This solves the issue I had with specific xx-XX.css admin lang which is now loaded after bootstrap and template css.

	<link href="/installmulti/joomla40/media/system/css/fields/switcher.min.css?a1bacb193a9e68d6496252f11a1d20e4" rel="stylesheet" />
	<link href="/installmulti/joomla40/administrator/templates/atum/css/bootstrap.min.css?a1bacb193a9e68d6496252f11a1d20e4" rel="stylesheet" />
	<link href="/installmulti/joomla40/administrator/templates/atum/css/template-rtl.min.css?a1bacb193a9e68d6496252f11a1d20e4" rel="stylesheet" />
	<link href="/installmulti/joomla40/administrator/language/fa-IR/fa-IR.css?a1bacb193a9e68d6496252f11a1d20e4" rel="stylesheet" />
	<link href="/installmulti/joomla40/administrator/templates/atum/css/fontawesome.min.css?a1bacb193a9e68d6496252f11a1d20e4" rel="stylesheet" />
etc.

@Fedik
Shall I set this to tested OK as I just tested the css?

@infograf768 yes if other part of the site still works good for you ?
but the whole patch need to be reviewed by @wilsonge and others

well, I have to fix a conflict first

I'm planning on looking at this and I'm aware of it - but I'm really busy with gsoc stuff as it ends this week. 20-30th I'm on holiday so I'm unlikely to be able to properly look at it until after I'm back from holiday. So please don't close this - and sorry it's taking me time to review it properly!

I have tested this item ✅ successfully on 5b2e082

@Fedik A far better approach for the web assets. Could you fix the conflicts please?

@wilsonge Have you managed to look at this? The sooner a decision is made about this, the better

where we are on this @release-joomla postpone to 5.x ?

5.x will be to late, it one of "now or never" :)

@mbabker , @wilsonge , @HLeithner

it fixes #27024 and #26077 (comment) also, by 6f6c835

New feature: an extension now can set template.active as dependency to current template, so their files will be loaded after template style/script files, even if extensions asset was enabled before template render.

With PR jquery-noconflict is not loading.

It does not required, but you can still load it if you need it

I have tested this item ✅ successfully on 9de1195

I have to say with this I'm slightly concerned that we are starting to make things much more complicated in the JSON structure. But at the same time as we're solving concrete problems I'm not sure there's much we can do about it. Can we please get the documentation and the JSON Schema updated please for this new approach

Thankyou for taking the time to investigating michael's review. It's very much appreciated by me :)

Schema update are there joomla/schemas#7
But do not merge for now please. I have to update a bit, about webcomponents ( to cover #27268)

I'm slightly concerned that we are starting to make things much more complicated in the JSON structure

yeah, me to, a bit :)
But it not that much complicated as much more content it contain now, because now an asset can contain only one file.
Also, because of this, I have introduced a "preset", a kind of collection that can "hold" a multiple different asset. It more like a "helper".
will see how it will work

the doc page I will look

btw, if extension has 1-2 asset files, it fine just use
$wa->registerAndUseScript('foobar.fancystuff', 'com_foobar/fancy-stuff.js'); instead of JSON.
JSON good for huge amount of assets, as we have in Joomla.

@Fedik Did you write up the documentation for the JSON format?

Documentation I have updated, it is there https://docs.joomla.org/J4.x:Web_Assets
And JSON schema are there https://github.com/joomla/schemas/blob/master/json-schema/web_assets.json (with properties description)

In documentation there just some examples of JSON, not sure what to write about schema.

@Fedik Thank you, I could not find the article on the docs.

btw, here is the "public link" to schema https://developer.joomla.org/schemas/json-schema/web_assets.json

@Fedik The only thing that is unclear to me is this:

"dependencies": [
        "core",
		"bootstrap"
      ],

How do I know which dependencies are available? The bootstrap is giving a fatal error now. I have no idea where to check what it is looking for. This might be something we can explain in the docs as well.

It some how this section https://docs.joomla.org/J4.x:Web_Assets#Register_an_asset
bootstrap actually part of vendors json media/vendor/joomla.asset.json

It should be available on on first access to WebAssetRegistry

But you have to check that file to get a correct name, there a couple of bootstrap variations, eg: bootstrap.css (styles), bootstrap.css.grid (another style), bootstrap.js (script), bootstrap.js.bundle (another script)

I had an idea to extend a debug plugin to print out all available assets, but this for some time later maybe, maybe for 4.2 or so ?

and the core asset is part of system json media/system/joomla.asset.json

Hey @Fedik Thank you for the feedback so far.

It should be available on on first access to WebAssetRegistry

That doesn't seem to be the case. When I inspect $wa in the index.php of the template, it has some json files loaded but nothing parsed.

When I add core as dependency in the templates/cassiopeia/joomla.asset.json file like this:

"name": "template.cassiopeia.ltr",
      "type": "preset",
      "dependencies": [
		"core",
        "template.cassiopeia.ltr#style",
        "template.cassiopeia#script"
      ]

It also bails with an error

Error: Unsatisfied dependency "core" for an asset "template.cassiopeia.ltr" of type "preset": Unsatisfied dependency "core" for an asset "template.cassiopeia.ltr" of type "preset"

It looks like, the json files need to be parsed first before I can load any preset/asset with a dependency. Any ideas about this?

It should be available on on first access to WebAssetRegistry
When I inspect $wa in the index.php of the template, it has some json files loaded but nothing parsed.

that correct, they will be parsed on "first access", mean on first $registry->get() call, that will be performed on any $wa->useScript('foobar') call

When I add core as dependency ... It also fails with an error.

That also correct, see what type of asset do you use. If your asset is a script then all dependency also must be script, if your asset are style then all dependency also must be type of style and so on, preset for presets.
There no support of "cross type" dependency (except for presets).

Your example:

"name": "template.cassiopeia.ltr",
"type": "preset", <----- Asset type
"dependencies": [
  "core",   <------ Looking for another "preset" with name "core", not for "script" asset
  "template.cassiopeia.ltr#style",
  "template.cassiopeia#script"
]

As error say, there no "preset" with name "core".
Here is about presets https://docs.joomla.org/J4.x:Web_Assets#Working_with_a_presets with explanation what is special in presets.

Correct would be:

"name": "template.cassiopeia.ltr",
"type": "preset",
"dependencies": [
  "core#script",
  "template.cassiopeia.ltr#style",
  "template.cassiopeia#script"
]

But again, this only for "preset" type, other asset types does not support "cross type" dependency.

@Fedik The exteneded explanation is much appreciated. This gives me a lot of insight and it is working now.

It was a bit different in first implementation,
In first implementation an asset hold multiple different files css, js, and then after some discussions I have change to handle 1 asset = 1 file