Moved template loaders management in Engine.

Passed the engine instance to loaders. This is a prerequisite for
looking up configuration on the engine instance instead of global
settings.

This is backwards incompatible for custom template loaders that override
__init__. However the documentation doesn't talk about __init__ and the
way to pass arguments to custom template loaders isn't specified. I'm
considering it a private API.

10 files changed, 70 insertions, 72 deletions

diff --git a/django/template/engine.py b/django/template/engine.py
index 600c74ee24..257042d497 100644
--- a/django/template/engine.py
+++ b/django/template/engine.py
@@ -2,12 +2,13 @@ import warnings
 
 from django.conf import settings
 from django.core.exceptions import ImproperlyConfigured
+from django.utils import lru_cache
+from django.utils import six
 from django.utils.deprecation import RemovedInDjango20Warning
 from django.utils.functional import cached_property
-from django.utils import lru_cache
+from django.utils.module_loading import import_string
 
 from .base import Context, Template, TemplateDoesNotExist
-from .loaders.utils import get_template_loaders
 
 
 _dirs_undefined = object()
@@ -54,7 +55,49 @@ class Engine(object):
 
     @cached_property
     def template_loaders(self):
-        return get_template_loaders(self.loaders)
+        return self.get_template_loaders(self.loaders)
+
+    def get_template_loaders(self, template_loaders):
+        loaders = []
+        for template_loader in template_loaders:
+            loader = self.find_template_loader(template_loader)
+            if loader is not None:
+                loaders.append(loader)
+        return loaders
+
+    def find_template_loader(self, loader):
+        if isinstance(loader, (tuple, list)):
+            args = list(loader[1:])
+            loader = loader[0]
+        else:
+            args = []
+
+        if isinstance(loader, six.string_types):
+            loader_class = import_string(loader)
+
+            if getattr(loader_class, '_accepts_engine_in_init', False):
+                args.insert(0, self)
+            else:
+                warnings.warn(
+                    "%s inherits from django.template.loader.BaseLoader "
+                    "instead of django.template.loaders.base.Loader. " %
+                    loader, RemovedInDjango20Warning, stacklevel=2)
+
+            loader_instance = loader_class(*args)
+
+            if not loader_instance.is_usable:
+                warnings.warn(
+                    "Your template loaders configuration includes %r, but "
+                    "your Python installation doesn't support that type of "
+                    "template loading. Consider removing that line from "
+                    "your settings." % loader)
+                return None
+            else:
+                return loader_instance
+
+        else:
+            raise ImproperlyConfigured(
+                "Invalid value in template loaders configuration: %r" % loader)
 
     def find_template(self, name, dirs=None):
         # Inner import to avoid circular dependency
diff --git a/django/template/loader.py b/django/template/loader.py
index 0c24e3d373..eb89ab5900 100644
--- a/django/template/loader.py
+++ b/django/template/loader.py
@@ -48,10 +48,11 @@ from .loaders import base
 
 
 class BaseLoader(base.Loader):
+    _accepts_engine_in_init = False
 
     def __init__(self, *args, **kwargs):
         warnings.warn(
-            "django.template.loader.BaseLoader was renamed to "
+            "django.template.loader.BaseLoader was superseded by "
             "django.template.loaders.base.Loader.",
             RemovedInDjango20Warning, stacklevel=2)
         super(BaseLoader, self).__init__(*args, **kwargs)
diff --git a/django/template/loaders/base.py b/django/template/loaders/base.py
index 03c58f7535..1a7df03f5e 100644
--- a/django/template/loaders/base.py
+++ b/django/template/loaders/base.py
@@ -4,10 +4,11 @@ from django.template.loader import get_template_from_string, make_origin
 
 class Loader(object):
     is_usable = False
+    # Only used to raise a deprecation warning. Remove in Django 2.0.
+    _accepts_engine_in_init = True
 
