fix(sync): Handle timezone-naive datetimes in sync.toml (#8477)

samcli/commands/sync/sync_context.py

@@ -129,9 +129,14 @@ def _toml_document_to_sync_state(toml_document: Dict) -> Optional[SyncState]:
     if resource_sync_states_toml_table:
         for resource_id in resource_sync_states_toml_table:
             resource_sync_state_toml_table = resource_sync_states_toml_table.get(resource_id)
+            sync_time_str = resource_sync_state_toml_table.get(SYNC_TIME)
+            # Parse datetime and ensure it's timezone-aware UTC (consistent with how we write)
+            sync_time = datetime.fromisoformat(sync_time_str)
+            if sync_time.tzinfo is None:
+                sync_time = sync_time.replace(tzinfo=timezone.utc)
             resource_sync_state = ResourceSyncState(
                 resource_sync_state_toml_table.get(HASH),
-                datetime.fromisoformat(resource_sync_state_toml_table.get(SYNC_TIME)),
+                sync_time,
             )
 
             # For Nested stack resources, replace "-" with "/"
@@ -142,9 +147,12 @@ def _toml_document_to_sync_state(toml_document: Dict) -> Optional[SyncState]:
     latest_infra_sync_time = None
     if sync_state_toml_table:
         dependency_layer = sync_state_toml_table.get(DEPENDENCY_LAYER)
-        latest_infra_sync_time = sync_state_toml_table.get(LATEST_INFRA_SYNC_TIME)
-        if latest_infra_sync_time:
-            latest_infra_sync_time = datetime.fromisoformat(str(latest_infra_sync_time))
+        latest_infra_sync_time_str = sync_state_toml_table.get(LATEST_INFRA_SYNC_TIME)
+        if latest_infra_sync_time_str:
+            # Parse datetime and ensure it's timezone-aware UTC (consistent with how we write)
+            latest_infra_sync_time = datetime.fromisoformat(str(latest_infra_sync_time_str))
+            if latest_infra_sync_time.tzinfo is None:
+                latest_infra_sync_time = latest_infra_sync_time.replace(tzinfo=timezone.utc)
     sync_state = SyncState(dependency_layer, resource_sync_states, latest_infra_sync_time)
 
     return sync_state

tests/unit/commands/sync/test_sync_context.py

@@ -22,7 +22,7 @@
 )
 from samcli.lib.build.build_graph import DEFAULT_DEPENDENCIES_DIR
 
-MOCK_RESOURCE_SYNC_TIME = datetime(2023, 2, 8, 12, 12, 12)
+MOCK_RESOURCE_SYNC_TIME = datetime(2023, 2, 8, 12, 12, 12, tzinfo=timezone.utc)
 MOCK_INFRA_SYNC_TIME = datetime.now(timezone.utc)
 
