Support php-error.php outside of WP_CONTENT_DIR

[brookedot]

Since 5.2 WordPress has supported a php-error.php drop-in which overwrites the error template:
​https://make.wordpress.org/core/2019/04/16/fatal-error-recovery-mode-in-5-2/

This is happening in class-wp-fatal-error-handler.php on 143
https://core.trac.wordpress.org/browser/trunk/src/wp-includes/class-wp-fatal-error-handler.php#L141

...
// Load custom PHP error template, if present.
$php_error_pluggable = WP_CONTENT_DIR . '/php-error.php';
...

In some cases, WP_CONTENT_DIR is read-only which means that this file cannot be used to customize the message. I'm open to other solutions but at the moment, I would like to propose we add an additional constant here instead.

if ( defined( 'WP_CONTENT_DIR' ) ) {
        // Load custom PHP error template, if present.
        if ( defined( WP_ERROR_TEMPLATE_DIR ) {
                $php_error_pluggable_dir = WP_ERROR_TEMPLATE_DIR;
        } else {
                $php_error_pluggable_dir = WP_CONTENT_DIR;
        }
        $php_error_pluggable = $php_error_pluggable_dir . '/php-error.php';
        if ( is_readable( $php_error_pluggable ) ) {
                require_once $php_error_pluggable;
                return;
        }
}

That conditional could probably be simplified too :)

[knutsp]

Hello, and welcome to Trac.

Is there a sane reason to set wp-content to read-only?

It's the location for all drop-ins, not just this one. It also used for uploads (by default) and often for cache. Everything else, but wp-content, set to read-only seems more sane.

[johnbillion]

Also the read-ability of this directory shouldn't be a concern. php-error.php is not a file that WordPress dynamically creates, it just exists in the same way that plugin and theme files exist.