[Type checker]: Classes Hashable and Equatable synthesis diagnostic

include/swift/AST/DiagnosticsSema.def

@@ -2710,6 +2710,9 @@ NOTE(missing_member_type_conformance_prevents_synthesis, none,
      "protocol %2, preventing synthesized conformance "
      "of %3 to %2",
      (unsigned, Type, Type, Type))
+NOTE(classes_automatic_protocol_synthesis,none,
+    "automatic synthesis of '%0' is not supported for classes",
+    (StringRef))
 
 // Dynamic Self
 ERROR(dynamic_self_non_method,none,

lib/Sema/DerivedConformanceEquatableHashable.cpp

@@ -165,6 +165,12 @@ void diagnoseFailedDerivation(DeclContext *DC, NominalTypeDecl *nominal,
           nominal->getDeclaredInterfaceType());
     }
   }
+
+  if (auto *classDecl = dyn_cast<ClassDecl>(nominal)) {
+    ctx.Diags.diagnose(classDecl->getLoc(),
+                       diag::classes_automatic_protocol_synthesis,
+                       protocol->getName().str());
+  }
 }
 
 /// Creates a named variable based on a prefix character and a numeric index.

test/Sema/classes_equatable_hashable.swift

@@ -0,0 +1,8 @@
+// RUN: %target-swift-frontend -typecheck -verify -primary-file %s
+
+class Foo: Equatable {} 
+// expected-error@-1 {{type 'Foo' does not conform to protocol 'Equatable'}} expected-note@-1 {{automatic synthesis of 'Equatable' is not supported for classes}}
+
+class Bar: Hashable {} 
+// expected-error@-1 {{type 'Bar' does not conform to protocol 'Hashable'}} expected-note@-1 {{automatic synthesis of 'Hashable' is not supported for classes}}
+// expected-error@-2 {{type 'Bar' does not conform to protocol 'Equatable'}} expected-note@-2 {{automatic synthesis of 'Equatable' is not supported for classes}}