ApplyTypeAnnotationsVisitor: fix default value of keyword only and po…

…sitional-only args (Instagram#314)

* ApplyTypeAnnotationsVisitor: fix default values of keyword only args

* ApplyTypeAnnotationsVisitor: fix default values of positional-only args

Co-authored-by: hauntsaninja <>

libcst/codemod/visitors/_apply_type_annotations.py

@@ -398,7 +398,14 @@ def update_annotation(
         return annotations.parameters.with_changes(
             params=update_annotation(
                 updated_node.params.params, annotations.parameters.params
-            )
+            ),
+            kwonly_params=update_annotation(
+                updated_node.params.kwonly_params, annotations.parameters.kwonly_params
+            ),
+            posonly_params=update_annotation(
+                updated_node.params.posonly_params,
+                annotations.parameters.posonly_params,
+            ),
         )
 
     def _insert_empty_line(

libcst/codemod/visitors/tests/test_apply_type_annotations.py

@@ -4,7 +4,9 @@
 # LICENSE file in the root directory of this source tree.
 #
 
+import sys
 import textwrap
+import unittest
 from typing import Type
 
 from libcst import parse_module
@@ -31,6 +33,25 @@ def foo() -> int:
                     return 1
                 """,
             ),
+            (
+                """
+                def foo(
+                    b: str, c: int = ..., *, d: str = ..., e: int, f: int = ...
+                ) -> int: ...
+                """,
+                """
+                def foo(
+                    b, c=5, *, d="a", e, f=10
+                ) -> int:
+                    return 1
+                """,
+                """
+                def foo(
+                    b: str, c: int=5, *, d: str="a", e: int, f: int=10
+                ) -> int:
+                    return 1
+                """,
+            ),
             (
                 """
                 import bar
@@ -612,6 +633,56 @@ def test_annotate_functions(self, stub: str, before: str, after: str) -> None:
         )
         self.assertCodemod(before, after, context_override=context)
 
+    @data_provider(
+        (
+            (
+                """
+                def foo(
+                    a: int, /, b: str, c: int = ..., *, d: str = ..., e: int, f: int = ...
+                ) -> int: ...
+                """,
+                """
+                def foo(
+                    a, /, b, c=5, *, d="a", e, f=10
+                ) -> int:
+                    return 1
+                """,
+                """
+                def foo(
+                    a: int, /, b: str, c: int=5, *, d: str="a", e: int, f: int=10
+                ) -> int:
+                    return 1
+                """,
+            ),
+            (
+                """
+                def foo(
+                    a: int, b: int = ..., /, c: int = ..., *, d: str = ..., e: int, f: int = ...
+                ) -> int: ...
+                """,
+                """
+                def foo(
+                    a, b = 5, /, c = 10, *, d = "a", e, f = 20
+                ) -> int:
+                    return 1
+                """,
+                """
+                def foo(
+                    a: int, b: int = 5, /, c: int = 10, *, d: str = "a", e: int, f: int = 20
+                ) -> int:
+                    return 1
+                """,
+            ),
+        )
+    )
+    @unittest.skipIf(sys.version_info < (3, 8), "Unsupported Python version")
+    def test_annotate_functions_py38(self, stub: str, before: str, after: str) -> None:
+        context = CodemodContext()
+        ApplyTypeAnnotationsVisitor.store_stub_in_context(
+            context, parse_module(textwrap.dedent(stub.rstrip()))
+        )
+        self.assertCodemod(before, after, context_override=context)
+
     @data_provider(
         (
             (