[AST] RuntimeMetadata: Reject attributes with custom arguments on protocol declarations

Author: xedin

include/swift/AST/DiagnosticsSema.def

@@ -6939,6 +6939,11 @@ ERROR(runtime_attribute_type_requirement_not_accessible,none,
       "(which is %select{private|fileprivate|internal|package|public|open}4)",
       (AccessLevel, DescriptiveDeclKind, DeclName, Type, AccessLevel))
 
+ERROR(cannot_use_attr_with_custom_arguments_on_protocol,none,
+      "reflection metadata attributes applied to protocols cannot have"
+      " additional attribute arguments; attribute arguments must be"
+      " explicitly written on the conforming type",
+      ())
 
 #define UNDEFINE_DIAGNOSTIC_MACROS
 #include "DefineDiagnosticMacros.h"

lib/Sema/TypeCheckAttr.cpp

@@ -3689,6 +3689,10 @@ void AttributeChecker::visitCustomAttr(CustomAttr *attr) {
     case DeclKind::Protocol: {
       // Allow on protocols because they are sources
       // of inference.
+      if (attr->hasArgs()) {
+        diagnoseAndRemoveAttr(
+            attr, diag::cannot_use_attr_with_custom_arguments_on_protocol);
+      }
       return;
     }
 

test/type/runtime_discoverable_attrs.swift

@@ -130,9 +130,12 @@ struct TestNoAmbiguity {
   @Flag func testInst(_: Int, _: Int) {} // Ok
 }
 
-@Flag("flag from protocol")
+@Flag
 protocol Flagged {}
 
+@Flag("flag from protocol") // expected-error {{reflection metadata attributes applied to protocols cannot have additional attribute arguments}}
+protocol InvalidFlagged {}
+
 struct Inference1 : Flagged {} // Ok
 class Inference2 : Flagged {}  // Ok
 enum Inference3 : Flagged {}   // Ok
@@ -277,7 +280,7 @@ extension EnumFlag where B == Void {
 }
 
 @available(*, unavailable)
-@EnumFlag extension EnumTypeTest { // expected-error {{@EnumFlag is already applied to type 'EnumTypeTest'; did you want to remove it?}} {{266:1-11=}}
+@EnumFlag extension EnumTypeTest { // expected-error {{@EnumFlag is already applied to type 'EnumTypeTest'; did you want to remove it?}} {{269:1-11=}}
 }
 
 @available(*, unavailable)