Inserter: Consider a prompt when replacing semantic patterns

[annezazu]

What problem does this address?

This feedback came in through the FSE Outreach Program. Essentially, when choosing a semantic pattern (aka related to template parts right now) from the Inserter, a few folks have expected that it would replace their current template part:

I thought is that clicking to add a Pattern and selecting a specific template part pattern that the current canvas/document template part will be replaced by the template part selected in the patterns. Example. I click Headers pattern and find a Header I want to use to replace the current canvas header. Clicking to add a new header I do not want two headers but I want to use the one I selected to replace the current one. OR atleast getting the option through a dialog modul which asks me if I want to replace the current header with the new I just selected.

What is your proposed solution?

Offer a prompt asking "do you want to insert this pattern or replace your current header?". This could perhaps only happen when clicking a pattern rather than drag & drop.

[talldan]

It used to work the other way, but it was changed in #44221 to create a new template part so that the user doesn't accidentally update all their templates. 😄

What are your thoughts on the idea of a prompt, @jameskoster?

[jameskoster]

It's really tricky to design a UI that accounts for all the possible user intentions. Selecting a header from the Pattern Inserter may mean:

1. You just want to insert the pattern as regular blocks (unlikely but possible)
2. You want to insert the new pattern and create a new template part straight away
3. You want to replace a semantically equivalent template part already in the document and create a new one based on the selected pattern
4. You want to update a semantically equivalent template part already in the document

Imho the latter two flows feel a bit antithetical to the Inserter purpose, which is to add blocks to the existing document, not update or replace pre-existing ones.

The fourth option seems best served by something like #47507, and the third can be addressed by the on-going design work in #36667. Notably offering a way to swap headers / footers in the dark sidebar when you drill into a template:

All that said, if we were to offer a prompt of any kind, I would suggest it's one that asks whether a template part should be created, or if the pattern should be inserted as regular blocks.