gutenberg_pre_init() does not prevent plugin from loading

[swissspidy]

Describe the bug

When using Gutenberg on WP < 5.3, gutenberg_pre_init() will trigger an admin notice and won't load lib/load.php because of that.

However, the rest of the code in gutenberg.php is still executed, including all the add_action calls, like gutenberg_menu().

That function in turn calls gutenberg_use_widgets_block_editor(), which only exists if load.php is loaded.

Because of that, on WP < 5.3 you will not get any admin notice, but instead this fatal error:

Fatal error: Call to undefined function gutenberg_use_widgets_block_editor() in /var/www/html/wp-content/plugins/gutenberg/gutenberg.php on line 47

To reproduce
Steps to reproduce the behavior:

1. Try to activate Gutenberg on WP < 5.3 (e.g. by using wp-env)
2. See fatal error

Expected behavior

Admin notice instead of fatal error

Screenshots
If applicable, add screenshots to help explain your problem.

Editor version (please complete the following information):

• WordPress version: Anything below 5.3
• Gutenberg version: 6.2

Additional context

• To report a security issue, please visit the WordPress HackerOne program: https://hackerone.com/wordpress.

[noisysocks]

We don't support versions less than 5.3.

gutenberg/gutenberg.php

Line 6 in 35a94fd

* Requires at least: 5.3

[swissspidy]

@noisysocks I think you misunderstood the purpose of this ticket. I'll try to explain it differently :)

I know that Gutenberg does not support WP < 5.3.

There's even this function that should warn the user about it:

gutenberg/gutenberg.php

Lines 139 to 151 in 35a94fd

	/**
	* Display a version notice and deactivate the Gutenberg plugin.
	*
	* @since 0.1.0
	*/
	function gutenberg_wordpress_version_notice() {
	echo '<div class="error"><p>';
	/* translators: %s: Minimum required version */
	printf( __( 'Gutenberg requires WordPress %s or later to function properly. Please upgrade WordPress before activating Gutenberg.', 'gutenberg' ), '5.3.0' );
	echo '</p></div>';
	deactivate_plugins( array( 'gutenberg/gutenberg.php' ) );
	}

However, it does not work as intended. Neither does gutenberg_build_files_notice run as intended.

That's because there's a fatal error happening before this code can even run.

This ticket is about this fatal error and how this logic needs to be fixed so that this notice is being displayed as intended.

[noisysocks]

Ah! Thanks for clarifying 🙂

[xavortm]

I have just installed WordPress-Develop and on latest master + latest master Gutenberg repository, I am still getting this fatal error after activating the plugin :/

Fatal error: Uncaught Error: Call to undefined function gutenberg_use_widgets_block_editor() in /var/www/src/wp-content/plugins/gutenberg/gutenberg.php:128 Stack trace: #0 /var/www/src/wp-includes/class-wp-hook.php(292): modify_admin_bar(Object(WP_Admin_Bar)) #1 /var/www/src/wp-includes/class-wp-hook.php(316): WP_Hook->apply_filters(NULL, Array) #2 /var/www/src/wp-includes/plugin.php(551): WP_Hook->do_action(Array) #3 /var/www/src/wp-includes/admin-bar.php(95): do_action_ref_array('admin_bar_menu', Array) #4 /var/www/src/wp-includes/class-wp-hook.php(292): wp_admin_bar_render('') #5 /var/www/src/wp-includes/class-wp-hook.php(316): WP_Hook->apply_filters('', Array) #6 /var/www/src/wp-includes/plugin.php(484): WP_Hook->do_action(Array) #7 /var/www/src/wp-includes/general-template.php(3037): do_action('wp_body_open') #8 /var/www/src/wp-content/themes/twentytwentyone/header.php(24): wp_body_open() #9 /var/www/src/wp-includes/template.php(730): require_once('/var/www/src/wp...') #10 /var/www/src/wp-includes/template.php(676): in /var/www/src/wp-content/plugins/gutenberg/gutenberg.php on line 128

So the WP version is 5.7, not <5.3; Gutenberg v.9.7.1

I might be missing something obvious, it's my first time setting up the two. Considering how the fatal error showed up right after doing the latest pull from both, I guess I might be wrong as I am not finding it reported, but still, posting if it helps. Apologies if this needs a separate ticket

[swissspidy]

@xavortm Since you are using Gutenberg master Have you built Gutenberg properly? npm install && npm run build

[xavortm]

Apologies :( I did npm install and then npm run build, the same error shows up. It was after the npm run dev that worked. Sorry!

[bph]

I saw the flaw in my logic just before I went to sleep - there is no concern for backwards compatibility at all.
Either a user is using an older version with the block-editor's capabilities of that time, or they are on a new WordPress version 5.5 +. Neither version would have problems. This only concerns the Gutenberg plugin and with setting the minimum requirement to WordPress 5.5 this seems to be sufficiently handled.

It's very likely, I am missing something essential, though. Please forgive my ignorance.
Turns out I did. Thanks to @swissspidy for the 'confused' signal.

[gziolo]

The mix of #30230 and #29938 should address this issue.

[gziolo]

The mix of #30230 and #29938 should address this issue.

Both PRs landed a while ago. Let's close this issue.