Bulletproof -fdiagnostics-format=json against bad locations (PR c++/90462)

PR c++/90462 reports an ICE with -fdiagnostics-format=json when
attempting to serialize a malformed location to JSON.

The compound location_t in question has meaningful "caret" and "start"
locations, but has UNKNOWN_LOCATION for its "finish" location,
leading to a NULL pointer dereference when attempting to build a JSON
string for the filename.

This patch bulletproofs the JSON output so that attempts to write
a JSON object for a location with a NULL file will lead to an object
with no "file" key, and attempts to write a compound location with
UNKNOWN_LOCATION for its start or finish will lead to the corresponding
JSON child object being omitted.

This patch also adds a json::object::get member function, for self-testing
the above.

gcc/ChangeLog:
	PR c++/90462
	* diagnostic-format-json.cc: Include "selftest.h".
	(json_from_expanded_location): Only add "file" key for non-NULL
	file strings.
	(json_from_location_range): Don't add "start" and "finish"
	children if they are UNKNOWN_LOCATION.
	(selftest::test_unknown_location): New selftest.
	(selftest::test_bad_endpoints): New selftest.
	(selftest::diagnostic_format_json_cc_tests): New function.
	* json.cc (json::object::get): New function.
	(selftest::test_object_get): New selftest.
	(selftest::json_cc_tests): Call it.
	* json.h (json::object::get): New decl.
	* selftest-run-tests.c (selftest::run_tests): Call
	selftest::diagnostic_format_json_cc_tests.
	* selftest.h (selftest::diagnostic_format_json_cc_tests): New
	decl.

gcc/testsuite/ChangeLog:
	PR c++/90462
	* g++.dg/pr90462.C: New test.

From-SVN: r271535

1 files changed, 29 insertions, 0 deletions

diff --git a/gcc/json.cc b/gcc/json.cc
index 2e8e21b..512e2e51 100644
--- a/gcc/json.cc
+++ b/gcc/json.cc
@@ -99,6 +99,22 @@ object::set (const char *key, value *v)
     m_map.put (xstrdup (key), v);
 }
 
+/* Get the json::value * for KEY.
+
+   The object retains ownership of the value.  */
+
+value *
+object::get (const char *key) const
+{
+  gcc_assert (key);
+
+  value **ptr = const_cast <map_t &> (m_map).get (key);
+  if (ptr)
+    return *ptr;
+  else
+    return NULL;
+}
+
 /* class json::array, a subclass of json::value, representing
    an ordered collection of values.  */
 
@@ -240,6 +256,18 @@ assert_print_eq (const json::value &jv, const char *expected_json)
   ASSERT_STREQ (expected_json, pp_formatted_text (&pp));
 }
 
+/* Verify that object::get works as expected.  */
+
+static void
+test_object_get ()
+{
+  object obj;
+  value *val = new json::string ("value");
+  obj.set ("foo", val);
+  ASSERT_EQ (obj.get ("foo"), val);
+  ASSERT_EQ (obj.get ("not-present"), NULL);
+}
+
 /* Verify that JSON objects are written correctly.  We can't test more than
    one key/value pair, as we don't impose a guaranteed ordering.  */
 
@@ -306,6 +334,7 @@ test_writing_literals ()
 void
 json_cc_tests ()
 {
+  test_object_get ();
   test_writing_objects ();
   test_writing_arrays ();
   test_writing_numbers ();