internal: Parse (nightly) const and async trait bounds

[compiler-errors]

Both of these bound modifiers were added recently:

• const trait bounds: Introduce const Trait (always-const trait bounds) rust#119099
• async trait bounds: Introduce support for async bound modifier on Fn* traits rust#120392

The latter will certainly will not do the right thing; namely, async Fn needs to be mapped to the AsyncFn trait. IDK how to do that, so advice would be appreciated, though perhaps we could land this first so the parser isn't complaining about these bounds?

[Veykril]

Can you adjust the grammar file here?

rust-analyzer/crates/syntax/rust.ungram

Lines 615 to 617 in bb0f93a

	TypeBound =
	Lifetime
	| ('?' | '~' 'const')? Type

Something like the following should be fine (ungrammar is not an exact representation of the AST)

TypeBound =
  Lifetime
| ('?' | '~')? ('const' | 'async')? Type

Then run the -p syntax tests to regenerate the AST.

[Veykril]

IDK how to do that, so advice would be appreciated, though perhaps we could land this first so the parser isn't complaining about these bounds?

Its fine to land the parser changes only, getting rid of the parser errors is the main concern here. The initial lowering of the bounds happen here

rust-analyzer/crates/hir-def/src/hir/type_ref.rs

Lines 345 to 380 in ead3691

	impl TypeBound {
	pub(crate) fn from_ast(ctx: &LowerCtx<'_>, node: ast::TypeBound) -> Self {
	let lower_path_type = |path_type: ast::PathType| ctx.lower_path(path_type.path()?);
	match node.kind() {
	ast::TypeBoundKind::PathType(path_type) => {
	let m = match node.question_mark_token() {
	Some(_) => TraitBoundModifier::Maybe,
	None => TraitBoundModifier::None,
	};
	lower_path_type(path_type)
	.map(|p| TypeBound::Path(p, m))
	.unwrap_or(TypeBound::Error)
	}
	ast::TypeBoundKind::ForType(for_type) => {
	let lt_refs = match for_type.generic_param_list() {
	Some(gpl) => gpl
	.lifetime_params()
	.flat_map(|lp| lp.lifetime().map(|lt| Name::new_lifetime(&lt)))
	.collect(),
	None => Box::default(),
	};
	let path = for_type.ty().and_then(|ty| match ty {
	ast::Type::PathType(path_type) => lower_path_type(path_type),
	_ => None,
	});
	match path {
	Some(p) => TypeBound::ForLifetime(lt_refs, p),
	None => TypeBound::Error,
	}
	}
	ast::TypeBoundKind::Lifetime(lifetime) => {
	TypeBound::Lifetime(LifetimeRef::new(&lifetime))
	}
	}
	}

, from there you should be able to follow anything else relevant by usages.

[compiler-errors]

👍

[compiler-errors]

opted for this because it's a bit more accurate representation of the real grammar rustc parses. I can change it if desired, though. I understand the parser modification up in generic_params.rs doesn't reflect all of the combinations that this one does.

[Veykril]

No that's fine as long as the possible tokens are represented.

[Veykril]

Thanks!
@bors r+

[bors]

📌 Commit 36020bb has been approved by Veykril

It is now in the queue for this repository.

[bors]

⌛ Testing commit 36020bb with merge 0932f89...

[bors]

☀️ Test successful - checks-actions
Approved by: Veykril
Pushing 0932f89 to master...