From f79d674f3e5abf595b83394b4144840a4babd2e6 Mon Sep 17 00:00:00 2001
From: Daniel D'Avella <dan.davella@pixee.ai>
Date: Fri, 17 Nov 2023 15:08:08 -0500
Subject: [PATCH] Preserve Optional type annotation if already present

---
 src/core_codemods/fix_mutable_params.py   | 11 +++++++++--
 tests/codemods/test_fix_mutable_params.py | 16 ++++++++++++++++
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/src/core_codemods/fix_mutable_params.py b/src/core_codemods/fix_mutable_params.py
index f6ab3dd4..d95bcb3b 100644
--- a/src/core_codemods/fix_mutable_params.py
+++ b/src/core_codemods/fix_mutable_params.py
@@ -30,18 +30,25 @@ def __init__(self, *args, **kwargs):
         self._matches_builtin = m.Call(func=m.Name("list") | m.Name("dict"))
 
     def _create_annotation(self, orig: cst.Param, updated: cst.Param):
+        match orig.annotation:
+            case cst.Annotation(annotation=cst.Subscript(sub)):
+                match sub:  # type: ignore
+                    case cst.Name("Optional"):
+                        # Already an Optional, so we can just preserve the original annotation
+                        return updated.annotation
+
         return (
             updated.annotation.with_changes(
                 annotation=cst.Subscript(
                     value=cst.Name("Optional"),
                     slice=[
                         cst.SubscriptElement(
-                            slice=cst.Index(value=orig.annotation.annotation)
+                            slice=cst.Index(value=updated.annotation.annotation)
                         )
                     ],
                 )
             )
-            if updated.annotation is not None
+            if orig.annotation is not None and updated.annotation is not None
             else None
         )
 
diff --git a/tests/codemods/test_fix_mutable_params.py b/tests/codemods/test_fix_mutable_params.py
index 267b82b9..8854570e 100644
--- a/tests/codemods/test_fix_mutable_params.py
+++ b/tests/codemods/test_fix_mutable_params.py
@@ -194,6 +194,22 @@ def foo(x = None, y: Optional[List[int]] = None, z: Optional[Dict[str, int]] = N
         """
         self.run_and_assert(tmpdir, input_code, expected_output)
 
+    def test_fix_type_already_optional(self, tmpdir):
+        input_code = """
+        from typing import Optional, List
+
+        def foo(x: Optional[List[int]] = []):
+            print(x)
+        """
+        expected_output = """
+        from typing import Optional, List
+
+        def foo(x: Optional[List[int]] = None):
+            x = [] if x is None else x
+            print(x)
+        """
+        self.run_and_assert(tmpdir, input_code, expected_output)
+
     def test_fix_respect_docstring(self, tmpdir):
         input_code = '''
         def func(foo=[]):