allow multiple assets to map to the same file on disk

src/WebpackAssetsManifest.js

@@ -82,7 +82,7 @@ class WebpackAssetsManifest
     // This is what gets JSON stringified
     this.assets = this.options.assets;
 
-    // hashed filename : original filename
+    // original filename : hashed filename
     this.assetNames = new Map();
 
     // This is passed to the customize() hook
@@ -357,7 +357,7 @@ class WebpackAssetsManifest
       maybeArrayWrap( assets[ chunkName ] )
         .filter( f => ! this.isHMR(f) ) // Remove hot module replacement files
         .forEach( filename => {
-          this.assetNames.set( filename, chunkName + this.getExtension( filename ) );
+          this.assetNames.set( chunkName + this.getExtension( filename ), filename );
         });
     });
 
@@ -449,7 +449,7 @@ class WebpackAssetsManifest
 
     this.processAssetsByChunkName( this.stats.assetsByChunkName );
 
-    for ( const [ hashedFile, filename ] of this.assetNames ) {
+    for ( const [ filename, hashedFile ] of this.assetNames ) {
       this.currentAsset = compilation.assets[ hashedFile ];
 
       // `integrity` may have already been set by another plugin, like `webpack-subresource-integrity`.
@@ -511,7 +511,7 @@ class WebpackAssetsManifest
    */
   handleAfterEmit(compilation)
   {
-    // Reset the internal mapping of hashed name to original name after every compilation.
+    // Reset the internal mapping of original name to hashed name after every compilation.
     this.assetNames.clear();
 
     if ( ! this.options.writeToDisk ) {
@@ -542,13 +542,15 @@ class WebpackAssetsManifest
     loaderContext.emitFile = (...args) => {
       const [ name ] = args;
 
-      if ( ! this.assetNames.has( name ) ) {
-        const originalName = path.join(
-          path.dirname(name),
-          path.basename(module.userRequest)
-        );
+      const originalName = path.join(
+        path.dirname(name),
+        path.basename(module.userRequest)
+      );
 
-        this.assetNames.set(name, originalName);
+      // ignore emitFile calls from mini-css-extract-plugin
+      // https://github.com/webpack-contrib/mini-css-extract-plugin/pull/177
+      if (!module.identifier().includes('/mini-css-extract-plugin/')) {
+        this.assetNames.set(originalName, name);
       }
 
       return emitFile.apply(module, args);

test/WebpackAssetsManifest-test.js

@@ -1064,7 +1064,13 @@ describe('WebpackAssetsManifest', function() {
           function(err, content) {
             assert.isNull(err, 'Error found reading manifest.json');
 
-            assert.include(content.toString(), 'images/Ginger.jpg');
+            const manifest = JSON.parse(content.toString());
+            const manifestKeys = Object.keys(manifest);
+
+            // despite being emitted to the same file, both image names should appear in manifest
+            assert.equal(manifest['images/Ginger.jpg'], manifest['images/Ginger-duplicate.jpg']);
+            assert.include(manifestKeys, 'images/Ginger.jpg');
+            assert.include(manifestKeys, 'images/Ginger-duplicate.jpg');
 
             done();
           }
@@ -1277,9 +1283,9 @@ describe('WebpackAssetsManifest', function() {
         main: [ 'main.123456.js', '0.123456.hot-update.js' ],
       });
 
-      assert.equal( manifest.assetNames.get('main.123456.js'), 'main.js' );
+      assert.equal( manifest.assetNames.get('main.js'), 'main.123456.js' );
 
-      assert.isFalse( manifest.assetNames.has('0.123456.hot-update.js') );
+      assert.notInclude( Object.values(manifest.assetNames), '0.123456.hot-update.js' );
     });
 
     it('isHMR should return false when hotUpdateChunkFilename is ambiguous', function() {

test/fixtures/client.js

@@ -1,3 +1,5 @@
 console.log('Client');
 
+// despite having the same hash, both files should appear in manifest
 require('./Ginger.jpg');
+require('./Ginger-duplicate.jpg');

test/fixtures/configs.js

@@ -58,7 +58,7 @@ function client()
       rules: [
         {
           test: /\.jpg$/i,
-          loader: 'file-loader?name=images/[name].[ext]',
+          loader: 'file-loader?name=images/[hash].[ext]',
         },
       ],
     },