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Fix subst issues with RPITIT

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This commit is contained in:
Michael Goulet 2022-09-26 23:13:12 +00:00
parent b8c35ca26b
commit c1aa9bf849
4 changed files with 69 additions and 10 deletions
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37
compiler/rustc_hir_analysis/src/check/compare_method.rs
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@ -551,15 +551,40 @@ pub fn collect_trait_impl_trait_tys<'tcx>(
let id_substs = InternalSubsts::identity_for_item(tcx, def_id);
debug!(?id_substs, ?substs);
let map: FxHashMap<ty::GenericArg<'tcx>, ty::GenericArg<'tcx>> =
substs.iter().enumerate().map(|(index, arg)| (arg, id_substs[index])).collect();
std::iter::zip(substs, id_substs).collect();
debug!(?map);
// NOTE(compiler-errors): RPITITs, like all other RPITs, have early-bound
// region substs that are synthesized during AST lowering. These are substs
// that are appended to the parent substs (trait and trait method). However,
// we're trying to infer the unsubstituted type value of the RPITIT inside
// the *impl*, so we can later use the impl's method substitutions to normalize
// an RPITIT to a concrete type.
//
// Due to the design of RPITITs, during AST lowering, we have no idea that
// an impl method is satisfying a trait method with RPITITs in it. Therefore,
// we don't have a list ofearly-bound region substs for the RPITIT in the impl.
// Since early region parameters are index-based, we can't just rebase these
// (trait method) early-bound region substs onto the impl, since region
// parameters are index-based, and there's no guarantee that the indices from
// the trait substs and impl substs line up -- so we subtract the number of
// trait substs and add the number of impl substs to *renumber* these early-
// bound regions to their corresponding indices in the impl's substitutions list.
//
// Also, we only need to account for a difference in trait and impl substs,
// since we previously enforce that the trait method and impl method have the
// same generics.
let num_trait_substs = trait_to_impl_substs.len();
let num_impl_substs = tcx.generics_of(impl_m.container_id(tcx)).params.len();
let ty = tcx.fold_regions(ty, |region, _| {
if let ty::ReFree(_) = region.kind() {
map[&region.into()].expect_region()
} else {
region
}
let ty::ReFree(_) = region.kind() else { return region; };
let ty::ReEarlyBound(e) = map[&region.into()].expect_region().kind()
else { bug!("expected ReFree to map to ReEarlyBound"); };
tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion {
def_id: e.def_id,
name: e.name,
index: (e.index as usize - num_trait_substs + num_impl_substs) as u32,
}))
});
debug!(%ty);
collected_tys.insert(def_id, ty);