Just checking that this shows up in the debug plugin - as we're already in the renderer.

Should be there, at least was in my test :)
All data in debug plugin is collected onAfterRespond.

We already have a use case for this PR. When it will be merged, we would have to add the deprecated flag and string to the 2 assets here: https://github.com/joomla/joomla-cms/blob/4.3-dev/build/media_source/com_templates/joomla.asset.json#L8-L31

They had been restored with my PR #39431 in the 4.3-dev branch, and in 5.0-dev they have will deleted when my PR #40302 gets merged, so the deprecation message would be for 5.0, or for 6.0 if my PR gets postponed until 6.0.

Maybe it would make sense to add that deprecation for the 2 assets to this PR here, so it can be tested with that use case?

Added :)

@Fedik A question regarding dependencies: Does the "dependencies": ["com_templates.admin-template-compare.es5"], of the "com_templates.admin-template-compare" asset mean that the "com_templates.admin-template-compare.es5" depends on the "com_templates.admin-template-compare"? In this case your last change would be right. Or does it mean that the "com_templates.admin-template-compare" depends on "com_templates.admin-template-compare.es5"? In this case you maybe should have added the deprecation to the "es5". Or am I completely wrong?

Ignore that dependency. In this case all .es5 scripts is a fallbacks for older browsers, they all will gone on Joomla 5 #39618

@Fedik But just for my understanding: Which one depends on which other one in that case?

of the "com_templates.admin-template-compare" asset mean that the "com_templates.admin-template-compare.es5" depends on the "com_templates.admin-template-compare"?

It is vice versa, com_templates.admin-template-compare depend from com_templates.admin-template-compare.es5

But, in current case they work each "stand alone", no real dependency.

The depndency here means when User use com_templates.admin-template-compare then the AssetManager will also load com_templates.admin-template-compare.es5.
Then in modern Browser will be executed only com_templates.admin-template-compare script,
and in old only com_templates.admin-template-compare.es5 script.

@Fedik So with your change users of old and new browsers both will cause the deprecated message in the log?

Only com_templates.admin-template-compare will cause the deprecated message in the log.
Because com_templates.admin-template-compare.es5 should not be used as stand alone asset.

When we delete blabla-script, we also delete blabla-script.es5 (if there any). No reason to spam deprecation log, it is already huge ;)

But yes, both users wil see that message.

I have tested this item ✅ successfully on 37c8839

I've successfully tested this PR as follows:

I've created an override in the Atum template for the "administrator/components/com_templates/tmpl/template/default.php" file.

Then I have added a line ->useScript('com_templates.admin-template-compare') before line 32 of the override file "administrator/templates/atum/html/com_templates/template/default.php".

Then with the PR applied I have verified that whenever I open the file editor view of the template manager, the deprecated message added by this PR to the asset is correctly logged in the "administrator/logs/deprecated.php" and also shown in the "Deprecated" tab of the debug bar if debug is enabled.

Finally I have verified that the new deprecated log does not happen when "Log deprecated" is switched off.

Thanks!