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Sema: Prefer class properties to protocol properties when ranking overloads #18206

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Sema: Prefer class properties to protocol properties when ranking overloads #18206

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20 changes: 20 additions & 0 deletions lib/Sema/CSRanking.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -939,6 +939,26 @@ SolutionCompareResult ConstraintSystem::compareSolutions(
}
}

// If both are properties and one is in a protocol, prefer the one not in
// a protocol.
//
// This is a Swift 4.1 compatibility hack. Changes elsewhere in the compiler
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Should we conditionalize it on language version?

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Arguably this is in line with preferring concrete implementations over protocol implementations. It is a little funny when the concrete implementation is a superclass, but…

// made this case ambiguous. Perhaps it was never meant to be unambiguous in
// the first place, because it only seemed to work for properties, and not
// methods, so I'm going to keep this intentionally narrow.
if (isa<VarDecl>(decl1) && isa<VarDecl>(decl2)) {
auto *nominal1 = dc1->getAsNominalTypeOrNominalTypeExtensionContext();
auto *nominal2 = dc2->getAsNominalTypeOrNominalTypeExtensionContext();

if (nominal1 && nominal2 && nominal1 != nominal2) {
if (isa<ProtocolDecl>(nominal1))
score2 += weight;

if (isa<ProtocolDecl>(nominal2))
score1 += weight;
}
}

// If we haven't found a refinement, record whether one overload is in
// any way more constrained than another. We'll only utilize this
// information in the case of a potential ambiguity.
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20 changes: 20 additions & 0 deletions test/Constraints/ranking.swift
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Expand Up @@ -155,3 +155,23 @@ func testDerived(b: B) {
f0(f1(b))
// CHECK: end sil function '$S7ranking11testDerived1byAA1BC_tF'
}

protocol X {
var z: Int { get }
}

class Y {
var z: Int = 0
}

// CHECK-LABEL: sil hidden @$S7ranking32testGenericPropertyProtocolClassyyxAA1YCRbzAA1XRzlF
func testGenericPropertyProtocolClass<T : X & Y>(_ t: T) {
// CHECK: class_method {{%.*}} : $Y, #Y.z!getter.1
_ = t.z
}

// CHECK-LABEL: sil hidden @$S7ranking36testExistentialPropertyProtocolClassyyAA1X_AA1YCXcF
func testExistentialPropertyProtocolClass(_ t: X & Y) {
// CHECK: class_method {{%.*}} : $Y, #Y.z!getter.1
_ = t.z
}