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[ConstraintSystem] Make it possible to infer subtype bindings through argument conversions

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Enable solver to transitively infer bindings through argument conversion
constraints. That helps to infer bindings for (generic) parameters
from their arguments e.g.

```swift
func foo<T: ExpressibleByStringLiteral>(_: String, _: T) -> T {
  fatalError()
}

func bar(_: Any?) {}

func test() {
  bar(foo("", ""))
}
```

In this case `T` can currently only be inferred as `Any?`
(based on parameter type of `bar`) although a complete
set of bindings for that type variable includes `String`
as well, which comes from use of `T` in argument position.

Resolves: rdar://problem/56212087
This commit is contained in:
Pavel Yaskevich
2020-02-21 17:29:19 -08:00
parent ed255596a6
commit 3e01160a2f
2 changed files with 23 additions and 9 deletions
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21
lib/Sema/CSBindings.cpp
View File

@@ -30,14 +30,17 @@ void ConstraintSystem::inferTransitiveSupertypeBindings(
llvm::SmallVector<Constraint *, 4> subtypeOf;
// First, let's collect all of the `subtype` constraints associated
// with this type variable.
llvm::copy_if(bindings.Sources, std::back_inserter(subtypeOf),
[&](const Constraint *constraint) -> bool {
if (constraint->getKind() != ConstraintKind::Subtype)
return false;
llvm::copy_if(
bindings.Sources, std::back_inserter(subtypeOf),
[&](const Constraint *constraint) -> bool {
if (constraint->getKind() != ConstraintKind::Subtype &&
constraint->getKind() != ConstraintKind::ArgumentConversion &&
constraint->getKind() != ConstraintKind::OperatorArgumentConversion)
return false;
auto rhs = simplifyType(constraint->getSecondType());
return rhs->getAs<TypeVariableType>() == typeVar;
});
auto rhs = simplifyType(constraint->getSecondType());
return rhs->getAs<TypeVariableType>() == typeVar;
});
if (subtypeOf.empty())
return;
@@ -618,7 +621,7 @@ ConstraintSystem::getPotentialBindings(TypeVariableType *typeVar) const {
continue;
literalBindings.push_back(
{defaultType, AllowedBindingKind::Subtypes, constraint});
{defaultType, AllowedBindingKind::Exact, constraint});
continue;
}
@@ -644,7 +647,7 @@ ConstraintSystem::getPotentialBindings(TypeVariableType *typeVar) const {
if (!matched) {
exactTypes.insert(defaultType->getCanonicalType());
literalBindings.push_back(
{defaultType, AllowedBindingKind::Subtypes, constraint});
{defaultType, AllowedBindingKind::Exact, constraint});
}
break;

11
test/Constraints/default_literals.swift
View File

@@ -42,3 +42,14 @@ extension Int {
var (div, mod) = (9 / 4, 9 % 4)
// rdar://problem/56212087 - solver fails to infer correct type for a generic parameter (Any vs. String)
func test_transitive_inference_of_default_literal_types() {
func foo<T: ExpressibleByStringLiteral>(_: String, _: T) -> T {
fatalError()
}
func bar(_: Any?) {}
bar(foo("", "")) // Ok
}