correctly handle uninferred consts

[lcnr]

fixes the ICE mentioned in #70507 (comment)

I originally tried to generalize need_type_info_err to also work with consts which was not as much fun as I hoped 😅

It might be easier to have some duplication here and handle consts separately.

r? @varkor

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[varkor]

I originally tried to generalize need_type_info_err to also work with consts which was not as much fun as I hoped 😅

Yeah, I also had this experience, which put me off. Splitting it might be the way to go for now. It would be good to emit suggestions in the cases we can think of (which might involve just comparing with the type parameter version).

[lcnr]

Afaict we need something similar to https://doc.rust-lang.org/nightly/nightly-rustc/rustc_infer/infer/struct.InferCtxtInner.html#structfield.type_variable_storage to get a more precise span for const inferences vars.

rust/src/librustc_infer/infer/error_reporting/need_type_info.rs

Lines 198 to 201 in 9912925

	let ty_vars = &inner.type_variables();
	let var_origin = ty_vars.var_origin(ty_vid);
	if let TypeVariableOriginKind::TypeParameterDefinition(name, def_id) = var_origin.kind {
	let parent_def_id = def_id.and_then(|def_id| self.tcx.parent(def_id));

I don't have the capacity for this at the moment, so IMO we should use this as is to at least not cause an ICE in unrelated places and open an issue so we don't forget this.

[lcnr]

@varkor Do you feel comfortable landing this as is or should I close this PR?

[varkor]

Sorry, I lost track of this.

I don't have the capacity for this at the moment, so IMO we should use this as is to at least not cause an ICE in unrelated places and open an issue so we don't forget this.

Yes, I think this is probably best for now. Could you open an issue to track this is?

Thanks for the PR! @bors r+ rollup

[bors]

📌 Commit 3702d43 has been approved by varkor

[lcnr]

opened #72328

[RalfJung]

This failed in rollup #72326 and needs rebasing to adjust for current error messages.

@bors r-

[lcnr]

Should be fixed

[varkor]

@bors r+

[bors]

📌 Commit 5da7430 has been approved by varkor