[icon-themes] explore using attribute selectors to allow name patterns and simplify implementation

[aeschli]

We currently use css classes to match file icons to file names.
Using attribute selectors could simplify this and allow to support name patterns

[basename^="hello-"][ext="ts"] {
    background-color: red;
}

[basename$="Bar"][ext="ts"] {
    background-color: yellow;
}
[basename="unique-Bar"][ext="ts"] {
    background-color: green;
}

<div basename="hello-world" ext="ts">hello-world.ts</div>
<div basename="hello-world" ext="js">hello-world.js</div>
<div basename="fooBar" ext="ts">fooBar.ts</div>
<div basename="barBar" ext="ts">barBar.ts</div>
<div basename="hello-Bar" ext="ts">hello-Bar.ts</div>
<div basename="unique-Bar" ext="ts">unique-Bar.ts</div>

[zm-cttae]

Very very nice. I like that this moves the heavy lifting for theme keys back to the file icon side. Minor notes:

• The attributes contributed in iconLabel.ts need to use data- attributes for HTML5 semantic correctness.
  If we don't do this, we will get ⚠ warnings in the devtools console.
• We can support surrounding wildcards (as in *selector*) using [attr*="selector"] in CSS service
• If we want to implement the feature request in [icon-themes] Support for globs in file associations (Icon themes) #12493, we would need to add globbing in extensions

I believe I might have thought of this in #12493 but didn't devise it or sketch it out.
I guess I was just hyper-focused on getting the original use cases implemented in linear time 😄

[aeschli]

Thanks @zm-cttae. I agree with all your points!
Yes, the idea is that the patterns can also be used for extensions
Still to be clarified is how we deal with multi-segment extensions: hello.test.ts. Right now we generate multiple class names test.ts-ext-file-icon and ts-ext-file-icon and icon themes can match again ts or test.ts

Maybe move the dot inside the extension and use the $ to match?

<div data-basename="hello" ext=".json">hello.ts</div>
<div data-basename="hello" ext=".test.json">hello.test.ts</div>

/* extension: "ts" */
[data-ext$=".ts"] { 
    background-color: red;
}
/* extension: "test.ts" */
[data-ext$=".test.ts"] {
    background-color: blue;
}

However, that would limit the patterns that can be used in extensions.

[zm-cttae]

We can use data attribute and ext class to cover full functionality I think? Sucks we can't do it in one..

[zm-cttae]

Would you like me to try refactor #174286 again, see if this could work?

[zm-cttae]

I've implemented this into #174286, but it does need a change to the icon label API (PR description updated)