Introduce a custom installer plugin for Composer dependencies.

composer.json

@@ -23,10 +23,18 @@
 		"squizlabs/php_codesniffer": "3.13.2",
 		"wp-coding-standards/wpcs": "~3.2.0",
 		"phpcompatibility/phpcompatibility-wp": "~2.1.3",
+		"wordpress/custom-installer-plugin": "@dev",
 		"yoast/phpunit-polyfills": "^1.1.0"
 	},
+	"repositories": [
+		{
+			"type": "path",
+			"url": "tools/composer"
+		}
+	],
 	"config": {
 		"allow-plugins": {
+			"wordpress/custom-installer-plugin": true,
 			"dealerdirect/phpcodesniffer-composer-installer": true
 		},
 		"lock": false

tools/composer/composer.json

@@ -0,0 +1,17 @@
+{
+	"name": "wordpress/custom-installer-plugin",
+	"description": "Custom Composer installer plugin for WordPress vendor dependencies",
+	"type": "composer-plugin",
+	"license": "GPL-2.0-or-later",
+	"require": {
+		"composer-plugin-api": "^2.0"
+	},
+	"autoload": {
+		"psr-4": {
+			"WordPress\\Composer\\": "src/"
+		}
+	},
+	"extra": {
+		"class": "WordPress\\Composer\\CustomInstallerPlugin"
+	}
+}

tools/composer/src/CustomInstaller.php

@@ -0,0 +1,171 @@
+<?php
+/**
+ * Installer for handling custom installation paths.
+ */
+
+namespace WordPress\Composer;
+
+use Composer\PartialComposer;
+use Composer\IO\IOInterface;
+use Composer\Installer\LibraryInstaller;
+use Composer\Installer\BinaryInstaller;
+use Composer\Package\PackageInterface;
+use Composer\Repository\InstalledRepositoryInterface;
+use Composer\Util\Filesystem;
+use React\Promise\PromiseInterface;
+
+/**
+ * Installer class.
+ */
+final class CustomInstaller extends LibraryInstaller {
+	/**
+	 * Custom installer paths configuration.
+	 */
+	private array $installerPaths = array();
+
+	/**
+	 * Initializes library installer.
+	 */
+	public function __construct(
+		IOInterface $io,
+		PartialComposer $composer,
+		?string $type = 'library',
+		?Filesystem $filesystem = null,
+		?BinaryInstaller $binaryInstaller = null
+	) {
+		parent::__construct( $io, $composer, $type, $filesystem, $binaryInstaller );
+
+		$this->installerPaths = $this->composer->getPackage()->getExtra()['installer-paths'];
+	}
+
+	/**
+	 * Check if this installer supports the given package type.
+	 *
+	 * @param string $packageType The package type.
+	 * @return bool
+	 */
+	public function supports( $packageType ) {
+		return true;
+	}
+
+	/**
+	 * Get the installation path for a package.
+	 *
+	 * @param PackageInterface $package The package.
+	 * @return string The installation path.
+	 */
+	public function getInstallPath( PackageInterface $package ) {
+		$packageName = $package->getName();
+
+		if ( ! isset( $this->installerPaths[ $packageName ] ) ) {
+			return parent::getInstallPath( $package );
+		}
+
+		return realpath( getcwd() ) . '/' . $this->installerPaths[ $packageName ]['target'];
+	}
+
+	/**
+	 * Install a package.
+	 *
+	 * @param InstalledRepositoryInterface $repo    The installed repository.
+	 * @param PackageInterface             $package The package to install.
+	 * @return PromiseInterface|null
+	 */
+	public function install( InstalledRepositoryInterface $repo, PackageInterface $package ) {
+		$installer = parent::install( $repo, $package );
+
+		if ( $installer instanceof PromiseInterface ) {
+			return $installer->then( fn() => $this->modifyPaths( $package ) );
+		}
+
+		$this->modifyPaths( $package );
+		return null;
+	}
+
+	/**
+	 * Update a package.
+	 *
+	 * @param InstalledRepositoryInterface $repo    The installed repository.
+	 * @param PackageInterface             $initial The initial package.
+	 * @param PackageInterface             $target  The target package.
+	 * @return PromiseInterface|null
+	 */
+	public function update( InstalledRepositoryInterface $repo, PackageInterface $initial, PackageInterface $target ) {
+		$updater = parent::update( $repo, $initial, $target );
+
+		if ( $updater instanceof PromiseInterface ) {
+			return $updater->then( fn() => $this->modifyPaths( $target ) );
+		}
+
+		$this->modifyPaths( $target );
+		return null;
+	}
+
+	/**
+	 * Modify installation paths based on source subdirectory and ignore patterns.
+	 *
+	 * @param PackageInterface $package The package.
+	 */
+	private function modifyPaths( PackageInterface $package ): void {
+		$installPath = $this->getInstallPath( $package );
+
+		$this->applySourceSubdirectory( $package, $installPath );
+		$this->applyIgnorePatterns( $package, $installPath );
+	}
+
+	/**
+	 * Apply ignore patterns to remove unwanted files after installation.
+	 *
+	 * @param PackageInterface $package The package.
+	 * @param string           $installPath The installation path.
+	 */
+	private function applyIgnorePatterns( PackageInterface $package, string $installPath ): void {
+		$packageName = $package->getName();
+
+		if ( ! isset( $this->installerPaths[ $packageName ]['ignore'] ) ) {
+			return;
+		}
+
+		$filesystem = new Filesystem();
+
+		foreach ( $this->installerPaths[ $packageName ]['ignore'] as $pattern ) {
+			$matches = glob( $installPath . '/' . $pattern );
+
+			if ( empty( $matches ) ) {
+				throw new \RuntimeException( "Failed to glob pattern '{$pattern}' in package '{$package->getName()}'." );
+			}
+
+			foreach ( $matches as $path ) {
+				$filesystem->remove( $path );
+			}
+		}
+	}
+
+	/**
+	 * Apply source subdirectory to flatten directory structure.
+	 *
+	 * @param PackageInterface $package     The package.
+	 * @param string           $installPath The installation path.
+	 */
+	private function applySourceSubdirectory( PackageInterface $package, string $installPath ): void {
+		$packageName = $package->getName();
+
+		if ( ! isset( $this->installerPaths[ $packageName ]['source'] ) ) {
+			return;
+		}
+
+		$sourceSubdir = $this->installerPaths[ $packageName ]['source'];
+		$sourceDir    = $installPath . '/' . $sourceSubdir;
+
+		if ( ! is_dir( $sourceDir ) ) {
+			throw new \RuntimeException( "Source directory '{$sourceSubdir}' does not exist in package '{$packageName}'." );
+		}
+
+		$filesystem = new Filesystem();
+		$tempDir    = $installPath . '_temp';
+
+		$filesystem->rename( $sourceDir, $tempDir );
+		$filesystem->removeDirectory( $installPath );
+		$filesystem->rename( $tempDir, $installPath );
+	}
+}

