feat(preprocessor): Add sourcemap support

Adds sourcemap support to the preprocessor. If the file being
processed has a sourcemap property, it is merged with the output
from the coverage instrumentation. This enables better debugging
on instrumented code.

Closes karma-runner#109

lib/preprocessor.js

@@ -1,5 +1,7 @@
 var istanbul  = require('istanbul'),
     minimatch = require('minimatch'),
+    SourceMapConsumer = require('source-map').SourceMapConsumer,
+    SourceMapGenerator = require('source-map').SourceMapGenerator,
     globalSourceCache = require('./sourceCache'),
     extend = require('util')._extend,
     coverageMap = require('./coverageMap');
@@ -53,14 +55,40 @@ var createCoveragePreprocessor = function(logger, basePath, reporters, coverageR
       }
     }
 
-    var instrumenter = new instrumenters[instrumenterLiteral].Instrumenter(instrumentersOptions[instrumenterLiteral] || {});
+    var codeGenerationOptions = null;
 
+    if (file.sourceMap) {
+      log.debug('Enabling source map generation for "%s".', file.originalPath);
+      codeGenerationOptions = extend({
+        format: {
+          compact: !instrumentersOptions[instrumenterLiteral].noCompact
+        },
+        sourceMap: file.sourceMap.file,
+        sourceMapWithCode: true,
+        file: file.path
+      }, instrumentersOptions[instrumenterLiteral].codeGenerationOptions || {});
+    }
+
+    var options = extend({}, instrumentersOptions[instrumenterLiteral] || {});
+    options = extend(options, {codeGenerationOptions: codeGenerationOptions});
+
+    var instrumenter = new instrumenters[instrumenterLiteral].Instrumenter(options);
     instrumenter.instrument(content, jsPath, function(err, instrumentedCode) {
 
       if (err) {
         log.error('%s\n  at %s', err.message, file.originalPath);
       }
 
+      if (file.sourceMap) {
+        var consumer = new SourceMapConsumer(file.sourceMap);
+        log.debug('Adding source map to instrumented file for "%s".', file.originalPath);
+        var generator = SourceMapGenerator.fromSourceMap(new SourceMapConsumer(instrumenter.lastSourceMap().toString()));
+        generator.applySourceMap(new SourceMapConsumer(file.sourceMap));
+        file.sourceMap = JSON.parse(generator.toString());
+        instrumentedCode += '\n//# sourceMappingURL=data:application/json;charset=utf-8;base64,';
+        instrumentedCode += new Buffer(JSON.stringify(file.sourceMap)).toString('base64') + '\n';
+      }
+
       // remember the actual immediate instrumented JS for given original path
       sourceCache[jsPath] = content;
 
@@ -69,9 +97,9 @@ var createCoveragePreprocessor = function(logger, basePath, reporters, coverageR
         var coverageObjMatch = coverageObjRegex.exec(instrumentedCode);
 
         if (coverageObjMatch !== null) {
-			var coverageObj = JSON.parse(coverageObjMatch[0]);
-			
-			coverageMap.add(coverageObj);
+          var coverageObj = JSON.parse(coverageObjMatch[0]);
+
+          coverageMap.add(coverageObj);
         }
       }
 

package.json

@@ -21,7 +21,8 @@
   "dependencies": {
     "dateformat": "~1.0.6",
     "istanbul": "~0.3.0",
-    "minimatch": "^0.3.0"
+    "minimatch": "~0.3.0",
+    "source-map": "~0.4.2"
   },
   "peerDependencies": {
     "karma": ">=0.9"