refactor: raise when template data overwrites variables from context_processors (#1484)

CHANGELOG.md

@@ -6,6 +6,10 @@
 
 - Make django-component's position in Django's `INSTALLED_APPS` more lenient by not calling Django's `URLResolver._populate()` if `URLResolver` hasn't been resolved before ([See thread](https://discord.com/channels/1417824875023700000/1417825089675853906/1437034834118840411)).
 
+#### Refactor
+
+- Components now raise error if template data overwrites variables from `context_processors` ([#1482](https://github.com/django-components/django-components/issues/1482))
+
 ## v0.143.0
 
 #### Feat

src/django_components/component.py

@@ -3569,6 +3569,8 @@ class Component(metaclass=ComponentMeta):
         # 2. Prepare component state
         ######################################
 
+        context_processors_data = component.context_processors_data
+
         # Required for compatibility with Django's {% extends %} tag
         # See https://github.com/django-components/django-components/pull/859
         context.render_context.push(  # type: ignore[union-attr]
@@ -3653,6 +3655,17 @@ class Component(metaclass=ComponentMeta):
             ),
         )
 
+        # Check if template_data doesn't conflict with context_processors_data
+        # See https://github.com/django-components/django-components/issues/1482
+        # NOTE: This is done after on_component_data so extensions can modify the data first.
+        if context_processors_data:
+            for key in template_data:
+                if key in context_processors_data:
+                    raise ValueError(
+                        f"Variable '{key}' defined in component '{component_name}' conflicts "
+                        "with the same variable from context processors. Rename the variable in the component."
+                    )
+
         # Cache component's JS and CSS scripts, in case they have been evicted from the cache.
         cache_component_js(comp_cls, force=False)
         cache_component_css(comp_cls, force=False)
@@ -3697,7 +3710,7 @@ class Component(metaclass=ComponentMeta):
             with context.update(  # type: ignore[union-attr]
                 {
                     # Make data from context processors available inside templates
-                    **component.context_processors_data,
+                    **context_processors_data,
                     # Private context fields
                     _COMPONENT_CONTEXT_KEY: render_id,
                     COMPONENT_IS_NESTED_KEY: comp_is_nested,

tests/test_context.py

@@ -1,5 +1,6 @@
 from typing import Dict, Optional, cast
 
+import pytest
 from django.http import HttpRequest
 from django.template import Context, RequestContext, Template
 from pytest_django.asserts import assertHTMLEqual, assertInHTML
@@ -969,6 +970,43 @@ class TestContextProcessors:
 
         assert component.request == request
 
+    @djc_test(
+        # Same as settings in testutils.py, but also sets context_processors
+        django_settings={
+            "TEMPLATES": [
+                {
+                    "BACKEND": "django.template.backends.django.DjangoTemplates",
+                    "DIRS": [
+                        "tests/templates/",
+                        "tests/components/",
+                    ],
+                    "OPTIONS": {
+                        "builtins": [
+                            "django_components.templatetags.component_tags",
+                        ],
+                        "loaders": [
+                            "django.template.loaders.filesystem.Loader",
+                            "django.template.loaders.app_directories.Loader",
+                            "django_components.template_loader.Loader",
+                        ],
+                        "context_processors": [
+                            "django.template.context_processors.request",
+                        ],
+                    },
+                },
+            ],
+        }
+    )
+    def test_raises_on_conflict_with_template_data(self):
+        class TestComponent(Component):
+            def get_template_data(self, args, kwargs, slots, context):
+                return {
+                    "request": "OVERWRITTEN",
+                }
+
+        with pytest.raises(ValueError, match="Variable 'request' defined in component 'TestComponent' conflicts"):
+            TestComponent.render(request=HttpRequest())
+
 
 @djc_test
 class TestOuterContextProperty: