Auto merge of #138464 - compiler-errors:less-type-ir, r=lcnr

Use `rustc_type_ir` directly less in the codebase

cc https://github.com/rust-lang/rust/issues/138449

This is a somewhat opinionated bundle of changes that will make working on https://github.com/rust-lang/rust/issues/138449 more easy, since it cuts out the bulk of the changes that would be necessitated by the lint. Namely:

1. Fold `rustc_middle::ty::fold` and `rustc_middle::ty::visit` into `rustc_middle::ty`. This is because we already reexport some parts of these modules into `rustc_middle::ty`, and there's really no benefit from namespacing away the rest of these modules's functionality given how important folding and visiting is to the type layer.
2. Rename `{Decodable,Encodable}_Generic` to `{Decodable,Encodable}_NoContext`[^why], change it to be "perfect derive" (`synstructure::AddBounds::Fields`), use it throughout `rustc_type_ir` instead of `TyEncodable`/`TyDecodable`.
3. Make `TyEncodable` and `TyDecodable` derives use `::rustc_middle::ty::codec::TyEncoder` (etc) for its generated paths, and move the `rustc_type_ir::codec` module back to `rustc_middle::ty::codec` :tada:.
4. Stop using `rustc_type_ir` in crates that aren't "fundamental" to the type system, namely middle/infer/trait-selection. This amounted mostly to changing imports from `use rustc_type_ir::...` to `use rustc_middle::ty::...`, but also this means that we can't glob import `TyKind::*` since the reexport into `rustc_middle::ty::TyKind` is a type alias. Instead, use the prefixed variants like `ty::Str` everywhere -- IMO this is a good change, since it makes it more regularized with most of the rest of the compiler.

[^why]: `_NoContext` is the name for derive macros with no additional generic bounds and which do "perfect derive" by generating bounds based on field types. See `HashStable_NoContext`.

I'm happy to cut out some of these changes into separate PRs to make landing it a bit easier, though I don't expect to have much trouble with bitrot.

r? lcnr

4 files changed, 31 insertions, 34 deletions

diff --git a/compiler/rustc_ty_utils/src/implied_bounds.rs b/compiler/rustc_ty_utils/src/implied_bounds.rs
index aeaa83c77b5..088d5e76b86 100644
--- a/compiler/rustc_ty_utils/src/implied_bounds.rs
+++ b/compiler/rustc_ty_utils/src/implied_bounds.rs
@@ -6,8 +6,7 @@ use rustc_hir::def::DefKind;
 use rustc_hir::def_id::LocalDefId;
 use rustc_middle::bug;
 use rustc_middle::query::Providers;
-use rustc_middle::ty::fold::fold_regions;
-use rustc_middle::ty::{self, Ty, TyCtxt};
+use rustc_middle::ty::{self, Ty, TyCtxt, fold_regions};
 use rustc_span::Span;
 
 pub(crate) fn provide(providers: &mut Providers) {
diff --git a/compiler/rustc_ty_utils/src/instance.rs b/compiler/rustc_ty_utils/src/instance.rs
index 90b3517eded..962e1353ebc 100644
--- a/compiler/rustc_ty_utils/src/instance.rs
+++ b/compiler/rustc_ty_utils/src/instance.rs
@@ -7,11 +7,10 @@ use rustc_middle::query::Providers;
 use rustc_middle::traits::{BuiltinImplSource, CodegenObligationError};
 use rustc_middle::ty::util::AsyncDropGlueMorphology;
 use rustc_middle::ty::{
-    self, GenericArgsRef, Instance, PseudoCanonicalInput, TyCtxt, TypeVisitableExt,
+    self, ClosureKind, GenericArgsRef, Instance, PseudoCanonicalInput, TyCtxt, TypeVisitableExt,
 };
 use rustc_span::sym;
 use rustc_trait_selection::traits;
-use rustc_type_ir::ClosureKind;
 use tracing::debug;
 use traits::translate_args;
 
diff --git a/compiler/rustc_ty_utils/src/sig_types.rs b/compiler/rustc_ty_utils/src/sig_types.rs
index d6f9277813d..5bb96f90029 100644
--- a/compiler/rustc_ty_utils/src/sig_types.rs
+++ b/compiler/rustc_ty_utils/src/sig_types.rs
@@ -4,10 +4,8 @@
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::LocalDefId;
 use rustc_middle::span_bug;
-use rustc_middle::ty::visit::{VisitorResult, try_visit};
-use rustc_middle::ty::{self, TyCtxt};
+use rustc_middle::ty::{self, TyCtxt, TypeVisitable, VisitorResult, try_visit};
 use rustc_span::Span;
-use rustc_type_ir::visit::TypeVisitable;
 use tracing::{instrument, trace};
 
