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[ConstraintSystem] Make sure that read-only keypath is preferred for … #25276

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Merged
merged 1 commit into from
Jun 6, 2019
Merged

[ConstraintSystem] Make sure that read-only keypath is preferred for … #25276

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6 changes: 4 additions & 2 deletions lib/Sema/CSSimplify.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4114,8 +4114,10 @@ performMemberLookup(ConstraintKind constraintKind, DeclName memberName,
if (auto *storage = dyn_cast<AbstractStorageDecl>(decl)) {
// If this is an attempt to access read-only member via
// writable key path, let's fail this choice early.
auto &ctx = getASTContext();
if (isReadOnlyKeyPathComponent(storage) &&
keyPath == getASTContext().getWritableKeyPathDecl()) {
(keyPath == ctx.getWritableKeyPathDecl() ||
keyPath == ctx.getReferenceWritableKeyPathDecl())) {
result.addUnviable(
candidate,
MemberLookupResult::UR_WritableKeyPathOnReadOnlyMember);
Expand All @@ -4126,7 +4128,7 @@ performMemberLookup(ConstraintKind constraintKind, DeclName memberName,
// on the other hand if setter is mutating there is no point
// of attempting `ReferenceWritableKeyPath` overload.
if (storage->isSetterMutating() &&
keyPath == getASTContext().getReferenceWritableKeyPathDecl()) {
keyPath == ctx.getReferenceWritableKeyPathDecl()) {
result.addUnviable(
candidate,
MemberLookupResult::UR_ReferenceWritableKeyPathOnMutatingMember);
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35 changes: 35 additions & 0 deletions test/Constraints/keypath_dynamic_member_lookup.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -250,3 +250,38 @@ func test_recursive_dynamic_lookup(_ lens: Lens<Lens<Point>>) {
// CHECK-NEXT: keypath $KeyPath<Lens<Lens<Rectangle>>, Lens<Lens<Int>>>, (root $Lens<Lens<Rectangle>>; settable_property $Lens<Lens<Point>>, id @$s29keypath_dynamic_member_lookup4LensV0B6MemberACyqd__Gs15WritableKeyPathCyxqd__G_tcluig : {{.*}})
_ = \Lens<Lens<Rectangle>>.topLeft.x
}

@dynamicMemberLookup
struct RefWritableBox<T> {
var obj: T

init(_ obj: T) {
self.obj = obj
}

subscript<U>(dynamicMember member: KeyPath<T, U>) -> U {
get { return obj[keyPath: member] }
}

subscript<U>(dynamicMember member: ReferenceWritableKeyPath<T, U>) -> U {
get { return obj[keyPath: member] }
set { obj[keyPath: member] = newValue }
}
}

func prefer_readonly_keypath_over_reference_writable() {
class C {
let foo: Int

init(_ foo: Int) {
self.foo = foo
}
}

var box = RefWritableBox(C(42))
// expected-warning@-1 {{variable 'box' was never mutated; consider changing to 'let' constant}}

// CHECK: function_ref RefWritableBox.subscript.getter
// CHECK-NEXT: function_ref @$s29keypath_dynamic_member_lookup14RefWritableBoxV0B6Memberqd__s7KeyPathCyxqd__G_tcluig
_ = box.foo
}