Merging upstream version 1.68.2+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

38 files changed, 1062 insertions, 1686 deletions

diff --git a/compiler/rustc_infer/src/infer/at.rs b/compiler/rustc_infer/src/infer/at.rs
index 4429e4f43..d816a9ed3 100644
--- a/compiler/rustc_infer/src/infer/at.rs
+++ b/compiler/rustc_infer/src/infer/at.rs
@@ -411,7 +411,7 @@ impl<'tcx> ToTrace<'tcx> for ty::PolyTraitRef<'tcx> {
     }
 }
 
-impl<'tcx> ToTrace<'tcx> for ty::ProjectionTy<'tcx> {
+impl<'tcx> ToTrace<'tcx> for ty::AliasTy<'tcx> {
     fn to_trace(
         tcx: TyCtxt<'tcx>,
         cause: &ObligationCause<'tcx>,
@@ -419,11 +419,23 @@ impl<'tcx> ToTrace<'tcx> for ty::ProjectionTy<'tcx> {
         a: Self,
         b: Self,
     ) -> TypeTrace<'tcx> {
-        let a_ty = tcx.mk_projection(a.item_def_id, a.substs);
-        let b_ty = tcx.mk_projection(b.item_def_id, b.substs);
+        let a_ty = tcx.mk_projection(a.def_id, a.substs);
+        let b_ty = tcx.mk_projection(b.def_id, b.substs);
         TypeTrace {
             cause: cause.clone(),
             values: Terms(ExpectedFound::new(a_is_expected, a_ty.into(), b_ty.into())),
         }
     }
 }
+
+impl<'tcx> ToTrace<'tcx> for ty::FnSig<'tcx> {
+    fn to_trace(
+        _: TyCtxt<'tcx>,
+        cause: &ObligationCause<'tcx>,
+        a_is_expected: bool,
+        a: Self,
+        b: Self,
+    ) -> TypeTrace<'tcx> {
+        TypeTrace { cause: cause.clone(), values: Sigs(ExpectedFound::new(a_is_expected, a, b)) }
+    }
+}
diff --git a/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs b/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs
index 3dc0d60b1..091635e6c 100644
--- a/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs
+++ b/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs
@@ -6,8 +6,7 @@
 //! [c]: https://rust-lang.github.io/chalk/book/canonical_queries/canonicalization.html
 
 use crate::infer::canonical::{
-    Canonical, CanonicalTyVarKind, CanonicalVarInfo, CanonicalVarKind, Canonicalized,
-    OriginalQueryValues,
+    Canonical, CanonicalTyVarKind, CanonicalVarInfo, CanonicalVarKind, OriginalQueryValues,
 };
 use crate::infer::InferCtxt;
 use rustc_middle::ty::flags::FlagComputation;
@@ -40,7 +39,7 @@ impl<'tcx> InferCtxt<'tcx> {
         &self,
         value: V,
         query_state: &mut OriginalQueryValues<'tcx>,
-    ) -> Canonicalized<'tcx, V>
+    ) -> Canonical<'tcx, V>
     where
         V: TypeFoldable<'tcx>,
     {
@@ -59,7 +58,7 @@ impl<'tcx> InferCtxt<'tcx> {
         &self,
         value: V,
         query_state: &mut OriginalQueryValues<'tcx>,
-    ) -> Canonicalized<'tcx, V>
+    ) -> Canonical<'tcx, V>
     where
         V: TypeFoldable<'tcx>,
     {
@@ -99,7 +98,7 @@ impl<'tcx> InferCtxt<'tcx> {
     /// out the [chapter in the rustc dev guide][c].
     ///
     /// [c]: https://rust-lang.github.io/chalk/book/canonical_queries/canonicalization.html#canonicalizing-the-query-result
-    pub fn canonicalize_response<V>(&self, value: V) -> Canonicalized<'tcx, V>
+    pub fn canonicalize_response<V>(&self, value: V) -> Canonical<'tcx, V>
     where
         V: TypeFoldable<'tcx>,
     {
@@ -113,7 +112,7 @@ impl<'tcx> InferCtxt<'tcx> {
         )
     }
 
