Prevent head method mapping to coerce action name (#7729)

rest_framework/schemas/coreapi.py

@@ -198,7 +198,11 @@ class SchemaGenerator(BaseSchemaGenerator):
 
         if is_custom_action(action):
             # Custom action, eg "/users/{pk}/activate/", "/users/active/"
-            if len(view.action_map) > 1:
+            mapped_methods = {
+                # Don't count head mapping, e.g. not part of the schema
+                method for method in view.action_map if method != 'head'
+            }
+            if len(mapped_methods) > 1:
                 action = self.default_mapping[method.lower()]
                 if action in self.coerce_method_names:
                     action = self.coerce_method_names[action]

tests/schemas/test_coreapi.py

@@ -754,6 +754,67 @@ class TestSchemaGeneratorWithManyToMany(TestCase):
         assert schema == expected
 
 
+@unittest.skipUnless(coreapi, 'coreapi is not installed')
+@override_settings(REST_FRAMEWORK={'DEFAULT_SCHEMA_CLASS': 'rest_framework.schemas.AutoSchema'})
+class TestSchemaGeneratorActionKeysViewSets(TestCase):
+    def test_action_not_coerced_for_get_and_head(self):
+        """
+        Ensure that action name is preserved when action map contains "head".
+        """
+        class CustomViewSet(GenericViewSet):
+            serializer_class = EmptySerializer
+
+            @action(methods=['get', 'head'], detail=True)
+            def custom_read(self, request, pk):
+                raise NotImplementedError
+
+            @action(methods=['put', 'patch'], detail=True)
+            def custom_mixed_update(self, request, pk):
+                raise NotImplementedError
+
+        self.router = DefaultRouter()
+        self.router.register('example', CustomViewSet, basename='example')
+        self.patterns = [
+            path('', include(self.router.urls))
+        ]
+
+        generator = SchemaGenerator(title='Example API', patterns=self.patterns)
+        schema = generator.get_schema()
+
+        expected = coreapi.Document(
+            url='',
+            title='Example API',
+            content={
+                'example': {
+                    'custom_read': coreapi.Link(
+                        url='/example/{id}/custom_read/',
+                        action='get',
+                        fields=[
+                            coreapi.Field('id', required=True, location='path', schema=coreschema.String()),
+                        ]
+                    ),
+                    'custom_mixed_update': {
+                        'update': coreapi.Link(
+                            url='/example/{id}/custom_mixed_update/',
+                            action='put',
+                            fields=[
+                                coreapi.Field('id', required=True, location='path', schema=coreschema.String()),
+                            ]
+                        ),
+                        'partial_update': coreapi.Link(
+                            url='/example/{id}/custom_mixed_update/',
+                            action='patch',
+                            fields=[
+                                coreapi.Field('id', required=True, location='path', schema=coreschema.String()),
+                            ]
+                        )
+                    }
+                }
+            }
+        )
+        assert schema == expected
+
+
 @unittest.skipUnless(coreapi, 'coreapi is not installed')
 @override_settings(REST_FRAMEWORK={'DEFAULT_SCHEMA_CLASS': 'rest_framework.schemas.AutoSchema'})
 class Test4605Regression(TestCase):