gdb/tui: convert if/error to an assert

While working on the previous commit, I realised that there was an
error in tui_set_focus_command that could never be triggered.

Since the big tui rewrite (adding dynamic layouts) it is no longer
true that there is a tui_win_info object for every window at all
times.  We now only create a tui_win_info object for a particular
window, when the window is part of the current layout.  As a result,
if we have a tui_win_info pointer, then the window must be visible
inside tui_set_focus_command (this function calls tui_enable as its
first action, which makes the current layout visible).

The gdb.tui/tui-focus.exp test script exercises this area of code, and
doesn't trigger the assert, nor do any of our other existing tui
tests.

1 files changed, 5 insertions, 2 deletions

diff --git a/gdb/tui/tui-win.c b/gdb/tui/tui-win.c
index 9c08889..4fc8e7a 100644
--- a/gdb/tui/tui-win.c
+++ b/gdb/tui/tui-win.c
@@ -720,8 +720,11 @@ tui_set_focus_command (const char *arg, int from_tty)
 
   if (win_info == NULL)
     error (_("Unrecognized window name \"%s\""), arg);
-  if (!win_info->is_visible ())
-    error (_("Window \"%s\" is not visible"), arg);
+
+  /* If a window is part of the current layout then it will have a
+     tui_win_info associated with it and be visible, otherwise, there will
+     be no tui_win_info and the above error will have been raised.  */
+  gdb_assert (win_info->is_visible ());
 
   if (!win_info->can_focus ())
     error (_("Window \"%s\" cannot be focused"), arg);