From 9a2eae6316ad598ca37355b6abf6c2f56ecb8741 Mon Sep 17 00:00:00 2001
From: hauntsaninja <>
Date: Tue, 3 Aug 2021 22:12:13 -0700
Subject: [PATCH] Skip overlapping overload checks in ignored files

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.
---
 mypy/checker.py | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/mypy/checker.py b/mypy/checker.py
index ae93b8558add..a2b66b123aae 100644
--- 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: