fix: merging cells onto already merged cells throws error

[rilrom]

Description

Closes #4470, #5853.

This fix ensures that the merge cells button does not appear when attempting to merge already merged cells onto unmerged cells. This prevents an error from appearing which eventually causes the table to be unusable.

I do see potential for being able to merge already merged cells onto unmerged cells in certain situations, but that should be revisited separately, for now resolving the error is the priority.

Test plan

1. Create a table.
2. Attempt to merge already merged cells onto unmerged cells.
3. The merge cells button should not appear in the table action menu.

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Comments	Updated (UTC)
lexical	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Sep 6, 2024 4:32pm
lexical-playground	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Sep 6, 2024 4:32pm

[github-actions]

size-limit report 📦

Path	Size
lexical - cjs	29.66 KB (0%)
lexical - esm	29.48 KB (0%)
@lexical/rich-text - cjs	38.07 KB (0%)
@lexical/rich-text - esm	31.32 KB (0%)
@lexical/plain-text - cjs	36.65 KB (0%)
@lexical/plain-text - esm	28.66 KB (0%)
@lexical/react - cjs	39.83 KB (0%)
@lexical/react - esm	32.75 KB (0%)

[etrepum]

I think the priority here should be test coverage, to confirm that this does actually fix the issue and to make it easier to properly fix the edge case that this fix is avoiding. If the problem is just that the selection is getting lost, I think that should be straightforward to fix properly.

[rilrom]

I think the priority here should be test coverage, to confirm that this does actually fix the issue and to make it easier to properly fix the edge case that this fix is avoiding. If the problem is just that the selection is getting lost, I think that should be straightforward to fix properly.

Understood, I will create a regression test for it.

[etrepum]

After looking closer I think the correct fix here is #6607 but will take some time to write additional tests and probably fix another edge case or two while I'm in there

[rilrom]

After looking closer I think the correct fix here is #6607 but will take some time to write additional tests and probably fix another edge case or two while I'm in there

If you've managed to allow for merging already merged cells onto unmerged cells without throwing an error then I absolutely agree that's the better fix here.

This has been a relatively long-standing issue so I'm glad I was able to get the discussion rolling.

I'll do some testing on your PR, thanks @etrepum.

Edit: closing this PR in favour of #6607.