Supported multiple template engines in render_to_string.

Adjusted its API through a deprecation path according to the DEP.

django/shortcuts.py

@@ -3,6 +3,8 @@ This module collects helper functions and classes that "span" multiple levels
 of MVC. In other words, these functions/classes introduce controlled coupling
 for convenience's sake.
 """
+import warnings
+
 from django.template import loader, RequestContext
 from django.http import HttpResponse, Http404
 from django.http import HttpResponseRedirect, HttpResponsePermanentRedirect
@@ -11,6 +13,7 @@ from django.db.models.manager import Manager
 from django.db.models.query import QuerySet
 from django.core import urlresolvers
 from django.utils import six
+from django.utils.deprecation import RemovedInDjango20Warning
 
 
 def render_to_response(*args, **kwargs):
@@ -20,7 +23,12 @@ def render_to_response(*args, **kwargs):
     """
     httpresponse_kwargs = {'content_type': kwargs.pop('content_type', None)}
 
-    return HttpResponse(loader.render_to_string(*args, **kwargs), **httpresponse_kwargs)
+    # TODO: refactor to avoid the deprecated code path.
+    with warnings.catch_warnings():
+        warnings.filterwarnings("ignore", category=RemovedInDjango20Warning)
+        content = loader.render_to_string(*args, **kwargs)
+
+    return HttpResponse(content, **httpresponse_kwargs)
 
 
 def render(request, *args, **kwargs):
@@ -45,8 +53,12 @@ def render(request, *args, **kwargs):
 
     kwargs['context_instance'] = context_instance
 
-    return HttpResponse(loader.render_to_string(*args, **kwargs),
-                        **httpresponse_kwargs)
+    # TODO: refactor to avoid the deprecated code path.
+    with warnings.catch_warnings():
+        warnings.filterwarnings("ignore", category=RemovedInDjango20Warning)
+        content = loader.render_to_string(*args, **kwargs)
+
+    return HttpResponse(content, **httpresponse_kwargs)
 
 
 def redirect(to, *args, **kwargs):

django/template/engine.py

@@ -12,6 +12,8 @@ from .base import Context, Lexer, Parser, Template, TemplateDoesNotExist
 from .context import _builtin_context_processors
 
 
+_context_instance_undefined = object()
+_dictionary_undefined = object()
 _dirs_undefined = object()
 
 
@@ -165,14 +167,22 @@ class Engine(object):
             template = Template(template, origin, template_name, engine=self)
         return template
 
-    def render_to_string(self, template_name, dictionary=None, context_instance=None,
-                         dirs=_dirs_undefined):
+    def render_to_string(self, template_name, context=None,
+                         context_instance=_context_instance_undefined,
+                         dirs=_dirs_undefined,
+                         dictionary=_dictionary_undefined):
         """
         Loads the given template_name and renders it with the given dictionary as
         context. The template_name may be a string to load a single template using
         get_template, or it may be a tuple to use select_template to find one of
         the templates in the list. Returns a string.
         """
+        if context_instance is _context_instance_undefined:
+            context_instance = None
+        else:
+            warnings.warn(
+                "The context_instance argument of render_to_string is "
+                "deprecated.", RemovedInDjango20Warning, stacklevel=2)
         if dirs is _dirs_undefined:
             # Do not set dirs to None here to avoid triggering the deprecation
             # warning in select_template or get_template.
@@ -181,23 +191,30 @@ class Engine(object):
             warnings.warn(
                 "The dirs argument of render_to_string is deprecated.",
                 RemovedInDjango20Warning, stacklevel=2)
+        if dictionary is _dictionary_undefined:
+            dictionary = None
+        else:
+            warnings.warn(
+                "The dictionary argument of render_to_string was renamed to "
+                "context.", RemovedInDjango20Warning, stacklevel=2)
+            context = dictionary
 
