From 6854998c8f405248c304cf14ecc46617e8a9f206 Mon Sep 17 00:00:00 2001
From: Aymeric Augustin <aymeric.augustin@m4x.org>
Date: Thu, 27 Nov 2014 21:30:35 +0100
Subject: [PATCH] Looked up the default template engine in the list of all
 engines.

---
 django/template/engine.py | 45 ++++++++++++++++++++++++++++-----------
 django/template/utils.py  | 14 ++++++------
 2 files changed, 40 insertions(+), 19 deletions(-)

diff --git a/django/template/engine.py b/django/template/engine.py
index 5838877a9f..8a48be46cc 100644
--- a/django/template/engine.py
+++ b/django/template/engine.py
@@ -1,6 +1,5 @@
 import warnings
 
-from django.conf import settings
 from django.core.exceptions import ImproperlyConfigured
 from django.utils import lru_cache
 from django.utils import six
@@ -8,6 +7,7 @@ from django.utils.deprecation import RemovedInDjango20Warning
 from django.utils.functional import cached_property
 from django.utils.module_loading import import_string
 
+from . import engines
 from .base import Context, Lexer, Parser, Template, TemplateDoesNotExist
 from .context import _builtin_context_processors
 
@@ -45,19 +45,38 @@ class Engine(object):
         self.string_if_invalid = string_if_invalid
         self.file_charset = file_charset
 
-    @classmethod
+    @staticmethod
     @lru_cache.lru_cache()
-    def get_default(cls):
-        """Transitional method for refactoring."""
-        return cls(
-            dirs=settings.TEMPLATE_DIRS,
-            allowed_include_roots=settings.ALLOWED_INCLUDE_ROOTS,
-            context_processors=settings.TEMPLATE_CONTEXT_PROCESSORS,
-            debug=settings.TEMPLATE_DEBUG,
-            loaders=settings.TEMPLATE_LOADERS,
-            string_if_invalid=settings.TEMPLATE_STRING_IF_INVALID,
-            file_charset=settings.FILE_CHARSET,
-        )
+    def get_default():
+        """
+        When only one DjangoTemplates backend is configured, returns it.
+
+        Raises ImproperlyConfigured otherwise.
+
+        This is required for preserving historical APIs that rely on a
+        globally available, implicitly configured engine such as:
+
+        >>> from django.template import Context, Template
+        >>> template = Template("Hello {{ name }}!")
+        >>> context = Context({'name': "world"})
+        >>> template.render(context)
+        'Hello world!'
+        """
+        # Since DjangoTemplates is a wrapper around this Engine class, a local
+        # import is mandatory to avoid an import loop.
+        from django.template.backends.django import DjangoTemplates
+        django_engines = [engine for engine in engines.all()
+                          if isinstance(engine, DjangoTemplates)]
+        if len(django_engines) == 1:
+            # Unwrap the Engine instance inside DjangoTemplates
+            return django_engines[0].engine
+        elif len(django_engines) == 0:
+            raise ImproperlyConfigured(
+                "No DjangoTemplates backend is configured.")
+        else:
+            raise ImproperlyConfigured(
+                "Several DjangoTemplates backends are configured. "
+                "You must select one explicitly.")
 
     @cached_property
     def template_context_processors(self):
diff --git a/django/template/utils.py b/django/template/utils.py
index 3303c1ccb7..140d591e53 100644
--- a/django/template/utils.py
+++ b/django/template/utils.py
@@ -1,14 +1,14 @@
 from collections import Counter, OrderedDict
 import os
 import sys
-import warnings
+# import warnings
 
 from django.apps import apps
 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.deprecation import RemovedInDjango20Warning
 from django.utils.functional import cached_property
 from django.utils.module_loading import import_string
 
@@ -32,10 +32,12 @@ class EngineHandler(object):
             self._templates = settings.TEMPLATES
 
         if not self._templates:
-            warnings.warn(
-                "You haven't defined a TEMPLATES setting. You must do so "
-                "before upgrading to Django 2.0. Otherwise Django will be "
-                "unable to load templates.", RemovedInDjango20Warning)
+            # TODO: re-enable this warning once the entire test suite has been
+            #       updated to rely on TEMPLATES instead of legacy settings.
+            # warnings.warn(
+            #     "You haven't defined a TEMPLATES setting. You must do so "
+            #     "before upgrading to Django 2.0. Otherwise Django will be "
+            #     "unable to load templates.", RemovedInDjango20Warning)
             self._templates = [
                 {
                     'BACKEND': 'django.template.backends.django.DjangoTemplates',