improve AST validation (#3864)

lib/ast.js

@@ -784,6 +784,7 @@ var AST_Sequence = DEFNODE("Sequence", "expressions", {
         });
     },
     _validate: function() {
+        if (this.expressions.length < 2) throw new Error("expressions must contain multiple elements");
         must_be_expressions(this, "expressions");
     },
 });

lib/mozilla-ast.js

@@ -111,7 +111,7 @@
             var args = {
                 start    : my_start_token(key),
                 end      : my_end_token(M.value),
-                key      : key.type == "Identifier" ? key.name : key.value,
+                key      : "" + key[key.type == "Identifier" ? "name" : "value"],
                 value    : from_moz(M.value)
             };
             if (M.kind == "init") return new AST_ObjectKeyVal(args);