fix: return '0' on error for backwards compatibility

Author: vietcgi

src/wp-admin/includes/class-wp-filesystem-direct.php

@@ -252,13 +252,13 @@ public function owner( $file ) {
 	 * @since 2.5.0
 	 *
 	 * @param string $file Path to the file.
-	 * @return string|false Mode of the file (the last 3 digits), false on failure.
+	 * @return string Mode of the file (the last 3 digits), or the string "0" on failure.
 	 */
 	public function getchmod( $file ) {
 		$perms = @fileperms( $file );
 
 		if ( false === $perms ) {
-			return false;
+			return '0';
 		}
 
 		return substr( decoct( $perms ), -3 );

tests/phpunit/tests/filesystem/wpFilesystemDirect/getchmod.php

@@ -33,16 +33,16 @@ public function test_should_get_chmod_for_a_path_that_exists( $path ) {
 
 	/**
 	 * Tests that `WP_Filesystem_Direct::getchmod()` returns
-	 * false for a path that does not exist.
+	 * "0" for a path that does not exist.
 	 *
 	 * @dataProvider data_paths_that_do_not_exist
 	 *
 	 * @ticket 57774
 	 *
 	 * @param string $path The path.
 	 */
-	public function test_should_return_false_for_a_path_that_does_not_exist( $path ) {
+	public function test_should_return_zero_for_a_path_that_does_not_exist( $path ) {
 		$actual = self::$filesystem->getchmod( self::$file_structure['test_dir']['path'] . $path );
-		$this->assertFalse( $actual );
+		$this->assertSame( '0', $actual );
 	}
 }