Merge pull request swiftlang#79849 from tshortli/allow-unavailable-proto-requirements-in-swiftinterface

Sema: Downgrade diagnostics about unavailable requirements in swiftinterfaces

Author: tshortli

lib/Sema/TypeCheckAttr.cpp

@@ -5106,7 +5106,10 @@ void AttributeChecker::checkAvailableAttrs(ArrayRef<AvailableAttr *> attrs) {
         if (VD->isProtocolRequirement() && !PD->isObjC()) {
           diagnoseAndRemoveAttr(
               const_cast<AvailableAttr *>(attr.getParsedAttr()),
-              diag::unavailable_method_non_objc_protocol);
+              diag::unavailable_method_non_objc_protocol)
+              .warnInSwiftInterface(D->getDeclContext());
+          // Be lenient in interfaces to accomodate @_spi_available, which has
+          // been accepted historically.
           return;
         }
       }

test/ModuleInterface/availability-storage-macos.swift renamed to test/ModuleInterface/availability-macos.swift

@@ -64,3 +64,16 @@ public enum EnumWithAssociatedValues {
   @available(macOS 51, *)
   case introducedAtDeploymentWithAssoc(Int)
 }
+
+// CHECK-LABEL: public protocol Proto
+public protocol Proto {
+  // CHECK:      @available(macOS 99, *)
+  // CHECK-NEXT: func reqIntroducedAfterDeployment()
+  @available(macOS 99, *)
+  func reqIntroducedAfterDeployment()
+
+  // CHECK:      @available(macOS, unavailable)
+  // CHECK-NEXT: func reqIntroducedAsSPIAfterDeployment()
+  @_spi_available(macOS 99, *)
+  func reqIntroducedAsSPIAfterDeployment()
+}