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_data_structures/src/unord.rs b/compiler/rustc_data_structures/src/unord.rs
index 34895d3efe6..14c3162165c 100644
--- a/compiler/rustc_data_structures/src/unord.rs
+++ b/compiler/rustc_data_structures/src/unord.rs
@@ -9,7 +9,7 @@ use std::iter::{Product, Sum};
 use std::ops::Index;
 
 use rustc_hash::{FxHashMap, FxHashSet};
-use rustc_macros::{Decodable_Generic, Encodable_Generic};
+use rustc_macros::{Decodable_NoContext, Encodable_NoContext};
 
 use crate::fingerprint::Fingerprint;
 use crate::stable_hasher::{HashStable, StableCompare, StableHasher, ToStableHashKey};
@@ -224,7 +224,7 @@ trait UnordCollection {}
 ///
 /// See [MCP 533](https://github.com/rust-lang/compiler-team/issues/533)
 /// for more information.
-#[derive(Debug, Eq, PartialEq, Clone, Encodable_Generic, Decodable_Generic)]
+#[derive(Debug, Eq, PartialEq, Clone, Encodable_NoContext, Decodable_NoContext)]
 pub struct UnordSet<V: Eq + Hash> {
     inner: FxHashSet<V>,
 }
@@ -415,7 +415,7 @@ impl<HCX, V: Hash + Eq + HashStable<HCX>> HashStable<HCX> for UnordSet<V> {
 ///
 /// See [MCP 533](https://github.com/rust-lang/compiler-team/issues/533)
 /// for more information.
-#[derive(Debug, Eq, PartialEq, Clone, Encodable_Generic, Decodable_Generic)]
+#[derive(Debug, Eq, PartialEq, Clone, Encodable_NoContext, Decodable_NoContext)]
 pub struct UnordMap<K: Eq + Hash, V> {
     inner: FxHashMap<K, V>,
 }
@@ -639,7 +639,7 @@ impl<HCX, K: Hash + Eq + HashStable<HCX>, V: HashStable<HCX>> HashStable<HCX> fo
 ///
 /// See [MCP 533](https://github.com/rust-lang/compiler-team/issues/533)
 /// for more information.
-#[derive(Default, Debug, Eq, PartialEq, Clone, Encodable_Generic, Decodable_Generic)]
+#[derive(Default, Debug, Eq, PartialEq, Clone, Encodable_NoContext, Decodable_NoContext)]
 pub struct UnordBag<V> {
     inner: Vec<V>,
 }