Feature request: distinguish mut keyword in semantic highlighting

[0xc0]

The mut keyword does not have any semantic modifiers to distinguish it from other keywords under semantic highlighting.

A semantic modifier (e.g., mutable) could be added to the mut keyword. This way, a different style for the mut keyword could be specified in user settings.json.

(This is possible with semantic highlighting disabled and using the textmate scope storage.modifier.mut.rust. However, semantic highlighting enabled overrides the textmate scope.)

[Veykril]

Sounds reasonable to give that keyword the mutable modifier, we'll have to overwrite the underlining *.mutable rule for that though so we don't underline it by default.

Relevant code is here

rust-analyzer/crates/ide/src/syntax_highlighting/highlight.rs

Lines 153 to 190 in 7322a98

	fn keyword(
	sema: &Semantics<RootDatabase>,
	token: SyntaxToken,
	kind: SyntaxKind,
	) -> Option<Highlight> {
	let h = Highlight::new(HlTag::Keyword);
	let h = match kind {
	T![await] => h | HlMod::Async | HlMod::ControlFlow,
	T![async] => h | HlMod::Async,
	T![break]
	| T![continue]
	| T![else]
	| T![if]
	| T![in]
	| T![loop]
	| T![match]
	| T![return]
	| T![while]
	| T![yield] => h | HlMod::ControlFlow,
	T![for] if parent_matches::<ast::ForExpr>(&token) => h | HlMod::ControlFlow,
	T![unsafe] => h | HlMod::Unsafe,
	T![true] | T![false] => HlTag::BoolLiteral.into(),
	// crate is handled just as a token if it's in an `extern crate`
	T![crate] if parent_matches::<ast::ExternCrate>(&token) => h,
	// self, crate, super and `Self` are handled as either a Name or NameRef already, unless they
	// are inside unmapped token trees
	T![self] | T![crate] | T![super] | T![Self] if parent_matches::<ast::NameRef>(&token) => {
	return None
	}
	T![self] if parent_matches::<ast::Name>(&token) => return None,
	T![ref] => match token.parent().and_then(ast::IdentPat::cast) {
	Some(ident) if sema.is_unsafe_ident_pat(&ident) => h | HlMod::Unsafe,
	_ => h,
	},
	_ => h,
	};
	Some(h)
	}

And then we should add a keyword.mutable:rust: [], rule after this one here

rust-analyzer/editors/code/package.json

Lines 1505 to 1508 in 7322a98

	],
	"*.mutable": [
	"markup.underline"
	]

I am not 100% sure this will reset the underlining part for them but it should, we would need to test that.

[ArchitBhonsle]

From what I can tell we want to get rid of the underline below mut... but there isn't one?

[bjorn3]

The request is to add a new semantic highlighting tag for the mut keyword so that users can customize how it is highlighted. For example by adding underlining or changing the color.

[ArchitBhonsle]

Which explains this part:

And then we should add a keyword.mutable:rust: [], rule after this one here

rust-analyzer/editors/code/package.json

Lines 1505 to 1508 in 7322a98

	],
	"*.mutable": [
	"markup.underline"
	]

I am not 100% sure this will reset the underlining part for them but it should, we would need to test that.

But what exactly is the following supposed to achieve?

Sounds reasonable to give that keyword the mutable modifier, we'll have to overwrite the underlining *.mutable rule for that though so we don't underline it by default.

Relevant code is here

rust-analyzer/crates/ide/src/syntax_highlighting/highlight.rs

Lines 153 to 190 in 7322a98

	fn keyword(
	sema: &Semantics<RootDatabase>,
	token: SyntaxToken,
	kind: SyntaxKind,
	) -> Option<Highlight> {
	let h = Highlight::new(HlTag::Keyword);
	let h = match kind {
	T![await] => h | HlMod::Async | HlMod::ControlFlow,
	T![async] => h | HlMod::Async,
	T![break]
	| T![continue]
	| T![else]
	| T![if]
	| T![in]
	| T![loop]
	| T![match]
	| T![return]
	| T![while]
	| T![yield] => h | HlMod::ControlFlow,
	T![for] if parent_matches::<ast::ForExpr>(&token) => h | HlMod::ControlFlow,
	T![unsafe] => h | HlMod::Unsafe,
	T![true] | T![false] => HlTag::BoolLiteral.into(),
	// crate is handled just as a token if it's in an `extern crate`
	T![crate] if parent_matches::<ast::ExternCrate>(&token) => h,
	// self, crate, super and `Self` are handled as either a Name or NameRef already, unless they
	// are inside unmapped token trees
	T![self] | T![crate] | T![super] | T![Self] if parent_matches::<ast::NameRef>(&token) => {
	return None
	}
	T![self] if parent_matches::<ast::Name>(&token) => return None,
	T![ref] => match token.parent().and_then(ast::IdentPat::cast) {
	Some(ident) if sema.is_unsafe_ident_pat(&ident) => h | HlMod::Unsafe,
	_ => h,
	},
	_ => h,
	};
	Some(h)
	}

Since there isn't an arm for T![mut] so I assume it's caught by _ which is just the normal HlTag::Keyword. Does this "underline it by default"?

Edit: I guess I just don't have sufficient project knowledge for this now. Maybe I'll give it a shot later.

[Veykril]

We don't yet emit any modifiers for the mut keyword, that is what this issue is about

[ArchitBhonsle]

This should do it right?

https://github.com/ArchitBhonsle/rust-analyzer/blob/0f8bb903197ffbd74b5f16b51420028a5252498e/crates/ide/src/syntax_highlighting/highlight.rs#L173

and

https://github.com/ArchitBhonsle/rust-analyzer/blob/0f8bb903197ffbd74b5f16b51420028a5252498e/editors/code/package.json#L1510

Should I create a pull request for this then?

master...ArchitBhonsle:rust-analyzer:mut-semantic-hl

[Veykril]

That should do it, but again I do not know for certain that this rule overwrite works as I expect it to, so that would need some manualy testing (just debug running the vscode extension)

[ArchitBhonsle]

I don't know this is done but the crude way I tested this was by doing this in editors/code/package.json:

"keyword.mutable:rust": [ "markup.underline" ]

Which did underline the mut in the editor.

[domyd]

Hello! I've tried the suggested fix here locally, but I cannot get the semanticTokenScopes rule override to work. It seems like VS Code merges all the TextMate scopes, and mut gets underlined no matter what. I'm not sure if it's supposed to work like that, since the docs don't mention overlapping scopes at all.

Are there other things we can try?

[Veykril]

Hm, looks like we can't do this then it seems