-    def __init__(self, *args, **kwargs):
-        # XXX dropping arguments silently may not be the best idea.
-        pass
+    def __init__(self, engine):
+        self.engine = engine
 
     def __call__(self, template_name, template_dirs=None):
         return self.load_template(template_name, template_dirs)
diff --git a/django/template/loaders/cached.py b/django/template/loaders/cached.py
index 925abbe31f..b8cf48d237 100644
--- a/django/template/loaders/cached.py
+++ b/django/template/loaders/cached.py
@@ -9,18 +9,16 @@ from django.template.loader import get_template_from_string, make_origin
 from django.utils.encoding import force_bytes
 
 from .base import Loader as BaseLoader
-from .utils import get_template_loaders
 
 
 class Loader(BaseLoader):
     is_usable = True
 
-    def __init__(self, loaders):
+    def __init__(self, engine, loaders):
         self.template_cache = {}
         self.find_template_cache = {}
-        # Use the private, non-caching version of get_template_loaders
-        # in case loaders isn't hashable.
-        self.loaders = get_template_loaders(loaders)
+        self.loaders = engine.get_template_loaders(loaders)
+        super(Loader, self).__init__(engine)
 
     def cache_key(self, template_name, template_dirs):
         if template_dirs:
diff --git a/django/template/loaders/locmem.py b/django/template/loaders/locmem.py
index ba6b15ef51..3085d69258 100644
--- a/django/template/loaders/locmem.py
+++ b/django/template/loaders/locmem.py
@@ -10,8 +10,9 @@ from .base import Loader as BaseLoader
 class Loader(BaseLoader):
     is_usable = True
 
-    def __init__(self, templates_dict):
+    def __init__(self, engine, templates_dict):
         self.templates_dict = templates_dict
+        super(Loader, self).__init__(engine)
 
     def load_template_source(self, template_name, template_dirs=None):
         try:
diff --git a/django/template/loaders/utils.py b/django/template/loaders/utils.py
deleted file mode 100644
index 8b742f89fd..0000000000
--- a/django/template/loaders/utils.py
+++ /dev/null
@@ -1,38 +0,0 @@
-import warnings
-
-from django.core.exceptions import ImproperlyConfigured
-from django.utils import six
-from django.utils.module_loading import import_string
-
-
-def get_template_loaders(template_loaders):
-    loaders = []
-    for template_loader in template_loaders:
-        loader = find_template_loader(template_loader)
-        if loader is not None:
-            loaders.append(loader)
-    return loaders
-
-
-def find_template_loader(loader):
-    if isinstance(loader, (tuple, list)):
-        loader, args = loader[0], loader[1:]
-    else:
-        args = []
-
-    if isinstance(loader, six.string_types):
-        loader_class = import_string(loader)
-        loader_instance = loader_class(*args)
-
-        if not loader_instance.is_usable:
-            warnings.warn(
-                "Your TEMPLATE_LOADERS setting includes %r, but your Python "
-                "installation doesn't support that type of template loading. "
-                "Consider removing that line from TEMPLATE_LOADERS." % loader)
-            return None
-        else:
-            return loader_instance
-
-    else:
-        raise ImproperlyConfigured(
-            "Invalid value in TEMPLATE_LOADERS: %r" % loader)
diff --git a/django/test/signals.py b/django/test/signals.py
index 013d293203..648162b8ae 100644
--- a/django/test/signals.py
+++ b/django/test/signals.py
@@ -98,13 +98,6 @@ def clear_context_processors_cache(**kwargs):
 
 
 @receiver(setting_changed)
-def clear_template_loaders_cache(**kwargs):
-    if kwargs['setting'] == 'TEMPLATE_LOADERS':
-        from django.template.loaders.utils import get_template_loaders
-        get_template_loaders.cache_clear()
-
-
-@receiver(setting_changed)
 def clear_serializers_cache(**kwargs):
     if kwargs['setting'] == 'SERIALIZATION_MODULES':
         from django.core import serializers
diff --git a/django/views/debug.py b/django/views/debug.py
index 06a27069f6..ab32d866a5 100644
--- a/django/views/debug.py
+++ b/django/views/debug.py
@@ -12,7 +12,7 @@ from django.http import (HttpResponse, HttpResponseNotFound, HttpRequest,
     build_request_repr)
 from django.template import Template, Context, TemplateDoesNotExist
 from django.template.defaultfilters import force_escape, pprint
-from django.template.loaders.utils import get_template_loaders
+from django.template.engine import Engine
 from django.utils.datastructures import MultiValueDict
 from django.utils.html import escape
 from django.utils.encoding import force_bytes, smart_text
@@ -282,7 +282,8 @@ class ExceptionReporter(object):
             # If Django fails in get_template_loaders, provide an empty list
             # for the following loop to not fail.
             try:
-                template_loaders = get_template_loaders()
+                # TODO: handle multiple template engines.
+                template_loaders = Engine.get_default().template_loaders
             except Exception:
                 template_loaders = []
             for loader in template_loaders:
diff --git a/tests/template_tests/test_loaders.py b/tests/template_tests/test_loaders.py
index 220f766077..66957dc90e 100644
--- a/tests/template_tests/test_loaders.py
+++ b/tests/template_tests/test_loaders.py
@@ -22,7 +22,7 @@ except ImportError:
 
