/**
  * Process a single compound annotation, returning its Attribute. Used from MemberEnter for
  * attaching the attributes to the annotated symbol.
  */
 Attribute.Compound enterAnnotation(JCAnnotation a, Type expected, Env<AttrContext> env) {
   // The annotation might have had its type attributed (but not checked)
   // by attr.attribAnnotationTypes during MemberEnter, in which case we do not
   // need to do it again.
   Type at =
       (a.annotationType.type != null
           ? a.annotationType.type
           : attr.attribType(a.annotationType, env));
   a.type = chk.checkType(a.annotationType.pos(), at, expected);
   if (a.type.isErroneous())
     return new Attribute.Compound(a.type, List.<Pair<MethodSymbol, Attribute>>nil());
   if ((a.type.tsym.flags() & Flags.ANNOTATION) == 0) {
     log.error(a.annotationType.pos(), "not.annotation.type", a.type.toString());
     return new Attribute.Compound(a.type, List.<Pair<MethodSymbol, Attribute>>nil());
   }
   List<JCExpression> args = a.args;
   if (args.length() == 1 && args.head.getTag() != JCTree.ASSIGN) {
     // special case: elided "value=" assumed
     args.head = make.at(args.head.pos).Assign(make.Ident(names.value), args.head);
   }
   ListBuffer<Pair<MethodSymbol, Attribute>> buf = new ListBuffer<Pair<MethodSymbol, Attribute>>();
   for (List<JCExpression> tl = args; tl.nonEmpty(); tl = tl.tail) {
     JCExpression t = tl.head;
     if (t.getTag() != JCTree.ASSIGN) {
       log.error(t.pos(), "annotation.value.must.be.name.value");
       continue;
     }
     JCAssign assign = (JCAssign) t;
     if (assign.lhs.getTag() != JCTree.IDENT) {
       log.error(t.pos(), "annotation.value.must.be.name.value");
       continue;
     }
     JCIdent left = (JCIdent) assign.lhs;
     Symbol method =
         rs.resolveQualifiedMethod(left.pos(), env, a.type, left.name, List.<Type>nil(), null);
     left.sym = method;
     left.type = method.type;
     if (method.owner != a.type.tsym)
       log.error(left.pos(), "no.annotation.member", left.name, a.type);
     Type result = method.type.getReturnType();
     Attribute value = enterAttributeValue(result, assign.rhs, env);
     if (!method.type.isErroneous())
       buf.append(new Pair<MethodSymbol, Attribute>((MethodSymbol) method, value));
     t.type = result;
   }
   return new Attribute.Compound(a.type, buf.toList());
 }