Feature: dependency map

index.js

@@ -45,6 +45,12 @@ function Newer(options) {
     }
   }
 
+  if (options.dependencyMap) {
+    if (typeof options.dependencyMap !== 'object') {
+      throw new PluginError(PLUGIN_NAME, 'Requires options.dependencyMap to be an object of string to array of strings');
+    }
+  }
+
   /**
    * Path to destination directory or file.
    * @type {string}
@@ -94,6 +100,45 @@ function Newer(options) {
    */
   this._extraStats = null;
 
+  /**
+   * Changing any dependencies of a file should force the file itself to be
+   * rebuilt.
+   * @type Promise({[string]: {mtime: int}})?
+   */
+  this._dependencyMapStats = null;
+
+  if (options.dependencyMap) {
+    const depMapStats = {};
+    for (var key in options.dependencyMap) {
+      const deps = options.dependencyMap[key];
+      const depsStats = deps.map(fn => Q.nfcall(fs.stat, fn).fail(e => null));
+      depMapStats[key] = Q.all(depsStats)
+        .then(function(resolvedStats) {
+          return resolvedStats.reduce((a, b) => {
+            if (!a) return b;
+            if (!b) return a;
+            return a.mtime > b.mtime ? a : b;
+          });
+        })
+        .fail(err => {
+          // Ignore missing files, deps might have changed.
+        });
+    }
+    this._dependencyMapStats = Q.all(Object.keys(depMapStats).map(k => depMapStats[k]))
+      // Resolve to depMapStats' promises' data.
+      .then(_ => depMapStats)
+      .then(promiseMap => {
+        const map = {};
+        const setValue = key => value => {
+          map[key] = value;
+        };
+        for (var key in promiseMap) {
+          promiseMap[key].then(setValue(key));
+        }
+        return map;
+      });
+  }
+
   if (options.extra) {
     var extraFiles = [];
     for (var i = 0; i < options.extra.length; ++i) {
@@ -148,8 +193,8 @@ Newer.prototype._transform = function(srcFile, encoding, done) {
     return;
   }
   var self = this;
-  Q.resolve([this._destStats, this._extraStats])
-    .spread(function(destStats, extraStats) {
+  Q.resolve([this._destStats, this._extraStats, this._dependencyMapStats])
+    .spread(function(destStats, extraStats, depMapStats) {
       if ((destStats && destStats.isDirectory()) || self._ext || self._map) {
         // stat dest/relative file
         var relative = srcFile.relative;
@@ -162,29 +207,32 @@ Newer.prototype._transform = function(srcFile, encoding, done) {
         }
         var destFileJoined = self._dest ?
           path.join(self._dest, destFileRelative) : destFileRelative;
-        return Q.all([Q.nfcall(fs.stat, destFileJoined), extraStats]);
+        return Q.all([Q.nfcall(fs.stat, destFileJoined), extraStats, depMapStats]);
       } else {
         // wait to see if any are newer, then pass through all
         if (!self._bufferedFiles) {
           self._bufferedFiles = [];
         }
-        return [destStats, extraStats];
+        return [destStats, extraStats, depMapStats];
       }
     }).fail(function(err) {
       if (err.code === 'ENOENT') {
         // dest file or directory doesn't exist, pass through all
-        return Q.resolve([null, this._extraStats]);
+        return Q.resolve([null, this._extraStats, this._dependencyMapStats]);
       } else {
         // unexpected error
         return Q.reject(err);
       }
-    }).spread(function(destFileStats, extraFileStats) {
+    }).spread(function(destFileStats, extraFileStats, depMapStats) {
       var newer = !destFileStats || srcFile.stat.mtime > destFileStats.mtime;
       // If *any* extra file is newer than a destination file, then ALL
       // are newer.
       if (extraFileStats && extraFileStats.mtime > destFileStats.mtime) {
         newer = true;
       }
+      if (depMapStats && depMapStats[srcFile.path] && depMapStats[srcFile.path].mtime > destFileStats.mtime) {
+        newer = true;
+      }
       if (self._all) {
         self.push(srcFile);
       } else if (!newer) {

readme.md

@@ -71,6 +71,7 @@ gulp.task('concat', function() {
  * **options.ext** - `string` Source files will be matched to destination files with the provided extension (e.g. '.css').
  * **options.map** - `function` Map relative source paths to relative destination paths (e.g. `function(relativePath) { return relativePath + '.bak'; }`)
  * **options.extra** - `string` or `array` An extra file, file glob, or list of extra files and/or globs, to check for updated time stamp(s). If any of these files are newer than the destination files, then all source files will be passed into the stream.
+ * **options.dependencyMap** - `object` A map of source paths to an `array` of file paths of their dependencies.  These files will be checked for updated time stamp(s). If any of these dependency files are newer than the destination files, then all source files will be passed into the stream.  For example, this can be used with source maps of CSS builds where many input files map to many output files.
 
 Create a [transform stream](http://nodejs.org/api/stream.html#stream_class_stream_transform_1) that passes through files whose modification time is more recent than the corresponding destination file's modification time.