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

Expand the automatic implementation of `MetaSized` and `PointeeSized` so
that it is also implemented on non-`Sized` types, just not `ty::Foreign`
(extern type).

5 files changed, 60 insertions, 111 deletions

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 434e2a818bd..a300558c0c9 100644
--- a/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs
@@ -8,6 +8,7 @@ use std::ops::ControlFlow;
 use derive_where::derive_where;
 use rustc_type_ir::inherent::*;
 use rustc_type_ir::lang_items::TraitSolverLangItem;
+use rustc_type_ir::solve::SizedTraitKind;
 use rustc_type_ir::{
     self as ty, Interner, TypeFoldable, TypeSuperVisitable, TypeVisitable, TypeVisitableExt as _,
     TypeVisitor, TypingMode, Upcast as _, elaborate,
@@ -203,31 +204,15 @@ where
         goal: Goal<I, Self>,
     ) -> Result<Candidate<I>, NoSolution>;
 
-    /// A type is `Sized` if its tail component is `Sized`.
+    /// A type is `Sized` if its tail component is `Sized` and 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_sized_candidate(
-        ecx: &mut EvalCtxt<'_, D>,
-        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(
+    /// [`structural_traits::instantiate_constituent_tys_for_sizedness_trait`].
+    fn consider_builtin_sizedness_candidates(
         ecx: &mut EvalCtxt<'_, D>,
         goal: Goal<I, Self>,
+        sizedness: SizedTraitKind,
     ) -> Result<Candidate<I>, NoSolution>;
 
     /// A type is `Copy` or `Clone` if its components are `Copy` or `Clone`.
@@ -484,12 +469,14 @@ where
             G::consider_trait_alias_candidate(self, goal)
         } else {
             match cx.as_lang_item(trait_def_id) {
-                Some(TraitSolverLangItem::Sized) => G::consider_builtin_sized_candidate(self, goal),
+                Some(TraitSolverLangItem::Sized) => {
+                    G::consider_builtin_sizedness_candidates(self, goal, SizedTraitKind::Sized)
+                }
                 Some(TraitSolverLangItem::MetaSized) => {
-                    G::consider_builtin_meta_sized_candidate(self, goal)
+                    G::consider_builtin_sizedness_candidates(self, goal, SizedTraitKind::MetaSized)
                 }
                 Some(TraitSolverLangItem::PointeeSized) => {
-                    G::consider_builtin_pointee_sized_candidate(self, goal)
+                    unreachable!("`PointeeSized` is removed during lowering");
                 }
                 Some(TraitSolverLangItem::Copy | TraitSolverLangItem::Clone) => {
                     G::consider_builtin_copy_clone_candidate(self, goal)
diff --git a/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs b/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
index 4a2a7761f7f..f39d3226009 100644
--- a/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
@@ -5,6 +5,7 @@ use derive_where::derive_where;
 use rustc_type_ir::data_structures::HashMap;
 use rustc_type_ir::inherent::*;
 use rustc_type_ir::lang_items::TraitSolverLangItem;
+use rustc_type_ir::solve::SizedTraitKind;
 use rustc_type_ir::solve::inspect::ProbeKind;
 use rustc_type_ir::{
     self as ty, FallibleTypeFolder, Interner, Movability, Mutability, TypeFoldable,
@@ -104,8 +105,9 @@ where
 }
 
