[CSBindings] Delay binding chain result if type is an optional of a… #33740
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…ype variable If subtyping is allowed for a result type of an implicit member chain, let's delay binding it to an optional until its object type resolved too or it has been determined that there is no possibility to resolve it. Otherwise we might end up missing solutions since it's allowed to implicitly unwrap base type but it can't be done early - type variable representing chain's result type has a different l-valueness comparing to generic parameter of an optional. This used to work before due to a hack in constraint generator where unresolved member with arguments would return base type (which doesn't allow l-value) instead of a result type. Resolves: rdar://problem/68094328
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@swift-ci please smoke test |
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/cc @Jumhyn |
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@swift-ci please test source compatibility |
DougGregor
approved these changes
Sep 1, 2020
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… type variable
If subtyping is allowed for a result type of an implicit member chain,
let's delay binding it to an optional until its object type resolved too or
it has been determined that there is no possibility to resolve it.
Otherwise we might end up missing solutions since it's allowed to
implicitly unwrap base type but it can't be done early - type variable
representing chain's result type has a different l-valueness comparing
to generic parameter of an optional.
This used to work before due to a hack in constraint generator where
unresolved member with arguments would return base type (which
doesn't allow l-value) instead of a result type.
Resolves: rdar://problem/68094328