[lcnr]

fixes #164054

this was previously fixed in #116530 and later reverted in #118736.

It impacts the new solver more than the old one as the new solver depends significantly more on region identity, see the relevant stabilization report section.

The old solver has significantly less region identity dependence. It does rely on region identity when merging candidates during normalization:

rust/compiler/rustc_trait_selection/src/traits/project.rs

Lines 103 to 107 in 69bccf0

	// Duplicates can happen inside ParamEnv. In the case, we
	// perform a lazy deduplication.
	if current == &candidate {
	return false;
	}

This check results in additional ICE with the old solver while instead triggering the potentially region dependent goals check with the new one

rust/compiler/rustc_trait_selection/src/traits/query/type_op/custom.rs

Lines 94 to 95 in 14f0018

	let value = op(&ocx).map_err(|_| {
	infcx.tcx.check_potentially_region_dependent_goals(root_def_id).err().unwrap_or_else(

r? types

[rustbot]

🤖 A dedicated #t-types/nominated topic has been opened for humans to discuss this issue 🤖

[rustbot]

miri is developed in its own repository. If the Miri part of this change can be broken out, consider making this change to rust-lang/miri instead. However, if Miri needs adjusting for rustc changes, just ignore this message.

cc @rust-lang/miri

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[RalfJung]

Is a fail test the best test we can have now for #135316 ? It means we're not even hitting vtable generation any more.

View changes since the review