[Diagnostics] Split "only concrete types conform to protocols" into a separate note

Author: xedin

include/swift/AST/DiagnosticsSema.def

@@ -1842,9 +1842,11 @@ ERROR(use_of_equal_instead_of_equality,none,
       "use of '=' in a boolean context, did you mean '=='?", ())
 ERROR(type_cannot_conform, none,
       "%select{type %1|protocol %1 as a type}0 cannot conform to "
-      "%select{%3|the protocol itself}2; "
-      "only concrete types such as structs, enums and classes can conform to protocols",
+      "%select{%3|the protocol itself}2",
       (bool, Type, bool, Type))
+NOTE(only_concrete_types_conform_to_protocols,none,
+     "only concrete types such as structs, enums and classes can conform to protocols",
+     ())
 NOTE(required_by_opaque_return,none,
     "required by opaque return type of %0 %1", (DescriptiveDeclKind, DeclName))
 NOTE(required_by_decl,none,

lib/Sema/CSDiagnostics.cpp

@@ -516,6 +516,8 @@ bool MissingConformanceFailure::diagnoseTypeCannotConform(
                  nonConformingType->isEqual(protocolType),
                  protocolType);
 
+  emitDiagnostic(diag::only_concrete_types_conform_to_protocols);
+
   if (auto *OTD = dyn_cast<OpaqueTypeDecl>(AffectedDecl)) {
     auto *namingDecl = OTD->getNamingDecl();
     if (auto *repr = namingDecl->getOpaqueResultTypeRepr()) {
@@ -2171,6 +2173,7 @@ bool ContextualFailure::diagnoseAsError() {
         emitDiagnostic(diag::type_cannot_conform,
                        /*isExistentialType=*/true, fromType, 
                        fromType->isEqual(toType), toType);
+        emitDiagnostic(diag::only_concrete_types_conform_to_protocols);
         return true;
       }
 

lib/Sema/TypeCheckProtocol.cpp

@@ -4735,6 +4735,8 @@ void swift::diagnoseConformanceFailure(Type T,
       diags.diagnose(ComplainLoc, diag::type_cannot_conform, true,
                      T, T->isEqual(Proto->getDeclaredInterfaceType()), 
                      Proto->getDeclaredInterfaceType());
+      diags.diagnose(ComplainLoc,
+                     diag::only_concrete_types_conform_to_protocols);
       return;
     }