-    pub fn canonicalize_user_type_annotation<V>(&self, value: V) -> Canonicalized<'tcx, V>
+    pub fn canonicalize_user_type_annotation<V>(&self, value: V) -> Canonical<'tcx, V>
     where
         V: TypeFoldable<'tcx>,
     {
@@ -135,7 +134,7 @@ impl<'tcx> InferCtxt<'tcx> {
         &self,
         value: V,
         query_state: &mut OriginalQueryValues<'tcx>,
-    ) -> Canonicalized<'tcx, V>
+    ) -> Canonical<'tcx, V>
     where
         V: TypeFoldable<'tcx>,
     {
@@ -453,10 +452,9 @@ impl<'cx, 'tcx> TypeFolder<'tcx> for Canonicalizer<'cx, 'tcx> {
             | ty::Dynamic(..)
             | ty::Never
             | ty::Tuple(..)
-            | ty::Projection(..)
+            | ty::Alias(..)
             | ty::Foreign(..)
-            | ty::Param(..)
-            | ty::Opaque(..) => {
+            | ty::Param(..) => {
                 if t.flags().intersects(self.needs_canonical_flags) {
                     t.super_fold_with(self)
                 } else {
@@ -525,7 +523,7 @@ impl<'cx, 'tcx> Canonicalizer<'cx, 'tcx> {
         tcx: TyCtxt<'tcx>,
         canonicalize_region_mode: &dyn CanonicalizeMode,
         query_state: &mut OriginalQueryValues<'tcx>,
-    ) -> Canonicalized<'tcx, V>
+    ) -> Canonical<'tcx, V>
     where
         V: TypeFoldable<'tcx>,
     {
diff --git a/compiler/rustc_infer/src/infer/canonical/query_response.rs b/compiler/rustc_infer/src/infer/canonical/query_response.rs
index 996b1c40e..3d49182f0 100644
--- a/compiler/rustc_infer/src/infer/canonical/query_response.rs
+++ b/compiler/rustc_infer/src/infer/canonical/query_response.rs
@@ -9,7 +9,7 @@
 
 use crate::infer::canonical::substitute::{substitute_value, CanonicalExt};
 use crate::infer::canonical::{
-    Canonical, CanonicalVarValues, CanonicalizedQueryResponse, Certainty, OriginalQueryValues,
+    Canonical, CanonicalQueryResponse, CanonicalVarValues, Certainty, OriginalQueryValues,
     QueryOutlivesConstraint, QueryRegionConstraints, QueryResponse,
 };
 use crate::infer::nll_relate::{NormalizationStrategy, TypeRelating, TypeRelatingDelegate};
@@ -57,7 +57,7 @@ impl<'tcx> InferCtxt<'tcx> {
         inference_vars: CanonicalVarValues<'tcx>,
         answer: T,
         fulfill_cx: &mut dyn TraitEngine<'tcx>,
-    ) -> Fallible<CanonicalizedQueryResponse<'tcx, T>>
+    ) -> Fallible<CanonicalQueryResponse<'tcx, T>>
     where
         T: Debug + TypeFoldable<'tcx>,
         Canonical<'tcx, QueryResponse<'tcx, T>>: ArenaAllocatable<'tcx>,
@@ -151,11 +151,12 @@ impl<'tcx> InferCtxt<'tcx> {
         })
     }
 
-    fn take_opaque_types_for_query_response(&self) -> Vec<(Ty<'tcx>, Ty<'tcx>)> {
-        self.inner
-            .borrow_mut()
-            .opaque_type_storage
-            .take_opaque_types()
+    /// FIXME: This method should only be used for canonical queries and therefore be private.
+    ///
+    /// As the new solver does canonicalization slightly differently, this is also used there
+    /// for now. This should hopefully change fairly soon.
+    pub fn take_opaque_types_for_query_response(&self) -> Vec<(Ty<'tcx>, Ty<'tcx>)> {
+        std::mem::take(&mut self.inner.borrow_mut().opaque_type_storage.opaque_types)
             .into_iter()
             .map(|(k, v)| (self.tcx.mk_opaque(k.def_id.to_def_id(), k.substs), v.hidden_type.ty))
             .collect()
diff --git a/compiler/rustc_infer/src/infer/combine.rs b/compiler/rustc_infer/src/infer/combine.rs
index cf895ed0d..72676b718 100644
--- a/compiler/rustc_infer/src/infer/combine.rs
+++ b/compiler/rustc_infer/src/infer/combine.rs
@@ -219,7 +219,7 @@ impl<'tcx> InferCtxt<'tcx> {
     ///
     /// As `3 + 4` contains `N` in its substs, this must not succeed.
     ///
-    /// See `src/test/ui/const-generics/occurs-check/` for more examples where this is relevant.
+    /// See `tests/ui/const-generics/occurs-check/` for more examples where this is relevant.
     #[instrument(level = "debug", skip(self))]
     fn unify_const_variable(
         &self,
@@ -331,7 +331,7 @@ impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> {
         debug_assert!(self.infcx.inner.borrow_mut().type_variables().probe(b_vid).is_unknown());
 
