gdb/testsuite/tui: more testing of the 'focus' command

I noticed that we didn't have many tests of the tui 'focus' command,
so I started adding some.  This exposed a bug in GDB; we are able to
focus windows that should not be focusable, e.g. the 'status' window.

This is harmless until we then do 'focus next' or 'focus prev', along
this code path we assert that the currently focused window is
focusable, which obviously, is not always true, so GDB fails with an
assertion error.

The fix is simple; add a check to the tui_set_focus_command function
to ensure that the selected window is focusable.  If it is not then an
error is thrown.  The new tests I've added cover this case.

3 files changed, 93 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.tui/tui-focus.c b/gdb/testsuite/gdb.tui/tui-focus.c
new file mode 100644
index 00000000000..3a264f239ed
--- /dev/null
+++ b/gdb/testsuite/gdb.tui/tui-focus.c
@@ -0,0 +1,22 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2023 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+int
+main ()
+{
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.tui/tui-focus.exp b/gdb/testsuite/gdb.tui/tui-focus.exp
new file mode 100644
index 00000000000..9e2a1cd0935
--- /dev/null
+++ b/gdb/testsuite/gdb.tui/tui-focus.exp
@@ -0,0 +1,68 @@
+# Copyright 2023 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Minimal testcase that just checks that the various "layout $foo"
+# commands do not cause gdb to crash.
+
+require allow_tui_tests
+
+tuiterm_env
+
+standard_testfile
+
+if {[prepare_for_testing "failed to prepare" ${testfile} ${srcfile}]} {
+    return -1
+}
+
+# Run a series of tests based on various test specifications.
+#
+# Each test specification is a tuple where the first item is the name of a
+# window, and the second item is a boolean indicating if we expect that
+# window to be present in the default (src) layout.
+foreach spec {{src true} {cmd true} {status true} {regs false} {asm false}} {
+    lassign $spec window valid_p
+    with_test_prefix "window=$window" {
+
+	Term::clean_restart 24 80 $binfile
+	if {![Term::prepare_for_tui]} {
+	    unsupported "TUI not supported"
+	    return
+	}
+
+	Term::command_no_prompt_prefix "focus $window"
+
+	if {$valid_p} {
+	    # The 'status' window is special, it's present in the
+	    # default (src) layout, but is not focusable.
+	    if {$window == "status"} {
+		Term::check_region_contents "check focus error" 0 16 80 1 \
+		    "^Window \"$window\" cannot be focused\\s*"
+	    } else {
+		Term::check_region_contents "check focus message" 0 16 80 1 \
+		    "^Focus set to $window window\\.\\s*"
+	    }
+	} else {
+	    Term::check_region_contents "check focus error" 0 16 80 1 \
+		"^Unrecognized window name \"$window\"\\s*"
+	}
+
+	Term::check_box "check src box" 0 0 80 15
+
+	# At one point the following 'focus prev' command would trigger a
+	# crash in GDB, GDB was allowing users to set focus to the 'status'
+	# window, and 'focus prev' would then trigger an assert.
+	Term::command "focus prev"
+    }
+}
diff --git a/gdb/tui/tui-win.c b/gdb/tui/tui-win.c
index 58372005ff8..9c088899817 100644
--- a/gdb/tui/tui-win.c
+++ b/gdb/tui/tui-win.c
@@ -723,6 +723,9 @@ tui_set_focus_command (const char *arg, int from_tty)
   if (!win_info->is_visible ())
     error (_("Window \"%s\" is not visible"), arg);
 
+  if (!win_info->can_focus ())
+    error (_("Window \"%s\" cannot be focused"), arg);
+
   tui_set_win_focus_to (win_info);
   gdb_printf (_("Focus set to %s window.\n"),
 	      tui_win_with_focus ()->name ());