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Improve print_type. #144625

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7 changes: 6 additions & 1 deletion compiler/rustc_const_eval/src/util/type_name.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -42,11 +42,16 @@ impl<'tcx> Printer<'tcx> for AbsolutePathPrinter<'tcx> {
| ty::UnsafeBinder(_) => self.pretty_print_type(ty),

// Placeholders (all printed as `_` to uniformize them).
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@RalfJung RalfJung Jul 29, 2025

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This does sound like the _ was deliberate -- but I don't have a strong opinion either way.

ty::Param(_) | ty::Bound(..) | ty::Placeholder(_) | ty::Infer(_) | ty::Error(_) => {
ty::Bound(..) | ty::Placeholder(_) | ty::Infer(_) | ty::Error(_) => {
write!(self, "_")?;
Ok(())
}

ty::Param(param_ty) => {
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@RalfJung RalfJung Jul 29, 2025

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Can you add a comment here? All the other sections in this match have a nice comment.

write!(self, "{}", param_ty.name)?;
Ok(())
}

// Types with identity (print the module path).
ty::Adt(ty::AdtDef(Interned(&ty::AdtDefData { did: def_id, .. }, _)), args)
| ty::FnDef(def_id, args)
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2 changes: 1 addition & 1 deletion tests/ui/issues/issue-61894.rs
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Expand Up @@ -17,5 +17,5 @@ impl<M> Bar<M> {
}

fn main() {
assert_eq!(Bar(()).foo(), "issue_61894::Bar<_>::foo::f");
assert_eq!(Bar(()).foo(), "issue_61894::Bar<M>::foo::f");
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@RalfJung RalfJung Jul 29, 2025

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What is confusing about this is that there is no M in scope when printing the name. If M shadows the name of some other type, this could become misleading.

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@oli-obk oli-obk Jul 29, 2025

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yea, iirc printing _ was on purpose, because it can't have been relevant for the type name if it's still an uninstantiated param. If there are two impl<M> Bar<M> (e.g. with different bounds, which is where such "dupliate impl blocks" are common), then the type names would still be the same, so adding the M does not really bring any benefit

}
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