Rollup merge of rust-lang#117586 - compiler-errors:the-canonicalizer, r=lcnr

Uplift the (new solver) canonicalizer into `rustc_next_trait_solver`

Uplifts the new trait solver's canonicalizer into a new crate called `rustc_next_trait_solver`.

The crate name is literally a bikeshed-avoidance name, so let's not block this PR on that -- renames are welcome later.

There are a host of other changes that were required to make this possible:
* Expose a `ConstTy` trait to get the `Interner::Ty` from a `Interner::Const`.
* Expose some constructor methods to construct `Bound` variants. These are currently methods defined on the interner themselves, but they could be pulled into traits later.
* Expose a `IntoKind` trait to turn a `Ty`/`Const`/`Region` into their corresponding `*Kind`s.
* Some minor tweaks to other APIs in `rustc_type_ir`.

The canonicalizer code itself is best reviewed **with whitespace ignored.**

r? `@lcnr`

Author: compiler-errors

Cargo.lock

@@ -4308,6 +4308,13 @@ dependencies = [
  "tracing",
 ]
 
+[[package]]
+name = "rustc_next_trait_solver"
+version = "0.0.0"
+dependencies = [
+ "rustc_type_ir",
+]
+
 [[package]]
 name = "rustc_parse"
 version = "0.0.0"
@@ -4576,6 +4583,7 @@ dependencies = [
  "rustc_infer",
  "rustc_macros",
  "rustc_middle",
+ "rustc_next_trait_solver",
  "rustc_parse_format",
  "rustc_query_system",
  "rustc_session",

compiler/rustc_infer/src/infer/mod.rs

@@ -345,37 +345,61 @@ pub struct InferCtxt<'tcx> {
 impl<'tcx> ty::InferCtxtLike for InferCtxt<'tcx> {
     type Interner = TyCtxt<'tcx>;
 
-    fn universe_of_ty(&self, ty: ty::InferTy) -> Option<ty::UniverseIndex> {
-        use InferTy::*;
-        match ty {
-            // FIXME(BoxyUwU): this is kind of jank and means that printing unresolved
-            // ty infers will give you the universe of the var it resolved to not the universe
-            // it actually had. It also means that if you have a `?0.1` and infer it to `u8` then
-            // try to print out `?0.1` it will just print `?0`.
-            TyVar(ty_vid) => match self.probe_ty_var(ty_vid) {
-                Err(universe) => Some(universe),
-                Ok(_) => None,
-            },
-            IntVar(_) | FloatVar(_) | FreshTy(_) | FreshIntTy(_) | FreshFloatTy(_) => None,
+    fn interner(&self) -> TyCtxt<'tcx> {
+        self.tcx
+    }
+
+    fn universe_of_ty(&self, vid: TyVid) -> Option<ty::UniverseIndex> {
+        // FIXME(BoxyUwU): this is kind of jank and means that printing unresolved
+        // ty infers will give you the universe of the var it resolved to not the universe
+        // it actually had. It also means that if you have a `?0.1` and infer it to `u8` then
+        // try to print out `?0.1` it will just print `?0`.
+        match self.probe_ty_var(vid) {
+            Err(universe) => Some(universe),
+            Ok(_) => None,
         }
     }
 
-    fn universe_of_ct(&self, ct: ty::InferConst) -> Option<ty::UniverseIndex> {
-        use ty::InferConst::*;
-        match ct {
-            // Same issue as with `universe_of_ty`
-            Var(ct_vid) => match self.probe_const_var(ct_vid) {
-                Err(universe) => Some(universe),
-                Ok(_) => None,
-            },
-            EffectVar(_) => None,
-            Fresh(_) => None,
+    fn universe_of_ct(&self, ct: ConstVid) -> Option<ty::UniverseIndex> {
+        // Same issue as with `universe_of_ty`
+        match self.probe_const_var(ct) {
+            Err(universe) => Some(universe),
+            Ok(_) => None,
         }
     }
 
     fn universe_of_lt(&self, lt: ty::RegionVid) -> Option<ty::UniverseIndex> {
         Some(self.universe_of_region_vid(lt))
     }
+
+    fn root_ty_var(&self, vid: TyVid) -> TyVid {
+        self.root_var(vid)
+    }
+
+    fn probe_ty_var(&self, vid: TyVid) -> Option<Ty<'tcx>> {
+        self.probe_ty_var(vid).ok()
+    }
+
+    fn root_lt_var(&self, vid: ty::RegionVid) -> ty::RegionVid {
+        self.root_region_var(vid)
+    }
+
+    fn probe_lt_var(&self, vid: ty::RegionVid) -> Option<ty::Region<'tcx>> {
+        let re = self
+            .inner
+            .borrow_mut()
+            .unwrap_region_constraints()
+            .opportunistic_resolve_var(self.tcx, vid);
+        if re.is_var() { None } else { Some(re) }
+    }
+
+    fn root_ct_var(&self, vid: ConstVid) -> ConstVid {
+        self.root_const_var(vid)
+    }
+
+    fn probe_ct_var(&self, vid: ConstVid) -> Option<ty::Const<'tcx>> {
+        self.probe_const_var(vid).ok()
+    }
 }
 