         // Generalize type of `a_ty` appropriately depending on the
-        // direction.  As an example, assume:
+        // direction. As an example, assume:
         //
         // - `a_ty == &'x ?1`, where `'x` is some free region and `?1` is an
         //   inference variable,
@@ -675,7 +675,7 @@ impl<'tcx> TypeRelation<'tcx> for Generalizer<'_, 'tcx> {
                 // relatable.
                 Ok(t)
             }
-            ty::Opaque(def_id, substs) => {
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs, .. }) => {
                 let s = self.relate(substs, substs)?;
                 Ok(if s == substs { t } else { self.infcx.tcx.mk_opaque(def_id, s) })
             }
diff --git a/compiler/rustc_infer/src/infer/equate.rs b/compiler/rustc_infer/src/infer/equate.rs
index 8682f4d3b..46e7813d9 100644
--- a/compiler/rustc_infer/src/infer/equate.rs
+++ b/compiler/rustc_infer/src/infer/equate.rs
@@ -100,11 +100,15 @@ impl<'tcx> TypeRelation<'tcx> for Equate<'_, '_, 'tcx> {
                 self.fields.instantiate(a, RelationDir::EqTo, b_id, self.a_is_expected)?;
             }
 
-            (&ty::Opaque(a_def_id, _), &ty::Opaque(b_def_id, _)) if a_def_id == b_def_id => {
+            (
+                &ty::Alias(ty::Opaque, ty::AliasTy { def_id: a_def_id, .. }),
+                &ty::Alias(ty::Opaque, ty::AliasTy { def_id: b_def_id, .. }),
+            ) if a_def_id == b_def_id => {
                 self.fields.infcx.super_combine_tys(self, a, b)?;
             }
-            (&ty::Opaque(did, ..), _) | (_, &ty::Opaque(did, ..))
-                if self.fields.define_opaque_types && did.is_local() =>
+            (&ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }), _)
+            | (_, &ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }))
+                if self.fields.define_opaque_types && def_id.is_local() =>
             {
                 self.fields.obligations.extend(
                     infcx
@@ -178,6 +182,11 @@ impl<'tcx> TypeRelation<'tcx> for Equate<'_, '_, 'tcx> {
     where
         T: Relate<'tcx>,
     {
+        // A binder is equal to itself if it's structually equal to itself
+        if a == b {
+            return Ok(a);
+        }
+
         if a.skip_binder().has_escaping_bound_vars() || b.skip_binder().has_escaping_bound_vars() {
             self.fields.higher_ranked_sub(a, b, self.a_is_expected)?;
             self.fields.higher_ranked_sub(b, a, self.a_is_expected)?;
diff --git a/compiler/rustc_infer/src/infer/error_reporting/mod.rs b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
index 987559d7e..28fd03b87 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/mod.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
@@ -1,4 +1,3 @@
-// ignore-tidy-filelength
 //! Error Reporting Code for the inference engine
 //!
 //! Because of the way inference, and in particular region inference,
@@ -56,6 +55,7 @@ use crate::infer::ExpectedFound;
 use crate::traits::error_reporting::report_object_safety_error;
 use crate::traits::{
     IfExpressionCause, MatchExpressionArmCause, ObligationCause, ObligationCauseCode,
+    PredicateObligation,
 };
 
 use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
@@ -92,8 +92,12 @@ pub mod nice_region_error;
 pub struct TypeErrCtxt<'a, 'tcx> {
     pub infcx: &'a InferCtxt<'tcx>,
     pub typeck_results: Option<std::cell::Ref<'a, ty::TypeckResults<'tcx>>>,
-    pub normalize_fn_sig: Box<dyn Fn(ty::PolyFnSig<'tcx>) -> ty::PolyFnSig<'tcx> + 'a>,
     pub fallback_has_occurred: bool,
+
+    pub normalize_fn_sig: Box<dyn Fn(ty::PolyFnSig<'tcx>) -> ty::PolyFnSig<'tcx> + 'a>,
+
+    pub autoderef_steps:
+        Box<dyn Fn(Ty<'tcx>) -> Vec<(Ty<'tcx>, Vec<PredicateObligation<'tcx>>)> + 'a>,
 }
 
