feat(reporter): cache SourceMapConsumer

Error formatting is very slow on big files. This makes it a lot faster.

lib/reporter.js

@@ -3,6 +3,7 @@ var log = require('./logger').create('reporter');
 var MultiReporter = require('./reporters/multi');
 var baseReporterDecoratorFactory = require('./reporters/base').decoratorFactory;
 var SourceMapConsumer = require('source-map').SourceMapConsumer;
+var memoizeWeak = require('memoizee/weak');
 
 var createErrorFormatter = function(basePath, emitter, SourceMapConsumer) {
   var lastServedFiles = [];
@@ -30,6 +31,10 @@ var createErrorFormatter = function(basePath, emitter, SourceMapConsumer) {
                               '(\\:(\\d+))?' +    // column
                               '', 'g');
 
+  var getSourceMapConsumer = memoizeWeak(function(sourceMap) {
+    return new SourceMapConsumer(sourceMap);
+  });
+
   return function(msg, indentation) {
     // remove domain and timestamp from source files
     // and resolve base path / absolute path urls into absolute path
@@ -45,9 +50,9 @@ var createErrorFormatter = function(basePath, emitter, SourceMapConsumer) {
         line = parseInt(line || '0', 10);
         column = parseInt(column || '0', 10);
 
-        var smc = new SourceMapConsumer(file.sourceMap);
         try {
-          var original = smc.originalPositionFor({line: line, column: column});
+          var original = getSourceMapConsumer(file.sourceMap)
+            .originalPositionFor({line: line, column: column});
 
           return util.format('%s:%d:%d <- %s:%d:%d', path, line, column, original.source,
             original.line, original.column);

package.json

@@ -179,7 +179,8 @@
     "useragent": "~2.0.4",
     "graceful-fs": "~2.0.1",
     "connect": "~2.26.0",
-    "source-map": "~0.1.31"
+    "source-map": "~0.1.31",
+    "memoizee": "~0.3.8"
   },
   "devDependencies": {
     "LiveScript": "^1.3.0",

test/unit/reporter.spec.coffee

@@ -76,7 +76,7 @@ describe 'reporter', ->
 
       class MockSourceMapConsumer
         constructor: (sourceMap) ->
-          @source = sourceMap.replace 'SOURCE MAP ', '/original/'
+          @source = sourceMap.content.replace 'SOURCE MAP ', '/original/'
         originalPositionFor: (position) ->
           if position.line == 0
             throw new TypeError('Line must be greater than or equal to 1, got 0')
@@ -88,8 +88,8 @@ describe 'reporter', ->
       it 'should rewrite stack traces', (done) ->
         formatError = m.createErrorFormatter '/some/base', emitter, MockSourceMapConsumer
         servedFiles = [new File('/some/base/a.js'), new File('/some/base/b.js')]
-        servedFiles[0].sourceMap = 'SOURCE MAP a.js'
-        servedFiles[1].sourceMap = 'SOURCE MAP b.js'
+        servedFiles[0].sourceMap = {content: 'SOURCE MAP a.js'}
+        servedFiles[1].sourceMap = {content: 'SOURCE MAP b.js'}
 
         emitter.emit 'file_list_modified', q(served: servedFiles)
 
@@ -118,7 +118,7 @@ describe 'reporter', ->
         beforeEach ->
           formatError = m.createErrorFormatter '/some/base', emitter, MockSourceMapConsumer
           servedFiles = [new File('C:/a/b/c.js')]
-          servedFiles[0].sourceMap = 'SOURCE MAP b.js'
+          servedFiles[0].sourceMap = {content: 'SOURCE MAP b.js'}
 
         it 'should correct rewrite stack traces without sha', (done) ->
           emitter.emit 'file_list_modified', q(served: servedFiles)