Upload: Return a translatable error instead of a fatal error when zlib is missing during PclZip extraction

src/wp-admin/includes/file.php

@@ -1880,6 +1880,20 @@ function _unzip_file_ziparchive( $file, $to, $needed_dirs = array() ) {
 function _unzip_file_pclzip( $file, $to, $needed_dirs = array() ) {
 	global $wp_filesystem;
 
+	/**
+	 * Filters whether the zlib PHP extension is available for PclZip to extract archives.
+	 *
+	 * PclZip requires `gzopen()`, provided by the zlib extension. Without it, extraction
+	 * cannot proceed.
+	 *
+	 * @since 7.2.0
+	 *
+	 * @param bool $zlib_available Whether the zlib extension is available. Default is the result of `function_exists( 'gzopen' )`.
+	 */
+	if ( ! apply_filters( 'unzip_file_pclzip_zlib_available', function_exists( 'gzopen' ) ) ) {
+		return new WP_Error( 'unzip_file_missing_zlib', __( 'PHP does not have the zlib extension enabled, which is required to extract this archive.' ) );
+	}
+
 	mbstring_binary_safe_encoding();
 
 	require_once ABSPATH . 'wp-admin/includes/class-pclzip.php';

tests/phpunit/tests/filesystem/unzipFilePclzip.php

@@ -83,4 +83,19 @@ public function test_should_apply_unzip_file_filters() {
 		$this->assertSame( 1, $filter->get_call_count(), 'The filter should be called once.' );
 		$this->assertSame( self::$test_data_dir . 'archive.zip', $filter->get_args()[0][1], 'The $file parameter should be correct.' );
 	}
+
+	/**
+	 * Tests that _unzip_file_pclzip() returns a translatable WP_Error instead of
+	 * fatal-erroring when the zlib extension is unavailable.
+	 *
+	 * @ticket 30963
+	 */
+	public function test_should_return_wp_error_when_zlib_extension_is_unavailable() {
+		add_filter( 'unzip_file_pclzip_zlib_available', '__return_false' );
+
+		$result = _unzip_file_pclzip( self::$test_data_dir . 'archive.zip', self::$test_data_dir . 'archive/' );
+
+		$this->assertWPError( $result, 'A WP_Error should be returned instead of a fatal error.' );
+		$this->assertSame( 'unzip_file_missing_zlib', $result->get_error_code(), 'The error code should identify the missing zlib extension.' );
+	}
 }