[Sema] Don't warn for availability of extensions with no public members

rdar://problem/61879659

Author: xymus

lib/Sema/TypeCheckAvailability.cpp

@@ -2862,6 +2862,27 @@ void swift::checkExplicitAvailability(Decl *decl) {
     valueDecl = extension->getExtendedNominal();
     if (!valueDecl)
       return;
+
+    // Skip extensions without public members or conformances.
+    auto members = extension->getMembers();
+    auto hasMembers = std::any_of(members.begin(), members.end(),
+                                  [](const Decl *D) -> bool {
+      if (auto VD = dyn_cast<ValueDecl>(D))
+        if (declNeedsExplicitAvailability(VD))
+          return true;
+      return false;
+    });
+
+    auto protocols = extension->getLocalProtocols(ConformanceLookupKind::OnlyExplicit);
+    auto hasProtocols = std::any_of(protocols.begin(), protocols.end(),
+                                    [](const ProtocolDecl *PD) -> bool {
+      AccessScope scope =
+        PD->getFormalAccessScope(/*useDC*/nullptr,
+                                 /*treatUsableFromInlineAsPublic*/true);
+      return scope.isPublic();
+    });
+
+    if (!hasMembers && !hasProtocols) return;
   }
 
   if (declNeedsExplicitAvailability(valueDecl)) {

test/attr/require_explicit_availability.swift

@@ -1,3 +1,5 @@
+// Test the -require-explicit-availability flag
+
 // RUN: %swiftc_driver -typecheck -parse-stdlib -target x86_64-apple-macosx10.10 -Xfrontend -verify -require-explicit-availability -require-explicit-availability-target "macOS 10.10"  %s
 // RUN: %swiftc_driver -typecheck -parse-stdlib -target x86_64-apple-macosx10.10 -warnings-as-errors %s
 
@@ -43,8 +45,21 @@ public class C { } // expected-warning {{public declarations should have an avai
 
 public protocol P { } // expected-warning {{public declarations should have an availability attribute when building with -require-explicit-availability}} {{1-1=@available(macOS 10.10, *)\n}}
 
+private protocol PrivateProto { }
+
 extension S { // expected-warning {{public declarations should have an availability attribute when building with -require-explicit-availability}} {{1-1=@available(macOS 10.10, *)\n}}
-  func ok() { }
+  public func warnForPublicMembers() { } // expected-warning {{public declarations should have an availability attribute when building with -require-explicit-availability}} {{3-3=@available(macOS 10.10, *)\n  }}
+}
+
+extension S {
+  internal func dontWarnWithoutPublicMembers() { }
+  private func dontWarnWithoutPublicMembers1() { }
+}
+
+extension S : P { // expected-warning {{public declarations should have an availability attribute when building with -require-explicit-availability}} {{1-1=@available(macOS 10.10, *)\n}}
+}
+
+extension S : PrivateProto {
 }
 
 open class OpenClass { } // expected-warning {{public declarations should have an availability attribute when building with -require-explicit-availability}} {{1-1=@available(macOS 10.10, *)\n}}