 #[instrument(level = "trace", skip(ecx), ret)]
-pub(in crate::solve) fn instantiate_constituent_tys_for_sized_trait<D, I>(
+pub(in crate::solve) fn instantiate_constituent_tys_for_sizedness_trait<D, I>(
     ecx: &EvalCtxt<'_, D>,
+    sizedness: SizedTraitKind,
     ty: I::Ty,
 ) -> Result<ty::Binder<I, Vec<I::Ty>>, NoSolution>
 where
@@ -113,8 +115,9 @@ where
     I: Interner,
 {
     match ty.kind() {
-        // impl Sized for u*, i*, bool, f*, FnDef, FnPtr, *(const/mut) T, char, &mut? T, [T; N], dyn* Trait, !
-        // impl Sized for Coroutine, CoroutineWitness, Closure, CoroutineClosure
+        // impl {Meta,}Sized for u*, i*, bool, f*, FnDef, FnPtr, *(const/mut) T, char
+        // impl {Meta,}Sized for &mut? T, [T; N], dyn* Trait, !, Coroutine, CoroutineWitness
+        // impl {Meta,}Sized for Closure, CoroutineClosure
         ty::Infer(ty::IntVar(_) | ty::FloatVar(_))
         | ty::Uint(_)
         | ty::Int(_)
@@ -135,13 +138,16 @@ where
         | ty::Dynamic(_, _, ty::DynStar)
         | ty::Error(_) => Ok(ty::Binder::dummy(vec![])),
 
-        ty::Str
-        | ty::Slice(_)
-        | ty::Dynamic(..)
-        | ty::Foreign(..)
-        | ty::Alias(..)
-        | ty::Param(_)
-        | ty::Placeholder(..) => Err(NoSolution),
+        // impl {Meta,}Sized for str, [T], dyn Trait
+        ty::Str | ty::Slice(_) | ty::Dynamic(..) => match sizedness {
+            SizedTraitKind::Sized => Err(NoSolution),
+            SizedTraitKind::MetaSized => Ok(ty::Binder::dummy(vec![])),
+        },
+
+        // impl {} for extern type
+        ty::Foreign(..) => Err(NoSolution),
+
+        ty::Alias(..) | ty::Param(_) | ty::Placeholder(..) => Err(NoSolution),
 
         ty::Bound(..)
         | ty::Infer(ty::TyVar(_) | ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => {
@@ -150,22 +156,27 @@ where
 
         ty::UnsafeBinder(bound_ty) => Ok(bound_ty.map_bound(|ty| vec![ty])),
 
-        // impl Sized for ()
-        // impl Sized for (T1, T2, .., Tn) where Tn: Sized if n >= 1
+        // impl {Meta,}Sized for ()
+        // impl {Meta,}Sized for (T1, T2, .., Tn) where Tn: {Meta,}Sized if n >= 1
         ty::Tuple(tys) => Ok(ty::Binder::dummy(tys.last().map_or_else(Vec::new, |ty| vec![ty]))),
 
-        // impl Sized for Adt<Args...> where sized_constraint(Adt)<Args...>: Sized
-        //   `sized_constraint(Adt)` is the deepest struct trail that can be determined
-        //   by the definition of `Adt`, independent of the generic args.
-        // impl Sized for Adt<Args...> if sized_constraint(Adt) == None
-        //   As a performance optimization, `sized_constraint(Adt)` can return `None`
-        //   if the ADTs definition implies that it is sized by for all possible args.
+        // impl {Meta,}Sized for Adt<Args...>
+        //   where {meta,pointee,}sized_constraint(Adt)<Args...>: {Meta,}Sized
+        //
+        //   `{meta,pointee,}sized_constraint(Adt)` is the deepest struct trail that can be
+        //   determined by the definition of `Adt`, independent of the generic args.
+        //
+        // impl {Meta,}Sized for Adt<Args...>
+        //   if {meta,pointee,}sized_constraint(Adt) == None
+        //
+        //   As a performance optimization, `{meta,pointee,}sized_constraint(Adt)` can return `None`
+        //   if the ADTs definition implies that it is {meta,}sized by for all possible args.
         //   In this case, the builtin impl will have no nested subgoals. This is a
-        //   "best effort" optimization and `sized_constraint` may return `Some`, even
-        //   if the ADT is sized for all possible args.
+        //   "best effort" optimization and `{meta,pointee,}sized_constraint` may return `Some`,
+        //   even if the ADT is {meta,pointee,}sized for all possible args.
         ty::Adt(def, args) => {
-            if let Some(sized_crit) = def.sized_constraint(ecx.cx()) {
-                Ok(ty::Binder::dummy(vec![sized_crit.instantiate(ecx.cx(), args)]))
+            if let Some(crit) = def.sizedness_constraint(ecx.cx(), sizedness) {
+                Ok(ty::Binder::dummy(vec![crit.instantiate(ecx.cx(), args)]))
             } else {
                 Ok(ty::Binder::dummy(vec![]))
             }
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 dda00a0a2c5..1690c908d12 100644
--- a/compiler/rustc_next_trait_solver/src/solve/effect_goals.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/effect_goals.rs
@@ -4,6 +4,7 @@
 use rustc_type_ir::fast_reject::DeepRejectCtxt;
 use rustc_type_ir::inherent::*;
 use rustc_type_ir::lang_items::TraitSolverLangItem;
+use rustc_type_ir::solve::SizedTraitKind;
 use rustc_type_ir::solve::inspect::ProbeKind;
 use rustc_type_ir::{self as ty, Interner, elaborate};
 use tracing::instrument;
@@ -198,25 +199,12 @@ where
         unreachable!("trait aliases are never const")
     }
 
