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Rollup merge of #113625 - compiler-errors:structurally-norm-in-select…
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…ion, r=lcnr

Structurally normalize in selection

We need to do this because of the fact that we're checking the `Ty::kind` on a type during selection, but goals passed into select are not necessarily normalized.

Right now, we're (kinda) unnecessarily normalizing the RHS of a trait upcasting goal, which is broken for different reasons (#113393). But I'm waiting for this PR to land before discussing that one.

r? `@lcnr`
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matthiaskrgr authored Jul 15, 2023
2 parents 7a17f57 + 7fb27e4 commit da18cf8
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Showing 2 changed files with 51 additions and 6 deletions.
39 changes: 33 additions & 6 deletions compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs
Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@ use rustc_hir::def_id::DefId;
use rustc_infer::infer::{DefineOpaqueTypes, InferCtxt, InferOk};
use rustc_infer::traits::util::supertraits;
use rustc_infer::traits::{
Obligation, PolyTraitObligation, PredicateObligation, Selection, SelectionResult,
Obligation, PolyTraitObligation, PredicateObligation, Selection, SelectionResult, TraitEngine,
};
use rustc_middle::traits::solve::{CanonicalInput, Certainty, Goal};
use rustc_middle::traits::{
Expand All @@ -20,6 +20,8 @@ use crate::solve::eval_ctxt::{EvalCtxt, GenerateProofTree};
use crate::solve::inspect::ProofTreeBuilder;
use crate::solve::search_graph::OverflowHandler;
use crate::traits::vtable::{count_own_vtable_entries, prepare_vtable_segments, VtblSegment};
use crate::traits::StructurallyNormalizeExt;
use crate::traits::TraitEngineExt;

pub trait InferCtxtSelectExt<'tcx> {
fn select_in_new_trait_solver(
Expand Down Expand Up @@ -228,18 +230,24 @@ fn rematch_object<'tcx>(
goal: Goal<'tcx, ty::TraitPredicate<'tcx>>,
mut nested: Vec<PredicateObligation<'tcx>>,
) -> SelectionResult<'tcx, Selection<'tcx>> {
let self_ty = goal.predicate.self_ty();
let ty::Dynamic(data, _, source_kind) = *self_ty.kind() else { bug!() };
let source_trait_ref = data.principal().unwrap().with_self_ty(infcx.tcx, self_ty);
let a_ty = structurally_normalize(goal.predicate.self_ty(), infcx, goal.param_env, &mut nested);
let ty::Dynamic(data, _, source_kind) = *a_ty.kind() else { bug!() };
let source_trait_ref = data.principal().unwrap().with_self_ty(infcx.tcx, a_ty);

let (is_upcasting, target_trait_ref_unnormalized) =
if Some(goal.predicate.def_id()) == infcx.tcx.lang_items().unsize_trait() {
assert_eq!(source_kind, ty::Dyn, "cannot upcast dyn*");
if let ty::Dynamic(data, _, ty::Dyn) = goal.predicate.trait_ref.args.type_at(1).kind() {
let b_ty = structurally_normalize(
goal.predicate.trait_ref.args.type_at(1),
infcx,
goal.param_env,
&mut nested,
);
if let ty::Dynamic(data, _, ty::Dyn) = *b_ty.kind() {
// FIXME: We also need to ensure that the source lifetime outlives the
// target lifetime. This doesn't matter for codegen, though, and only
// *really* matters if the goal's certainty is ambiguous.
(true, data.principal().unwrap().with_self_ty(infcx.tcx, self_ty))
(true, data.principal().unwrap().with_self_ty(infcx.tcx, a_ty))
} else {
bug!()
}
Expand Down Expand Up @@ -447,3 +455,22 @@ fn rematch_unsize<'tcx>(

Ok(Some(ImplSource::Builtin(nested)))
}

fn structurally_normalize<'tcx>(
ty: Ty<'tcx>,
infcx: &InferCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
nested: &mut Vec<PredicateObligation<'tcx>>,
) -> Ty<'tcx> {
if matches!(ty.kind(), ty::Alias(..)) {
let mut engine = <dyn TraitEngine<'tcx>>::new(infcx);
let normalized_ty = infcx
.at(&ObligationCause::dummy(), param_env)
.structurally_normalize(ty, &mut *engine)
.expect("normalization shouldn't fail if we got to here");
nested.extend(engine.pending_obligations());
normalized_ty
} else {
ty
}
}
18 changes: 18 additions & 0 deletions tests/ui/traits/new-solver/trait-upcast-lhs-needs-normalization.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,18 @@
// check-pass
// compile-flags: -Ztrait-solver=next

pub trait A {}
pub trait B: A {}

pub trait Mirror {
type Assoc: ?Sized;
}
impl<T: ?Sized> Mirror for T {
type Assoc = T;
}

pub fn foo<'a>(x: &'a <dyn B + 'static as Mirror>::Assoc) -> &'a (dyn A + 'static) {
x
}

fn main() {}

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