[ConstraintSystem] Increase score only if members found on Optional…
#35381
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hborla
approved these changes
Jan 12, 2021
… and its unwrapped type Unresolved member lookup is allowed to perform implicit optional unwrap of a base type to find members. Previously if there were any members directly on `Optional`, lookup would stop there. But since SR-13815 it became possible for solver to attempt members found on unwrapped type even if there are viable ones on `Optional` as well. New score kind has been introduced to guard against possible ambiguities with new scheme - `SK_UnresolvedMemberViaOptional`. It's used very time member found via base type unwrap is attempted. Unfortunately, doing so can lead to behavior changes in existing code because it's possible that base was wrapped into optional implicitly based on context e.g. unresolved member passed in as an argument to a parameter of optional type. To fix situations like that, `SK_UnresolvedMemberViaOptional` should only be increased if there is a mix of members to attempt - both directly on `Optional` and on unwrapped type, in all other cases score should stay the same because there could be no ambiguity. Resolves: rdar://73027153
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… and its unwrapped type
Unresolved member lookup is allowed to perform implicit optional
unwrap of a base type to find members. Previously if there were
any members directly on
Optional, lookup would stop there. Butsince SR-13815 it became possible for solver to attempt members
found on unwrapped type even if there are viable ones on
Optionalas well.New score kind has been introduced to guard against possible ambiguities
with new scheme -
SK_UnresolvedMemberViaOptional. It's used verytime member found via base type unwrap is attempted. Unfortunately,
doing so can lead to behavior changes in existing code because it's
possible that base was wrapped into optional implicitly based on
context e.g. unresolved member passed in as an argument to a parameter
of optional type.
To fix situations like that,
SK_UnresolvedMemberViaOptionalshouldonly be increased if there is a mix of members to attempt - both directly
on
Optionaland on unwrapped type, in all other cases score should staythe same because there could be no ambiguity.
Resolves: rdar://73027153