Sema: Fix existential member access type erasure around metatypes #73103
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AnthonyLatsis
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AnthonyLatsis
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Apr 18, 2024
test/Constraints/issue-67337.swift
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Incorporated this test into test/decl/protocol/existential_member_accesses_self_assoctype.swift here .
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Apr 18, 2024
The only case a singleton metatype transforms into an existential metatype is when the instance type transforms into an existential from a non-existential.
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The only case a singleton metatype transforms into an existential metatype is when the instance type transforms into an existential from a non-existential.
Resolves #72941.
NB: Type erasure correctness is not enough to fix crashes in cases like the one in the linked issue —
A?.TypetoB?.TypewhereA <: B— because the compiler does not support these correct conversions to begin with. With nothing stopping them from surviving the constraint solver, they either trip an assertion somewhere down the line or sometimes even compile. Handle these cases gracefully by requiring the constraint system to certify conversions associated with existential member accesses.