Fix panic with duplicate named expressions in type aliases #1883 #1889
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…1883) Named expressions (walrus operator `:=`) are not allowed inside type aliases per PEP 695. Python raises a SyntaxError for this case. Previously, pyrefly would panic with "key lacking binding" when processing code like: type T = (a := 1) type U = (a := 1) The root cause was that the definitions phase incorrectly collected walrus operator names from type alias values at module level, but during binding these were processed in the type alias scope, causing a key/binding mismatch. This fix: - Adds `in_type_alias()` method to check if we're in a type alias scope - Reports "named expression cannot be used within a type alias" error - Removes incorrect walrus name collection from type alias values
yangdanny97
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Dec 18, 2025
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Named expressions (walrus operator
:=) are not allowed inside type aliases per PEP 695. Python raises a SyntaxError for this case.Previously, pyrefly would panic with "key lacking binding" when processing code like:
The root cause was that the definitions phase incorrectly collected walrus operator names from type alias values at module level, but during binding these were
processed in the type alias scope, causing a key/binding mismatch.
This fix:
Fixes #1883
Test Plan