Fixed #17085, #24783 -- Refactored template library registration.

* Converted the ``libraries`` and ``builtins`` globals of
  ``django.template.base`` into properties of the Engine class.
* Added a public API for explicit registration of libraries and builtins.

12 files changed, 87 insertions, 1 deletions

diff --git a/tests/template_backends/apps/__init__.py b/tests/template_backends/apps/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/tests/template_backends/apps/__init__.py
diff --git a/tests/template_backends/apps/good/__init__.py b/tests/template_backends/apps/good/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/tests/template_backends/apps/good/__init__.py
diff --git a/tests/template_backends/apps/good/templatetags/__init__.py b/tests/template_backends/apps/good/templatetags/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/tests/template_backends/apps/good/templatetags/__init__.py
diff --git a/tests/template_backends/apps/good/templatetags/empty.py b/tests/template_backends/apps/good/templatetags/empty.py
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/tests/template_backends/apps/good/templatetags/empty.py
diff --git a/tests/template_backends/apps/good/templatetags/good_tags.py b/tests/template_backends/apps/good/templatetags/good_tags.py
new file mode 100644
index 0000000000..9bec93d8e5
--- /dev/null
+++ b/tests/template_backends/apps/good/templatetags/good_tags.py
@@ -0,0 +1,3 @@
+from django.template import Library
+
+register = Library()
diff --git a/tests/template_backends/apps/good/templatetags/override.py b/tests/template_backends/apps/good/templatetags/override.py
new file mode 100644
index 0000000000..9bec93d8e5
--- /dev/null
+++ b/tests/template_backends/apps/good/templatetags/override.py
@@ -0,0 +1,3 @@
+from django.template import Library
+
+register = Library()
diff --git a/tests/template_backends/apps/good/templatetags/subpackage/__init__.py b/tests/template_backends/apps/good/templatetags/subpackage/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/tests/template_backends/apps/good/templatetags/subpackage/__init__.py
diff --git a/tests/template_backends/apps/good/templatetags/subpackage/tags.py b/tests/template_backends/apps/good/templatetags/subpackage/tags.py
new file mode 100644
index 0000000000..9bec93d8e5
--- /dev/null
+++ b/tests/template_backends/apps/good/templatetags/subpackage/tags.py
@@ -0,0 +1,3 @@
+from django.template import Library
+
+register = Library()
diff --git a/tests/template_backends/apps/importerror/__init__.py b/tests/template_backends/apps/importerror/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/tests/template_backends/apps/importerror/__init__.py
diff --git a/tests/template_backends/apps/importerror/templatetags/__init__.py b/tests/template_backends/apps/importerror/templatetags/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/tests/template_backends/apps/importerror/templatetags/__init__.py
diff --git a/tests/template_backends/apps/importerror/templatetags/broken_tags.py b/tests/template_backends/apps/importerror/templatetags/broken_tags.py
new file mode 100644
index 0000000000..4f240e5923
--- /dev/null
+++ b/tests/template_backends/apps/importerror/templatetags/broken_tags.py
@@ -0,0 +1 @@
+import DoesNotExist  # noqa
diff --git a/tests/template_backends/test_django.py b/tests/template_backends/test_django.py
index a8cc0d58b8..2a21b04b5a 100644
--- a/tests/template_backends/test_django.py
+++ b/tests/template_backends/test_django.py
@@ -2,7 +2,8 @@ from template_tests.test_response import test_processor_name
 
 from django.template import RequestContext
 from django.template.backends.django import DjangoTemplates
-from django.test import RequestFactory, ignore_warnings
+from django.template.library import InvalidTemplateLibrary
+from django.test import RequestFactory, ignore_warnings, override_settings
 from django.utils.deprecation import RemovedInDjango20Warning
 
 from .test_dummy import TemplateStringsTests
@@ -51,3 +52,78 @@ class DjangoTemplatesTests(TemplateStringsTests):
                "the two arguments refer to the same request.")
         with self.assertRaisesMessage(ValueError, msg):
             template.render(request_context, other_request)
+
+    @override_settings(INSTALLED_APPS=['template_backends.apps.good'])
+    def test_templatetag_discovery(self):
+        engine = DjangoTemplates({
+            'DIRS': [],
+            'APP_DIRS': False,
+            'NAME': 'django',
+            'OPTIONS': {
+                'libraries': {
+                    'alternate': 'template_backends.apps.good.templatetags.good_tags',
+                    'override': 'template_backends.apps.good.templatetags.good_tags',
+                },
+            },
+        })
+
+        # libraries are discovered from installed applications
+        self.assertEqual(
+            engine.engine.libraries['good_tags'],
+            'template_backends.apps.good.templatetags.good_tags',
+        )
+        self.assertEqual(
+            engine.engine.libraries['subpackage.tags'],
+            'template_backends.apps.good.templatetags.subpackage.tags',
+        )
+        # libraries are discovered from django.templatetags
+        self.assertEqual(
+            engine.engine.libraries['static'],
+            'django.templatetags.static',
+        )
+        # libraries passed in OPTIONS are registered
+        self.assertEqual(
+            engine.engine.libraries['alternate'],
+            'template_backends.apps.good.templatetags.good_tags',
+        )
+        # libraries passed in OPTIONS take precedence over discovered ones
+        self.assertEqual(
+            engine.engine.libraries['override'],
+            'template_backends.apps.good.templatetags.good_tags',
+        )
+
+    @override_settings(INSTALLED_APPS=['template_backends.apps.importerror'])
+    def test_templatetag_discovery_import_error(self):
+        """
+        Import errors in tag modules should be reraised with a helpful message.
+        """
+        with self.assertRaisesMessage(
+            InvalidTemplateLibrary,
+            "ImportError raised when trying to load "
+            "'template_backends.apps.importerror.templatetags.broken_tags'"
+        ):
+            DjangoTemplates({
+                'DIRS': [],
+                'APP_DIRS': False,
+                'NAME': 'django',
+                'OPTIONS': {},
+            })
+
+    def test_builtins_discovery(self):
+        engine = DjangoTemplates({
+            'DIRS': [],
+            'APP_DIRS': False,
+            'NAME': 'django',
+            'OPTIONS': {
+                'builtins': ['template_backends.apps.good.templatetags.good_tags'],
+            },
+        })
+
+        self.assertEqual(
+            engine.engine.builtins, [
+                'django.template.defaulttags',
+                'django.template.defaultfilters',
+                'django.template.loader_tags',
+                'template_backends.apps.good.templatetags.good_tags',
+            ]
+        )