Skip overlapping overload checks in ignored files (#10922)

hauntsaninja · web-flow · commit 805bbde281eb · 2021-08-03T23:15:20.000-07:00
Resolves #9691 As mentioned in that issue, this is a huge performance win. On the codebase I'm currently working on, it halves a cacheless interpreted mypy runtime. The linked issue contains some more measurement. Co-authored-by: hauntsaninja <>
diff --git a/mypy/checker.py b/mypy/checker.py
@@ -466,6 +466,13 @@ def check_overlapping_overloads(self, defn: OverloadedFuncDef) -> None:
         # At this point we should have set the impl already, and all remaining
         # items are decorators
 
+        if self.msg.errors.file in self.msg.errors.ignored_files:
+            # This is a little hacky, however, the quadratic check here is really expensive, this
+            # method has no side effects, so we should skip it if we aren't going to report
+            # anything. In some other places we swallow errors in stubs, but this error is very
+            # useful for stubs!
+            return
+
         # Compute some info about the implementation (if it exists) for use below
         impl_type: Optional[CallableType] = None
         if defn.impl:
