Custom Blocks don't show up in Widgets

[JanP2ER]

Describe the bug

Custom-created Blocks can't be accessed in the widget-editor (e.g. in the Footer)

To reproduce
Steps to reproduce the behavior:

1. Register custom block
2. Click on 'Gutenberg' --> 'Widgets'
3. Try to add a new block to any selection
4. Custom blocks don't show up

Expected behavior
Custom created blocks should be displayed and accessible.

Screenshots
Block selection of regular posts:

Block selection of widgets:

Desktop

• OS: macOS10.14.4
• Browser: all browsers

Additional context

• Gutenberg version: 5.7.0
• Wordpress version: 5.2

[swissspidy]

How did you register your block types? Have you verified your scripts are loaded on that screen?

[adambiggs]

I just ran into this issue. @swissspidy do you have any more info about how custom blocks should be registered so they show up in the widget editor?

I would have expected that if a block is registered successfully and shows up when editing a post, that it would automatically also show up in the widget editor, but that doesn't seem to be the case.

[adamziel]

The root cause are these two checks:

https://github.com/WordPress/wordpress-develop/blob/23528d419ab2968f250392e8552095783b138fec/src/wp-includes/script-loader.php#L2165
https://github.com/WordPress/wordpress-develop/blob/23528d419ab2968f250392e8552095783b138fec/src/wp-includes/script-loader.php#L2199

Neither widgets nor navigation editors are marked block editor pages which seems to be required for custom block types to be loaded. Unfortunately the resolution is not as simple as marking them as block editor pages since it results in the following:

It seems like is_block_editor() is responsible for too many things at once. I suggest resolving this one by updating script-loader.php to rely on a filter as follows:

	$is_block_editor_screen = ( $current_screen instanceof WP_Screen ) && ! $current_screen->is_block_editor();
	$should_load_block_scripts_and_styles = apply_filters( 'should_load_block_scripts_and_styles', $is_block_editor_screen, $current_screen );
	if ( is_admin() && ! $should_load_block_scripts_and_styles ) {
		return;
	}

[adamziel]

Since this requires updating the core, I created a core PR and a Trac ticket:

WordPress/wordpress-develop#537
https://core.trac.wordpress.org/ticket/51330

[annezazu]

Removing the needs testing label and changing this to a WP Core Bug since this requires a core update.

[adamziel]

Now that the core patch is merged, I started working on the Gutenberg part here: #25826