[Sema] Adding deprecation warning for protocol inheritance class keyword syntax

Author: LucianoPAlmeida

include/swift/AST/DiagnosticsSema.def

@@ -2611,6 +2611,9 @@ WARNING(duplicate_anyobject_class_inheritance,none,
   "redundant inheritance from 'AnyObject' and Swift 3 'class' keyword", ())
 ERROR(inheritance_from_protocol_with_superclass,none,
   "inheritance from class-constrained protocol composition type %0", (Type))
+WARNING(anyobject_class_inheritance_deprecated,none,
+  "using 'class' keyword for protocol inheritance is deprecated; "
+  "use 'AnyObject' instead", ())
 ERROR(multiple_inheritance,none,
   "multiple inheritance from classes %0 and %1", (Type, Type))
 ERROR(inheritance_from_non_protocol_or_class,none,

lib/Sema/TypeCheckDeclPrimary.cpp

@@ -179,6 +179,20 @@ static void checkInheritanceClause(
     // GenericSignatureBuilder (for protocol inheritance) or the
     // ConformanceLookupTable (for protocol conformance).
     if (inheritedTy->isAnyObject()) {
+      // Warn inherited AnyObject written as 'class' as deprecated
+      // for Swift >= 5.
+      auto sourceRange = inherited.getSourceRange();
+      bool isWrittenAsClass =
+          (isa<ProtocolDecl>(decl) || isa<AbstractTypeParamDecl>(decl)) &&
+          Lexer::getTokenAtLocation(ctx.SourceMgr, sourceRange.Start)
+              .is(tok::kw_class);
+      if (ctx.LangOpts.isSwiftVersionAtLeast(5) && isWrittenAsClass) {
+        diags
+            .diagnose(sourceRange.Start,
+                      diag::anyobject_class_inheritance_deprecated)
+            .fixItReplace(sourceRange, "AnyObject");
+      }
+
       if (inheritedAnyObject) {
         // If the first occurrence was written as 'class', downgrade the error
         // to a warning in such case for backward compatibility with