 impl TypeErrCtxt<'_, '_> {
@@ -184,7 +188,7 @@ fn msg_span_from_early_bound_and_free_regions<'tcx>(
             let text = if br.has_name() {
                 format!("the lifetime `{}` as defined here", br.name)
             } else {
-                format!("the anonymous lifetime as defined here")
+                "the anonymous lifetime as defined here".to_string()
             };
             (text, sp)
         }
@@ -203,7 +207,7 @@ fn msg_span_from_early_bound_and_free_regions<'tcx>(
                             sp = param.span;
                         }
                         let text = if name == kw::UnderscoreLifetime {
-                            format!("the anonymous lifetime as defined here")
+                            "the anonymous lifetime as defined here".to_string()
                         } else {
                             format!("the lifetime `{}` as defined here", name)
                         };
@@ -303,6 +307,7 @@ pub fn unexpected_hidden_region_diagnostic<'tcx>(
                     None,
                     format!("captures `{}`", hidden_region),
                     None,
+                    Some(reg_info.def_id),
                 )
             }
         }
@@ -310,7 +315,7 @@ pub fn unexpected_hidden_region_diagnostic<'tcx>(
             // Ugh. This is a painful case: the hidden region is not one
             // that we can easily summarize or explain. This can happen
             // in a case like
-            // `src/test/ui/multiple-lifetimes/ordinary-bounds-unsuited.rs`:
+            // `tests/ui/multiple-lifetimes/ordinary-bounds-unsuited.rs`:
             //
             // ```
             // fn upper_bounds<'a, 'b>(a: Ordinary<'a>, b: Ordinary<'b>) -> impl Trait<'a, 'b> {
@@ -339,11 +344,13 @@ pub fn unexpected_hidden_region_diagnostic<'tcx>(
 impl<'tcx> InferCtxt<'tcx> {
     pub fn get_impl_future_output_ty(&self, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
         let (def_id, substs) = match *ty.kind() {
-            ty::Opaque(def_id, substs) => (def_id, substs),
-            ty::Projection(data)
-                if self.tcx.def_kind(data.item_def_id) == DefKind::ImplTraitPlaceholder =>
+            ty::Alias(_, ty::AliasTy { def_id, substs, .. })
+                if matches!(
+                    self.tcx.def_kind(def_id),
+                    DefKind::OpaqueTy | DefKind::ImplTraitPlaceholder
+                ) =>
             {
-                (data.item_def_id, data.substs)
+                (def_id, substs)
             }
             _ => return None,
         };
@@ -357,7 +364,7 @@ impl<'tcx> InferCtxt<'tcx> {
                     .kind()
                     .map_bound(|kind| match kind {
                         ty::PredicateKind::Clause(ty::Clause::Projection(projection_predicate))
-                            if projection_predicate.projection_ty.item_def_id == item_def_id =>
+                            if projection_predicate.projection_ty.def_id == item_def_id =>
                         {
                             projection_predicate.term.ty()
                         }
@@ -727,7 +734,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                             format!("this and all prior arms are found to be of type `{}`", t),
                         );
                     }
-                    let outer_error_span = if any_multiline_arm {
+                    let outer = if any_multiline_arm || !source_map.is_multiline(cause.span) {
                         // Cover just `match` and the scrutinee expression, not
                         // the entire match body, to reduce diagram noise.
                         cause.span.shrink_to_lo().to(scrut_span)
@@ -735,7 +742,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                         cause.span
                     };
                     let msg = "`match` arms have incompatible types";
-                    err.span_label(outer_error_span, msg);
+                    err.span_label(outer, msg);
                     self.suggest_remove_semi_or_return_binding(
                         err,
                         prior_arm_block_id,
@@ -1393,7 +1400,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
     /// `swap_secondary_and_primary` is used to make projection errors in particular nicer by using
     /// the message in `secondary_span` as the primary label, and apply the message that would
     /// otherwise be used for the primary label on the `secondary_span` `Span`. This applies on
-    /// E0271, like `src/test/ui/issues/issue-39970.stderr`.
+    /// E0271, like `tests/ui/issues/issue-39970.stderr`.
     #[instrument(
         level = "debug",
         skip(self, diag, secondary_span, swap_secondary_and_primary, prefer_label)
@@ -1426,8 +1433,8 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         impl<'tcx> OpaqueTypesVisitor<'tcx> {
             fn visit_expected_found(
                 tcx: TyCtxt<'tcx>,
-                expected: Ty<'tcx>,
-                found: Ty<'tcx>,
+                expected: impl TypeVisitable<'tcx>,
+                found: impl TypeVisitable<'tcx>,
                 ignore_span: Span,
             ) -> Self {
                 let mut types_visitor = OpaqueTypesVisitor {
@@ -1567,6 +1574,11 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                             _ => (false, Mismatch::Fixed("type")),
                         }
                     }
+                    ValuePairs::Sigs(infer::ExpectedFound { expected, found }) => {
+                        OpaqueTypesVisitor::visit_expected_found(self.tcx, expected, found, span)
+                            .report(diag);
+                        (false, Mismatch::Fixed("signature"))
+                    }
                     ValuePairs::TraitRefs(_) | ValuePairs::PolyTraitRefs(_) => {
                         (false, Mismatch::Fixed("trait"))
                     }
@@ -1730,7 +1742,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     let extra = expected == found;
                     let sort_string = |ty: Ty<'tcx>, path: Option<PathBuf>| {
                         let mut s = match (extra, ty.kind()) {
-                            (true, ty::Opaque(def_id, _)) => {
+                            (true, ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. })) => {
                                 let sm = self.tcx.sess.source_map();
                                 let pos = sm.lookup_char_pos(self.tcx.def_span(*def_id).lo());
                                 format!(
@@ -1740,12 +1752,12 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                                     pos.col.to_usize() + 1,
                                 )
                             }
-                            (true, ty::Projection(proj))
-                                if self.tcx.def_kind(proj.item_def_id)
+                            (true, ty::Alias(ty::Projection, proj))
+                                if self.tcx.def_kind(proj.def_id)
                                     == DefKind::ImplTraitPlaceholder =>
                             {
                                 let sm = self.tcx.sess.source_map();
-                                let pos = sm.lookup_char_pos(self.tcx.def_span(proj.item_def_id).lo());
+                                let pos = sm.lookup_char_pos(self.tcx.def_span(proj.def_id).lo());
                                 format!(
                                     " (trait associated opaque type at <{}:{}:{}>)",
                                     sm.filename_for_diagnostics(&pos.file.name),
@@ -1770,9 +1782,9 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                             // like when you have two references but one is `usize` and the other
                             // is `f32`. In those cases we still want to show the `note`. If the
                             // value from `ef` is `Infer(_)`, then we ignore it.
-                            if !ef.expected.is_ty_infer() {
+                            if !ef.expected.is_ty_or_numeric_infer() {
                                 ef.expected != values.expected
-                            } else if !ef.found.is_ty_infer() {
+                            } else if !ef.found.is_ty_or_numeric_infer() {
                                 ef.found != values.found
                             } else {
                                 false
@@ -1834,7 +1846,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
 
