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Add a separate error for `dyn Trait` in `const fn` by WaffleLapkin · Pull Reques...

 2 years ago
source link: https://github.com/rust-lang/rust/pull/89021
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@estebank estebank on Sep 17

For the cases of fields like this one it would be nice to have a span_note pointing at the type and field's type to show how it is a trait object.

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@WaffleLapkin WaffleLapkin on Sep 17

It would be really nice! Can we implement this though? It seems like we only check locals and not expressions:

for (idx, local) in body.local_decls.iter_enumerated() { // Handle the return place below. if idx == RETURN_PLACE || local.internal { continue; } self.span = local.source_info.span; self.check_local_or_return_ty(local.ty, idx); } // impl trait is gone in MIR, so check the return type of a const fn by its signature // instead of the type of the return place. self.span = body.local_decls[RETURN_PLACE].source_info.span; let return_ty = tcx.fn_sig(def_id).output(); self.check_local_or_return_ty(return_ty.skip_binder(), RETURN_PLACE);

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@estebank estebank on Sep 17

I'm not sure if we can't get that info from local.local_info or local.source_info (I'm not that familiar with const eval and have to relearn it every time I look at it).

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@WaffleLapkin WaffleLapkin on Sep 18

Hm, after reading docs I can't see how we can get the expression, but maybe I'm missing something

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@estebank estebank 29 days ago •

edited

Can you check what the contents of local.local_info are? I assume it is going to be a VarBindingForm. If it is, what are the contents of opt_match_place?

Alternatively, if the data isn't there, it could potentially be added.

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@WaffleLapkin WaffleLapkin 27 days ago

So in the case of our interest (field access) local.local_info is simply None :(

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@estebank estebank 27 days ago

In that case, we'll have to make more dramatic changes so that we can track that data :-/

It's probably not high priority, but if you desire to take that on, I'd be more than happy to see it through!

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@WaffleLapkin WaffleLapkin 27 days ago

I don't think I'm interested enough in that. Thanks for offering help though!


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