Supported multiple template engines in get_template and select_template.

This commit changes the return type of these two functions. Instead of
returning a django.template.Template they return a backend-specific
Template class that must implement render(self, context).

django/template/backends/django.py

@@ -3,7 +3,7 @@ from __future__ import absolute_import
 
 from django.conf import settings
 from django.template.context import Context, RequestContext
-from django.template.engine import Engine
+from django.template.engine import _dirs_undefined, Engine
 
 
 from .base import BaseEngine
@@ -24,8 +24,8 @@ class DjangoTemplates(BaseEngine):
     def from_string(self, template_code):
         return Template(self.engine.from_string(template_code))
 
-    def get_template(self, template_name):
+    def get_template(self, template_name, dirs=_dirs_undefined):
-        return Template(self.engine.get_template(template_name))
+        return Template(self.engine.get_template(template_name, dirs))
 
 
 class Template(object):
@@ -33,7 +33,15 @@ class Template(object):
     def __init__(self, template):
         self.template = template
 
+    @property
+    def origin(self):
+        # TODO: define the Origin API. For now simply forwarding to the
+        #       underlying Template preserves backwards-compatibility.
+        return self.template.origin
+
     def render(self, context=None, request=None):
+        # TODO: require context to be a dict -- through a deprecation path?
+        if not isinstance(context, Context):
             if request is None:
                 context = Context(context)
             else:

django/template/base.py

@@ -1266,6 +1266,8 @@ class Library(object):
                     if not getattr(self, 'nodelist', False):
                         if isinstance(file_name, Template):
                             t = file_name
+                        elif isinstance(getattr(file_name, 'template', None), Template):
+                            t = file_name.template
                         elif not isinstance(file_name, six.string_types) and is_iterable(file_name):
                             t = context.engine.select_template(file_name)
                         else:

django/template/loader.py

@@ -2,8 +2,10 @@ import warnings
 
 from django.utils.deprecation import RemovedInDjango20Warning
 
-from .base import Origin
+from . import engines
-from .engine import Engine
+from .backends.django import DjangoTemplates
+from .base import Origin, TemplateDoesNotExist
+from .engine import _dirs_undefined, Engine
 
 
 class LoaderOrigin(Origin):
@@ -19,8 +21,62 @@ def find_template(*args, **kwargs):
     return Engine.get_default().find_template(*args, **kwargs)
 
 
-def get_template(*args, **kwargs):
+def get_template(template_name, dirs=_dirs_undefined, using=None):
-    return Engine.get_default().get_template(*args, **kwargs)
+    """
+    Loads and returns a template for the given name.
+
+    Raises TemplateDoesNotExist if no such template exists.
+    """
+    engines = _engine_list(using)
+    for engine in engines:
+        try:
+            # This is required for deprecating the dirs argument. Simply
+            # return engine.get_template(template_name) in Django 2.0.
+            if isinstance(engine, DjangoTemplates):
+                return engine.get_template(template_name, dirs)
+            elif dirs is not _dirs_undefined:
+                warnings.warn(
+                    "Skipping template backend %s because its get_template "
+                    "method doesn't support the dirs argument." % engine.name,
+                    stacklevel=2)
+            else:
+                return engine.get_template(template_name)
+        except TemplateDoesNotExist:
+            pass
+
+    raise TemplateDoesNotExist(template_name)
+
+
+def select_template(template_name_list, dirs=_dirs_undefined, using=None):
+    """
+    Loads and returns a template for one of the given names.
+
+    Tries names in order and returns the first template found.
+
+    Raises TemplateDoesNotExist if no such template exists.
+    """
+    engines = _engine_list(using)
+    for template_name in template_name_list:
+        for engine in engines:
+            try:
+                # This is required for deprecating the dirs argument. Simply
+                # use engine.get_template(template_name) in Django 2.0.
+                if isinstance(engine, DjangoTemplates):
+                    return engine.get_template(template_name, dirs)
+                elif dirs is not _dirs_undefined:
+                    warnings.warn(
+                        "Skipping template backend %s because its get_template "
+                        "method doesn't support the dirs argument." % engine.name,
+                        stacklevel=2)
+                else:
+                    return engine.get_template(template_name)
+            except TemplateDoesNotExist:
+                pass
+
+    if template_name_list:
+        raise TemplateDoesNotExist(', '.join(template_name_list))
+    else:
+        raise TemplateDoesNotExist("No template names provided")
 
 
 def get_template_from_string(*args, **kwargs):
@@ -31,8 +87,8 @@ def render_to_string(*args, **kwargs):
     return Engine.get_default().render_to_string(*args, **kwargs)
 
 
-def select_template(*args, **kwargs):
+def _engine_list(using=None):
-    return Engine.get_default().select_template(*args, **kwargs)
+    return engines.all() if using is None else [engines[using]]
 
 
 # This line must remain at the bottom to avoid import loops.

tests/template_tests/tests.py

@@ -85,7 +85,7 @@ class TemplateLoaderTests(SimpleTestCase):
         # We also rely on the fact the file system and app directories loaders
         # both inherit the load_template method from the base Loader class, so
         # we only need to test one of them.
-        template = loader.get_template(load_name)
+        template = loader.get_template(load_name).template
         template_name = template.nodelist[0].source[0].name
         self.assertTrue(template_name.endswith(load_name),
             'Template loaded by filesystem loader has incorrect name for debug page: %s' % template_name)
@@ -100,12 +100,12 @@ class TemplateLoaderTests(SimpleTestCase):
         load_name = 'login.html'
 
         # Test the cached loader separately since it overrides load_template.
-        template = loader.get_template(load_name)
+        template = loader.get_template(load_name).template
         template_name = template.nodelist[0].source[0].name
         self.assertTrue(template_name.endswith(load_name),
             'Template loaded through cached loader has incorrect name for debug page: %s' % template_name)
 
-        template = loader.get_template(load_name)
+        template = loader.get_template(load_name).template
         template_name = template.nodelist[0].source[0].name
         self.assertTrue(template_name.endswith(load_name),
             'Cached template loaded through cached loader has incorrect name for debug page: %s' % template_name)