Fix errors in templates propagting when DEBUG is enabled. (#52)

.gitignore

@@ -29,3 +29,6 @@ pip-log.txt
 
 # Editor files
 .idea
+
+# Virtual environment
+.venv

render_block/django.py

@@ -28,26 +28,29 @@ def django_render_block(template, block_name, context, request=None):
     else:
         context_instance = Context(context)
 
-    # Get the underlying django.template.base.Template object.
+    # Get the underlying django.template.base.Template object from the backend.
     template = template.template
 
     # Bind the template to the context.
-    with context_instance.bind_template(template):
-        # Before trying to render the template, we need to traverse the tree of
-        # parent templates and find all blocks in them.
-        parent_template = _build_block_context(template, context_instance)
-
-        try:
-            return _render_template_block(template, block_name, context_instance)
-        except BlockNotFound:
-            # The block wasn't found in the current template.
-
-            # If there's no parent template (i.e. no ExtendsNode), re-raise.
-            if not parent_template:
-                raise
-
-            # Check the parent template for this block.
-            return _render_template_block(parent_template, block_name, context_instance)
+    with context_instance.render_context.push_state(template):
+        with context_instance.bind_template(template):
+            # Before trying to render the template, we need to traverse the tree of
+            # parent templates and find all blocks in them.
+            parent_template = _build_block_context(template, context_instance)
+
+            try:
+                return _render_template_block(template, block_name, context_instance)
+            except BlockNotFound:
+                # The block wasn't found in the current template.
+
+                # If there's no parent template (i.e. no ExtendsNode), re-raise.
+                if not parent_template:
+                    raise
+
+                # Check the parent template for this block.
+                return _render_template_block(
+                    parent_template, block_name, context_instance
+                )
 
 
 def _build_block_context(template, context):

tests/templates/test_exception.html

@@ -0,0 +1,5 @@
+{% load test_tags %}
+
+{% block exception_block %}
+    {% raise_exception %}
+{% endblock exception_block %}

tests/templatetags/test_tags.py

@@ -0,0 +1,8 @@
+from django import template
+
+register = template.Library()
+
+
+@register.simple_tag()
+def raise_exception():
+    raise Exception("Exception raised in template tag.")

tests/tests.py

@@ -91,6 +91,19 @@ def test_subblock_no_parent(self):
         result = render_block_to_string("test_sub.html", "first")
         self.assertEqual(result, "\nbar\n")
 
+    def test_exceptions(self):
+        with self.assertRaises(Exception) as e:
+            render_block_to_string("test_exception.html", "exception_block")
+        self.assertEqual(str(e.exception), "Exception raised in template tag.")
+
+    @override_settings(DEBUG=True)
+    def test_exceptions_debug(self):
+        with self.assertRaises(Exception) as exc:
+            render_block_to_string("test_exception.html", "exception_block")
+        self.assertExceptionMessageEquals(
+            exc.exception, "Exception raised in template tag."
+        )
+
     def test_context(self):
         """Test that a context is properly rendered in a template."""
         data = "block2 from test5"