Fix leaking error messages during overload selection #5211
Merged
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Fixes #5210 (?)
When mypy tries selecting an appropriate overload alternative, it swaps out the current 'msg' object with a placeholder. If this placeholder does not accumulate any error messages, we know that alternative is a successful match.
Previously, we replaced only
checkexpr.ExpressionChecker
's msg object with the placeholder. However, since checkexpr can sometimes callchecker.TypeChecker
, we need to replace its msg object as well to prevent error messages that would normally be silenced from leaking.More broadly, the current overload implementation broke the invariant that both msg fields refer to the same underlying MessageBuilder object. This pull request fixes that oversight.