Const generic param unknown type

[A4-Tacks]

rust-analyzer version: rust-analyzer 1.90.0-nightly (9748d87 2025-07-21)

rustc version: rustc 1.90.0-nightly (9748d87dc 2025-07-21)

editor or extension: VIM-9.1 coc-rust-analyzer

code snippet to reproduce:

fn foo<const N: usize>() {}

fn main() {
    foo::<3usize>();
}

Hover on 3usize output {unknown}

[ShoyuVanilla]

It seems that we don't collect const expressions into InferenceResult while lowering consts, so when we try to get type of them, it returns TyKind::Error as a fallback here:

rust-analyzer/crates/hir-ty/src/infer.rs

Lines 615 to 619 in 48ccbe0

	impl Index<ExprId> for InferenceResult {
	type Output = Ty;
	fn index(&self, expr: ExprId) -> &Ty {
	self.type_of_expr.get(expr).unwrap_or(&self.standard_types.unknown)

We might poke something like on_lower_const: impl FnMut(ExprId, Ty) into TyLoweringContext though it would make TyLoweringContext more ugly but I wonder whether it improve other type inferences or not 🤔