         // In some (most?) cases cause.body_id points to actual body, but in some cases
         // it's an actual definition. According to the comments (e.g. in
-        // rustc_hir_analysis/check/compare_method.rs:compare_predicate_entailment) the latter
+        // rustc_hir_analysis/check/compare_impl_item.rs:compare_predicate_entailment) the latter
         // is relied upon by some other code. This might (or might not) need cleanup.
         let body_owner_def_id =
             self.tcx.hir().opt_local_def_id(cause.body_id).unwrap_or_else(|| {
@@ -1911,6 +1923,22 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                         (ty::Tuple(fields), _) => {
                             self.emit_tuple_wrap_err(&mut err, span, found, fields)
                         }
+                        // If a byte was expected and the found expression is a char literal
+                        // containing a single ASCII character, perhaps the user meant to write `b'c'` to
+                        // specify a byte literal
+                        (ty::Uint(ty::UintTy::U8), ty::Char) => {
+                            if let Ok(code) = self.tcx.sess().source_map().span_to_snippet(span)
+                                && let Some(code) = code.strip_prefix('\'').and_then(|s| s.strip_suffix('\''))
+                                && code.chars().next().map_or(false, |c| c.is_ascii())
+                            {
+                                err.span_suggestion(
+                                    span,
+                                    "if you meant to write a byte literal, prefix with `b`",
+                                    format!("b'{}'", escape_literal(code)),
+                                    Applicability::MachineApplicable,
+                                );
+                            }
+                        }
                         // If a character was expected and the found expression is a string literal
                         // containing a single character, perhaps the user meant to write `'c'` to
                         // specify a character literal (issue #92479)
@@ -2038,6 +2066,17 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     ret => ret,
                 }
             }
+            infer::Sigs(exp_found) => {
+                let exp_found = self.resolve_vars_if_possible(exp_found);
+                if exp_found.references_error() {
+                    return None;
+                }
+                let (exp, fnd) = self.cmp_fn_sig(
+                    &ty::Binder::dummy(exp_found.expected),
+                    &ty::Binder::dummy(exp_found.found),
+                );
+                Some((exp, fnd, None, None))
+            }
         }
     }
 
