Django2: Use new custom template loader interface

The new template loader interface is described here:
https://docs.djangoproject.com/en/2.0/ref/templates/api/#loader-methods

The old interface was deprecated in Django 1.9, and the old interface
load_template_sources() was removed in Django 2.0.
https://docs.djangoproject.com/en/2.0/releases/1.9/#template-loader-apis-have-changed

According to the UT result, force_escape in _detail_overview.html
looks unnecessary. If force_escape is used, the returned string will
be double-escaped and it is not what we expect.

blueprint django2-support
Change-Id: I8a5a79cb61a6ebd25453bde3e0ec64f5b5f50e1b

horizon/loaders.py

@@ -14,26 +14,19 @@
 Wrapper for loading templates from "templates" directories in panel modules.
 """
 
-import io
 import os
 
-import django
-from django.conf import settings
-from django.template.engine import Engine
-from django.template.loaders.base import Loader as tLoaderCls
+from django.core.exceptions import SuspiciousFileOperation
+from django.template.loaders import filesystem as filesystem_loader
+from django.template import Origin
 from django.utils._os import safe_join
 
-if django.VERSION >= (1, 9):
-    from django.template.exceptions import TemplateDoesNotExist
-else:
-    from django.template.base import TemplateDoesNotExist
 
 # Set up a cache of the panel directories to search.
 panel_template_dirs = {}
 
 
-class TemplateLoader(tLoaderCls):
-    is_usable = True
+class TemplateLoader(filesystem_loader.Loader):
 
     def get_template_sources(self, template_name):
         bits = template_name.split('/', 2)
@@ -43,23 +36,14 @@ class TemplateLoader(tLoaderCls):
             if key in panel_template_dirs:
                 template_dir = panel_template_dirs[key]
                 try:
-                    yield safe_join(template_dir, panel_name, remainder)
+                    name = safe_join(template_dir, panel_name, remainder)
+                    yield Origin(name=name,
+                                 template_name=template_name,
+                                 loader=self)
                 except UnicodeDecodeError:
                     # The template dir name wasn't valid UTF-8.
                     raise
-                except ValueError:
-                    # The joined path was located outside of template_dir.
+                except SuspiciousFileOperation:
+                    # The joined path was located outside of this template_dir
+                    # (it might be inside another one, so this isn't fatal).
                     pass
-
-    def load_template_source(self, template_name, template_dirs=None):
-        for path in self.get_template_sources(template_name):
-            try:
-                with io.open(path, encoding=settings.FILE_CHARSET) as file:
-                    return (file.read(), path)
-            except IOError:
-                pass
-        raise TemplateDoesNotExist(template_name)
-
-
-e = Engine()
-_loader = TemplateLoader(e)

horizon/themes.py

@@ -17,22 +17,15 @@
 Allows Dynamic Theme Loading.
 """
 
-import io
 import os
 import threading
 
-import django
 from django.conf import settings
 from django.core.exceptions import SuspiciousFileOperation
-from django.template.engine import Engine
-from django.template.loaders.base import Loader as tLoaderCls
+from django.template.loaders import filesystem as filesystem_loader
+from django.template import Origin
 from django.utils._os import safe_join
 
-if django.VERSION >= (1, 9):
-    from django.template.exceptions import TemplateDoesNotExist
-else:
-    from django.template.base import TemplateDoesNotExist
-
 
 # Local thread storage to retrieve the currently set theme
 _local = threading.local()
@@ -126,7 +119,7 @@ class ThemeMiddleware(object):
         return response
 
 
-class ThemeTemplateLoader(tLoaderCls):
+class ThemeTemplateLoader(filesystem_loader.Loader):
     """Theme-aware template loader.
 
     Themes can contain template overrides, so we need to check the
@@ -162,32 +155,22 @@ class ThemeTemplateLoader(tLoaderCls):
                 this_theme[2],
                 'templates'
             )
+            name = None
             if not template_name.startswith('/'):
                 try:
-                    yield safe_join(template_path, template_name)
+                    name = safe_join(template_path, template_name)
                 except SuspiciousFileOperation:
-                    yield os.path.join(
+                    name = os.path.join(
                         this_theme[2], 'templates', template_name
                     )
             elif template_path in template_name:
-                yield template_name
+                name = template_name
+
+            if name:
+                yield Origin(name=name,
+                             template_name=template_name,
+                             loader=self)
 
         except UnicodeDecodeError:
             # The template dir name wasn't valid UTF-8.
             raise
-        except ValueError:
-            # The joined path was located outside of template_dir.
-            pass
-
-    def load_template_source(self, template_name, template_dirs=None):
-        for path in self.get_template_sources(template_name):
-            try:
-                with io.open(path, encoding=settings.FILE_CHARSET) as file:
-                    return file.read(), path
-            except IOError:
-                pass
-        raise TemplateDoesNotExist(template_name)
-
-
-e = Engine()
-_loader = ThemeTemplateLoader(e)

openstack_dashboard/dashboards/project/instances/templates/instances/_detail_overview.html

@@ -122,8 +122,8 @@
       {% endif %}
       {% with default_item_value="<em>"|add:_("N/A")|add:"</em>" %}
       {% for key, value in instance.metadata.items %}
-        <dt>{{ key|force_escape }}</dt>
-        <dd>{{ value|force_escape|default:default_item_value }}</dd>
+        <dt>{{ key }}</dt>
+        <dd>{{ value|default:default_item_value }}</dd>
       {% endfor %}
       {% endwith %}
     </dl>