bjoernager/rust
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Auto merge of #113393 - compiler-errors:next-solver-unsize-rhs, r=lcnr

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Normalize the RHS of an `Unsize` goal in the new solver

`Unsize` goals are... tricky. Not only do they structurally match on their self type, but they're also structural on their other type parameter. I'm pretty certain that it is both incomplete and also just plain undesirable to not consider normalizing the RHS of an unsize goal. More practically, I'd like for this code to work:

```rust
trait A {}
trait B: A {}

impl A for usize {}
impl B for usize {}

trait Mirror {
    type Assoc: ?Sized;
}

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

fn main() {
    // usize: Unsize<dyn B>
    let x = Box::new(1usize) as Box<<dyn B as Mirror>::Assoc>;
    // dyn A: Unsize<dyn B>
    let y = x as Box<<dyn A as Mirror>::Assoc>;
}
```

---

In order to achieve this, we add `EvalCtxt::normalize_non_self_ty` (naming modulo bikeshedding), which *must* be used for all non-self type arguments that are structurally matched in candidate assembly. Currently this is only necessary for `Unsize`'s argument, but I could see future traits requiring this (hopefully rarely) in the future. It uses `repeat_while_none` to limit infinite looping, and normalizes the self type until it is no longer an alias.

Also, we need to fix feature gate detection for `trait_upcasting` and `unsized_tuple_coercion` when HIR typeck has unnormalized types. We can do that by checking the `ImplSource` returned by selection, which necessitates adding a new impl source for tuple upcasting.
This commit is contained in:
bors 2023-07-25 17:10:31 +00:00
commit 8327047b23
27 changed files with 638 additions and 568 deletions
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5
compiler/rustc_const_eval/src/transform/check_consts/check.rs
View file

@ -8,6 +8,7 @@ use rustc_infer::infer::TyCtxtInferExt;
use rustc_infer::traits::{ImplSource, Obligation, ObligationCause};
use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor};
use rustc_middle::mir::*;
use rustc_middle::traits::BuiltinImplSource;
use rustc_middle::ty::{self, adjustment::PointerCoercion, Instance, InstanceDef, Ty, TyCtxt};
use rustc_middle::ty::{GenericArgKind, GenericArgs};
use rustc_middle::ty::{TraitRef, TypeVisitableExt};
@ -766,7 +767,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
};
match implsrc {
Ok(Some(ImplSource::Param(_, ty::BoundConstness::ConstIfConst))) => {
Ok(Some(ImplSource::Param(ty::BoundConstness::ConstIfConst, _))) => {
debug!(
"const_trait_impl: provided {:?} via where-clause in {:?}",
trait_ref, param_env
@ -774,7 +775,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
return;
}
// Closure: Fn{Once|Mut}
Ok(Some(ImplSource::Builtin(_)))
Ok(Some(ImplSource::Builtin(BuiltinImplSource::Misc, _)))
if trait_ref.self_ty().is_closure()
&& tcx.fn_trait_kind_from_def_id(trait_id).is_some() =>
{

4
compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs
View file

@ -7,6 +7,7 @@ use rustc_hir::LangItem;
use rustc_infer::infer::TyCtxtInferExt;
use rustc_middle::mir;
use rustc_middle::mir::*;
use rustc_middle::traits::BuiltinImplSource;
use rustc_middle::ty::{self, AdtDef, GenericArgsRef, Ty};
use rustc_trait_selection::traits::{
self, ImplSource, Obligation, ObligationCause, ObligationCtxt, SelectionContext,
@ -172,7 +173,8 @@ impl Qualif for NeedsNonConstDrop {
if !matches!(
impl_src,
ImplSource::Builtin(_) | ImplSource::Param(_, ty::BoundConstness::ConstIfConst)
ImplSource::Builtin(BuiltinImplSource::Misc, _)
| ImplSource::Param(ty::BoundConstness::ConstIfConst, _)
) {
// If our const destruct candidate is not ConstDestruct or implied by the param env,
// then it's bad