From 160c38b5ca9308dfa565dafedea43f3e4f44edfb Mon Sep 17 00:00:00 2001
From: Igor Minar <igor@angularjs.org>
Date: Wed, 27 May 2015 18:26:28 -0700
Subject: [PATCH] build(broccoli): improve error messaging from TreeDiffer

---
 tools/broccoli/tree-differ.spec.ts | 11 +++++++++++
 tools/broccoli/tree-differ.ts      |  4 +++-
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/tools/broccoli/tree-differ.spec.ts b/tools/broccoli/tree-differ.spec.ts
index b80fe0d01b..661036e26a 100644
--- a/tools/broccoli/tree-differ.spec.ts
+++ b/tools/broccoli/tree-differ.spec.ts
@@ -177,6 +177,17 @@ describe('TreeDiffer', () => {
     });
 
 
+    it("should throw an error if an extension isn't prefixed with doc", () => {
+      // includeExtensions
+      expect(() => new TreeDiffer('testLabel', 'dir1', ['js']))
+          .toThrowError("Extension must begin with '.'. Was: 'js'");
+
+      // excludeExtentions
+      expect(() => new TreeDiffer('testLabel', 'dir1', [], ['js']))
+          .toThrowError("Extension must begin with '.'. Was: 'js'");
+    });
+
+
     it('should ignore files with extensions not listed in includeExtensions', () => {
       let testDir = {
         'dir1': {
diff --git a/tools/broccoli/tree-differ.ts b/tools/broccoli/tree-differ.ts
index f83243cbc4..912fad9601 100644
--- a/tools/broccoli/tree-differ.ts
+++ b/tools/broccoli/tree-differ.ts
@@ -31,7 +31,9 @@ export class TreeDiffer {
     this.exclude = (excludeExtensions || []).length ? buildRegexp(excludeExtensions) : null;
 
     function combine(prev, curr) {
-      if (curr.charAt(0) !== ".") throw new TypeError("Extension must begin with '.'");
+      if (curr.charAt(0) !== ".") {
+        throw new Error(`Extension must begin with '.'. Was: '${curr}'`);
+      }
       let kSpecialRegexpChars = /[\-\[\]\/\{\}\(\)\*\+\?\.\\\^\$\|]/g;
       curr = '(' + curr.replace(kSpecialRegexpChars, '\\$&') + ')';
       return prev ? (prev + '|' + curr) : curr;