Do not modify body of abstractmethods for fix-mutable-params

src/core_codemods/fix_mutable_params.py

@@ -140,6 +140,14 @@ def _build_new_body(self, new_var_decls, body):
         new_body.extend(body[offset:])
         return new_body
 
+    def _is_abstractmethod(self, node: cst.FunctionDef) -> bool:
+        for decorator in node.decorators:
+            match decorator.decorator:
+                case cst.Name("abstractmethod"):
+                    return True
+
+        return False
+
     def leave_FunctionDef(
         self,
         original_node: cst.FunctionDef,
@@ -151,7 +159,11 @@ def leave_FunctionDef(
             new_var_decls,
             add_annotation,
         ) = self._gather_and_update_params(original_node, updated_node)
-        new_body = self._build_new_body(new_var_decls, updated_node.body.body)
+        new_body = (
+            self._build_new_body(new_var_decls, updated_node.body.body)
+            if not self._is_abstractmethod(original_node)
+            else updated_node.body.body
+        )
         if new_var_decls:
             # If we're adding statements to the body, we know a change took place
             self.add_change(original_node, self.CHANGE_DESCRIPTION)

tests/codemods/test_fix_mutable_params.py

@@ -237,3 +237,22 @@ def func(foo=None):
             print(foo)
         """
         self.run_and_assert(tmpdir, input_code, expected_output)
+
+    def test_dont_modify_abstractmethod_body(self, tmpdir):
+        input_code = """
+        from abc import ABC, abstractmethod
+
+        class Foo(ABC):
+            @abstractmethod
+            def foo(self, bar=[]):
+                pass
+        """
+        expected_output = """
+        from abc import ABC, abstractmethod
+
+        class Foo(ABC):
+            @abstractmethod
+            def foo(self, bar=None):
+                pass
+        """
+        self.run_and_assert(tmpdir, input_code, expected_output)