From 96eeee66e95d2fe05ea783ec4f013dd0d38d8317 Mon Sep 17 00:00:00 2001
From: Richard van der Hoff <richard@matrix.org>
Date: Fri, 8 Jan 2021 13:10:35 +0000
Subject: [PATCH] Fix validate_config on nested objects

---
 changelog.d/9054.bugfix   |  1 +
 synapse/config/_util.py   |  2 +-
 tests/config/test_util.py | 53 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 55 insertions(+), 1 deletion(-)
 create mode 100644 changelog.d/9054.bugfix
 create mode 100644 tests/config/test_util.py

diff --git a/changelog.d/9054.bugfix b/changelog.d/9054.bugfix
new file mode 100644
index 000000000000..0bfe951f173f
--- /dev/null
+++ b/changelog.d/9054.bugfix
@@ -0,0 +1 @@
+Fix a minor bug which could cause confusing error messages from invalid configurations.
diff --git a/synapse/config/_util.py b/synapse/config/_util.py
index 1bbe83c317dd..8fce7f6bb133 100644
--- a/synapse/config/_util.py
+++ b/synapse/config/_util.py
@@ -56,7 +56,7 @@ def json_error_to_config_error(
     """
     # copy `config_path` before modifying it.
     path = list(config_path)
-    for p in list(e.path):
+    for p in list(e.absolute_path):
         if isinstance(p, int):
             path.append("<item %i>" % p)
         else:
diff --git a/tests/config/test_util.py b/tests/config/test_util.py
new file mode 100644
index 000000000000..10363e3765d9
--- /dev/null
+++ b/tests/config/test_util.py
@@ -0,0 +1,53 @@
+# -*- coding: utf-8 -*-
+# Copyright 2021 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from synapse.config import ConfigError
+from synapse.config._util import validate_config
+
+from tests.unittest import TestCase
+
+
+class ValidateConfigTestCase(TestCase):
+    """Test cases for synapse.config._util.validate_config"""
+
+    def test_bad_object_in_array(self):
+        """malformed objects within an array should be validated correctly"""
+
+        # consider a structure:
+        #
+        # array_of_objs:
+        #   - r: 1
+        #     foo: 2
+        #
+        #   - r: 2
+        #     bar: 3
+        #
+        # ... where each entry must contain an "r": check that the path
+        # to the required item is correclty reported.
+
+        schema = {
+            "type": "object",
+            "properties": {
+                "array_of_objs": {
+                    "type": "array",
+                    "items": {"type": "object", "required": ["r"]},
+                },
+            },
+        }
+
+        with self.assertRaises(ConfigError) as c:
+            validate_config(schema, {"array_of_objs": [{}]}, ("base",))
+
+        self.assertEqual(c.exception.path, ["base", "array_of_objs", "<item 0>"])