From e7fcd3c1202343c4f82e2fdb3f54b620efb0816e Mon Sep 17 00:00:00 2001
From: tsudol <tsudol@google.com>
Date: Wed, 3 Jan 2024 11:22:35 -0800
Subject: [PATCH] Make sure dataclasses.replace actually has args to unpack.

PiperOrigin-RevId: 595455184
---
 pytype/overlays/dataclass_overlay.py | 12 ++++++++++++
 pytype/tests/test_dataclasses.py     | 15 +++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/pytype/overlays/dataclass_overlay.py b/pytype/overlays/dataclass_overlay.py
index 8d45f2ad0..e046d99e2 100644
--- a/pytype/overlays/dataclass_overlay.py
+++ b/pytype/overlays/dataclass_overlay.py
@@ -234,6 +234,18 @@ def _match_args_sequentially(self, node, args, alias_map, match_all_views):
     ret = super()._match_args_sequentially(
         node, args, alias_map, match_all_views
     )
+    if not args.posargs:
+      # This is a weird case where pytype thinks the call can succeed, but
+      # there's no concrete `__obj` in the posargs.
+      # This can happen when `dataclasses.replace` is called with **kwargs:
+      #   @dataclasses.dataclass
+      #   class A:
+      #     replace = dataclasses.replace
+      #     def do(self, **kwargs):
+      #       return self.replace(**kwargs)
+      # (Yes, this is a simplified example of real code.)
+      # Since **kwargs is opaque magic, we can't do more type checking.
+      return ret
     # _match_args_sequentially has succeeded, so we know we have 1 posarg (the
     # object) and some number of named args (the new fields).
     (obj,) = args.posargs
diff --git a/pytype/tests/test_dataclasses.py b/pytype/tests/test_dataclasses.py
index 30120c797..f5d6e847d 100644
--- a/pytype/tests/test_dataclasses.py
+++ b/pytype/tests/test_dataclasses.py
@@ -1333,5 +1333,20 @@ class Z:
         name: str
     """)
 
+  def test_replace_as_method_with_kwargs(self):
+    # This is a weird case where replace is added as a method, then called
+    # with kwargs. This makes pytype unable to see that `self` is the object
+    # being modified, and also caused a crash when the dataclass overlay tries
+    # to unpack the object being modified from the args.
+    self.Check("""
+      import dataclasses
+      @dataclasses.dataclass
+      class WithKwargs:
+        replace = dataclasses.replace
+        def do(self, **kwargs):
+            return self.replace(**kwargs)
+    """)
+
+
 if __name__ == "__main__":
   test_base.main()