Accept GitHub source highlight URL argument format

Changelog: added

app/assets/javascripts/line_highlighter.js

@@ -117,8 +117,8 @@ LineHighlighter.prototype.clearHighlight = function () {
 //
 // Returns an Array
 LineHighlighter.prototype.hashToRange = function (hash) {
-  // ?L(\d+)(?:-(\d+))?$/)
-  const matches = hash.match(/^#?L(\d+)(?:-(\d+))?$/);
+  // ?L(\d+)(?:-L?(\d+))?$/)
+  const matches = hash.match(/^#?L(\d+)(?:-L?(\d+))?$/);
   if (matches && matches.length) {
     const first = parseInt(matches[1], 10);
     const last = matches[2] ? parseInt(matches[2], 10) : null;

spec/frontend/line_highlighter_spec.js

@@ -49,6 +49,15 @@ describe('LineHighlighter', () => {
       }
     });
 
+    it('highlights a range of lines given in the URL hash using GitHub format', () => {
+      new LineHighlighter({ hash: '#L5-L25' });
+
+      expect($(`.${testContext.css}`).length).toBe(21);
+      for (let line = 5; line <= 25; line += 1) {
+        expect($(`#LC${line}`)).toHaveClass(testContext.css);
+      }
+    });
+
     it('scrolls to the first highlighted line on initial load', () => {
       jest.spyOn(utils, 'scrollToElement');
       new LineHighlighter({ hash: '#L5-25' });