Custom meta boxes do not show up

[zodiac1978]

Using the Gutenberg plugin custom meta boxes showed up ( added with add_meta_box() ).

With 5.0-alpha-43818 alone (no Gutenberg plugin active) these custom meta boxes do not show up for me.

You can try this plugin for testing:
​https://wordpress.org/plugins/very-simple-event-list/

[zodiac1978]

No custom meta boxes with 5.0-alpha-43818

[zodiac1978]

With Gutenberg plugin active the custom meta boxes appear (and an unexptected error message)

[zodiac1978]

For the unexpected error message, see #45112

[zodiac1978]

After update to 5.0-beta1-43823 still the same problem.

[SergeyBiryukov]

#45184 was marked as a duplicate.

[mcsf]

We suspect this may be caused by the priority (and possibly implementation) of core's wpautop, which differs from the Gutenberg's plugin override gutenberg_wpautop, registered with priority 8.

See ​GitHub comment in this (generally unrelated) Gutenberg issue.

cc @pento (who will be gracious enough to excuse my constant summoning)

[pento]

That priority only mattered for the Gutenberg plugin: it was to ensure that wpautop() was removed from the the_content filter, before the function was run. The has_blocks() check is now part of wpautop(), so there's no need to remove it from the filter anymore.

I'll write up a patch to fix this.

[pento]

The equivalent of gutenberg_collect_meta_box_data() was missing. Rather than just merge that function it, which is basically a duplicate of a large chunk of edit-format-advanced.php, I moved the common code to a new function, which both edit forms are now able to call.

45172.diff​ is a first pass at this, it needs testing.

[designsimply]

Closed ​https://github.com/WordPress/gutenberg/issues/11058 as a duplicate but then noticed that that issue mentions wp_add_dashboard_widget() and this issue mentions add_meta_box() and I was wondering if a separate issue should be opened for the one I closed or if it's covered by the work here?

[zodiac1978]

@designsimply I think this is handled already in #45112

[designsimply]

Thanks @zodiac1978! (updated my link to point to 45112 instead)

[peterwilsoncc]

I've tested 45172.diff​ with the various ​callback arguments introduced for 5.0.

• __block_editor_compatible_meta_box does toggle the display correctly on the new editor. Setting the option to false does not cause the post type to fall back to the classic editor but that can be dealt with on another ticket.
• __back_compat_meta_box also toggles display correctly.

There are a few coding standards fixes required. As the patch mostyly moves existing code, these can be handled in the 5.1 release.

[pento]

In 43837:

Block Editor: Fix meta boxes not showing.

The block editor needs to duplicate the classic meta box behaviour, so it can extract the registered meta boxes, and import them into the block editor.

To match the classic editor behaviour as closely as possible, this moves the relevant code from the classic editor, into a new function, so it can be called by both.

Props pento, peterwilsoncc.
Fixes #45172.

[SergeyBiryukov]

Reopening for trunk.

[jeremyfelt]

In 44214:

Block Editor: Fix meta boxes not showing.

The block editor needs to duplicate the classic meta box behaviour, so it can extract the registered meta boxes, and import them into the block editor.

To match the classic editor behaviour as closely as possible, this moves the relevant code from the classic editor, into a new function, so it can be called by both.

Merges [43837] from the 5.0 branch to trunk.

Props pento, peterwilsoncc.
Fixes #45172.