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

1 files changed, 4 insertions, 4 deletions

diff --git a/compiler/rustc_index/src/bit_set.rs b/compiler/rustc_index/src/bit_set.rs
index 598409c9051..07934389158 100644
--- a/compiler/rustc_index/src/bit_set.rs
+++ b/compiler/rustc_index/src/bit_set.rs
@@ -7,7 +7,7 @@ use std::{fmt, iter, slice};
 
 use Chunk::*;
 #[cfg(feature = "nightly")]
-use rustc_macros::{Decodable_Generic, Encodable_Generic};
+use rustc_macros::{Decodable_NoContext, Encodable_NoContext};
 use smallvec::{SmallVec, smallvec};
 
 use crate::{Idx, IndexVec};
@@ -114,7 +114,7 @@ macro_rules! bit_relations_inherent_impls {
 /// to or greater than the domain size. All operations that involve two bitsets
 /// will panic if the bitsets have differing domain sizes.
 ///
-#[cfg_attr(feature = "nightly", derive(Decodable_Generic, Encodable_Generic))]
+#[cfg_attr(feature = "nightly", derive(Decodable_NoContext, Encodable_NoContext))]
 #[derive(Eq, PartialEq, Hash)]
 pub struct DenseBitSet<T> {
     domain_size: usize,
@@ -1392,7 +1392,7 @@ impl<T: Idx> From<DenseBitSet<T>> for GrowableBitSet<T> {
 ///
 /// All operations that involve a row and/or column index will panic if the
 /// index exceeds the relevant bound.
-#[cfg_attr(feature = "nightly", derive(Decodable_Generic, Encodable_Generic))]
+#[cfg_attr(feature = "nightly", derive(Decodable_NoContext, Encodable_NoContext))]
 #[derive(Clone, Eq, PartialEq, Hash)]
 pub struct BitMatrix<R: Idx, C: Idx> {
     num_rows: usize,
@@ -1816,7 +1816,7 @@ impl std::fmt::Debug for FiniteBitSet<u32> {
 
 /// A fixed-sized bitset type represented by an integer type. Indices outwith than the range
 /// representable by `T` are considered set.
-#[cfg_attr(feature = "nightly", derive(Decodable_Generic, Encodable_Generic))]
+#[cfg_attr(feature = "nightly", derive(Decodable_NoContext, Encodable_NoContext))]
 #[derive(Copy, Clone, Eq, PartialEq)]
 pub struct FiniteBitSet<T: FiniteBitSetTy>(pub T);