Handle correctly passing a bad interpreter name to new-ui

When a bad interpreter name is passed to new-ui, such as:

  (gdb)  new-ui bloop /dev/pts/10

A partially created UI is left in the UI list, with interp set to NULL.
Trying to do anything that will print on this UI (such as "start") will
cause a segmentation fault.

Changes in v2:

  - Use with_test_prefix to namespace test procedures
  - Give an explicit stable test name
  - Add a "bad terminal path" test
  - Remove useless runto_main
  - Add missing intro comments

I did not factor out the pty spawn, as there is some magic involved I
don't quite understand.  But it wouldn't bring that much anyway.

gdb/ChangeLog:

	* top.h (make_delete_ui_cleanup): New declaration.
	* top.c (delete_ui_cleanup): New function.
	(make_delete_ui_cleanup): New function.
	(new_ui_command): Create restore_ui cleanup earlier, create a
	delete_ui cleanup and discard it on success.

gdb/testsuite/ChangeLog:

	* gdb.base/new-ui.exp (do_test_invalid_args): New
	procedure.

1 files changed, 28 insertions, 1 deletions

diff --git a/gdb/testsuite/gdb.base/new-ui.exp b/gdb/testsuite/gdb.base/new-ui.exp
index f3f66db..22e8b79 100644
--- a/gdb/testsuite/gdb.base/new-ui.exp
+++ b/gdb/testsuite/gdb.base/new-ui.exp
@@ -143,4 +143,31 @@ proc do_test {} {
     }
 }
 
-do_test
+# Test missing / invalid arguments.
+
+proc do_test_invalid_args {} {
+    global testfile
+
+    clean_restart $testfile
+
+    spawn -pty
+    set extra_tty_name $spawn_out(slave,name)
+
+    # Test bad terminal path.
+    gdb_test "new-ui console /non/existent/path" \
+	     "opening terminal failed: No such file or directory\." \
+	     "new-ui with bad terminal path"
+
+    # Test bad interpreter name.
+    gdb_test "new-ui bloop $extra_tty_name" \
+	     "Interpreter `bloop' unrecognized" \
+	     "new-ui with bad interpreter name"
+
+    # Test that we can continue working normally.
+    if ![runto_main] {
+	fail "could not run to main"
+    }
+}
+
+with_test_prefix "do_test" do_test
+with_test_prefix "do_test_invalid_args" do_test_invalid_args