBOOL_TRUE;
+
 	  throw;
 	}
 
-- 
2.51.0