Show friendly error if decorator usage wasn't updated

Author: Rob Hudson

csp/decorators.py

@@ -2,6 +2,14 @@
 
 
 def csp_exempt(REPORT_ONLY=None):
+    if callable(REPORT_ONLY):
+        raise RuntimeError(
+            "Incompatible `csp_exempt` decorator usage. This decorator now requires arguments, "
+            "even if none are passed. Change bare decorator usage (@csp_exempt) to parameterized "
+            "decorator usage (@csp_exempt()). See the django-csp 4.0 migration guide for more "
+            "information."
+        )
+
     def decorator(f):
         @wraps(f)
         def _wrapped(*a, **kw):
@@ -17,7 +25,17 @@ def _wrapped(*a, **kw):
     return decorator
 
 
-def csp_update(config, *, REPORT_ONLY=False):
+# Error message for deprecated decorator arguments.
+DECORATOR_DEPRECATION_ERROR = (
+    "Incompatible `{fname}` decorator arguments. This decorator now takes a single dict argument. "
+    "See the django-csp 4.0 migration guide for more information."
+)
+
+
+def csp_update(config=None, REPORT_ONLY=False, **kwargs):
+    if config is None and kwargs:
+        raise RuntimeError(DECORATOR_DEPRECATION_ERROR.format(fname="csp_update"))
+
     def decorator(f):
         @wraps(f)
         def _wrapped(*a, **kw):
@@ -33,7 +51,10 @@ def _wrapped(*a, **kw):
     return decorator
 
 
-def csp_replace(config, *, REPORT_ONLY=False):
+def csp_replace(config=None, REPORT_ONLY=False, **kwargs):
+    if config is None and kwargs:
+        raise RuntimeError(DECORATOR_DEPRECATION_ERROR.format(fname="csp_replace"))
+
     def decorator(f):
         @wraps(f)
         def _wrapped(*a, **kw):
@@ -49,7 +70,10 @@ def _wrapped(*a, **kw):
     return decorator
 
 
-def csp(config, *, REPORT_ONLY=False):
+def csp(config=None, REPORT_ONLY=False, **kwargs):
+    if config is None and kwargs:
+        raise RuntimeError(DECORATOR_DEPRECATION_ERROR.format(fname="csp"))
+
     config = {k: [v] if isinstance(v, str) else v for k, v in config.items()}
 
     def decorator(f):

csp/tests/test_decorators.py

@@ -253,3 +253,46 @@ def view_with_decorator(request):
     mw.process_response(request, response)
     policy_list = sorted(response[HEADER].split("; "))
     assert policy_list == ["font-src bar.com", "img-src foo.com"]
+
+
+# Deprecation tests
+
+
+def test_csp_exempt_error():
+    with pytest.raises(RuntimeError) as excinfo:
+
+        @csp_exempt
+        def view(request):
+            return HttpResponse()
+
+    assert "Incompatible `csp_exempt` decorator usage" in str(excinfo.value)
+
+
+def test_csp_update_error():
+    with pytest.raises(RuntimeError) as excinfo:
+
+        @csp_update(IMG_SRC="bar.com")
+        def view(request):
+            return HttpResponse()
+
+    assert "Incompatible `csp_update` decorator arguments" in str(excinfo.value)
+
+
+def test_csp_replace_error():
+    with pytest.raises(RuntimeError) as excinfo:
+
+        @csp_replace(IMG_SRC="bar.com")
+        def view(request):
+            return HttpResponse()
+
+    assert "Incompatible `csp_replace` decorator arguments" in str(excinfo.value)
+
+
+def test_csp_error():
+    with pytest.raises(RuntimeError) as excinfo:
+
+        @csp(IMG_SRC=["bar.com"])
+        def view(request):
+            return HttpResponse()
+
+    assert "Incompatible `csp` decorator arguments" in str(excinfo.value)