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Rollup merge of #107146 - compiler-errors:unsizing-params, r=cjgillot

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Make `unsizing_params_for_adt` into a query

Addresses a FIXME in confirmation.

r? ``@ghost``
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Dylan DPC 2023-01-30 15:11:45 +05:30 • committed by GitHub
commit e19ae977ec
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3 changed files with 71 additions and 44 deletions
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54
compiler/rustc_trait_selection/src/traits/select/confirmation.rs
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@ -8,12 +8,11 @@
//! https://rustc-dev-guide.rust-lang.org/traits/resolution.html#confirmation
use rustc_data_structures::stack::ensure_sufficient_stack;
use rustc_hir::lang_items::LangItem;
use rustc_index::bit_set::GrowableBitSet;
use rustc_infer::infer::InferOk;
use rustc_infer::infer::LateBoundRegionConversionTime::HigherRankedType;
use rustc_middle::ty::{
self, Binder, GenericArg, GenericArgKind, GenericParamDefKind, InternalSubsts, SubstsRef,
ToPolyTraitRef, ToPredicate, TraitRef, Ty, TyCtxt, TypeVisitable,
self, Binder, GenericParamDefKind, InternalSubsts, SubstsRef, ToPolyTraitRef, ToPredicate,
TraitRef, Ty, TyCtxt, TypeVisitable,
};
use rustc_session::config::TraitSolver;
use rustc_span::def_id::DefId;
@ -1064,51 +1063,18 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
// `Struct<T>` -> `Struct<U>`
(&ty::Adt(def, substs_a), &ty::Adt(_, substs_b)) => {
let maybe_unsizing_param_idx = |arg: GenericArg<'tcx>| match arg.unpack() {
GenericArgKind::Type(ty) => match ty.kind() {
ty::Param(p) => Some(p.index),
_ => None,
},
// Lifetimes aren't allowed to change during unsizing.
GenericArgKind::Lifetime(_) => None,
GenericArgKind::Const(ct) => match ct.kind() {
ty::ConstKind::Param(p) => Some(p.index),
_ => None,
},
};
// FIXME(eddyb) cache this (including computing `unsizing_params`)
// by putting it in a query; it would only need the `DefId` as it
// looks at declared field types, not anything substituted.
// The last field of the structure has to exist and contain type/const parameters.
let (tail_field, prefix_fields) =
def.non_enum_variant().fields.split_last().ok_or(Unimplemented)?;
let tail_field_ty = tcx.bound_type_of(tail_field.did);
let mut unsizing_params = GrowableBitSet::new_empty();
for arg in tail_field_ty.0.walk() {
if let Some(i) = maybe_unsizing_param_idx(arg) {
unsizing_params.insert(i);
}
}
// Ensure none of the other fields mention the parameters used
// in unsizing.
for field in prefix_fields {
for arg in tcx.type_of(field.did).walk() {
if let Some(i) = maybe_unsizing_param_idx(arg) {
unsizing_params.remove(i);
}
}
}
let unsizing_params = tcx.unsizing_params_for_adt(def.did());
if unsizing_params.is_empty() {
return Err(Unimplemented);
}
let tail_field = def
.non_enum_variant()
.fields
.last()
.expect("expected unsized ADT to have a tail field");
let tail_field_ty = tcx.bound_type_of(tail_field.did);
// Extract `TailField<T>` and `TailField<U>` from `Struct<T>` and `Struct<U>`,
// normalizing in the process, since `type_of` returns something directly from
// astconv (which means it's un-normalized).