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[ConstraintSystem] Allow solving same-type requirements for associated types... #29520

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Merged
merged 1 commit into from
Jan 29, 2020
Merged

[ConstraintSystem] Allow solving same-type requirements for associated types... #29520

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25 changes: 15 additions & 10 deletions lib/Sema/CSSimplify.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3331,10 +3331,13 @@ bool ConstraintSystem::repairFailures(
if (lhs->hasHole() || rhs->hasHole())
return true;

// If dependent members are present here it's because
// base doesn't conform to associated type's protocol.
if (lhs->hasDependentMember() || rhs->hasDependentMember())
break;
// If dependent members are present here it's because the base doesn't
// conform to the associated type's protocol. We can only get here if we
// already applied a fix for the conformance failure.
if (lhs->hasDependentMember() || rhs->hasDependentMember()) {
increaseScore(SK_Fix);
return true;
}

// If requirement is something like `T == [Int]` let's let
// type matcher a chance to match generic parameters before
Expand Down Expand Up @@ -3949,12 +3952,14 @@ ConstraintSystem::matchTypes(Type type1, Type type2, ConstraintKind kind,
llvm_unreachable("type variables should have already been handled by now");

case TypeKind::DependentMember: {
// If one of the dependent member types has no type variables,
// this comparison is effectively illformed, because dependent
// member couldn't be simplified down to the actual type, and
// we wouldn't be able to solve this constraint, so let's just fail.
if (!desugar1->hasTypeVariable() || !desugar2->hasTypeVariable())
return getTypeMatchFailure(locator);
// If one of the dependent member types has no type variables, the
// dependent member can't be simplified because the base doesn't conform
// to the associated type's protocol. We can only get here if we already
// applied a fix for the conformance failure.
if (!desugar1->hasTypeVariable() || !desugar2->hasTypeVariable()) {
increaseScore(SK_Fix);
return getTypeMatchSuccess();
}

// Nothing we can solve yet, since we need to wait until
// type variables will get resolved.
Expand Down
22 changes: 22 additions & 0 deletions test/Constraints/same_types.swift
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Expand Up @@ -333,3 +333,25 @@ class R<T>: P7 where T: P7, T.A == T.Type { // expected-note {{'T' declared as p

R.fn(args: R.self) // expected-error {{generic parameter 'T' could not be inferred}}
// expected-note@-1 {{explicitly specify the generic arguments to fix this issue}}

// rdar://problem/58607155
protocol AssocType1 { associatedtype A }
protocol AssocType2 { associatedtype A }

func rdar58607155() {
func f<T1: AssocType1, T2: AssocType2>(t1: T1, t2: T2) where T1.A == T2.A {}
// expected-note@-1 2 {{where 'T2' = 'MissingConformance'}}
// expected-note@-2 2 {{where 'T1' = 'MissingConformance'}}

class Conformance: AssocType1, AssocType2 { typealias A = Int }
class MissingConformance {}

// One generic argument has a conformance failure
f(t1: MissingConformance(), t2: Conformance()) // expected-error {{local function 'f(t1:t2:)' requires that 'MissingConformance' conform to 'AssocType1'}}
f(t1: Conformance(), t2: MissingConformance()) // expected-error {{local function 'f(t1:t2:)' requires that 'MissingConformance' conform to 'AssocType2'}}

// Both generic arguments have a conformance failure
f(t1: MissingConformance(), t2: MissingConformance())
// expected-error@-1 {{local function 'f(t1:t2:)' requires that 'MissingConformance' conform to 'AssocType1'}}
// expected-error@-2 {{local function 'f(t1:t2:)' requires that 'MissingConformance' conform to 'AssocType2'}}
}