errors,tools: alphabetize-errors lint rule

To make sure errors in lib/internal/errors.js (are defined via `E`)
will stay in alphabetical order going forward.

PR-URL: https://github.com/nodejs/node/pull/15083
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

lib/internal/errors.js

@@ -1,3 +1,5 @@
+/* eslint-enable alphabetize-errors */
+
 'use strict';
 
 // The whole point behind this internal module is to allow Node.js to no

tools/eslint-rules/alphabetize-errors.js

@@ -0,0 +1,36 @@
+'use strict';
+
+const message = 'Errors in lib/internal/errors.js must be alphabetized';
+
+function errorForNode(node) {
+  return node.expression.arguments[0].value;
+}
+
+function isAlphabetized(previousNode, node) {
+  return errorForNode(previousNode).localeCompare(errorForNode(node)) < 0;
+}
+
+function isDefiningError(node) {
+  return node.expression &&
+         node.expression.type === 'CallExpression' &&
+         node.expression.callee &&
+         node.expression.callee.name === 'E';
+}
+
+module.exports = {
+  create: function(context) {
+    var previousNode;
+
+    return {
+      ExpressionStatement: function(node) {
+        if (isDefiningError(node)) {
+          if (previousNode && !isAlphabetized(previousNode, node)) {
+            context.report({ node: node, message: message });
+          }
+
+          previousNode = node;
+        }
+      }
+    };
+  }
+};