Driveby fixes

compiler/rustc_hir_typeck/src/writeback.rs

@@ -984,8 +984,8 @@ impl<'cx, 'tcx> Resolver<'cx, 'tcx> {
         // borrowck, and specifically region constraints will be populated during
         // MIR typeck which is run on the new body.
         //
-        // We're not using `tcx.erase_and_anonymize_regions` as that also anonymizes bound variables,
-        // regressing borrowck diagnostics.
+        // We're not using `tcx.erase_and_anonymize_regions` as that also
+        // anonymizes bound variables, regressing borrowck diagnostics.
         value = fold_regions(tcx, value, |_, _| tcx.lifetimes.re_erased);
 
         // Normalize consts in writeback, because GCE doesn't normalize eagerly.

compiler/rustc_middle/src/ty/util.rs

@@ -131,9 +131,8 @@ impl<'tcx> TyCtxt<'tcx> {
     /// Creates a hash of the type `Ty` which will be the same no matter what crate
     /// context it's calculated within. This is used by the `type_id` intrinsic.
     pub fn type_id_hash(self, ty: Ty<'tcx>) -> Hash128 {
-        // We want the type_id be independent of the types free regions, so we
-        // erase them. We also want type_id to be independnt of the names of bound
-        // regions so we anonymize them.
+        // We don't have region information, so we erase all free regions. Equal types
+        // must have the same `TypeId`, so we must anonymize all bound regions as well.
         let ty = self.erase_and_anonymize_regions(ty);
 
         self.with_stable_hashing_context(|mut hcx| {

compiler/rustc_mir_build/src/check_tail_calls.rs

@@ -64,7 +64,7 @@ impl<'tcx> TailCallCkVisitor<'_, 'tcx> {
                 "`become` outside of functions should have been disallowed by hir_typeck"
             )
         };
-        // While the `caller_sig` does have its regions erased, it does not have its
+        // While the `caller_sig` does have its free regions erased, it does not have its
         // binders anonymized. We call `erase_and_anonymize_regions` once again to anonymize any binders
         // within the signature, such as in function pointer or `dyn Trait` args.
         let caller_sig = self.tcx.erase_and_anonymize_regions(caller_sig);

compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs

@@ -350,6 +350,8 @@ pub fn dtorck_constraint_for_ty_inner<'tcx>(
             // Note that we don't care about whether the resume type has any drops since this is
             // redundant; there is no storage for the resume type, so if it is actually stored
             // in the interior, we'll already detect the need for a drop by checking the interior.
+            //
+            // FIXME(@lcnr): Why do we erase regions in the env here? Seems odd
             let typing_env = tcx.erase_and_anonymize_regions(typing_env);
             let needs_drop = tcx.mir_coroutine_witnesses(def_id).is_some_and(|witness| {
                 witness.field_tys.iter().any(|field| field.ty.needs_drop(tcx, typing_env))

compiler/rustc_transmute/src/layout/tree.rs

@@ -426,9 +426,7 @@ pub(crate) mod rustc {
             assert!(def.is_enum());
 
             // Computes the layout of a variant.
-            let layout_of_variant = |index,
-                                     encoding: Option<TagEncoding<VariantIdx>>|
-             -> Result<Self, Err> {
+            let layout_of_variant = |index, encoding: Option<_>| -> Result<Self, Err> {
                 let variant_layout = ty_variant(cx, (ty, layout), index);
                 if variant_layout.is_uninhabited() {
                     return Ok(Self::uninhabited());

compiler/rustc_type_ir/src/visit.rs

@@ -398,7 +398,7 @@ impl std::fmt::Debug for HasTypeFlagsVisitor {
 // looks, particular for `Ty`/`Predicate` where it's just a field access.
 //
 // N.B. The only case where this isn't totally true is binders, which also
-// add `HAS_{RE,TY,CT}_LATE_BOUND` flag depending on the *bound variables* that
+// add `HAS_BINDER_VARS` flag depending on the *bound variables* that
 // are present, regardless of whether those bound variables are used. This
 // is important for anonymization of binders in `TyCtxt::erase_and_anonymize_regions`. We
 // specifically detect this case in `visit_binder`.