Auto merge of rust-lang#107924 - eggyal:move_fold_visit_traits_to_typ…

…e_lib_with_trait_alias, r=oli-obk

Move folding & visiting traits into type library

This is a rework of rust-lang#107712, following feedback on that PR.

In particular, this version uses trait aliases to reduce the API churn for trait consumers.  Doing so requires a workaround for rust-lang#107747 until its fix in rust-lang#107803 is merged into the stage0 compiler; this workaround, which uses conditional compilation based on the `bootstrap` configuration predicate, sits in dedicated commit b409329 for ease of reversion.

The possibility of the `rustc_middle` crate retaining its own distinct versions of each folding/visiting trait, blanket-implemented on all types that implement the respective trait in the type library, was also explored: however since this would necessitate making each `rustc_middle` trait a subtrait of the respective type library trait (so that such blanket implementations can delegate their generic methods), no benefit would be gained.

r? types

clippy_utils/src/mir/possible_borrower.rs

@@ -4,7 +4,7 @@ use rustc_data_structures::fx::FxHashMap;
 use rustc_index::bit_set::{BitSet, HybridBitSet};
 use rustc_lint::LateContext;
 use rustc_middle::mir::{self, visit::Visitor as _, Mutability};
-use rustc_middle::ty::{self, visit::TypeVisitor};
+use rustc_middle::ty::{self, visit::ir::TypeVisitor, TyCtxt};
 use rustc_mir_dataflow::{impls::MaybeStorageLive, Analysis, ResultsCursor};
 use std::borrow::Cow;
 use std::ops::ControlFlow;
@@ -136,7 +136,7 @@ impl<'a, 'b, 'tcx> mir::visit::Visitor<'tcx> for PossibleBorrowerVisitor<'a, 'b,
 
 struct ContainsRegion;
 
-impl TypeVisitor<'_> for ContainsRegion {
+impl TypeVisitor<TyCtxt<'_>> for ContainsRegion {
     type BreakTy = ();
 
     fn visit_region(&mut self, _: ty::Region<'_>) -> ControlFlow<Self::BreakTy> {

clippy_utils/src/ty.rs

@@ -17,7 +17,7 @@ use rustc_lint::LateContext;
 use rustc_middle::mir::interpret::{ConstValue, Scalar};
 use rustc_middle::ty::{
     self, AdtDef, AliasTy, AssocKind, Binder, BoundRegion, DefIdTree, FnSig, IntTy, List, ParamEnv, Predicate,
-    PredicateKind, Region, RegionKind, SubstsRef, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitor, UintTy,
+    PredicateKind, Region, RegionKind, SubstsRef, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, ir::TypeVisitor, UintTy,
     VariantDef, VariantDiscr,
 };
 use rustc_middle::ty::{GenericArg, GenericArgKind};
@@ -838,7 +838,7 @@ pub fn for_each_top_level_late_bound_region<B>(
         index: u32,
         f: F,
     }
-    impl<'tcx, B, F: FnMut(BoundRegion) -> ControlFlow<B>> TypeVisitor<'tcx> for V<F> {
+    impl<'tcx, B, F: FnMut(BoundRegion) -> ControlFlow<B>> TypeVisitor<TyCtxt<'tcx>> for V<F> {
         type BreakTy = B;
         fn visit_region(&mut self, r: Region<'tcx>) -> ControlFlow<Self::BreakTy> {
             if let RegionKind::ReLateBound(idx, bound) = r.kind() && idx.as_u32() == self.index {