Merge pull request swiftlang#36326 from slavapestov/witness-availability-fix

Sema: Relax witness availability check

Author: slavapestov

lib/Sema/TypeCheckDecl.cpp

@@ -1670,8 +1670,8 @@ bool TypeChecker::isAvailabilitySafeForConformance(
     return true;
 
   auto &Context = proto->getASTContext();
-  NominalTypeDecl *conformingDecl = dc->getSelfNominalTypeDecl();
-  assert(conformingDecl && "Must have conforming declaration");
+  assert(dc->getSelfNominalTypeDecl() &&
+         "Must have a nominal or extension context");
 
   // Make sure that any access of the witness through the protocol
   // can only occur when the witness is available. That is, make sure that
@@ -1688,8 +1688,7 @@ bool TypeChecker::isAvailabilitySafeForConformance(
   requirementInfo = AvailabilityInference::availableRange(requirement, Context);
 
   AvailabilityContext infoForConformingDecl =
-      overApproximateAvailabilityAtLocation(conformingDecl->getLoc(),
-                                            conformingDecl);
+      overApproximateAvailabilityAtLocation(dc->getAsDecl()->getLoc(), dc);
 
   // Constrain over-approximates intersection of version ranges.
   witnessInfo.constrainWith(infoForConformingDecl);

test/Sema/availability_versions.swift

@@ -1388,7 +1388,7 @@ protocol ProtocolWithRequirementMentioningUnavailable {
 
 protocol HasMethodF {
   associatedtype T
-  func f(_ p: T) // expected-note 5{{protocol requirement here}}
+  func f(_ p: T) // expected-note 4{{protocol requirement here}}
 }
 
 class TriesToConformWithFunctionIntroducedOn10_51 : HasMethodF {
@@ -1439,7 +1439,8 @@ extension HasNoMethodF1 : HasMethodF {
 class HasNoMethodF2 { }
 @available(OSX, introduced: 10.51)
 extension HasNoMethodF2 : HasMethodF {
-  func f(_ p: Int) { } // expected-error {{protocol 'HasMethodF' requires 'f' to be available in macOS 10.50.0 and newer}}
+  // This is OK, because the conformance was introduced by an extension.
+  func f(_ p: Int) { }
 }
 
 @available(OSX, introduced: 10.51)
@@ -1453,7 +1454,7 @@ extension HasNoMethodF3 : HasMethodF {
 
 @available(OSX, introduced: 10.51)
 protocol HasMethodFOn10_51 {
-  func f(_ p: Int) // expected-note {{protocol requirement here}}
+  func f(_ p: Int)
 }
 
 class ConformsToUnavailableProtocolWithUnavailableWitness : HasMethodFOn10_51 {
@@ -1465,7 +1466,8 @@ class ConformsToUnavailableProtocolWithUnavailableWitness : HasMethodFOn10_51 {
 class HasNoMethodF4 { }
 @available(OSX, introduced: 10.52)
 extension HasNoMethodF4 : HasMethodFOn10_51 {
-  func f(_ p: Int) { } // expected-error {{protocol 'HasMethodFOn10_51' requires 'f' to be available in macOS 10.51 and newer}}
+  // This is OK, because the conformance was introduced by an extension.
+  func f(_ p: Int) { }
 }
 
 @available(OSX, introduced: 10.51)

test/Sema/conformance_availability.swift

@@ -322,3 +322,32 @@ func usesUnavailableHashable(_ c: UnavailableHashable) {
   // expected-error@-1 2 {{conformance of 'UnavailableHashable' to 'Hashable' is only available in macOS 100 or newer}}
   // expected-note@-2 2 {{add 'if #available' version check}}
 }
+
+// Actually make sure we check witness availability correctly.
+protocol Vehicle {
+  func move() // expected-note {{protocol requirement here}}
+}
+
+@available(macOS 100, *)
+struct Pony : Vehicle {
+  func move() {}
+}
+
+struct Bike {}
+
+@available(macOS 100, *)
+extension Bike : Vehicle {
+  func move() {}
+}
+
+class Car {}
+class ClownCar : Car {}
+
+@available(macOS 200, *)
+extension Car {
+  func move() {} // expected-note {{'move()' declared here}}
+}
+
+@available(macOS 100, *)
+extension ClownCar : Vehicle {}
+// expected-error@-1 {{protocol 'Vehicle' requires 'move()' to be available in macOS 100 and newer}}