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Rollup merge of #92248 - compiler-errors:normalize-type-for-pointee, …
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…r=jackh726

Normalize struct tail type when checking Pointee trait

Let's go ahead and implement the FIXMEs by properly normalizing the struct-tail type when satisfying a Pointee obligation. This should fix the ICE when we try to calculate a layout depending on `<Ty as Pointee>::Metadata` later.
Fixes #92128
Fixes #92577

Additionally, mark the obligation as ambiguous if there are any infer types in that struct-tail type. This has the effect of causing `<_ as Pointee>::Metadata` to be properly replaced with an infer variable ([here](https://github.com/rust-lang/rust/blob/master/compiler/rustc_trait_selection/src/traits/project.rs#L813)) and registered as an obligation... this turns out to be very important in unifying function parameters with formals that are assoc types.

Fixes #91446
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matthiaskrgr authored Jan 10, 2022
2 parents d63a8d9 + 5a1c460 commit 6466f89
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Showing 4 changed files with 61 additions and 10 deletions.
9 changes: 6 additions & 3 deletions compiler/rustc_middle/src/ty/sty.rs
Original file line number Diff line number Diff line change
Expand Up @@ -2143,9 +2143,12 @@ impl<'tcx> TyS<'tcx> {
}

/// Returns the type of metadata for (potentially fat) pointers to this type.
pub fn ptr_metadata_ty(&'tcx self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
// FIXME: should this normalize?
let tail = tcx.struct_tail_without_normalization(self);
pub fn ptr_metadata_ty(
&'tcx self,
tcx: TyCtxt<'tcx>,
normalize: impl FnMut(Ty<'tcx>) -> Ty<'tcx>,
) -> Ty<'tcx> {
let tail = tcx.struct_tail_with_normalize(self, normalize);
match tail.kind() {
// Sized types
ty::Infer(ty::IntVar(_) | ty::FloatVar(_))
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_middle/src/ty/util.rs
Original file line number Diff line number Diff line change
Expand Up @@ -192,7 +192,7 @@ impl<'tcx> TyCtxt<'tcx> {
pub fn struct_tail_with_normalize(
self,
mut ty: Ty<'tcx>,
normalize: impl Fn(Ty<'tcx>) -> Ty<'tcx>,
mut normalize: impl FnMut(Ty<'tcx>) -> Ty<'tcx>,
) -> Ty<'tcx> {
let recursion_limit = self.recursion_limit();
for iteration in 0.. {
Expand Down
38 changes: 32 additions & 6 deletions compiler/rustc_trait_selection/src/traits/project.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1400,8 +1400,17 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
// Any type with multiple potential metadata types is therefore not eligible.
let self_ty = selcx.infcx().shallow_resolve(obligation.predicate.self_ty());

// FIXME: should this normalize?
let tail = selcx.tcx().struct_tail_without_normalization(self_ty);
let tail = selcx.tcx().struct_tail_with_normalize(self_ty, |ty| {
normalize_with_depth(
selcx,
obligation.param_env,
obligation.cause.clone(),
obligation.recursion_depth + 1,
ty,
)
.value
});

match tail.kind() {
ty::Bool
| ty::Char
Expand Down Expand Up @@ -1435,7 +1444,12 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
| ty::Bound(..)
| ty::Placeholder(..)
| ty::Infer(..)
| ty::Error(_) => false,
| ty::Error(_) => {
if tail.has_infer_types() {
candidate_set.mark_ambiguous();
}
false
},
}
}
super::ImplSource::Param(..) => {
Expand Down Expand Up @@ -1640,18 +1654,30 @@ fn confirm_pointee_candidate<'cx, 'tcx>(
_: ImplSourcePointeeData,
) -> Progress<'tcx> {
let tcx = selcx.tcx();

let self_ty = selcx.infcx().shallow_resolve(obligation.predicate.self_ty());
let substs = tcx.mk_substs([self_ty.into()].iter());

let mut obligations = vec![];
let metadata_ty = self_ty.ptr_metadata_ty(tcx, |ty| {
normalize_with_depth_to(
selcx,
obligation.param_env,
obligation.cause.clone(),
obligation.recursion_depth + 1,
ty,
&mut obligations,
)
});

let substs = tcx.mk_substs([self_ty.into()].iter());
let metadata_def_id = tcx.require_lang_item(LangItem::Metadata, None);

let predicate = ty::ProjectionPredicate {
projection_ty: ty::ProjectionTy { substs, item_def_id: metadata_def_id },
ty: self_ty.ptr_metadata_ty(tcx),
ty: metadata_ty,
};

confirm_param_env_candidate(selcx, obligation, ty::Binder::dummy(predicate), false)
.with_addl_obligations(obligations)
}

fn confirm_fn_pointer_candidate<'cx, 'tcx>(
Expand Down
22 changes: 22 additions & 0 deletions src/test/ui/traits/pointee-deduction.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,22 @@
// run-pass

#![feature(ptr_metadata)]

use std::alloc::Layout;
use std::ptr::Pointee;

trait Foo {
type Bar;
}

impl Foo for () {
type Bar = ();
}

struct Wrapper1<T: Foo>(<T as Foo>::Bar);
struct Wrapper2<T: Foo>(<Wrapper1<T> as Pointee>::Metadata);

fn main() {
let _: Wrapper2<()> = Wrapper2(());
let _ = Layout::new::<Wrapper2<()>>();
}

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