Source

File: wp-includes/class-wp-recovery-mode.php

protected function get_extension_for_error( $error ) {
		global $wp_theme_directories;

		if ( ! isset( $error['file'] ) ) {
			return false;
		}

		if ( ! defined( 'WP_PLUGIN_DIR' ) ) {
			return false;
		}

		$error_file    = wp_normalize_path( $error['file'] );
		$wp_plugin_dir = wp_normalize_path( WP_PLUGIN_DIR );

		if ( 0 === strpos( $error_file, $wp_plugin_dir ) ) {
			$path  = str_replace( $wp_plugin_dir . '/', '', $error_file );
			$parts = explode( '/', $path );

			return array(
				'type' => 'plugin',
				'slug' => $parts[0],
			);
		}

		if ( empty( $wp_theme_directories ) ) {
			return false;
		}

		foreach ( $wp_theme_directories as $theme_directory ) {
			$theme_directory = wp_normalize_path( $theme_directory );

			if ( 0 === strpos( $error_file, $theme_directory ) ) {
				$path  = str_replace( $theme_directory . '/', '', $error_file );
				$parts = explode( '/', $path );

				return array(
					'type' => 'theme',
					'slug' => $parts[0],
				);
			}
		}

		return false;
	}