Widget Importer: ensure it works with importing menus

[annezazu]

This was found as part of the FSE Outreach Program's twentieth call for testing:

For me, only the calendar widget imported. The menu and categories widgets did not import. I could repeat this several times once I knew what to do to allow importing the widget areas.

I could only replicate issues with the menu import using GB 15.0 and WordPress 6.1.1:

[Mamaduka]

The Menu and Meta core widgets don't have transformations to blocks; it is the reason it's skipped during import. See #45509 (comment).

The Legacy Widget block doesn't work in Site Editor; We try to transform widgets into blocks; if this fails, we'll skip them and display the notice.

@noisysocks, do you remember the complications of adding the Menu widget transformation?

[noisysocks]

There isn't a transformation for the Meta widget because we have no analogous block for it. Should there be a Meta block, @mtias?

There isn't a transformation for the Menu widget because there was no need for one in the Widgets Editor which currently does not support the Navigation block (see #36469 for why).

It should be easy enough to add a Menu widget → Navigation block transformation but continue to disable the Navigation block in the Widgets Editor.

[Mamaduka]

Thank you for the context, @noisysocks!

[noisysocks]

It should be easy enough to add a Menu widget → Navigation block transformation

I started looking into this and the difficult bit is that we need to load the classic menu in order to transform it but unfortunately we don't yet support async transforms (#14755). We can either implement async transforms or add some wacky classicMenu attribute to the navigation block which tells the block to convert a classic menu upon initialisation.

[Mamaduka]

I personally would preferer using async transforms, and the feature would also be helpful in other places. The Navigation block is complicated; it doesn't seem right to add extra logic just for this case.

[noisysocks]

Yeah agreed.

[Mamaduka]

@annezazu, I think it makes sense to punt this for WP 6.3 and implement it properly with async transformations.

[annezazu]

Sounds good. I trust your read here!

[noisysocks]

I no longer think async transforms are a practical option. See #14755 (comment).

I started trying to solve this using the approach I outlined in that comment but then ran into a drawback that I don't like which is that doing this involves fetching all of the menus and menu items when the block editor is initialised.

Back to the drawing board 😅