SemanticTokensModifier: Add unused token modifier

[kjeremy]

I was thinking today how one might implement "grey out unreachable code" and I think we could do it with semantic tokens. Furthermore it's a pretty common operation spanning many languages. As such I think a modifier for "unused" or "unreachable" should be added to the protocol for consistency across languages.

[Gama11]

The LSP already supports this via DiagnosticTag.Unnecessary. See also microsoft/vscode#92157.

[dbaeumer]

@aeschli what it your take on this. I actually do think we should support unused / unreachable code in semantics as well.

[aeschli]

If you want to just mark a single token e.g identifier of a variable or parameter declaration as unused, yes, having a unused modifier is feasible.
If you want to mark a whole range as unreachable, then semantic tokens are not the right thing to use. We don't allow overlapping ranges.
From your description it sounds that it's range of unused code...

[kjeremy]

Yes I was originally thinking a whole range which is why I proposed "unreachable" but agree that if we are to mark single tokens (and I think that's entirely reasonable and desired) as unused then there should be an "unused" modifier.

[dbaeumer]

@aeschli any take of adding the modifier?

[aeschli]

I created microsoft/vscode#97063 to collect proposals for new standard token types/modifiers.

[dbaeumer]

Thanks @aeschli

[dbaeumer]

Lets wait for the outcome in VS Code.

[starball5]

Related on Stack Overflow: How can I disable problem underlines for unused code with the Rust Analyzer VS Code extension and instead highlight it gray?