Improve Over-Availability Diagnostic for Implicit Decls

We used to attach this diagnostic to the implicit decl. Now, attach it to the enclosing decl and offer an extra note that states the availability of the implicit declaration that is at conflict with the availability of the enclosing scope.

rdar://74513654

Author: CodaFi

include/swift/AST/DiagnosticsSema.def

@@ -5578,6 +5578,10 @@ ERROR(availability_decl_more_than_enclosing, none,
       "%0 cannot be more available than enclosing scope",
       (DescriptiveDeclKind))
 
+NOTE(availability_implicit_decl_here, none,
+     "%0 implicitly declared here with availability of %1 %2 or newer",
+     (DescriptiveDeclKind, StringRef, llvm::VersionTuple))
+
 NOTE(availability_decl_more_than_enclosing_enclosing_here, none,
      "enclosing scope requires availability of %0 %1 or newer",
      (StringRef, llvm::VersionTuple))

lib/Sema/TypeCheckAttr.cpp

@@ -1713,6 +1713,12 @@ void AttributeChecker::visitAvailableAttr(AvailableAttr *attr) {
       diagnose(D->isImplicit() ? EnclosingDecl->getLoc() : attr->getLocation(),
                diag::availability_decl_more_than_enclosing,
                D->getDescriptiveKind());
+      if (D->isImplicit())
+        diagnose(EnclosingDecl->getLoc(),
+                 diag::availability_implicit_decl_here,
+                 D->getDescriptiveKind(),
+                 prettyPlatformString(targetPlatform(Ctx.LangOpts)),
+                 AttrRange.getOSVersion().getLowerEndpoint());
       diagnose(EnclosingDecl->getLoc(),
                diag::availability_decl_more_than_enclosing_enclosing_here,
                prettyPlatformString(targetPlatform(Ctx.LangOpts)),

test/attr/Inputs/custom-modules/available_nsobject.h

@@ -0,0 +1,16 @@
+@import Foundation;
+
+__attribute__((availability(macosx,introduced=10.0)))
+__attribute__((availability(ios,introduced=2.0)))
+__attribute__((availability(tvos,introduced=1.0)))
+__attribute__((availability(watchos,introduced=2.0)))
+__attribute__((availability(maccatalyst,introduced=13.1)))
+@interface NSBaseClass : NSObject
+- (instancetype) init
+  __attribute__((objc_designated_initializer))
+  __attribute__((availability(macosx,introduced=10.0)))
+  __attribute__((availability(ios,introduced=2.0)))
+  __attribute__((availability(tvos,introduced=1.0)))
+  __attribute__((availability(watchos,introduced=2.0)))
+  __attribute__((availability(maccatalyst,introduced=13.1)));
+@end

test/attr/Inputs/custom-modules/module.map

@@ -1,3 +1,4 @@
 module AttrObjc_FooClangModule { header "attr_objc_foo_clang_module.h" }
 module Testable_ClangModule { header "testable_clang.h" }
 module ObjcAsync { header "objc_async.h" }
+module Available_NSObject { header "available_nsobject.h" }

test/attr/attr_availability_maccatalyst_implicit.swift

@@ -0,0 +1,13 @@
+// RUN: %target-swift-frontend -I %t -I %S/Inputs/custom-modules -parse-stdlib -parse-as-library -typecheck -verify -target x86_64-apple-ios15.4-macabi %s
+
+// REQUIRES: objc_interop
+// REQUIRES: maccatalyst_support
+
+import Available_NSObject
+
+@available(iOS 15.0, *)
+open class OverAvailableClass: NSBaseClass {}
+// expected-error@-1 {{initializer cannot be more available than enclosing scope}}
+// expected-note@-2 {{initializer implicitly declared here with availability of Mac Catalyst 13.1 or newer}}
+// expected-note@-3 {{enclosing scope requires availability of Mac Catalyst 15.0 or newer}}
+