feat: useLegacyEmit option (#246)

* Use same hook for both webpack 4 and 5

* Add useLegacyEmit option

This option is used as compat option for older plugins.

* Add Unit test for useLegacyEmit option

This commit adds a new unit test in the options section that tests the new useLegacyEmit option.
The test runs DependencyExtractionWebpackPlugin that is locked on version 3.1.0. This version emits the main.asset.json on the emit hook.
If useLegacyEmit is set to false the test fails on the webpack v5 tests.

README.md

@@ -165,6 +165,15 @@ Default: `false`
 
 If `true`, the keys specified in the `entry` property will be used as keys in the manifest. No file extension will be added (unless specified as part of an `entry` property key).
 
+### `useLegacyEmit`
+
+Type: `Boolean`<br>
+Default: `false`
+
+If `true`, the manifest will be written on the deprecated webpack `emit` hook to be compatible with not yet updated webpack plugins.
+
+A lot of webpack plugins are not yet updated to match the new webpack 5 API. This is a problem when other plugins use the deprecated `emit` hook. The manifest will be written before these other plugins and thus files are missing on the manifest.
+
 ### `writeToFileEmit`
 
 Type: `Boolean`<br>

lib/index.js

@@ -23,6 +23,7 @@ const defaults = {
   sort: null,
   transformExtensions: /^(gz|map)$/i,
   useEntryKeys: false,
+  useLegacyEmit: false,
   writeToFileEmit: false
 };
 
@@ -57,7 +58,7 @@ class WebpackManifestPlugin {
       hook.tap(hookOptions, normalModuleLoader);
     });
 
-    if (webpack.version.startsWith('4')) {
+    if (webpack.version.startsWith('4') || this.options.useLegacyEmit === true) {
       compiler.hooks.emit.tap(hookOptions, emit);
     } else {
       compiler.hooks.thisCompilation.tap(hookOptions, (compilation) => {

package.json

@@ -42,6 +42,7 @@
   "devDependencies": {
     "@ava/babel": "^1.0.1",
     "@svgr/webpack": "^5.4.0",
+    "@wordpress/dependency-extraction-webpack-plugin": "^3.1.0",
     "ava": "^3.13.0",
     "codecov": "^3.1.0",
     "copy-webpack-plugin": "^6.2.1",

test/unit/options.js

@@ -2,6 +2,7 @@ const { join } = require('path');
 
 const test = require('ava');
 const CopyPlugin = require('copy-webpack-plugin');
+const DependencyExtractionWebpackPlugin = require('@wordpress/dependency-extraction-webpack-plugin');
 const del = require('del');
 
 const { compile } = require('../helpers/unit');
@@ -119,3 +120,24 @@ test('useEntryKeys, exclude sourcemap', async (t) => {
 
   t.snapshot(manifest);
 });
+
+test('useLegacyEmit', async (t) => {
+  const config = {
+    context: __dirname,
+    entry: {
+      main: '../fixtures/file.js'
+    },
+    output: {
+      filename: '[name].js',
+      path: join(outputPath, 'useLegacyEmit')
+    },
+    plugins: [
+      new DependencyExtractionWebpackPlugin({
+        outputFormat: 'json'
+      })
+    ]
+  };
+  const { manifest } = await compile(config, t, { useLegacyEmit: true });
+
+  t.snapshot(manifest);
+});

test/unit/snapshots/options.js.md

@@ -56,3 +56,12 @@ Generated by [AVA](https://avajs.dev).
       main: 'main.js',
       'main.js.map': 'main.js.map',
     }
+
+## useLegacyEmit
+
+> Snapshot 1
+
+    {
+      'main.js': 'main.js',
+      'main.json': 'main.asset.json',
+    }