updated with PR feedback

lib/builder.js

@@ -174,22 +174,28 @@ Builder.prototype.reset = function(baseLoader) {
 
   // allow a custom fetch hook
   var loaderFetch = loader.fetch;
-  loader.fetch = function(load) {
-    var self = this;
-    return Promise.resolve((builder.fetch || loaderFetch).call(this, load))
-      .then(function(source) {
-        // calling default fs.readFile fetch -> set timestamp as well for cache invalidation
-        return asp(fs.stat)(fromFileURL(load.address))
-        .then(function(stats) {
-          load.metadata.timestamp = stats.mtime.getTime();
+  var cachedFetch = function(load) {
+    return Promise.resolve(loaderFetch.call(this, load))
+    .then(function(source) {
+      // calling default fs.readFile fetch -> set timestamp as well for cache invalidation
+      return asp(fs.stat)(fromFileURL(load.address))
+      .then(function(stats) {
+        load.metadata.timestamp = stats.mtime.getTime();
+        return source;
+      }, function(err) {
+        // if the stat fails on a plugin, it may not be linked to the file itself
+        if (err.code == 'ENOENT' && load.metadata.loader)
           return source;
-        }, function(err) {
-          // if the stat fails on a plugin, it may not be linked to the file itself
-          if (err.code == 'ENOENT' && load.metadata.loader)
-            return source;
-          throw err;
-        });
+        throw err;
       });
+    });
+  };
+
+  loader.fetch = function(load) {
+    if (builder.fetch)
+      return Promise.resolve(builder.fetch.call(this, load, cachedFetch));
+    else  
+      return cachedFetch.call(this, load);
   };
 
   // this allows us to normalize package conditionals into package conditionals

test/test-build-cache.js

@@ -115,7 +115,7 @@ suite('Test compiler cache', function() {
     var builder = new Builder('test/output');
     fs.writeFileSync('./test/output/timestamp-module.js', source);
     var address = builder.loader.normalizeSync('./test/output/timestamp-module.js');
-    var load = { name: address, address, metadata: {} };
+    var load = { name: address, address: address, metadata: {} };
     return builder.loader.fetch(load)
       .then(function(text) {
          //console.log(JSON.stringify(load));