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Revert "Disallow conversions from IUOs to extistentials."

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Revert 7c665c105b because it results in a
much worse source compatibility regression than the one it was intended
to fix.

The problem is that it results in force-unwrapping IUOs, which can lead
to cases where we prefer type-checking solutions that choose methods
over properties where we used to choose properties. So for example a
collection literal like [x] will result in a collection with a method
named 'x' in it rather than a property named 'x'.

I'll be looking at other solutions which fix both the original
compatibility regression as well as retain the behavior in the new test
added here.

Fixes SR-3715 and rdar://problem/30176166.
This commit is contained in:
Mark Lacey
2017-01-25 16:05:06 -08:00
parent 3e671d2fe0
commit c57dc58dab
2 changed files with 20 additions and 18 deletions
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19
lib/Sema/CSSimplify.cpp
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@@ -2032,22 +2032,9 @@ ConstraintSystem::matchTypes(Type type1, Type type2, ConstraintKind kind,
// Instance type check for the above. We are going to check conformance once
// we hit commit_to_conversions below, but we have to add a token restriction
// to ensure we wrap the metatype value in a metatype erasure.
// Disallow direct IUO-to-Any conversions. This will allow us to
// force-unwrap the IUO before attempting to convert, which makes it
// possible to disambiguate certain cases where we would otherwise
// consider an IUO or plain optional to be equally desirable choices
// where we really want the IUO to decay to a plain optional.
{
bool disallowExistentialConversion = false;
if (type2->isAny() &&
type1->getRValueType()->getImplicitlyUnwrappedOptionalObjectType())
disallowExistentialConversion = true;
if (concrete && !disallowExistentialConversion &&
type2->isExistentialType() && kind >= ConstraintKind::Subtype) {
conversionsOrFixes.push_back(ConversionRestrictionKind::Existential);
}
if (concrete && type2->isExistentialType() &&
kind >= ConstraintKind::Subtype) {
conversionsOrFixes.push_back(ConversionRestrictionKind::Existential);
}
// A value of type T! can be converted to type U if T is convertible