[display] unused pattern variables should be marked as unused

[Gama11]

Similar to #7267 - value should have a "this code has no effect" diagnostic so vshaxe can gray it out.

import haxe.ds.Option;

class Main {
	public static function main() {
		switch ((null:Option<Int>)) {
			case Some(value):
			case None:
		}
	}
}

[Simn]

I don't know how I feel about that. It might be somewhat impractical, especially if you consider code-generation for switch expressions. It's also not exactly true to say that the code has no effect: It's actually required to match the structure and the only way to avoid warnings would be to use _ everywhere.

[Gama11]

The idea here is that we need the diagnostic to be able to gray the variables out in vshaxe, like we do for other unused code. You wouldn't even normally see the "this code has no effect" message, and that could be something else.

[Gama11]

We would probably also want to offer a "replace with _" code action for these, so it should probably be a different message / type, so we can properly distuingish it.

[Gama11]

Oh, and also note that we don't present any of the "unused" diagnostics as actual warnings anymore (so they also don't show up in the problems view). That would show green underlines in addition to the grayed-out-effect, which kind of destroys the subtlety.

https://github.com/vshaxe/haxe-languageserver/blob/38553fd756de2a194e53647348ae93adddf68256/src/haxeLanguageServer/features/DiagnosticsManager.hx#L152-L154

[Gama11]

Huh, was this accidentally fixed somehow? Now seems to be working:

I guess I'll add a test and close this.

[Gama11]

Oh, this is reported as DKRemovableCode, and the range on that is pretty off..

[Simn]

This is easy to fix but requires syncing with vshaxe which I currently cannot compile.

[Simn]

This (alongside vshaxe/haxe-language-server@0f3418b) now gives a more useful code action:

Adding a proper test is blocked on #9134.

[kLabz]

@Simn do you want the test to do something more here?

[Simn]

The replace range should always be tested for these.

[kLabz]

Should this be closed now or is there something still missing ?