Sema: Allow overrides to be unavailable in the current Swift language mode

lib/Sema/TypeCheckDeclOverride.cpp

@@ -2191,17 +2191,23 @@ static bool checkSingleOverride(ValueDecl *override, ValueDecl *base) {
     auto domain = unavailableAttr.getDomain();
     auto parsedAttr = unavailableAttr.getParsedAttr();
 
-    if (domain.isPlatform() || domain.isUniversal()) {
+    switch (domain.getKind()) {
+    case AvailabilityDomain::Kind::Universal:
+    case AvailabilityDomain::Kind::SwiftLanguage:
+    case AvailabilityDomain::Kind::PackageDescription:
+    case AvailabilityDomain::Kind::Platform:
       // FIXME: [availability] Diagnose as an error in a future Swift version.
       break;
+    case AvailabilityDomain::Kind::Embedded:
+    case AvailabilityDomain::Kind::Custom:
+      if (parsedAttr->getLocation().isValid())
+        ctx.Diags.diagnose(override, diag::override_unavailable, override)
+            .fixItRemove(parsedAttr->getRangeWithAt());
+      else
+        ctx.Diags.diagnose(override, diag::override_unavailable, override);
+      ctx.Diags.diagnose(base, diag::overridden_here);
+      break;
     }
-
-    if (parsedAttr->getLocation().isValid())
-      ctx.Diags.diagnose(override, diag::override_unavailable, override)
-          .fixItRemove(parsedAttr->getRangeWithAt());
-    else
-      ctx.Diags.diagnose(override, diag::override_unavailable, override);
-    ctx.Diags.diagnose(base, diag::overridden_here);
     break;
   }
   case OverrideAvailability::OverrideLessAvailable: {

test/Availability/availability_unavailable_overrides.swift

@@ -239,7 +239,6 @@ func testOverrideOfUnavailableDeclFromUnavailableDerivedType() {
   }
 }
 
-
 func testImplicitSuperInit() {
   // FIXME: The diagnostics for the implicit call to super.init() could be
   // relaxed since both initializers are unreachable and the developer cannot
@@ -256,3 +255,19 @@ func testImplicitSuperInit() {
     // expected-note@-2 {{call to unavailable initializer 'init()' from superclass 'Base' occurs implicitly at the end of this initializer}}
   }
 }
+
+func testUnavailableInSwiftOverrides() {
+  class Base {
+    func availableMethod() {}
+  }
+
+  class Derived1: Base {
+    @available(swift, introduced: 99)
+    override func availableMethod() {}
+  }
+
+  class Derived2: Base {
+    @available(swift, obsoleted: 1)
+    override func availableMethod() {}
+  }
+}

test/ClangImporter/objc_override.swift

@@ -83,6 +83,20 @@ class SomeCellSub5 : SomeCell {
   func otherIsEnabled() { } // should not conflict
 }
 
+class SomeCellSub6 : SomeCell {
+  @available(*, unavailable)
+  @objc override init(string: String) {
+    super.init(string: string)
+  }
+}
+
+class SomeCellSub7 : SomeCell {
+  @available(swift, obsoleted: 4)
+  @objc override init(string: String) {
+    super.init(string: string)
+  }
+}
+
 class FailSub : FailBase {
   override init(value: Int) { try! super.init(value: value) } // expected-error {{overriding a throwing '@objc' initializer with a non-throwing initializer is not supported}}
   override class func processValue() {} // expected-error {{overriding a throwing '@objc' method with a non-throwing method is not supported}}