From 12d3799dd2248a3c6e61191355ed5ac43869c691 Mon Sep 17 00:00:00 2001
From: Russell Keith-Magee <russell@keith-magee.com>
Date: Tue, 26 Jan 2010 01:38:50 +0000
Subject: [PATCH] =?UTF-8?q?Fixed=20#6587=20--=20Removed=20nasty=20=5F=5Fpa?=
 =?UTF-8?q?th=5F=5F=20hacking=20in=20templatetag=20loading.=20Thanks=20to?=
 =?UTF-8?q?=20=C3=98yvind=20Satvik=20and=20Andrew=20Badr=20for=20their=20w?=
 =?UTF-8?q?ork=20on=20this=20patch.?=
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git-svn-id: http://code.djangoproject.com/svn/django/trunk@12295 bcc190cf-cafb-0310-a4f2-bffc1f526a37
---
 django/contrib/admindocs/views.py        | 13 ++--
 django/template/__init__.py              | 76 +++++++++++++++++++-----
 django/template/defaulttags.py           |  2 +-
 django/templatetags/__init__.py          |  8 ---
 tests/regressiontests/templates/tests.py |  2 +-
 5 files changed, 73 insertions(+), 28 deletions(-)

diff --git a/django/contrib/admindocs/views.py b/django/contrib/admindocs/views.py
index 05c37b0f13..e154c9299a 100644
--- a/django/contrib/admindocs/views.py
+++ b/django/contrib/admindocs/views.py
@@ -309,12 +309,17 @@ def missing_docutils_page(request):
 
 def load_all_installed_template_libraries():
     # Load/register all template tag libraries from installed apps.
-    for e in templatetags.__path__:
-        libraries = [os.path.splitext(p)[0] for p in os.listdir(e) if p.endswith('.py') and p[0].isalpha()]
+    for module_name in template.get_templatetags_modules():
+        mod = import_module(module_name)
+        libraries = [
+            os.path.splitext(p)[0]
+            for p in os.listdir(os.path.dirname(mod.__file__))
+            if p.endswith('.py') and p[0].isalpha()
+        ]
         for library_name in libraries:
             try:
-                lib = template.get_library("django.templatetags.%s" % library_name.split('.')[-1])
-            except template.InvalidTemplateLibrary:
+                lib = template.get_library(library_name)
+            except template.InvalidTemplateLibrary, e:
                 pass
 
 def get_return_data_type(func_name):
diff --git a/django/template/__init__.py b/django/template/__init__.py
index 4c386bea30..af033222a8 100644
--- a/django/template/__init__.py
+++ b/django/template/__init__.py
@@ -809,7 +809,7 @@ class TextNode(Node):
 
     def render(self, context):
         return self.s
-    
+
 def _render_value_in_context(value, context):
     """
     Converts any value to a string to become part of a rendered template. This
@@ -966,22 +966,70 @@ class Library(object):
             return func
         return dec
 
-def get_library(module_name):
-    lib = libraries.get(module_name, None)
+def import_library(taglib_module):
+    """Load a template tag library module.
+
+    Verifies that the library contains a 'register' attribute, and
+    returns that attribute as the representation of the library
+    """
+    try:
+        mod = import_module(taglib_module)
+    except ImportError:
+        return None
+    try:
+        return mod.register
+    except AttributeError:
+        raise InvalidTemplateLibrary("Template library %s does not have a variable named 'register'" % taglib_module)
+
+templatetags_modules = []
+
+def get_templatetags_modules():
+    """Return the list of all available template tag modules.
+
+    Caches the result for faster access.
+    """
+    global templatetags_modules
+    if not templatetags_modules:
+        _templatetags_modules = []
+        # Populate list once per thread.
+        for app_module in ['django'] + list(settings.INSTALLED_APPS):
+            try:
+                templatetag_module = '%s.templatetags' % app_module
+                import_module(templatetag_module)
+                _templatetags_modules.append(templatetag_module)
+            except ImportError:
+                continue
+        templatetags_modules = _templatetags_modules
+    return templatetags_modules
+
+def get_library(library_name):
+    """
+    Load the template library module with the given name.
+
+    If library is not already loaded loop over all templatetags modules to locate it.
+
+    {% load somelib %} and {% load someotherlib %} loops twice.
+
+    Subsequent loads eg. {% load somelib %} in the same process will grab the cached
+    module from libraries.
+    """
+    lib = libraries.get(library_name, None)
     if not lib:
-        try:
-            mod = import_module(module_name)
-        except ImportError, e:
-            raise InvalidTemplateLibrary("Could not load template library from %s, %s" % (module_name, e))
-        try:
-            lib = mod.register
-            libraries[module_name] = lib
-        except AttributeError:
-            raise InvalidTemplateLibrary("Template library %s does not have a variable named 'register'" % module_name)
+        templatetags_modules = get_templatetags_modules()
+        tried_modules = []
+        for module in templatetags_modules:
+            taglib_module = '%s.%s' % (module, library_name)
+            tried_modules.append(taglib_module)
+            lib = import_library(taglib_module)
+            if lib:
+                libraries[library_name] = lib
+                break
+        if not lib:
+            raise InvalidTemplateLibrary("Template library %s not found, tried %s" % (library_name, ','.join(tried_modules)))
     return lib
 
-def add_to_builtins(module_name):
-    builtins.append(get_library(module_name))
+def add_to_builtins(module):
+    builtins.append(import_library(module))
 
 add_to_builtins('django.template.defaulttags')
 add_to_builtins('django.template.defaultfilters')
diff --git a/django/template/defaulttags.py b/django/template/defaulttags.py
index d703c6ab5e..f1b1de795b 100644
--- a/django/template/defaulttags.py
+++ b/django/template/defaulttags.py
@@ -920,7 +920,7 @@ def load(parser, token):
     for taglib in bits[1:]:
         # add the library to the parser
         try:
-            lib = get_library("django.templatetags.%s" % taglib)
+            lib = get_library(taglib)
             parser.add_library(lib)
         except InvalidTemplateLibrary, e:
             raise TemplateSyntaxError("'%s' is not a valid tag library: %s" %
diff --git a/django/templatetags/__init__.py b/django/templatetags/__init__.py
index 4033e5a8f6..e69de29bb2 100644
--- a/django/templatetags/__init__.py
+++ b/django/templatetags/__init__.py
@@ -1,8 +0,0 @@
-from django.conf import settings
-from django.utils import importlib
-
-for a in settings.INSTALLED_APPS:
-    try:
-        __path__.extend(importlib.import_module('.templatetags', a).__path__)
-    except ImportError:
-        pass
diff --git a/tests/regressiontests/templates/tests.py b/tests/regressiontests/templates/tests.py
index 29462086d8..88afc548dc 100644
--- a/tests/regressiontests/templates/tests.py
+++ b/tests/regressiontests/templates/tests.py
@@ -59,7 +59,7 @@ def do_echo(parser, token):
 
 register.tag("echo", do_echo)
 
-template.libraries['django.templatetags.testtags'] = register
+template.libraries['testtags'] = register
 
 #####################################
 # Helper objects for template tests #