Fixed #18986 -- Improved error message for missing files

in CachedStaticFilesStorage. Thanks zyegfryed for his work on the patch.

django/contrib/staticfiles/management/commands/collectstatic.py

@@ -116,6 +116,12 @@ class Command(NoArgsCommand):
             processor = self.storage.post_process(found_files,
                                                   dry_run=self.dry_run)
             for original_path, processed_path, processed in processor:
+                if isinstance(processed, Exception):
+                    self.stderr.write("Post-processing '%s' failed!" % original_path)
+                    # Add a blank line before the traceback, otherwise it's
+                    # too easy to miss the relevant part of the error message.
+                    self.stderr.write("")
+                    raise processed
                 if processed:
                     self.log("Post-processed '%s' as '%s'" %
                              (original_path, processed_path), level=1)

django/contrib/staticfiles/storage.py

@@ -251,7 +251,10 @@ class CachedFilesMixin(object):
                     for patterns in self._patterns.values():
                         for pattern, template in patterns:
                             converter = self.url_converter(name, template)
+                            try:
                                 content = pattern.sub(converter, content)
+                            except ValueError as exc:
+                                yield name, None, exc
                     if hashed_file_exists:
                         self.delete(hashed_name)
                     # then save the processed result

tests/staticfiles_tests/project/faulty/faulty.css

@@ -0,0 +1 @@
+@import url("missing.css");

tests/staticfiles_tests/tests.py

@@ -244,7 +244,7 @@ class TestCollection(CollectionTestCase, TestDefaults):
 
 class TestCollectionClear(CollectionTestCase):
     """
-    Test the ``--clear`` option of the ``collectstatic`` managemenet command.
+    Test the ``--clear`` option of the ``collectstatic`` management command.
     """
     def run_collectstatic(self, **kwargs):
         clear_filepath = os.path.join(settings.STATIC_ROOT, 'cleared.txt')
@@ -550,6 +550,21 @@ class TestCollectionCachedStorage(BaseCollectionTestCase,
             self.assertNotIn(b"cached/other.css", content)
             self.assertIn(b"other.d41d8cd98f00.css", content)
 
+    @override_settings(
+        STATICFILES_DIRS=(os.path.join(TEST_ROOT, 'project', 'faulty'),),
+        STATICFILES_FINDERS=('django.contrib.staticfiles.finders.FileSystemFinder',),
+    )
+    def test_post_processing_failure(self):
+        """
+        Test that post_processing indicates the origin of the error when it
+        fails. Regression test for #18986.
+        """
+        finders._finders.clear()
+        err = six.StringIO()
+        with self.assertRaises(Exception) as cm:
+            call_command('collectstatic', interactive=False, verbosity=0, stderr=err)
+        self.assertEqual("Post-processing 'faulty.css' failed!\n\n", err.getvalue())
+
 
 # we set DEBUG to False here since the template tag wouldn't work otherwise
 @override_settings(**dict(TEST_SETTINGS,