@@ -2126,18 +2165,21 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         // suggest adding an explicit lifetime bound to it.
         let generics = self.tcx.generics_of(generic_param_scope);
         // type_param_span is (span, has_bounds)
+        let mut is_synthetic = false;
+        let mut ast_generics = None;
         let type_param_span = match bound_kind {
             GenericKind::Param(ref param) => {
                 // Account for the case where `param` corresponds to `Self`,
                 // which doesn't have the expected type argument.
                 if !(generics.has_self && param.index == 0) {
                     let type_param = generics.type_param(param, self.tcx);
+                    is_synthetic = type_param.kind.is_synthetic();
                     type_param.def_id.as_local().map(|def_id| {
                         // Get the `hir::Param` to verify whether it already has any bounds.
                         // We do this to avoid suggesting code that ends up as `T: 'a'b`,
                         // instead we suggest `T: 'a + 'b` in that case.
                         let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
-                        let ast_generics = self.tcx.hir().get_generics(hir_id.owner.def_id);
+                        ast_generics = self.tcx.hir().get_generics(hir_id.owner.def_id);
                         let bounds =
                             ast_generics.and_then(|g| g.bounds_span_for_suggestions(def_id));
                         // `sp` only covers `T`, change it so that it covers
@@ -2169,18 +2211,71 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                 .unwrap_or("'lt".to_string())
         };
 
-        let add_lt_sugg = generics
-            .params
-            .first()
-            .and_then(|param| param.def_id.as_local())
-            .map(|def_id| (self.tcx.def_span(def_id).shrink_to_lo(), format!("{}, ", new_lt)));
+        let mut add_lt_suggs: Vec<Option<_>> = vec![];
+        if is_synthetic {
+            if let Some(ast_generics) = ast_generics {
+                let named_lifetime_param_exist = ast_generics.params.iter().any(|p| {
+                    matches!(
+                        p.kind,
+                        hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit }
+                    )
+                });
+                if named_lifetime_param_exist && let [param, ..] = ast_generics.params
+                {
+                    add_lt_suggs.push(Some((
+                        self.tcx.def_span(param.def_id).shrink_to_lo(),
+                        format!("{new_lt}, "),
+                    )));
+                } else {
+                    add_lt_suggs
+                        .push(Some((ast_generics.span.shrink_to_hi(), format!("<{new_lt}>"))));
+                }
+            }
+        } else {
+            if let [param, ..] = &generics.params[..] && let Some(def_id) = param.def_id.as_local()
+            {
+                add_lt_suggs
+                    .push(Some((self.tcx.def_span(def_id).shrink_to_lo(), format!("{new_lt}, "))));
+            }
+        }
+
+        if let Some(ast_generics) = ast_generics {
+            for p in ast_generics.params {
+                if p.is_elided_lifetime() {
+                    if self
+                        .tcx
+                        .sess
+                        .source_map()
+                        .span_to_prev_source(p.span.shrink_to_hi())
+                        .ok()
+                        .map_or(false, |s| *s.as_bytes().last().unwrap() == b'&')
+                    {
+                        add_lt_suggs
+                            .push(Some(
+                                (
+                                    p.span.shrink_to_hi(),
+                                    if let Ok(snip) = self.tcx.sess.source_map().span_to_next_source(p.span)
+                                        && snip.starts_with(' ')
+                                    {
+                                        format!("{new_lt}")
+                                    } else {
+                                        format!("{new_lt} ")
+                                    }
+                                )
+                            ));
+                    } else {
+                        add_lt_suggs.push(Some((p.span.shrink_to_hi(), format!("<{new_lt}>"))));
+                    }
+                }
+            }
+        }
 
         let labeled_user_string = match bound_kind {
             GenericKind::Param(ref p) => format!("the parameter type `{}`", p),
-            GenericKind::Projection(ref p) => format!("the associated type `{}`", p),
-            GenericKind::Opaque(def_id, substs) => {
-                format!("the opaque type `{}`", self.tcx.def_path_str_with_substs(def_id, substs))
-            }
+            GenericKind::Alias(ref p) => match p.kind(self.tcx) {
+                ty::AliasKind::Projection => format!("the associated type `{}`", p),
+                ty::AliasKind::Opaque => format!("the opaque type `{}`", p),
+            },
         };
 