tools/composer/src/CustomInstallerPlugin.php

@@ -0,0 +1,46 @@
+<?php
+/**
+ * Custom Composer installer plugin for WordPress.
+ */
+
+namespace WordPress\Composer;
+
+use Composer\Composer;
+use Composer\IO\IOInterface;
+use Composer\Plugin\PluginInterface;
+
+/**
+ * Custom installer plugin class.
+ */
+final class CustomInstallerPlugin implements PluginInterface {
+	/**
+	 * Apply plugin.
+	 *
+	 * @param Composer    $composer The Composer instance.
+	 * @param IOInterface $io       The IO interface.
+	 */
+	public function activate( Composer $composer, IOInterface $io ) {
+		$installer = new CustomInstaller( $io, $composer );
+		$composer->getInstallationManager()->addInstaller( $installer );
+	}
+
+	/**
+	 * Remove any hooks from Composer.
+	 *
+	 * @param Composer    $composer The Composer instance.
+	 * @param IOInterface $io       The IO interface.
+	 */
+	public function deactivate( Composer $composer, IOInterface $io ) {
+		// Nothing to do here.
+	}
+
+	/**
+	 * Prepare the plugin to be uninstalled.
+	 *
+	 * @param Composer    $composer The Composer instance.
+	 * @param IOInterface $io       The IO interface.
+	 */
+	public function uninstall( Composer $composer, IOInterface $io ) {
+		// Nothing to do here.
+	}
+}