Removing an item from a menu in the Nav block list view causes a focus loss.

[getdave]

Identified during a11y review #46939 (comment), when removing an item using the Nav block list view focus is completely lost. It should be returned to the previous node or at least somewhere within the list view.

[draganescu]

Investigating this I learned that:

• removing any block moves focus to the editor iframe
• removing a submenu items, both in canvas and in the inspector, moves focus to document's body
• removing a menu item via the canvas moves focus to the editor iframe
• removing a menu item via the inspector moves focus to document's body

[draganescu]

More investigation resulted in doubting the origina bug:

• removing any block moves focus to the editor, removing a menu item via the canvas moves focus to the editor, moves focus to the editor iframe, but using contentWindow.document.activeElement shows the correct focus is applied to best available blocks in canvas
• removing a menu item via the inspector moves the focus properly can't repro consistently my finding above
• removing a submenu items, both in canvas and in the inspector, this is where focus is lost.

We need to manage focus where we do the transforms between link and submenu wither in the store like we foce select of previous block or in the blocks themselves.

[draganescu]

It seems there is a problem with replaceBlocks and how we use it to "transform" submenu to link. But many block operations use a selectionHelper that handles most selection following updating the block tree, including REPLACE_BLOCKS. Debugging this I learned that there are moments when the selection state is empty and because of the code here we return an empty selection state. Attempted a fix for this in #48105

The problem in this particular issue is a problem visible in the left hand list view as well, when replacing blocks the focus is not managed well and ends up on the body of the document.

[getdave]

@draganescu Great research. Thank you. As #48105 was closed what are the next steps here?

[draganescu]

@getdave #48204 is the solution. Waiting for it to be reviewed and to land asap.

[getdave]

Great work on #48204 @draganescu 👏