         if let Some(SubregionOrigin::CompareImplItemObligation {
@@ -2202,15 +2297,17 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             type_param_span: Option<(Span, bool)>,
             bound_kind: GenericKind<'tcx>,
             sub: S,
-            add_lt_sugg: Option<(Span, String)>,
+            add_lt_suggs: Vec<Option<(Span, String)>>,
         ) {
             let msg = "consider adding an explicit lifetime bound";
             if let Some((sp, has_lifetimes)) = type_param_span {
                 let suggestion =
                     if has_lifetimes { format!(" + {}", sub) } else { format!(": {}", sub) };
                 let mut suggestions = vec![(sp, suggestion)];
-                if let Some(add_lt_sugg) = add_lt_sugg {
-                    suggestions.push(add_lt_sugg);
+                for add_lt_sugg in add_lt_suggs {
+                    if let Some(add_lt_sugg) = add_lt_sugg {
+                        suggestions.push(add_lt_sugg);
+                    }
                 }
                 err.multipart_suggestion_verbose(
                     format!("{msg}..."),
@@ -2234,9 +2331,11 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     };
                     let mut sugg =
                         vec![(sp, suggestion), (span.shrink_to_hi(), format!(" + {}", new_lt))];
-                    if let Some(lt) = add_lt_sugg.clone() {
-                        sugg.push(lt);
-                        sugg.rotate_right(1);
+                    for add_lt_sugg in add_lt_suggs.clone() {
+                        if let Some(lt) = add_lt_sugg {
+                            sugg.push(lt);
+                            sugg.rotate_right(1);
+                        }
                     }
                     // `MaybeIncorrect` due to issue #41966.
                     err.multipart_suggestion(msg, sugg, Applicability::MaybeIncorrect);
@@ -2340,7 +2439,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                 // for the bound is not suitable for suggestions when `-Zverbose` is set because it
                 // uses `Debug` output, so we handle it specially here so that suggestions are
                 // always correct.
-                binding_suggestion(&mut err, type_param_span, bound_kind, name, None);
+                binding_suggestion(&mut err, type_param_span, bound_kind, name, vec![]);
                 err
             }
 
@@ -2353,7 +2452,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     "{} may not live long enough",
                     labeled_user_string
                 );
-                binding_suggestion(&mut err, type_param_span, bound_kind, "'static", None);
+                binding_suggestion(&mut err, type_param_span, bound_kind, "'static", vec![]);
                 err
             }
 
@@ -2383,7 +2482,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                         // fn get_later<G, T>(g: G, dest: &mut T) -> impl FnOnce() + '_
                         // suggest:
                         // fn get_later<'a, G: 'a, T>(g: G, dest: &mut T) -> impl FnOnce() + '_ + 'a
-                        ty::Closure(_, _substs) | ty::Opaque(_, _substs) if return_impl_trait => {
+                        ty::Closure(..) | ty::Alias(ty::Opaque, ..) if return_impl_trait => {
                             new_binding_suggestion(&mut err, type_param_span);
                         }
                         _ => {
@@ -2392,7 +2491,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                                 type_param_span,
                                 bound_kind,
                                 new_lt,
-                                add_lt_sugg,
+                                add_lt_suggs,
                             );
                         }
                     }
@@ -2765,7 +2864,7 @@ impl TyCategory {
     pub fn from_ty(tcx: TyCtxt<'_>, ty: Ty<'_>) -> Option<(Self, DefId)> {
         match *ty.kind() {
             ty::Closure(def_id, _) => Some((Self::Closure, def_id)),
-            ty::Opaque(def_id, _) => Some((Self::Opaque, def_id)),
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }) => Some((Self::Opaque, def_id)),
             ty::Generator(def_id, ..) => {
                 Some((Self::Generator(tcx.generator_kind(def_id).unwrap()), def_id))
             }
diff --git a/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs b/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs
index 8ff1639a3..b8c843a8a 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs
@@ -20,7 +20,7 @@ use rustc_middle::ty::print::{FmtPrinter, PrettyPrinter, Print, Printer};
 use rustc_middle::ty::{self, DefIdTree, InferConst};
 use rustc_middle::ty::{GenericArg, GenericArgKind, SubstsRef};
 use rustc_middle::ty::{IsSuggestable, Ty, TyCtxt, TypeckResults};
-use rustc_span::symbol::{kw, Ident};
+use rustc_span::symbol::{kw, sym, Ident};
 use rustc_span::{BytePos, Span};
 use std::borrow::Cow;
 use std::iter;
@@ -78,8 +78,8 @@ impl InferenceDiagnosticsData {
     }
 
     fn where_x_is_kind(&self, in_type: Ty<'_>) -> &'static str {
-        if in_type.is_ty_infer() {
-            "empty"
+        if in_type.is_ty_or_numeric_infer() {
+            ""
         } else if self.name == "_" {
             // FIXME: Consider specializing this message if there is a single `_`
             // in the type.
@@ -183,13 +183,24 @@ fn fmt_printer<'a, 'tcx>(infcx: &'a InferCtxt<'tcx>, ns: Namespace) -> FmtPrinte
     printer
 }
 
