Package: Add @wordpress/custom-templated-path-webpack-plugin package

packages/custom-templated-path-webpack-plugin/README.md

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+# Custom Templated Path Webpack Plugin
+
+Webpack plugin for creating custom path template tags. Extend the [default set of template tags](https://webpack.js.org/configuration/output/#output-filename) with your own custom behavior. Hooks into Webpack's compilation process to allow you to replace tags with a substitute value.
+
+**Note:** This plugin targets Webpack 4.0 and newer, and is not compatible with older versions.
+
+## Usage
+
+Construct an instance of `CustomTemplatedPathPlugin` in your Webpack configurations `plugins` entry, passing an object where keys correspond to the template tag name. The value for each key is a function passed the original intended path and data corresponding to the asset.
+
+The following example creates a new `basename` tag to substitute the basename of each entry file in the build output file. When compiled, the built file will be output as `build-entry.js`.
+
+```js
+const { basename } = require( 'path' );
+const CustomTemplatedPathPlugin = require( '@wordpress/custom-templated-path-webpack-plugin' );
+
+module.exports = {
+	// ...
+
+	entry: './entry',
+
+	output: {
+		filename: 'build-[basename].js',
+	},
+
+	plugins: [
+		new CustomTemplatedPathPlugin( {
+			basename( path, data ) {
+				let rawRequest;
+
+				const entryModule = get( data, [ 'chunk', 'entryModule' ], {} );
+				switch ( entryModule.type ) {
+					case 'javascript/auto':
+						rawRequest = entryModule.rawRequest;
+						break;
+
+					case 'javascript/esm':
+						rawRequest = entryModule.rootModule.rawRequest;
+						break;
+				}
+
+				if ( rawRequest ) {
+					return basename( rawRequest );
+				}
+
+				return path;
+			},
+		} ),
+	],
+};
+```
+
+For more examples, refer to Webpack's own [`TemplatedPathPlugin.js`](https://github.com/webpack/webpack/blob/v4.1.1/lib/TemplatedPathPlugin.js), which implements the base set of template tags.

packages/custom-templated-path-webpack-plugin/package.json

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+{
+	"name": "@wordpress/custom-templated-path-webpack-plugin",
+	"version": "1.0.0",
+	"description": "Webpack plugin for creating custom path template tags",
+	"author": "WordPress",
+	"license": "GPL-2.0-or-later",
+	"keywords": [
+		"webpack",
+		"webpack-plugin"
+	],
+	"homepage": "https://github.com/WordPress/packages/tree/master/packages/custom-templated-path-webpack-plugin/",
+	"repository": {
+		"type": "git",
+		"url": "https://github.com/WordPress/packages.git"
+	},
+	"bugs": {
+		"url": "https://github.com/WordPress/packages/issues"
+	},
+	"main": "build/index.js",
+	"module": "build-module/index.js",
+	"publishConfig": {
+		"access": "public"
+	},
+	"dependencies": {
+		"escape-string-regexp": "^1.0.5"
+	},
+	"devDependencies": {
+		"webpack": "^4.1.1"
+	},
+	"peerDependencies": {
+		"webpack": "^4.0.0"
+	}
+}

packages/custom-templated-path-webpack-plugin/src/index.js

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+/**
+ * External dependencies
+ */
+const escapeStringRegexp = require( 'escape-string-regexp' );
+
+/**
+ * Webpack plugin for handling specific template tags in Webpack configuration
+ * values like those supported in the base Webpack functionality (e.g. `name`).
+ *
+ * @see webpack.TemplatedPathPlugin
+ */
+class CustomTemplatedPathPlugin {
+	/**
+	 * CustomTemplatedPathPlugin constructor. Initializes handlers as a tuple
+	 * set of RegExp, handler, where the regular expression is used in matching
+	 * a Webpack asset path.
+	 *
+	 * @param {Object.<string,Function>} handlers Object keyed by tag to match,
+	 *                                            with function value returning
+	 *                                            replacement string.
+	 */
+	constructor( handlers ) {
+		this.handlers = [];
+
+		for ( const [ key, handler ] of Object.entries( handlers ) ) {
+			const regexp = new RegExp( `\\[${ escapeStringRegexp( key ) }\\]`, 'gi' );
+			this.handlers.push( [ regexp, handler ] );
+		}
+	}
+
+	/**
+	 * Webpack plugin application logic.
+	 *
+	 * @param {Object} compiler Webpack compiler
+	 */
+	apply( compiler ) {
+		compiler.hooks.compilation.tap( 'CustomTemplatedPathPlugin', ( compilation ) => {
+			compilation.mainTemplate.hooks.assetPath.tap( 'CustomTemplatedPathPlugin', ( path, data ) => {
+				for ( let i = 0; i < this.handlers.length; i++ ) {
+					const [ regexp, handler ] = this.handlers[ i ];
+					if ( regexp.test( path ) ) {
+						return path.replace( regexp, handler( path, data ) );
+					}
+				}
+
+				return path;
+			} );
+		} );
+	}
+}
+
+module.exports = CustomTemplatedPathPlugin;

packages/custom-templated-path-webpack-plugin/test/fixtures/.gitignore

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+entry.js

packages/custom-templated-path-webpack-plugin/test/fixtures/entry/index.js

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+module.exports = null;

packages/custom-templated-path-webpack-plugin/test/fixtures/webpack.config.js

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+/**
+ * External dependencies
+ */
+
+const { basename } = require( 'path' );
+
+/**
+ * Internal dependencies
+ */
+
+const CustomTemplatedPathPlugin = require( '../../' );
+
+module.exports = {
+	mode: 'development',
+	context: __dirname,
+	entry: './entry',
+	output: {
+		filename: '[basename].js',
+		path: __dirname,
+	},
+	plugins: [
+		new CustomTemplatedPathPlugin( {
+			basename( path, data ) {
+				console.log(data)
+
+				let rawRequest;
+				if ( data && data.chunk && data.chunk.entryModule ) {
+					rawRequest = data.chunk.entryModule.rawRequest;
+				}
+
+				if ( rawRequest ) {
+					return basename( rawRequest );
+				}
+
+				return path;
+			},
+		} ),
+	],
+};

packages/custom-templated-path-webpack-plugin/test/index.js

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+/**
+ * External dependencies
+ */
+
+const path = require( 'path' );
+const { promisify } = require( 'util' );
+const webpack = promisify( require( 'webpack' ) );
+const fs = require( 'fs' );
+const access = promisify( fs.access );
+const unlink = promisify( fs.unlink );
+
+/**
+ * Internal dependencies
+ */
+
+const config = require( './fixtures/webpack.config.js' );
+const CustomTemplatedPathPlugin = require( '../' );
+
+describe( 'CustomTemplatedPathPlugin', () => {
+	const outputFile = path.join( __dirname, '/fixtures/entry.js' )
+
+	beforeAll( async () => {
+		// Remove output file so as not to report false positive from previous
+		// test. Absorb error since the file may not exist (unlink will throw).
+		try {
+			await unlink( outputFile );
+		} catch ( error ) {}
+	} );
+
+	it( 'should resolve with basename output', async () => {
+		const stats = await webpack( config );
+		await access( outputFile );
+	} );
+} );