         if isinstance(template_name, (list, tuple)):
             t = self.select_template(template_name, dirs)
         else:
             t = self.get_template(template_name, dirs)
         if not context_instance:
-            # Django < 1.8 accepted a Context in `dictionary` even though that's
-            # unintended. Preserve this ability but don't rewrap `dictionary`.
-            if isinstance(dictionary, Context):
-                return t.render(dictionary)
+            # Django < 1.8 accepted a Context in `context` even though that's
+            # unintended. Preserve this ability but don't rewrap `context`.
+            if isinstance(context, Context):
+                return t.render(context)
             else:
-                return t.render(Context(dictionary))
-        if not dictionary:
+                return t.render(Context(context))
+        if not context:
             return t.render(context_instance)
-        # Add the dictionary to the context stack, ensuring it gets removed again
+        # Add the context to the context stack, ensuring it gets removed again
         # to keep the context_instance in the same state it started in.
-        with context_instance.push(dictionary):
+        with context_instance.push(context):
             return t.render(context_instance)
 
     def select_template(self, template_name_list, dirs=_dirs_undefined):

django/template/loader.py

@@ -5,7 +5,8 @@ from django.utils.deprecation import RemovedInDjango20Warning
 from . import engines
 from .backends.django import DjangoTemplates
 from .base import Origin, TemplateDoesNotExist
-from .engine import _dirs_undefined, Engine
+from .engine import (
+    _context_instance_undefined, _dictionary_undefined, _dirs_undefined)
 
 
 class LoaderOrigin(Origin):
@@ -75,8 +76,61 @@ def select_template(template_name_list, dirs=_dirs_undefined, using=None):
         raise TemplateDoesNotExist("No template names provided")
 
 
-def render_to_string(*args, **kwargs):
-    return Engine.get_default().render_to_string(*args, **kwargs)
+def render_to_string(template_name, context=None,
+                     context_instance=_context_instance_undefined,
+                     dirs=_dirs_undefined,
+                     dictionary=_dictionary_undefined,
+                     using=None):
+    """
+    Loads a template and renders it with a context. Returns a string.
+
+    template_name may be a string or a list of strings.
+    """
+    if (context_instance is _context_instance_undefined
+            and dirs is _dirs_undefined
+            and dictionary is _dictionary_undefined):
+        # No deprecated arguments were passed - use the new code path
+        if isinstance(template_name, (list, tuple)):
+            template = select_template(template_name, using=using)
+        else:
+            template = get_template(template_name, using=using)
+        return template.render(context)
+
+    else:
+        # Some deprecated arguments were passed - use the legacy code path
+        for engine in _engine_list(using):
+            try:
+                # This is required for deprecating arguments specific to Django
+                # templates. Simply return engine.render_to_string(template_name,
+                # context) in Django 2.0.
+                if isinstance(engine, DjangoTemplates):
+                    # Hack -- use the internal Engine instance of DjangoTemplates.
+                    return engine.engine.render_to_string(
+                        template_name, context, context_instance, dirs, dictionary)
+                elif context_instance is not _context_instance_undefined:
+                    warnings.warn(
+                        "Skipping template backend %s because its render_to_string "
+                        "method doesn't support the context_instance argument." %
+                        engine.name, stacklevel=2)
+                elif dirs is not _dirs_undefined:
+                    warnings.warn(
+                        "Skipping template backend %s because its render_to_string "
+                        "method doesn't support the dirs argument." % engine.name,
+                        stacklevel=2)
+                elif dictionary is not _dictionary_undefined:
+                    warnings.warn(
+                        "Skipping template backend %s because its render_to_string "
+                        "method doesn't support the dictionary argument." %
+                        engine.name, stacklevel=2)
+            except TemplateDoesNotExist:
+                continue
+
+        if template_name:
+            if isinstance(template_name, (list, tuple)):
+                template_name = ', '.join(template_name)
+            raise TemplateDoesNotExist(template_name)
+        else:
+            raise TemplateDoesNotExist("No template names provided")
 
 
 def _engine_list(using=None):

docs/internals/deprecation.txt

@@ -88,6 +88,11 @@ details on these changes.
 * The backwards compatibility alias ``django.template.loader.BaseLoader`` will
   be removed.
 