-    fn consider_builtin_sized_candidate(
+    fn consider_builtin_sizedness_candidates(
         _ecx: &mut EvalCtxt<'_, D>,
         _goal: Goal<I, Self>,
+        _sizedness: SizedTraitKind,
     ) -> Result<Candidate<I>, NoSolution> {
-        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")
+        unreachable!("Sized/MetaSized is never const")
     }
 
     fn consider_builtin_copy_clone_candidate(
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 42aeb170d6b..d51c87fe68e 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
@@ -6,6 +6,7 @@ mod opaque_types;
 use rustc_type_ir::fast_reject::DeepRejectCtxt;
 use rustc_type_ir::inherent::*;
 use rustc_type_ir::lang_items::TraitSolverLangItem;
+use rustc_type_ir::solve::SizedTraitKind;
 use rustc_type_ir::{self as ty, Interner, NormalizesTo, PredicateKind, Upcast as _};
 use tracing::instrument;
 
@@ -413,25 +414,12 @@ where
         panic!("trait aliases do not have associated types: {:?}", goal);
     }
 
-    fn consider_builtin_sized_candidate(
+    fn consider_builtin_sizedness_candidates(
         _ecx: &mut EvalCtxt<'_, D>,
         goal: Goal<I, Self>,
+        _sizedness: SizedTraitKind,
     ) -> Result<Candidate<I>, NoSolution> {
-        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);
+        panic!("`Sized`/`MetaSized` does not have an associated type: {:?}", goal);
     }
 
     fn consider_builtin_copy_clone_candidate(
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 50a7647be62..a8bbc2d60f1 100644
--- a/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
@@ -4,7 +4,7 @@ use rustc_type_ir::data_structures::IndexSet;
 use rustc_type_ir::fast_reject::DeepRejectCtxt;
 use rustc_type_ir::inherent::*;
 use rustc_type_ir::lang_items::TraitSolverLangItem;
-use rustc_type_ir::solve::CanonicalResponse;
+use rustc_type_ir::solve::{CanonicalResponse, SizedTraitKind};
 use rustc_type_ir::{
     self as ty, Interner, Movability, TraitPredicate, TypeVisitableExt as _, TypingMode,
     Upcast as _, elaborate,
@@ -245,9 +245,10 @@ where
         })
     }
 
-    fn consider_builtin_sized_candidate(
+    fn consider_builtin_sizedness_candidates(
         ecx: &mut EvalCtxt<'_, D>,
         goal: Goal<I, Self>,
+        sizedness: SizedTraitKind,
     ) -> Result<Candidate<I>, NoSolution> {
         if goal.predicate.polarity != ty::PredicatePolarity::Positive {
             return Err(NoSolution);
@@ -256,37 +257,11 @@ where
         ecx.probe_and_evaluate_goal_for_constituent_tys(
             CandidateSource::BuiltinImpl(BuiltinImplSource::Trivial),
             goal,
-            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> {
-        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,
+            |ecx, ty| {
+                structural_traits::instantiate_constituent_tys_for_sizedness_trait(
+                    ecx, sizedness, ty,
+                )
+            },
         )
     }