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Sema: Restore old behavior of generic parameters with associated type inference #71548

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Merged
merged 1 commit into from
Feb 12, 2024
Merged

Sema: Restore old behavior of generic parameters with associated type inference #71548

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44 changes: 21 additions & 23 deletions lib/Sema/AssociatedTypeInference.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2440,29 +2440,6 @@ AssociatedTypeInference::computeAbstractTypeWitness(
void AssociatedTypeInference::collectAbstractTypeWitnesses(
TypeWitnessSystem &system,
ArrayRef<AssociatedTypeDecl *> unresolvedAssocTypes) const {
// Look for suitably-named generic parameters first, before we go digging
// through same-type requirements of protocols.
if (auto genericSig = dc->getGenericSignatureOfContext()) {
for (auto *const assocType : unresolvedAssocTypes) {
// Ignore the generic parameters for AsyncIteratorProtocol.Failure and
// AsyncSequence.Failure.
if (isAsyncIteratorProtocolFailure(assocType))
continue;

for (auto *gp : genericSig.getInnermostGenericParams()) {
// Packs cannot witness associated type requirements.
if (gp->isParameterPack())
continue;

if (gp->getName() == assocType->getName()) {
system.addTypeWitness(assocType->getName(),
dc->mapTypeIntoContext(gp),
/*preferred=*/true);
}
}
}
}

auto considerProtocolRequirements = [&](ProtocolDecl *conformedProto) {
// FIXME: The RequirementMachine will assert on re-entrant construction.
// We should find a more principled way of breaking this cycle.
Expand Down Expand Up @@ -2515,7 +2492,28 @@ void AssociatedTypeInference::collectAbstractTypeWitnesses(
system.addDefaultTypeWitness(typeWitness->getType(),
typeWitness->getDefaultedAssocType(),
preferred);
} else {
// As a last resort, look for a generic parameter that matches the name
// of the associated type.
if (auto genericSig = dc->getGenericSignatureOfContext()) {
// Ignore the generic parameters for AsyncIteratorProtocol.Failure and
// AsyncSequence.Failure.
if (!isAsyncIteratorProtocolFailure(assocType)) {
for (auto *gp : genericSig.getInnermostGenericParams()) {
// Packs cannot witness associated type requirements.
if (gp->isParameterPack())
continue;

if (gp->getName() == assocType->getName()) {
system.addTypeWitness(assocType->getName(),
dc->mapTypeIntoContext(gp),
/*preferred=*/true);
}
}
}
}
}

}
}

Expand Down
5 changes: 3 additions & 2 deletions test/decl/protocol/req/associated_type_generic_param.swift
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@@ -1,10 +1,11 @@
// RUN: %target-typecheck-verify-swift -enable-experimental-associated-type-inference
// RUN: not %target-typecheck-verify-swift -disable-experimental-associated-type-inference
// RUN: %target-typecheck-verify-swift -disable-experimental-associated-type-inference

protocol P {
associatedtype A = Int
}

struct S<A>: P {}

let x: String.Type = S<String>.A.self
// This is unfortunate but it is the behavior of Swift 5.10.
let x: Int.Type = S<String>.A.self
Comment on lines +2 to +11
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Would looking for generic parameters before defaults but after same-type requirements not fix this at least?

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Maybe, but I would rather fix this in one shot by building a disjunction containing the default associated type and generic parameter, if any, in inferTypeWitnessesViaAssociatedType(), and having the solver walk through the solution space. This first requires better ranking rules and a smarter solver that won't go exponential as easily.

6 changes: 3 additions & 3 deletions test/decl/protocol/req/associated_type_inference_fixed_type_experimental_inference.swift
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Expand Up @@ -214,7 +214,7 @@ do {
// CHECK-NEXT: }
struct Conformer1: P17a {} // expected-error {{type 'Conformer1' does not conform to protocol 'P17a'}}
// CHECK-LABEL: Abstract type witness system for conformance of Conformer2<A> to P17b: {
// CHECK-NEXT: A => A (preferred), [[EQUIV_CLASS:0x[0-9a-f]+]]
// CHECK-NEXT: A => (unresolved), [[EQUIV_CLASS:0x[0-9a-f]+]]
// CHECK-NEXT: B => (unresolved)
// CHECK-NEXT: }
struct Conformer2<A>: P17b {} // expected-error {{type 'Conformer2<A>' does not conform to protocol 'P17b'}}
Expand All @@ -223,7 +223,7 @@ do {
// CHECK-NEXT: }
struct Conformer3: P17c {}
// CHECK-LABEL: Abstract type witness system for conformance of Conformer4<A> to P17d: {
// CHECK-NEXT: A => A (preferred), [[EQUIV_CLASS:0x[0-9a-f]+]]
// CHECK-NEXT: A => Int (preferred), [[EQUIV_CLASS:0x[0-9a-f]+]]
// CHECK-NEXT: B => Int (preferred), [[EQUIV_CLASS:0x[0-9a-f]+]]
// CHECK-NEXT: }
struct Conformer4<A>: P17d {}
Expand Down Expand Up @@ -645,7 +645,7 @@ protocol P37b {
}
do {
// CHECK-LABEL: Abstract type witness system for conformance of Conformer1<C> to P37b: {
// CHECK-NEXT: C => C (preferred),
// CHECK-NEXT: C => Self.B.A (preferred),
// CHECK-NEXT: }
struct Conformer1<C>: P37b {
struct Inner: P37a { typealias A = C }
Expand Down
4 changes: 3 additions & 1 deletion test/decl/protocol/req/associated_type_inference_stdlib_3.swift
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@@ -1,6 +1,8 @@
// RUN: %target-typecheck-verify-swift -enable-experimental-associated-type-inference
// RUN: not %target-typecheck-verify-swift -enable-experimental-associated-type-inference
// RUN: not %target-typecheck-verify-swift -disable-experimental-associated-type-inference

// FIXME: Get this passing with -enable-experimental-associated-type-inference again.

struct FooIterator<T: Sequence>: IteratorProtocol {
typealias Element = T.Element

Expand Down
14 changes: 14 additions & 0 deletions test/decl/protocol/req/rdar122587432.swift
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@@ -0,0 +1,14 @@
// RUN: %target-typecheck-verify-swift -enable-experimental-associated-type-inference
// RUN: %target-typecheck-verify-swift -disable-experimental-associated-type-inference

public struct S<Element: Hashable> {
public typealias A = [Element: Int]
}

extension S: Sequence {
public func makeIterator() -> A.Iterator {
fatalError()
}
}

let x: (key: String, value: Int).Type = S<String>.Element.self