Suboptimal rewrite handling causes plugin conflicts

[swissspidy]

I ran into constant rewrite issues with Polylang and the PWA plugin as reported here, so I had to disable the latter for now.

Turns out the way the PWA plugin adds and potentially flushes rewrite rules on init is flawed. See Chouby's explanation.

[westonruter]

Actually, the flushing is happening at admin_init. And is adding rewrite rules at init too early?

[swissspidy]

As per the support topic, Polylang deletes the rewrite_rules option so that WP generates it upon next page load.

The PWA code in question here:

pwa-wp/wp-includes/class-wp.php

Lines 9 to 31 in 62961cd

	/**
	* Adds rewrite rules to enable pretty permalinks for the service worker script.
	*
	* @global WP_Rewrite $wp_rewrite WordPress rewrite component.
	*/
	function pwa_add_rewrite_rules() {
	global $wp_rewrite;
	$rewrite_rule_regex = '^wp\.serviceworker$';
	$rules = $wp_rewrite->wp_rewrite_rules();
	if ( ! isset( $rules[ $rewrite_rule_regex ] ) ) {
	// Note: This logic will not be required as part of core merge since rewrite rules are flushed upon DB upgrade (as long as the DB version is bumped).
	add_action(
	'admin_init',
	function () {
	flush_rewrite_rules( false ); // phpcs:ignore WordPressVIPMinimum.Functions.RestrictedFunctions.flush_rewrite_rules_flush_rewrite_rules -- Not theme code.
	}
	);
	}
	add_rewrite_rule( $rewrite_rule_regex, 'index.php?' . WP_Service_Workers::QUERY_VAR . '=' . WP_Service_Workers::SCOPE_FRONT, 'top' );
	add_rewrite_tag( '%' . WP_Service_Workers::QUERY_VAR . '%', '([^?]+)' );
	}

The PWA plugin calls $wp_rewrite->wp_rewrite_rules() on init. If the option does not exist, it flushes the rewrite rules. If in the admin, this will cause 2 flushes because of the flush hooked into admin_init. That's why the quick fix would be to just call get_option( 'rewrite_rules') instead of $wp_rewrite->wp_rewrite_rules(). So just a 1 line change.

However, flushing like that should typically only occur on plugin activation/deactivation or when a new site is created in Multisite, or (if the plugin has that) in some sort of upgrade routine / migration script. That's how we do it in the Web Stories plugin for example: https://github.com/GoogleForCreators/web-stories-wp/blob/afe6e41af3f0086181a4cdf12060c2c2b6d4bf29/includes/Infrastructure/ServiceBasedPlugin.php#L116-L208

[westonruter]

Alternatively, we can avoid flushing the rules entirely because the plugin also contains this failsafe code which runs at the parse_query action:

pwa-wp/wp-includes/service-workers.php

Lines 215 to 218 in 62961cd

	// Handle case where rewrite rules have not yet been flushed.
	if ( 'wp.serviceworker' === $wp->request ) {
	$query->set( WP_Service_Workers::QUERY_VAR, 1 );
	}

[lkraav]

So is there a code change planned?

[westonruter]

Yes. I need to set aside some time this month to do this and the 0.8 release.

[westonruter]

Here we go: #1096