From a1eee4a1938d7c6431c4d4502b4167d24fc4914c Mon Sep 17 00:00:00 2001
From: Max Brunsfeld <maxbrunsfeld@gmail.com>
Date: Fri, 5 Apr 2019 13:04:12 -0700
Subject: [PATCH] Catch missing precedence values in JS

Fixes #305
---
 cli/src/generate/dsl.js | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/cli/src/generate/dsl.js b/cli/src/generate/dsl.js
index 651e6713..55594871 100644
--- a/cli/src/generate/dsl.js
+++ b/cli/src/generate/dsl.js
@@ -53,6 +53,7 @@ function optional(value) {
 }
 
 function prec(number, rule) {
+  checkPrecedence(number);
   checkArguments(
     arguments.length - 1,
     prec,
@@ -73,6 +74,7 @@ prec.left = function(number, rule) {
     number = 0;
   }
 
+  checkPrecedence(number);
   checkArguments(
     arguments.length - 1,
     prec.left,
@@ -93,6 +95,7 @@ prec.right = function(number, rule) {
     number = 0;
   }
 
+  checkPrecedence(number);
   checkArguments(
     arguments.length - 1,
     prec.right,
@@ -108,6 +111,7 @@ prec.right = function(number, rule) {
 }
 
 prec.dynamic = function(number, rule) {
+  checkPrecedence(number);
   checkArguments(
     arguments.length - 1,
     prec.dynamic,
@@ -371,6 +375,12 @@ function checkArguments(ruleCount, caller, callerName, suffix = '') {
   }
 }
 
+function checkPrecedence(value) {
+  if (value == null) {
+    throw new Error('Missing precedence value');
+  }
+}
+
 global.alias = alias;
 global.blank = blank;
 global.choice = choice;