 
@@ -288,3 +288,118 @@ def test_sync_context_has_no_previous_state_if_file_doesnt_exist(self, patched_r
             self.assertIsNone(self.sync_context._previous_state)
             self.assertIsNotNone(self.sync_context._current_state)
             patched_rmtree_if_exists.assert_not_called()
+
+
+class TestTimezoneNaiveDatetimeHandling(TestCase):
+    """Tests for Issue #8477: Timezone-naive datetime handling in sync.toml"""
+
+    def test_toml_to_sync_state_with_timezone_naive_timestamps(self):
+        """Test that timezone-naive timestamps are converted to UTC timezone-aware"""
+        # Create TOML with timezone-naive timestamps (missing +00:00)
+        toml_str = """
+[sync_state]
+dependency_layer = true
+latest_infra_sync_time = "2025-12-03T22:10:11.916279"
+
+[resource_sync_states]
+
+[resource_sync_states.MockResourceId]
+hash = "mock-hash"
+sync_time = "2025-12-03T22:10:35.345701"
+"""
+        toml_doc = tomlkit.loads(toml_str)
+        sync_state = _toml_document_to_sync_state(toml_doc)
+
+        # Verify latest_infra_sync_time is timezone-aware UTC
+        self.assertIsNotNone(sync_state.latest_infra_sync_time)
+        self.assertIsNotNone(sync_state.latest_infra_sync_time.tzinfo)
+        self.assertEqual(sync_state.latest_infra_sync_time.tzinfo, timezone.utc)
+
+        # Verify resource sync_time is timezone-aware UTC
+        resource_sync_state = sync_state.resource_sync_states.get("MockResourceId")
+        self.assertIsNotNone(resource_sync_state)
+        self.assertIsNotNone(resource_sync_state.sync_time.tzinfo)
+        self.assertEqual(resource_sync_state.sync_time.tzinfo, timezone.utc)
+
+    def test_toml_to_sync_state_with_timezone_aware_timestamps(self):
+        """Test that timezone-aware timestamps are preserved correctly"""
+        # Create TOML with timezone-aware timestamps (with +00:00)
+        toml_str = """
+[sync_state]
+dependency_layer = true
+latest_infra_sync_time = "2025-12-03T22:10:11.916279+00:00"
+
+[resource_sync_states]
+
+[resource_sync_states.MockResourceId]
+hash = "mock-hash"
+sync_time = "2025-12-03T22:10:35.345701+00:00"
+"""
+        toml_doc = tomlkit.loads(toml_str)
+        sync_state = _toml_document_to_sync_state(toml_doc)
+
+        # Verify latest_infra_sync_time is timezone-aware UTC
+        self.assertIsNotNone(sync_state.latest_infra_sync_time)
+        self.assertIsNotNone(sync_state.latest_infra_sync_time.tzinfo)
+        self.assertEqual(sync_state.latest_infra_sync_time.tzinfo, timezone.utc)
+
+        # Verify resource sync_time is timezone-aware UTC
+        resource_sync_state = sync_state.resource_sync_states.get("MockResourceId")
+        self.assertIsNotNone(resource_sync_state)
+        self.assertIsNotNone(resource_sync_state.sync_time.tzinfo)
+        self.assertEqual(resource_sync_state.sync_time.tzinfo, timezone.utc)
+
+    def test_toml_to_sync_state_mixed_timezone_formats(self):
+        """Test handling of mixed timezone-aware and timezone-naive timestamps"""
+        # Create TOML with mixed formats
+        toml_str = """
+[sync_state]
+dependency_layer = true
+latest_infra_sync_time = "2025-12-03T22:10:11.916279"
+
+[resource_sync_states]
+
+[resource_sync_states.Resource1]
+hash = "hash1"
+sync_time = "2025-12-03T22:10:35.345701+00:00"
+
+[resource_sync_states.Resource2]
+hash = "hash2"
+sync_time = "2025-12-03T22:10:40.123456"
+"""
+        toml_doc = tomlkit.loads(toml_str)
+        sync_state = _toml_document_to_sync_state(toml_doc)
+
+        # All timestamps should be timezone-aware UTC
+        self.assertIsNotNone(sync_state.latest_infra_sync_time.tzinfo)
+        self.assertEqual(sync_state.latest_infra_sync_time.tzinfo, timezone.utc)
+
+        resource1 = sync_state.resource_sync_states.get("Resource1")
+        self.assertIsNotNone(resource1.sync_time.tzinfo)
+        self.assertEqual(resource1.sync_time.tzinfo, timezone.utc)
+
+        resource2 = sync_state.resource_sync_states.get("Resource2")
+        self.assertIsNotNone(resource2.sync_time.tzinfo)
+        self.assertEqual(resource2.sync_time.tzinfo, timezone.utc)
+
+    def test_datetime_comparison_after_fix(self):
+        """Test that datetime comparison works after loading timezone-naive timestamps"""
+        # Simulate the bug scenario: load timezone-naive timestamp and compare with current time
+        toml_str = """
+[sync_state]
+dependency_layer = true
+latest_infra_sync_time = "2025-12-03T22:10:11.916279"
+
+[resource_sync_states]
+"""
+        toml_doc = tomlkit.loads(toml_str)
+        sync_state = _toml_document_to_sync_state(toml_doc)
+
+        # This should not raise TypeError: can't subtract offset-naive and offset-aware datetimes
+        current_time = datetime.now(timezone.utc)
+        try:
+            time_diff = current_time - sync_state.latest_infra_sync_time
+            # If we get here, the fix worked
+            self.assertIsNotNone(time_diff)
+        except TypeError as e:
+            self.fail(f"DateTime comparison failed with TypeError: {e}")