If you delete joomla.asset.json then you whole site will crash.

It not the file is required, but the content in it.
Empty file or removed an asset definition in the file may lead to crash as well

Yes, like I said: :-)

same happens if you make a typo in this file.

this is third reason ;)

• file removed
• typo in file (invalid json)
• file does not have all assets that used by template

In general the file:

• must be valid json
• should contain valid markup schema: https://developer.joomla.org/schemas/json-schema/web_assets.json
• should contain all assets definitions that used by template

But note: If the template defines all assets in its index.php (component.php etc) then file can be removed.

We could/should probably at least validate the JSON in the file

joomla.asset.json to be a protected file like index.php is and cannot be deleted using the web interface template manager.

So this one (I've just tested) is a bit more tricky. It fails because none of the assets cassiopeia uses in joomla.asset.json are being found (for obvious reasons).

However in a 3rd party template obviously this doesn't have to be the case. We even have the assetExists method which we use in some of our components for this.

I guess the reality though is probably if a component ships this file then it shouldn't be deleted however... We just need to be careful to ensure that we don't require templates to ship with one.

I guess the reality though is probably if a component ships this file then it shouldn't be deleted however

I agree, same for template, if template ships this file then it shouldn't be deleted.

We just need to be careful to ensure that we don't require templates to ship with one.

In documentation we already have a note:

Note: Having joomla.asset.json for your extension or template are recommend but not required to WebAssset to work (see next section).

Maybe can elaborate that note, somehow.

PR #31710