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[ConstraintSystem] Implement new rule for static member lookup in generic contexts

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Instead of requiring result type of the member to conform to declaring protocol,
as originally proposed by SE-0299, let's instead require `Self` to be bound to
some concrete type in extension that declares a static member.

This would make sure that:

1. Members are only visible on a particular type;
2. There is no ambiguity regarding what base of the member chain is going to be.
This commit is contained in:
Pavel Yaskevich
2021-02-04 15:47:07 -08:00
parent 55cd99bce8
commit c44a92ae0b
4 changed files with 50 additions and 57 deletions
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38
lib/Sema/CSSimplify.cpp
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@@ -6852,9 +6852,10 @@ performMemberLookup(ConstraintKind constraintKind, DeclNameRef memberName,
/* We're OK */
} else if (hasStaticMembers && baseObjTy->is<MetatypeType>() &&
instanceTy->isExistentialType()) {
// Static member lookup on protocol metatype requires that result type
// of a selected member to conform to protocol this method is being
// referred from.
// Static member lookup on protocol metatype in generic context
// requires `Self` of the protocol to be bound to some concrete
// type via same-type requirement, otherwise it would be
// impossible to find a witness for this member.
// Cannot instantiate a protocol or reference a member on
// protocol composition type.
@@ -6865,40 +6866,13 @@ performMemberLookup(ConstraintKind constraintKind, DeclNameRef memberName,
return;
}
Type resultTy;
if (isa<AbstractFunctionDecl>(decl)) {
auto refTy =
decl->getInterfaceType()->castTo<AnyFunctionType>()->getResult();
resultTy = refTy->castTo<FunctionType>()->getResult();
} else if (isa<SubscriptDecl>(decl)) {
resultTy =
decl->getInterfaceType()->castTo<AnyFunctionType>()->getResult();
if (getConcreteReplacementForProtocolSelfType(decl)) {
result.addViable(candidate);
} else {
resultTy = decl->getInterfaceType();
}
if (auto *fnType = resultTy->getAs<FunctionType>())
resultTy = fnType->getResult();
// No reason to suggest that `Void` doesn't conform to some protocol.
if (resultTy->isVoid()) {
result.addUnviable(candidate,
MemberLookupResult::UR_TypeMemberOnInstance);
return;
}
// If result is not a concrete type which could conform to the
// expected protocol, this method is only viable for diagnostics.
if (resultTy->isExistentialType() || resultTy->is<AnyFunctionType>() ||
resultTy->is<TupleType>() || resultTy->is<AnyMetatypeType>()) {
result.addUnviable(
candidate,
MemberLookupResult::UR_InvalidStaticMemberOnProtocolMetatype);
return;
}
result.addViable(candidate);
return;
} else {
if (!hasStaticMembers) {