Improve closure lookahead for custom attributes

Author: DougGregor

lib/AST/NameLookup.cpp

@@ -2625,6 +2625,7 @@ CustomAttrNominalRequest::evaluate(Evaluator &evaluator,
   }
 
   ctx.Diags.diagnose(attr->getLocation(), diag::unknown_attribute, typeName);
+  attr->setInvalid();
 
   return nullptr;
 }

lib/Parse/ParseDecl.cpp

@@ -5856,11 +5856,10 @@ void Parser::skipSILUntilSwiftDecl() {
 
 void Parser::skipAnyAttribute() {
   consumeToken(tok::at_sign);
-  if (!consumeIf(tok::identifier))
+  if (!Tok.is(tok::identifier))
     return;
 
-  if (consumeIf(tok::l_paren))
-    skipUntil(tok::r_paren);
+  (void)canParseCustomAttribute();
 }
 
 /// Returns a descriptive name for the given accessor/addressor kind.

lib/Sema/TypeCheckType.cpp

@@ -2112,6 +2112,10 @@ TypeResolver::resolveAttributedType(TypeAttributes &attrs, TypeRepr *repr,
     if (globalActorAttr == customAttr)
       continue;
 
+    // If this attribute was marked invalid, ignore it.
+    if (customAttr->isInvalid())
+      continue;
+
     // Diagnose the attribute, because we don't yet handle custom type
     // attributes.
     std::string typeName;
@@ -2123,6 +2127,7 @@ TypeResolver::resolveAttributedType(TypeAttributes &attrs, TypeRepr *repr,
     }
 
     diagnose(customAttr->getLocation(), diag::unknown_attribute, typeName);
+    customAttr->setInvalid();
   }
 
   // The type we're working with, in case we want to build it differently