trait_sel: `{Meta,Pointee}Sized` on `Sized` types

Introduce the `MetaSized` and `PointeeSized` traits as supertraits of
`Sized` and initially implement it on everything that currently
implements `Sized` to isolate any changes that simply adding the
traits introduces.

11 files changed, 101 insertions, 0 deletions

diff --git a/compiler/rustc_feature/src/unstable.rs b/compiler/rustc_feature/src/unstable.rs
index bd6ea850147..5e42b919f9d 100644
--- a/compiler/rustc_feature/src/unstable.rs
+++ b/compiler/rustc_feature/src/unstable.rs
@@ -237,6 +237,8 @@ declare_features! (
     (internal, profiler_runtime, "1.18.0", None),
     /// Allows using `rustc_*` attributes (RFC 572).
     (internal, rustc_attrs, "1.0.0", None),
+    /// Introduces a hierarchy of `Sized` traits (RFC 3729).
+    (unstable, sized_hierarchy, "CURRENT_RUSTC_VERSION", None),
     /// Allows using the `#[stable]` and `#[unstable]` attributes.
     (internal, staged_api, "1.0.0", None),
     /// Added for testing unstable lints; perma-unstable.
diff --git a/compiler/rustc_hir/src/lang_items.rs b/compiler/rustc_hir/src/lang_items.rs
index 21d36ed54cd..3a08e5ae336 100644
--- a/compiler/rustc_hir/src/lang_items.rs
+++ b/compiler/rustc_hir/src/lang_items.rs
@@ -165,6 +165,8 @@ pub fn extract(attrs: &[impl AttributeExt]) -> Option<(Symbol, Span)> {
 language_item_table! {
 //  Variant name,            Name,                     Getter method name,         Target                  Generic requirements;
     Sized,                   sym::sized,               sized_trait,                Target::Trait,          GenericRequirement::Exact(0);
+    MetaSized,               sym::meta_sized,          meta_sized_trait,           Target::Trait,          GenericRequirement::Exact(0);
+    PointeeSized,            sym::pointee_sized,       pointee_sized_trait,        Target::Trait,          GenericRequirement::Exact(0);
     Unsize,                  sym::unsize,              unsize_trait,               Target::Trait,          GenericRequirement::Minimum(1);
     /// Trait injected by `#[derive(PartialEq)]`, (i.e. "Partial EQ").
     StructuralPeq,           sym::structural_peq,      structural_peq_trait,       Target::Trait,          GenericRequirement::None;
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index fe4dd8d080b..6565d09936f 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -774,7 +774,9 @@ bidirectional_lang_item_map! {
     FutureOutput,
     Iterator,
     Metadata,
+    MetaSized,
     Option,
+    PointeeSized,
     PointeeTrait,
     Poll,
     Sized,
diff --git a/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs b/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs
index 0c267feefbe..434e2a818bd 100644
--- a/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs
@@ -212,6 +212,24 @@ where
         goal: Goal<I, Self>,
     ) -> Result<Candidate<I>, NoSolution>;
 
+    /// A type is `MetaSized` if its tail component is `MetaSized`.
+    ///
+    /// These components are given by built-in rules from
+    /// [`structural_traits::instantiate_constituent_tys_for_sized_trait`].
+    fn consider_builtin_meta_sized_candidate(
+        ecx: &mut EvalCtxt<'_, D>,
+        goal: Goal<I, Self>,
+    ) -> Result<Candidate<I>, NoSolution>;
+
+    /// A type is `PointeeSized` if its tail component is `PointeeSized`.
+    ///
+    /// These components are given by built-in rules from
+    /// [`structural_traits::instantiate_constituent_tys_for_sized_trait`].
+    fn consider_builtin_pointee_sized_candidate(
+        ecx: &mut EvalCtxt<'_, D>,
+        goal: Goal<I, Self>,
+    ) -> Result<Candidate<I>, NoSolution>;
+
     /// A type is `Copy` or `Clone` if its components are `Copy` or `Clone`.
     ///
     /// These components are given by built-in rules from
@@ -467,6 +485,12 @@ where
         } else {
             match cx.as_lang_item(trait_def_id) {
                 Some(TraitSolverLangItem::Sized) => G::consider_builtin_sized_candidate(self, goal),
+                Some(TraitSolverLangItem::MetaSized) => {
+                    G::consider_builtin_meta_sized_candidate(self, goal)
+                }
+                Some(TraitSolverLangItem::PointeeSized) => {
+                    G::consider_builtin_pointee_sized_candidate(self, goal)
+                }
                 Some(TraitSolverLangItem::Copy | TraitSolverLangItem::Clone) => {
                     G::consider_builtin_copy_clone_candidate(self, goal)
                 }
diff --git a/compiler/rustc_next_trait_solver/src/solve/effect_goals.rs b/compiler/rustc_next_trait_solver/src/solve/effect_goals.rs
index 8413c2abbb9..dda00a0a2c5 100644
--- a/compiler/rustc_next_trait_solver/src/solve/effect_goals.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/effect_goals.rs
@@ -205,6 +205,20 @@ where
         unreachable!("Sized is never const")
     }
 