 pub trait SpannedTypeVisitor<'tcx> {
diff --git a/compiler/rustc_ty_utils/src/ty.rs b/compiler/rustc_ty_utils/src/ty.rs
index bb61f4bee66..9dc4f11e456 100644
--- a/compiler/rustc_ty_utils/src/ty.rs
+++ b/compiler/rustc_ty_utils/src/ty.rs
@@ -5,8 +5,9 @@ use rustc_hir::def::DefKind;
 use rustc_index::bit_set::DenseBitSet;
 use rustc_middle::bug;
 use rustc_middle::query::Providers;
-use rustc_middle::ty::fold::fold_regions;
-use rustc_middle::ty::{self, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitor, Upcast};
+use rustc_middle::ty::{
+    self, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitor, Upcast, fold_regions,
+};
 use rustc_span::DUMMY_SP;
 use rustc_span::def_id::{CRATE_DEF_ID, DefId, LocalDefId};
 use rustc_trait_selection::traits;
@@ -14,49 +15,49 @@ use tracing::instrument;
 
 #[instrument(level = "debug", skip(tcx), ret)]
 fn sized_constraint_for_ty<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
-    use rustc_type_ir::TyKind::*;
-
     match ty.kind() {
         // these are always sized
-        Bool
-        | Char
-        | Int(..)
-        | Uint(..)
-        | Float(..)
-        | RawPtr(..)
-        | Ref(..)
-        | FnDef(..)
-        | FnPtr(..)
-        | Array(..)
-        | Closure(..)
-        | CoroutineClosure(..)
-        | Coroutine(..)
-        | CoroutineWitness(..)
-        | Never
-        | Dynamic(_, _, ty::DynStar) => None,
+        ty::Bool
+        | ty::Char
+        | ty::Int(..)
+        | ty::Uint(..)
+        | ty::Float(..)
+        | ty::RawPtr(..)
+        | ty::Ref(..)
+        | ty::FnDef(..)
+        | ty::FnPtr(..)
+        | ty::Array(..)
+        | ty::Closure(..)
+        | ty::CoroutineClosure(..)
+        | ty::Coroutine(..)
+        | ty::CoroutineWitness(..)
+        | ty::Never
+        | ty::Dynamic(_, _, ty::DynStar) => None,
 
         // these are never sized
-        Str | Slice(..) | Dynamic(_, _, ty::Dyn) | Foreign(..) => Some(ty),
+        ty::Str | ty::Slice(..) | ty::Dynamic(_, _, ty::Dyn) | ty::Foreign(..) => Some(ty),
 
-        Pat(ty, _) => sized_constraint_for_ty(tcx, *ty),
+        ty::Pat(ty, _) => sized_constraint_for_ty(tcx, *ty),
 
-        Tuple(tys) => tys.last().and_then(|&ty| sized_constraint_for_ty(tcx, ty)),
+        ty::Tuple(tys) => tys.last().and_then(|&ty| sized_constraint_for_ty(tcx, ty)),
 
         // recursive case
-        Adt(adt, args) => adt.sized_constraint(tcx).and_then(|intermediate| {
+        ty::Adt(adt, args) => adt.sized_constraint(tcx).and_then(|intermediate| {
             let ty = intermediate.instantiate(tcx, args);
             sized_constraint_for_ty(tcx, ty)
         }),
 
         // these can be sized or unsized.
-        Param(..) | Alias(..) | Error(_) => Some(ty),
+        ty::Param(..) | ty::Alias(..) | ty::Error(_) => Some(ty),
 
         // We cannot instantiate the binder, so just return the *original* type back,
         // but only if the inner type has a sized constraint. Thus we skip the binder,
         // but don't actually use the result from `sized_constraint_for_ty`.
-        UnsafeBinder(inner_ty) => sized_constraint_for_ty(tcx, inner_ty.skip_binder()).map(|_| ty),
+        ty::UnsafeBinder(inner_ty) => {
+            sized_constraint_for_ty(tcx, inner_ty.skip_binder()).map(|_| ty)
+        }
 
-        Placeholder(..) | Bound(..) | Infer(..) => {
+        ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) => {
             bug!("unexpected type `{ty:?}` in sized_constraint_for_ty")
         }
     }