skip attempting to annotate abstract methods

auto_type_annotate.py

@@ -52,6 +52,13 @@ def _args(node: ast.AsyncFunctionDef | ast.FunctionDef) -> Generator[ast.arg]:
             yield subnode
 
 
+def _is_abstract(node: ast.AST) -> bool:
+    return (
+        isinstance(node, ast.Attribute) and node.attr == 'abstractmethod' or
+        isinstance(node, ast.Name) and node.id == 'abstractmethod'
+    )
+
+
 class FindUntyped(ast.NodeVisitor):
     def __init__(self) -> None:
         self._mod: list[Mod] = []
@@ -73,7 +80,10 @@ def visit_FunctionDef(
             self,
             node: ast.AsyncFunctionDef | ast.FunctionDef,
     ) -> None:
-        if not self._in_func[-1]:
+        if (
+                not self._in_func[-1] and
+                not any(_is_abstract(dec) for dec in node.decorator_list)
+        ):
             args = tuple(_args(node))
             if node.name == '__init__' and len(args) > 1:
                 missing_annotation = False

tests/auto_type_annotate_test.py

@@ -90,6 +90,28 @@ def test_find_untyped_async_def():
     assert _find_untyped(src) == [(_MOD, 'f')]
 
 
+def test_find_untyped_skips_abstract():
+    src = '''\
+import abc
+
+class C:
+    @abc.abstractmethod
+    def f(self): pass
+'''
+    assert _find_untyped(src) == []
+
+
+def test_find_untyped_skips_abstract_from_imported():
+    src = '''\
+from abc import abstractmethod
+
+class C:
+    @abstractmethod
+    def f(self): pass
+'''
+    assert _find_untyped(src) == []
+
+
 @contextlib.contextmanager
 def _dmypy():
     subprocess.check_call((sys.executable, '-m', 'mypy.dmypy', 'run', '.'))