Handle gdb.LazyString in DAP

Andry pointed out that the DAP code did not properly handle
gdb.LazyString results from a pretty-printer, yielding:

    TypeError: Object of type LazyString is not JSON serializable

This patch fixes the problem, partly with a small patch in varref.py,
but mainly by implementing tp_str for LazyString.

Reviewed-By: Eli Zaretskii <eliz@gnu.org>

1 files changed, 23 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.dap/lazy-string.c b/gdb/testsuite/gdb.dap/lazy-string.c
new file mode 100644
index 0000000..9df48bf
--- /dev/null
+++ b/gdb/testsuite/gdb.dap/lazy-string.c
@@ -0,0 +1,23 @@
+/* Copyright 2023 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   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 ()
+{
+  const char *the_string = "DEI";
+  return 0;			/* STOP */
+}