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[5.7][CSSimplify] Disfavor choices that have injected callAsFunction #59106

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May 27, 2022
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1 change: 1 addition & 0 deletions lib/Sema/CSSimplify.cpp
Original file line number Diff line number Diff line change
Expand Up @@ -11402,6 +11402,7 @@ ConstraintSystem::simplifyApplicableFnConstraint(
FunctionType::get(trailingClosureTypes, callAsFunctionResultTy,
FunctionType::ExtInfo());

increaseScore(SK_DisfavoredOverload);
// Form an unsolved constraint to apply trailing closures to a
// callable type produced by `.init`. This constraint would become
// active when `callableType` is bound.
Expand Down
36 changes: 36 additions & 0 deletions test/Constraints/result_builder_callAsFunction.swift
Original file line number Diff line number Diff line change
@@ -0,0 +1,36 @@
// RUN: %target-typecheck-verify-swift -target %target-cpu-apple-macosx10.15 -swift-version 5 -debug-constraints > %t.log 2>&1
// RUN: %FileCheck %s < %t.log

// REQUIRES: objc_interop
// REQUIRES: OS=macosx

protocol View {}
protocol Callable {}

struct EmptyView : View {}

@resultBuilder struct ViewBuilder {
static func buildBlock<Content>(_ content: Content) -> Content where Content : View { fatalError() }
}

extension Callable {
func callAsFunction<T: View>(@ViewBuilder _: () -> T) -> some View { EmptyView() }
}

struct MyView<Content> : View {
init(v: Int, @ViewBuilder _: () -> Content) {}
}

extension MyView : Callable where Content == EmptyView {
init(v: Int) {}
}

// CHECK: (overload set choice binding $T6 := (Int) -> MyView<{{.*}}>)
// CHECK-NEXT: (increasing score due to disfavored overload)
// CHECK-NEXT: (solution is worse than the best solution)

func test() -> some View {
return MyView(v: 42) {
return EmptyView()
}
}