+* The ``dictionary`` and ``context_instance`` parameters for the following
+  functions will be removed:
+
+  * ``django.template.loader.render_to_string()``
+
 * The ``dirs`` parameter for the following functions will be removed:
 
   * ``django.template.loader.get_template()``

docs/ref/templates/api.txt

@@ -890,7 +890,7 @@ When :setting:`TEMPLATE_DEBUG` is ``True`` template objects will have an
 The ``render_to_string`` shortcut
 ===================================
 
-.. function:: loader.render_to_string(template_name, dictionary=None, context_instance=None)
+.. function:: loader.render_to_string(template_name, context=None, context_instance=None)
 
 To cut down on the repetitive nature of loading and rendering
 templates, Django provides a shortcut function which largely
@@ -906,16 +906,25 @@ The ``render_to_string`` shortcut takes one required argument --
 and render (or a list of template names, in which case Django will use
 the first template in the list that exists) -- and two optional arguments:
 
-dictionary
+``context``
     A dictionary to be used as variables and values for the
-    template's context. This can also be passed as the second
+    template's context. This should be passed as the second
     positional argument.
 
-context_instance
+    .. versionchanged:: 1.8
+
+       The ``context`` argument used to be called ``dictionary``. That name
+       is deprecated in Django 1.8 and will be removed in Django 2.0.
+
+``context_instance``
     An instance of :class:`~django.template.Context` or a subclass (e.g., an
     instance of :class:`~django.template.RequestContext`) to use as the
     template's context. This can also be passed as the third positional argument.
 
+    .. deprecated:: 1.8
+
+       The ``context_instance`` argument is deprecated. Simply use ``context``.
+
 See also the :func:`~django.shortcuts.render_to_response()` shortcut, which
 calls ``render_to_string`` and feeds the result into an :class:`~django.http.HttpResponse`
 suitable for returning directly from a view.

docs/releases/1.8.txt

@@ -1198,6 +1198,20 @@ to construct the "view on site" URL. This URL is now accessible using the
 sure to provide a default value for the ``form_class`` argument since it's
 now optional.
 
+``dictionary`` and ``context_instance`` arguments of rendering functions
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The following functions will no longer accept the ``dictionary`` and
+``context_instance`` parameters in Django 2.0:
+
+* ``django.template.loader.render_to_string()``
+
+Use the ``context`` parameter instead. When ``dictionary`` is passed as a
+positional argument, which is the most common idiom, no changes are needed.
+
+There is no replacement for ``context_instance``. All data must be passed to
+templates through the ``context`` dict.
+
 ``dirs`` argument of template-finding functions
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 

tests/template_tests/test_loaders.py

@@ -153,13 +153,6 @@ class RenderToStringTest(SimpleTestCase):
         self.assertEqual(loader.render_to_string('test_context.html',
                                                  {'obj': 'test'}), 'obj:test\n')
 
-    def test_existing_context_kept_clean(self):
-        context = Context({'obj': 'before'})
-        output = loader.render_to_string('test_context.html', {'obj': 'after'},
-                                         context_instance=context)
-        self.assertEqual(output, 'obj:after\n')
-        self.assertEqual(context['obj'], 'before')
-
     def test_empty_list(self):
         six.assertRaisesRegex(self, TemplateDoesNotExist,
             'No template names provided$',
@@ -170,6 +163,21 @@ class RenderToStringTest(SimpleTestCase):
             'No template names provided$',
             loader.select_template, [])
 
+
+@override_settings(
+    TEMPLATE_DIRS=(
+        os.path.join(os.path.dirname(upath(__file__)), 'templates'),
+    )
+)
+class DeprecatedRenderToStringTest(IgnorePendingDeprecationWarningsMixin, SimpleTestCase):
+
+    def test_existing_context_kept_clean(self):
+        context = Context({'obj': 'before'})
+        output = loader.render_to_string('test_context.html', {'obj': 'after'},
+                                         context_instance=context)
+        self.assertEqual(output, 'obj:after\n')
+        self.assertEqual(context['obj'], 'before')
+
     def test_no_empty_dict_pushed_to_stack(self):
         """
         No empty dict should be pushed to the context stack when render_to_string