Fix typevar default swapping with defaults#19447
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randolf-scholz wants to merge 1 commit intopython:masterfrom
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Fix typevar default swapping with defaults#19447randolf-scholz wants to merge 1 commit intopython:masterfrom
randolf-scholz wants to merge 1 commit intopython:masterfrom
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ilevkivskyi
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Oct 27, 2025
- Fixes #19444. (added `testTypeVarDefaultsSwap`) - Fixes #19362 (added `testTypeVarDefaultsSwap2`) Changed the logic for recursion guards of `TypeVarType`: Instead of always substituting `repl = repl.accept(self)`, and situationally updating `repl.default = repl.default.accept(self)` if the result is a `TypeVarType`, we now always update `repl.default = repl.default.accept(self)` a priori and then only choose the expanded `repl.accept(self)` if the result is a concrete type. ## New Tests - `testTypeVarDefaultsSwap` (https://mypy-play.net/?mypy=1.17.0&python=3.12&gist=d5a025a31ae3c8b9e2a36f4738aa1991) - `testTypeVarDefaultsSwap2` (https://mypy-play.net/?mypy=1.17.0&python=3.12&gist=d3ed42c82f7144967c97d846c4c041ef) PS: closed earlier PRs #19447, since it contained debugging changes, and #19448 because it didn't solve #19362.
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testTypeVarDefaultsSwapMy idea is that we should only return the result of
repl = repl.accept(self)if that result is no longer aTypeVarType, because if we are simply permuting the type variables, then this will be incorrect.