Prefer the last //# sourceMappingURL in a file instead of the first

It seems like some Webpack setups (including mine) end up outputting
several //# sourceMappingURL=... entries when both transpilation and
bundling is in the picture.

In general it seems like the safest bet to go for the last one, as
most tools tend to append the comment to the end of the file.
Thus the last one is most likely to pertain to the last operation
that happened, be it transpilation, bundling, or uglification :)

Author: papandreou

spec/stacktrace-gps-spec.js

@@ -327,6 +327,21 @@ describe('StackTraceGPS', function() {
             }
         });
 
+        it('ignores all but the last sourceMappingURL in the file', function (done) {
+            var source = 'var foo=function(){};\n//# sourceMappingURL=ignoreme.js.map\nfunction bar(){}var baz=eval("XXX");\n//@ sourceMappingURL=test.js.map';
+            jasmine.Ajax.stubRequest('http://localhost:9999/test.min.js').andReturn({responseText: source});
+            var sourceMap = '{"version":3,"sources":["./test.js"],"names":["foo","bar","baz","eval"],"mappings":"AAAA,GAAIA,KAAM,YACV,SAASC,QACT,GAAIC,KAAMC,KAAK","file":"test.min.js"}';
+            jasmine.Ajax.stubRequest('http://localhost:9999/test.js.map').andReturn({responseText: sourceMap});
+
+            var stackframe = new StackFrame({args: [], fileName: 'http://localhost:9999/test.min.js', lineNumber: 1, columnNumber: 5});
+            new StackTraceGPS().getMappedLocation(stackframe).then(callback, done.fail);
+
+            function callback(stackframe) {
+                expect(stackframe).toEqual(new StackFrame({functionName: 'foo', args: [], fileName: 'http://localhost:9999/test.js', lineNumber: 1, columnNumber: 4}));
+                done();
+            }
+        });
+
         describe('given source and source map that resolves', function() {
             beforeEach(function() {
                 var source = 'var foo=function(){};function bar(){}var baz=eval("XXX");\n//@ sourceMappingURL=test.js.map\n//# sourceURL=test.js';

stacktrace-gps.js

@@ -126,9 +126,14 @@
     }
 
     function _findSourceMappingURL(source) {
-        var m = /\/\/[#@] ?sourceMappingURL=([^\s'"]+)\s*$/m.exec(source);
-        if (m && m[1]) {
-            return m[1];
+        var sourceMappingUrlRegExp = /\/\/[#@] ?sourceMappingURL=([^\s'"]+)\s*$/mg;
+        var lastSourceMappingUrl;
+        var matchSourceMappingUrl;
+        while (matchSourceMappingUrl = sourceMappingUrlRegExp.exec(source)) {
+            lastSourceMappingUrl = matchSourceMappingUrl[1];
+        }
+        if (lastSourceMappingUrl) {
+            return lastSourceMappingUrl;
         } else {
             throw new Error('sourceMappingURL not found');
         }