Make unsizing_params_for_adt into a query

compiler/rustc_middle/src/query/mod.rs

@@ -183,6 +183,15 @@ rustc_queries! {
  separate_provide_extern
  }
 
+ query unsizing_params_for_adt(key: DefId) -> rustc_index::bit_set::BitSet<u32>
+ {
+ arena_cache
+ desc { |tcx|
+ "determining what parameters of `{}` can participate in unsizing",
+ tcx.def_path_str(key),
+ }
+ }
+
  query analysis(key: ()) -> Result<(), ErrorGuaranteed> {
  eval_always
  desc { "running analysis passes on this crate" }

compiler/rustc_trait_selection/src/traits/select/confirmation.rs

@@ -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).

compiler/rustc_ty_utils/src/ty.rs

@@ -1,5 +1,6 @@
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir as hir;
+use rustc_index::bit_set::BitSet;
 use rustc_middle::ty::{self, Binder, Predicate, PredicateKind, ToPredicate, Ty, TyCtxt};
 use rustc_session::config::TraitSolver;
 use rustc_span::def_id::{DefId, CRATE_DEF_ID};
@@ -406,6 +407,56 @@ fn asyncness(tcx: TyCtxt<'_>, def_id: DefId) -> hir::IsAsync {
  node.fn_sig().map_or(hir::IsAsync::NotAsync, |sig| sig.header.asyncness)
 }
 
+fn unsizing_params_for_adt<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> BitSet<u32> {
+ let def = tcx.adt_def(def_id);
+ let num_params = tcx.generics_of(def_id).count();
+
+ let maybe_unsizing_param_idx = |arg: ty::GenericArg<'tcx>| match arg.unpack() {
+ ty::GenericArgKind::Type(ty) => match ty.kind() {
+ ty::Param(p) => Some(p.index),
+ _ => None,
+ },
+
+ // We can't unsize a lifetime
+ ty::GenericArgKind::Lifetime(_) => None,
+
+ ty::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 Some((tail_field, prefix_fields)) =
+ def.non_enum_variant().fields.split_last() else
+ {
+ return BitSet::new_empty(num_params);
+ };
+
+ let mut unsizing_params = BitSet::new_empty(num_params);
+ for arg in tcx.bound_type_of(tail_field.did).subst_identity().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.bound_type_of(field.did).subst_identity().walk() {
+ if let Some(i) = maybe_unsizing_param_idx(arg) {
+ unsizing_params.remove(i);
+ }
+ }
+ }
+
+ unsizing_params
+}
+
 pub fn provide(providers: &mut ty::query::Providers) {
  *providers = ty::query::Providers {
  asyncness,
@@ -415,6 +466,7 @@ pub fn provide(providers: &mut ty::query::Providers) {
  instance_def_size_estimate,
  issue33140_self_ty,
  impl_defaultness,
+ unsizing_params_for_adt,
  ..*providers
  };
 }