fix: write file directly from the plugin

.gitignore

@@ -4,3 +4,4 @@ spec/webpack-out
 yarn.lock
 .nyc_output
 coverage
+spec/output/

lib/plugin.js

@@ -94,19 +94,17 @@ ManifestPlugin.prototype.apply = function(compiler) {
 
     var json = JSON.stringify(cache, null, 2);
 
-    compilation.assets[outputName] = {
-      source: function() {
-        return json;
-      },
-      size: function() {
-        return json.length;
-      }
-    };
+    var outputFolder = compilation.options.output.path;
+    var outputFile = path.join(outputFolder, this.opts.fileName);
+
+    var isMemoryFs = compiler.outputFileSystem.constructor.name === 'MemoryFileSystem';
 
-    if (this.opts.writeToFileEmit) {
-      var outputFolder = compilation.options.output.path;
-      var outputFile = path.join(outputFolder, this.opts.fileName);
+    if (isMemoryFs) {
+      compiler.outputFileSystem.mkdirpSync(path.dirname(outputFile));
+      compiler.outputFileSystem.writeFileSync(outputFile, json);
+    }
 
+    if (!isMemoryFs || this.opts.writeToFileEmit) {
       fse.outputFileSync(outputFile, json);
     }
 

package.json

@@ -22,6 +22,7 @@
     "jasmine": "^2.2.1",
     "memory-fs": "^0.2.0",
     "nyc": "^10.3.2",
+    "rimraf": "^2.6.1",
     "style-loader": "^0.8.3",
     "webpack": "^1.7.3"
   },

spec/plugin.integration.spec.js

@@ -0,0 +1,96 @@
+var fs = require('fs');
+var path = require('path');
+
+var _ = require('lodash');
+var webpack = require('webpack');
+var MemoryFileSystem = require('memory-fs');
+var rimraf = require('rimraf');
+
+var ManifestPlugin = require('../index.js');
+
+function webpackConfig(webpackOpts, opts) {
+  return _.merge({
+    plugins: [
+      new ManifestPlugin(opts.manifestOptions)
+    ]
+  }, webpackOpts);
+}
+
+function webpackCompile(config, compilerOps, cb) {
+  var compiler = webpack(config);
+
+  _.assign(compiler, compilerOps);
+
+  compiler.run(function(err, stats){
+    expect(err).toBeFalsy();
+    expect(stats.hasErrors()).toBe(false);
+
+    cb(stats);
+  });
+};
+
+describe('ManifestPlugin using real fs', function() {
+  beforeEach(function() {
+    rimraf.sync(path.join(__dirname, 'output/single-file'));
+  });
+
+  describe('basic behavior', function() {
+    it('outputs a manifest of one file', function (done) {
+      webpackCompile({
+        context: __dirname,
+        output: {
+          filename: '[name].js',
+          path: path.join(__dirname, 'output/single-file')
+        },
+        entry: './fixtures/file.js',
+        plugins: [
+          new ManifestPlugin()
+        ]
+      }, {}, function() {
+        var manifest = JSON.parse(fs.readFileSync(path.join(__dirname, 'output/single-file/manifest.json')))
+
+        expect(manifest).toBeDefined();
+        expect(manifest).toEqual({
+          'main.js': 'main.js'
+        });
+
+        done();
+      });
+    });
+  });
+});
+
+describe('ManifestPlugin with memory-fs', function() {
+  describe('writeToFileEmit', function() {
+    beforeEach(function() {
+      rimraf.sync(path.join(__dirname, 'output/emit'));
+    });
+
+    it('outputs a manifest of one file', function (done) {
+      webpackCompile({
+        context: __dirname,
+        output: {
+          filename: '[name].js',
+          path: path.join(__dirname, 'output/emit')
+        },
+        entry: './fixtures/file.js',
+        plugins: [
+          new ManifestPlugin({
+            writeToFileEmit: true
+          })
+        ]
+      }, {
+        outputFileSystem: new MemoryFileSystem()
+      }, function() {
+        var manifest = JSON.parse(fs.readFileSync(path.join(__dirname, 'output/emit/manifest.json')))
+
+        expect(manifest).toBeDefined();
+        expect(manifest).toEqual({
+          'main.js': 'main.js'
+        });
+
+        done();
+      });
+    });
+  });
+});