 /// See the `error_reporting` module for more details.
@@ -1347,6 +1371,10 @@ impl<'tcx> InferCtxt<'tcx> {
         self.inner.borrow_mut().type_variables().root_var(var)
     }
 
+    pub fn root_region_var(&self, var: ty::RegionVid) -> ty::RegionVid {
+        self.inner.borrow_mut().unwrap_region_constraints().root_var(var)
+    }
+
     pub fn root_const_var(&self, var: ty::ConstVid) -> ty::ConstVid {
         self.inner.borrow_mut().const_unification_table().find(var).vid
     }

compiler/rustc_infer/src/infer/region_constraints/mod.rs

@@ -623,6 +623,11 @@ impl<'tcx> RegionConstraintCollector<'_, 'tcx> {
         }
     }
 
+    pub fn root_var(&mut self, vid: ty::RegionVid) -> ty::RegionVid {
+        let mut ut = self.unification_table_mut(); // FIXME(rust-lang/ena#42): unnecessary mut
+        ut.find(vid).vid
+    }
+
     fn combine_map(&mut self, t: CombineMapType) -> &mut CombineMap<'tcx> {
         match t {
             Glb => &mut self.glbs,

compiler/rustc_middle/src/ty/consts.rs

@@ -1,6 +1,8 @@
 use crate::middle::resolve_bound_vars as rbv;
 use crate::mir::interpret::{AllocId, ErrorHandled, LitToConstInput, Scalar};
-use crate::ty::{self, GenericArgs, ParamEnv, ParamEnvAnd, Ty, TyCtxt, TypeVisitableExt};
+use crate::ty::{
+    self, ConstTy, GenericArgs, IntoKind, ParamEnv, ParamEnvAnd, Ty, TyCtxt, TypeVisitableExt,
+};
 use rustc_data_structures::intern::Interned;
 use rustc_error_messages::MultiSpan;
 use rustc_hir as hir;
@@ -26,6 +28,20 @@ use super::sty::ConstKind;
 #[rustc_pass_by_value]
 pub struct Const<'tcx>(pub(super) Interned<'tcx, WithCachedTypeInfo<ConstData<'tcx>>>);
 
+impl<'tcx> IntoKind for Const<'tcx> {
+    type Kind = ConstKind<'tcx>;
+
+    fn kind(self) -> ConstKind<'tcx> {
+        self.kind().clone()
+    }
+}
+
+impl<'tcx> ConstTy<TyCtxt<'tcx>> for Const<'tcx> {
+    fn ty(self) -> Ty<'tcx> {
+        self.ty()
+    }
+}
+
 /// Typed constant value.
 #[derive(PartialEq, Eq, PartialOrd, Ord, Hash, HashStable, TyEncodable, TyDecodable)]
 pub struct ConstData<'tcx> {

compiler/rustc_middle/src/ty/context.rs

@@ -130,6 +130,31 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
     ) -> (Self::Ty, ty::Mutability) {
         (ty, mutbl)
     }
+
+    fn mk_canonical_var_infos(self, infos: &[ty::CanonicalVarInfo<Self>]) -> Self::CanonicalVars {
+        self.mk_canonical_var_infos(infos)
+    }
+
+    fn mk_bound_ty(self, debruijn: ty::DebruijnIndex, var: ty::BoundVar) -> Self::Ty {
+        Ty::new_bound(self, debruijn, ty::BoundTy { var, kind: ty::BoundTyKind::Anon })
+    }
+
+    fn mk_bound_region(self, debruijn: ty::DebruijnIndex, var: ty::BoundVar) -> Self::Region {
+        Region::new_bound(
+            self,
+            debruijn,
+            ty::BoundRegion { var, kind: ty::BoundRegionKind::BrAnon },
+        )
+    }
+
+    fn mk_bound_const(
+        self,
+        debruijn: ty::DebruijnIndex,
+        var: ty::BoundVar,
+        ty: Self::Ty,
+    ) -> Self::Const {
+        Const::new_bound(self, debruijn, var, ty)
+    }
 }
 
 type InternedSet<'tcx, T> = ShardedHashMap<InternedInSet<'tcx, T>, ()>;

compiler/rustc_middle/src/ty/mod.rs

@@ -65,15 +65,10 @@ use std::ops::ControlFlow;
 use std::{fmt, str};
 
 pub use crate::ty::diagnostics::*;
-pub use rustc_type_ir::AliasKind::*;
 pub use rustc_type_ir::ConstKind::{
     Bound as BoundCt, Error as ErrorCt, Expr as ExprCt, Infer as InferCt, Param as ParamCt,
     Placeholder as PlaceholderCt, Unevaluated, Value,
 };
-pub use rustc_type_ir::DynKind::*;
-pub use rustc_type_ir::InferTy::*;
-pub use rustc_type_ir::RegionKind::*;
-pub use rustc_type_ir::TyKind::*;
 pub use rustc_type_ir::*;
 
 pub use self::binding::BindingMode;
@@ -474,6 +469,14 @@ pub struct CReaderCacheKey {
 #[rustc_pass_by_value]
 pub struct Ty<'tcx>(Interned<'tcx, WithCachedTypeInfo<TyKind<'tcx>>>);
 