+    fn consider_builtin_meta_sized_candidate(
+        _ecx: &mut EvalCtxt<'_, D>,
+        _goal: Goal<I, Self>,
+    ) -> Result<Candidate<I>, NoSolution> {
+        unreachable!("MetaSized is never const")
+    }
+
+    fn consider_builtin_pointee_sized_candidate(
+        _ecx: &mut EvalCtxt<'_, D>,
+        _goal: Goal<I, Self>,
+    ) -> Result<Candidate<I>, NoSolution> {
+        unreachable!("PointeeSized is never const")
+    }
+
     fn consider_builtin_copy_clone_candidate(
         _ecx: &mut EvalCtxt<'_, D>,
         _goal: Goal<I, Self>,
diff --git a/compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs b/compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs
index 2fddc0044cb..42aeb170d6b 100644
--- a/compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs
@@ -420,6 +420,20 @@ where
         panic!("`Sized` does not have an associated type: {:?}", goal);
     }
 
+    fn consider_builtin_meta_sized_candidate(
+        _ecx: &mut EvalCtxt<'_, D>,
+        goal: Goal<I, Self>,
+    ) -> Result<Candidate<I>, NoSolution> {
+        panic!("`MetaSized` does not have an associated type: {:?}", goal);
+    }
+
+    fn consider_builtin_pointee_sized_candidate(
+        _ecx: &mut EvalCtxt<'_, D>,
+        goal: Goal<I, Self>,
+    ) -> Result<Candidate<I>, NoSolution> {
+        panic!("`PointeeSized` does not have an associated type: {:?}", goal);
+    }
+
     fn consider_builtin_copy_clone_candidate(
         _ecx: &mut EvalCtxt<'_, D>,
         goal: Goal<I, Self>,
diff --git a/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs b/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
index 110c67a8e21..50a7647be62 100644
--- a/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
@@ -260,6 +260,36 @@ where
         )
     }
 
+    fn consider_builtin_meta_sized_candidate(
+        ecx: &mut EvalCtxt<'_, D>,
+        goal: Goal<I, Self>,
+    ) -> Result<Candidate<I>, NoSolution> {
+        if goal.predicate.polarity != ty::PredicatePolarity::Positive {
+            return Err(NoSolution);
+        }
+
+        ecx.probe_and_evaluate_goal_for_constituent_tys(
+            CandidateSource::BuiltinImpl(BuiltinImplSource::Misc),
+            goal,
+            structural_traits::instantiate_constituent_tys_for_sized_trait,
+        )
+    }
+
+    fn consider_builtin_pointee_sized_candidate(
+        ecx: &mut EvalCtxt<'_, D>,
+        goal: Goal<I, Self>,
+    ) -> Result<Candidate<I>, NoSolution> {
+        if goal.predicate.polarity != ty::PredicatePolarity::Positive {
+            return Err(NoSolution);
+        }
+
+        ecx.probe_and_evaluate_goal_for_constituent_tys(
+            CandidateSource::BuiltinImpl(BuiltinImplSource::Misc),
+            goal,
+            structural_traits::instantiate_constituent_tys_for_sized_trait,
+        )
+    }
+
     fn consider_builtin_copy_clone_candidate(
         ecx: &mut EvalCtxt<'_, D>,
         goal: Goal<I, Self>,
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index cb9ccf4cc3f..baadff16120 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -1355,6 +1355,7 @@ symbols! {
         memtag,
         message,
         meta,
+        meta_sized,
         metadata_type,
         min_const_fn,
         min_const_generics,
@@ -1613,6 +1614,7 @@ symbols! {
         plugin_registrar,
         plugins,
         pointee,
+        pointee_sized,
         pointee_trait,
         pointer,
         pointer_like,
@@ -2016,6 +2018,7 @@ symbols! {
         size_of,
         size_of_val,
         sized,
+        sized_hierarchy,
         skip,
         slice,
         slice_from_raw_parts,
diff --git a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
index 97ecf9702e6..93ffea3b031 100644
--- a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
@@ -89,6 +89,12 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 Some(LangItem::Sized) => {
                     self.assemble_builtin_sized_candidate(obligation, &mut candidates);
                 }
+                Some(LangItem::MetaSized) => {
+                    self.assemble_builtin_sized_candidate(obligation, &mut candidates);
+                }
+                Some(LangItem::PointeeSized) => {
+                    self.assemble_builtin_sized_candidate(obligation, &mut candidates);
+                }
                 Some(LangItem::Unsize) => {
                     self.assemble_candidates_for_unsizing(obligation, &mut candidates);
                 }
diff --git a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
index 786afd7cf48..93d3e3ba2a8 100644
--- a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
@@ -252,6 +252,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             let trait_def = obligation.predicate.def_id();
             let conditions = match tcx.as_lang_item(trait_def) {
                 Some(LangItem::Sized) => self.sized_conditions(obligation),
+                Some(LangItem::MetaSized) => self.sized_conditions(obligation),
+                Some(LangItem::PointeeSized) => self.sized_conditions(obligation),
                 Some(LangItem::Copy | LangItem::Clone) => self.copy_clone_conditions(obligation),
                 Some(LangItem::FusedIterator) => self.fused_iterator_conditions(obligation),
                 other => bug!("unexpected builtin trait {trait_def:?} ({other:?})"),
diff --git a/compiler/rustc_type_ir/src/lang_items.rs b/compiler/rustc_type_ir/src/lang_items.rs
index 699dd82fb22..3ee6e07b7a5 100644
--- a/compiler/rustc_type_ir/src/lang_items.rs
+++ b/compiler/rustc_type_ir/src/lang_items.rs
@@ -30,7 +30,9 @@ pub enum TraitSolverLangItem {
     FutureOutput,
     Iterator,
     Metadata,
+    MetaSized,
     Option,
+    PointeeSized,
     PointeeTrait,
     Poll,
     Sized,