 from django.template import TemplateDoesNotExist, Context
 from django.template.loaders.eggs import Loader as EggLoader
-from django.template.loaders.utils import find_template_loader
+from django.template.engine import Engine
 from django.template import loader
 from django.test import TestCase, override_settings
 from django.test.utils import IgnorePendingDeprecationWarningsMixin
@@ -86,26 +86,26 @@ class EggLoaderTest(TestCase):
     @override_settings(INSTALLED_APPS=['egg_empty'])
     def test_empty(self):
         "Loading any template on an empty egg should fail"
-        egg_loader = EggLoader()
+        egg_loader = EggLoader(Engine.get_default())
         self.assertRaises(TemplateDoesNotExist, egg_loader.load_template_source, "not-existing.html")
 
     @override_settings(INSTALLED_APPS=['egg_1'])
     def test_non_existing(self):
         "Template loading fails if the template is not in the egg"
-        egg_loader = EggLoader()
+        egg_loader = EggLoader(Engine.get_default())
         self.assertRaises(TemplateDoesNotExist, egg_loader.load_template_source, "not-existing.html")
 
     @override_settings(INSTALLED_APPS=['egg_1'])
     def test_existing(self):
         "A template can be loaded from an egg"
-        egg_loader = EggLoader()
+        egg_loader = EggLoader(Engine.get_default())
         contents, template_name = egg_loader.load_template_source("y.html")
         self.assertEqual(contents, "y")
         self.assertEqual(template_name, "egg:egg_1:templates/y.html")
 
     def test_not_installed(self):
         "Loading an existent template from an egg not included in any app should fail"
-        egg_loader = EggLoader()
+        egg_loader = EggLoader(Engine.get_default())
         self.assertRaises(TemplateDoesNotExist, egg_loader.load_template_source, "y.html")
 
 
@@ -129,7 +129,7 @@ class CachedLoader(TestCase):
 
     def test_missing_template_is_cached(self):
         "#19949 -- Check that the missing template is cached."
-        template_loader = find_template_loader(settings.TEMPLATE_LOADERS[0])
+        template_loader = Engine.get_default().template_loaders[0]
         # Empty cache, which may be filled from previous tests.
         template_loader.reset()
         # Check that 'missing.html' isn't already in cache before 'missing.html' is loaded
diff --git a/tests/template_tests/tests.py b/tests/template_tests/tests.py
index 80d7b727d6..397c6c4e11 100644
--- a/tests/template_tests/tests.py
+++ b/tests/template_tests/tests.py
@@ -14,8 +14,8 @@ from django.contrib.auth.models import Group
 from django.core import urlresolvers
 from django.template import (base as template_base, loader, Context,
     RequestContext, Template, TemplateSyntaxError)
+from django.template.engine import Engine
 from django.template.loaders import app_directories, filesystem
-from django.template.loaders.utils import get_template_loaders
 from django.test import RequestFactory, TestCase
 from django.test.utils import override_settings, extend_sys_path
 from django.utils.deprecation import RemovedInDjango19Warning, RemovedInDjango20Warning
@@ -160,8 +160,8 @@ class UTF8Class:
 class TemplateLoaderTests(TestCase):
 
     def test_loaders_security(self):
-        ad_loader = app_directories.Loader()
-        fs_loader = filesystem.Loader()
+        ad_loader = app_directories.Loader(Engine.get_default())
+        fs_loader = filesystem.Loader(Engine.get_default())
 
         def test_template_sources(path, template_dirs, expected_sources):
             if isinstance(expected_sources, list):
@@ -620,9 +620,7 @@ class TemplateTests(TestCase):
                                 if output != result:
                                     failures.append("Template test (Cached='%s', TEMPLATE_STRING_IF_INVALID='%s', TEMPLATE_DEBUG=%s): %s -- FAILED. Expected %r, got %r" % (is_cached, invalid_str, template_debug, name, result, output))
 
-                    # This relies on get_template_loaders() memoizing its
-                    # result. All callers get the same iterable of loaders.
-                    get_template_loaders()[0].reset()
+                    Engine.get_default().template_loaders[0].reset()
 
                 if template_base.invalid_var_format_string:
                     expected_invalid_str = 'INVALID'