+impl<'tcx> IntoKind for Ty<'tcx> {
+    type Kind = TyKind<'tcx>;
+
+    fn kind(self) -> TyKind<'tcx> {
+        self.kind().clone()
+    }
+}
+
 impl EarlyParamRegion {
     /// Does this early bound region have a name? Early bound regions normally
     /// always have names except when using anonymous lifetimes (`'_`).
@@ -1506,34 +1509,42 @@ pub struct Placeholder<T> {
 
 pub type PlaceholderRegion = Placeholder<BoundRegion>;
 
-impl rustc_type_ir::Placeholder for PlaceholderRegion {
-    fn universe(&self) -> UniverseIndex {
+impl PlaceholderLike for PlaceholderRegion {
+    fn universe(self) -> UniverseIndex {
         self.universe
     }
 
-    fn var(&self) -> BoundVar {
+    fn var(self) -> BoundVar {
         self.bound.var
     }
 
     fn with_updated_universe(self, ui: UniverseIndex) -> Self {
         Placeholder { universe: ui, ..self }
     }
+
+    fn new(ui: UniverseIndex, var: BoundVar) -> Self {
+        Placeholder { universe: ui, bound: BoundRegion { var, kind: BoundRegionKind::BrAnon } }
+    }
 }
 
 pub type PlaceholderType = Placeholder<BoundTy>;
 
-impl rustc_type_ir::Placeholder for PlaceholderType {
-    fn universe(&self) -> UniverseIndex {
+impl PlaceholderLike for PlaceholderType {
+    fn universe(self) -> UniverseIndex {
         self.universe
     }
 
-    fn var(&self) -> BoundVar {
+    fn var(self) -> BoundVar {
         self.bound.var
     }
 
     fn with_updated_universe(self, ui: UniverseIndex) -> Self {
         Placeholder { universe: ui, ..self }
     }
+
+    fn new(ui: UniverseIndex, var: BoundVar) -> Self {
+        Placeholder { universe: ui, bound: BoundTy { var, kind: BoundTyKind::Anon } }
+    }
 }
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable)]
@@ -1545,18 +1556,22 @@ pub struct BoundConst<'tcx> {
 
 pub type PlaceholderConst = Placeholder<BoundVar>;
 
-impl rustc_type_ir::Placeholder for PlaceholderConst {
-    fn universe(&self) -> UniverseIndex {
+impl PlaceholderLike for PlaceholderConst {
+    fn universe(self) -> UniverseIndex {
         self.universe
     }
 
-    fn var(&self) -> BoundVar {
+    fn var(self) -> BoundVar {
         self.bound
     }
 
     fn with_updated_universe(self, ui: UniverseIndex) -> Self {
         Placeholder { universe: ui, ..self }
     }
+
+    fn new(ui: UniverseIndex, var: BoundVar) -> Self {
+        Placeholder { universe: ui, bound: var }
+    }
 }
 
 /// When type checking, we use the `ParamEnv` to track

compiler/rustc_middle/src/ty/sty.rs

@@ -6,7 +6,7 @@ use crate::infer::canonical::Canonical;
 use crate::ty::visit::ValidateBoundVars;
 use crate::ty::InferTy::*;
 use crate::ty::{
-    self, AdtDef, Discr, Term, Ty, TyCtxt, TypeFlags, TypeSuperVisitable, TypeVisitable,
+    self, AdtDef, Discr, IntoKind, Term, Ty, TyCtxt, TypeFlags, TypeSuperVisitable, TypeVisitable,
     TypeVisitableExt, TypeVisitor,
 };
 use crate::ty::{GenericArg, GenericArgs, GenericArgsRef};
@@ -1477,6 +1477,14 @@ impl ParamConst {
 #[rustc_pass_by_value]
 pub struct Region<'tcx>(pub Interned<'tcx, RegionKind<'tcx>>);
 
+impl<'tcx> IntoKind for Region<'tcx> {
+    type Kind = RegionKind<'tcx>;
+
+    fn kind(self) -> RegionKind<'tcx> {
+        *self
+    }
+}
+
 impl<'tcx> Region<'tcx> {
     #[inline]
     pub fn new_early_param(

compiler/rustc_next_trait_solver/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "rustc_next_trait_solver"
+version = "0.0.0"
+edition = "2021"
+
+[dependencies]
+rustc_type_ir = { path = "../rustc_type_ir", default-features = false }
+
+[features]
+default = ["nightly"]
+nightly = [
+    "rustc_type_ir/nightly",
+]