DEWP: Check for magic comments before minification

packages/dependency-extraction-webpack-plugin/lib/index.js

@@ -162,6 +162,14 @@ class DependencyExtractionWebpackPlugin {
 		compiler.hooks.thisCompilation.tap(
 			this.constructor.name,
 			( compilation ) => {
+				compilation.hooks.processAssets.tap(
+					{
+						name: this.constructor.name,
+						stage: compiler.webpack.Compilation
+							.PROCESS_ASSETS_STAGE_OPTIMIZE_COMPATIBILITY,
+					},
+					() => this.checkForMagicComments( compilation )
+				);
 				compilation.hooks.processAssets.tap(
 					{
 						name: this.constructor.name,
@@ -174,6 +182,60 @@ class DependencyExtractionWebpackPlugin {
 		);
 	}
 
+	/**
+	 * Check for magic comments before minification, so minification doesn't have to preserve them.
+	 * @param {webpack.Compilation} compilation
+	 */
+	checkForMagicComments( compilation ) {
+		// Accumulate all entrypoint chunks, some of them shared
+		const entrypointChunks = new Set();
+		for ( const entrypoint of compilation.entrypoints.values() ) {
+			for ( const chunk of entrypoint.chunks ) {
+				entrypointChunks.add( chunk );
+			}
+		}
+
+		// Process each entrypoint chunk independently
+		for ( const chunk of entrypointChunks ) {
+			const chunkFiles = Array.from( chunk.files );
+
+			const jsExtensionRegExp = this.useModules ? /\.m?js$/i : /\.js$/i;
+
+			const chunkJSFile = chunkFiles.find( ( f ) =>
+				jsExtensionRegExp.test( f )
+			);
+			if ( ! chunkJSFile ) {
+				// There's no JS file in this chunk, no work for us. Typically a `style.css` from cache group.
+				continue;
+			}
+
+			// Prepare to look for magic comments, in order to decide whether
+			// `wp-polyfill` is needed.
+			const processContentsForMagicComments = ( content ) => {
+				const magicComments = [];
+
+				if ( content.includes( '/* wp:polyfill */' ) ) {
+					magicComments.push( 'wp-polyfill' );
+				}
+
+				return magicComments;
+			};
+
+			// Go through the assets to process the sources.
+			// This allows us to look for magic comments.
+			chunkFiles.sort().forEach( ( filename ) => {
+				const asset = compilation.getAsset( filename );
+				const content = asset.source.buffer();
+
+				const wpMagicComments =
+					processContentsForMagicComments( content );
+				compilation.updateAsset( filename, ( v ) => v, {
+					wpMagicComments,
+				} );
+			} );
+		}
+	}
+
 	/** @param {webpack.Compilation} compilation */
 	addAssets( compilation ) {
 		const {
@@ -286,8 +348,11 @@ class DependencyExtractionWebpackPlugin {
 
 			// Prepare to look for magic comments, in order to decide whether
 			// `wp-polyfill` is needed.
-			const processContentsForMagicComments = ( content ) => {
-				if ( content.includes( '/* wp:polyfill */' ) ) {
+			const handleMagicComments = ( info ) => {
+				if ( ! info ) {
+					return;
+				}
+				if ( info.includes( 'wp-polyfill' ) ) {
 					chunkStaticDeps.add( 'wp-polyfill' );
 				}
 			};
@@ -299,7 +364,7 @@ class DependencyExtractionWebpackPlugin {
 				const content = asset.source.buffer();
 
 				processContentsForHash( content );
-				processContentsForMagicComments( content );
+				handleMagicComments( asset.info.wpMagicComments );
 			} );
 
 			// Finalise hash.

packages/dependency-extraction-webpack-plugin/test/__snapshots__/build.js.snap

@@ -257,6 +257,13 @@ exports[`DependencyExtractionWebpackPlugin modules Webpack \`polyfill-magic-comm
 
 exports[`DependencyExtractionWebpackPlugin modules Webpack \`polyfill-magic-comment\` should produce expected output: External modules should match snapshot 1`] = `[]`;
 
+exports[`DependencyExtractionWebpackPlugin modules Webpack \`polyfill-magic-comment-minified\` should produce expected output: Asset file 'main.asset.php' should match snapshot 1`] = `
+"<?php return array('dependencies' => array('wp-polyfill'), 'version' => '31d6cfe0d16ae931b73c', 'type' => 'module');
+"
+`;
+
+exports[`DependencyExtractionWebpackPlugin modules Webpack \`polyfill-magic-comment-minified\` should produce expected output: External modules should match snapshot 1`] = `[]`;
+
 exports[`DependencyExtractionWebpackPlugin modules Webpack \`runtime-chunk-single\` should produce expected output: Asset file 'a.asset.php' should match snapshot 1`] = `
 "<?php return array('dependencies' => array('@wordpress/blob'), 'version' => 'a1906cfc819b623c86f8', 'type' => 'module');
 "
@@ -666,6 +673,13 @@ exports[`DependencyExtractionWebpackPlugin scripts Webpack \`polyfill-magic-comm
 
 exports[`DependencyExtractionWebpackPlugin scripts Webpack \`polyfill-magic-comment\` should produce expected output: External modules should match snapshot 1`] = `[]`;
 
+exports[`DependencyExtractionWebpackPlugin scripts Webpack \`polyfill-magic-comment-minified\` should produce expected output: Asset file 'main.asset.php' should match snapshot 1`] = `
+"<?php return array('dependencies' => array('wp-polyfill'), 'version' => '31d6cfe0d16ae931b73c');
+"
+`;
+
+exports[`DependencyExtractionWebpackPlugin scripts Webpack \`polyfill-magic-comment-minified\` should produce expected output: External modules should match snapshot 1`] = `[]`;
+
 exports[`DependencyExtractionWebpackPlugin scripts Webpack \`runtime-chunk-single\` should produce expected output: Asset file 'a.asset.php' should match snapshot 1`] = `
 "<?php return array('dependencies' => array('wp-blob'), 'version' => 'd3cda564b538b44d38ef');
 "

packages/dependency-extraction-webpack-plugin/test/fixtures/polyfill-magic-comment-minified/index.js

@@ -0,0 +1,3 @@
+/* wp:polyfill */
+
+// Nothing else, really.

packages/dependency-extraction-webpack-plugin/test/fixtures/polyfill-magic-comment-minified/webpack.config.js

@@ -0,0 +1,11 @@
+/**
+ * Internal dependencies
+ */
+const DependencyExtractionWebpackPlugin = require( '../../..' );
+
+module.exports = {
+	optimization: {
+		minimize: true,
+	},
+	plugins: [ new DependencyExtractionWebpackPlugin() ],
+};

tools/webpack/shared.js

@@ -25,7 +25,7 @@ const baseConfig = {
 				parallel: true,
 				terserOptions: {
 					output: {
-						comments: /(translators:|wp:polyfill)/i,
+						comments: /translators:/i,
 					},
 					compress: {
 						passes: 2,