-fn ty_to_string<'tcx>(infcx: &InferCtxt<'tcx>, ty: Ty<'tcx>) -> String {
+fn ty_to_string<'tcx>(
+    infcx: &InferCtxt<'tcx>,
+    ty: Ty<'tcx>,
+    called_method_def_id: Option<DefId>,
+) -> String {
     let printer = fmt_printer(infcx, Namespace::TypeNS);
     let ty = infcx.resolve_vars_if_possible(ty);
-    match ty.kind() {
+    match (ty.kind(), called_method_def_id) {
         // We don't want the regular output for `fn`s because it includes its path in
         // invalid pseudo-syntax, we want the `fn`-pointer output instead.
-        ty::FnDef(..) => ty.fn_sig(infcx.tcx).print(printer).unwrap().into_buffer(),
+        (ty::FnDef(..), _) => ty.fn_sig(infcx.tcx).print(printer).unwrap().into_buffer(),
+        (_, Some(def_id))
+            if ty.is_ty_or_numeric_infer()
+                && infcx.tcx.get_diagnostic_item(sym::iterator_collect_fn) == Some(def_id) =>
+        {
+            "Vec<_>".to_string()
+        }
+        _ if ty.is_ty_or_numeric_infer() => "/* Type */".to_string(),
         // FIXME: The same thing for closures, but this only works when the closure
         // does not capture anything.
         //
@@ -213,7 +224,7 @@ fn closure_as_fn_str<'tcx>(infcx: &InferCtxt<'tcx>, ty: Ty<'tcx>) -> String {
         .map(|args| {
             args.tuple_fields()
                 .iter()
-                .map(|arg| ty_to_string(infcx, arg))
+                .map(|arg| ty_to_string(infcx, arg, None))
                 .collect::<Vec<_>>()
                 .join(", ")
         })
@@ -221,7 +232,7 @@ fn closure_as_fn_str<'tcx>(infcx: &InferCtxt<'tcx>, ty: Ty<'tcx>) -> String {
     let ret = if fn_sig.output().skip_binder().is_unit() {
         String::new()
     } else {
-        format!(" -> {}", ty_to_string(infcx, fn_sig.output().skip_binder()))
+        format!(" -> {}", ty_to_string(infcx, fn_sig.output().skip_binder(), None))
     };
     format!("fn({}){}", args, ret)
 }
@@ -368,6 +379,7 @@ impl<'tcx> InferCtxt<'tcx> {
 }
 
 impl<'tcx> TypeErrCtxt<'_, 'tcx> {
+    #[instrument(level = "debug", skip(self, error_code))]
     pub fn emit_inference_failure_err(
         &self,
         body_id: Option<hir::BodyId>,
@@ -406,7 +418,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         let mut infer_subdiags = Vec::new();
         let mut multi_suggestions = Vec::new();
         match kind {
-            InferSourceKind::LetBinding { insert_span, pattern_name, ty } => {
+            InferSourceKind::LetBinding { insert_span, pattern_name, ty, def_id } => {
                 infer_subdiags.push(SourceKindSubdiag::LetLike {
                     span: insert_span,
                     name: pattern_name.map(|name| name.to_string()).unwrap_or_else(String::new),
@@ -415,7 +427,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     prefix: arg_data.kind.try_get_prefix().unwrap_or_default(),
                     arg_name: arg_data.name,
                     kind: if pattern_name.is_some() { "with_pattern" } else { "other" },
-                    type_name: ty_to_string(self, ty),
+                    type_name: ty_to_string(self, ty, def_id),
                 });
             }
             InferSourceKind::ClosureArg { insert_span, ty } => {
@@ -427,7 +439,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     prefix: arg_data.kind.try_get_prefix().unwrap_or_default(),
                     arg_name: arg_data.name,
                     kind: "closure",
-                    type_name: ty_to_string(self, ty),
+                    type_name: ty_to_string(self, ty, None),
                 });
             }
             InferSourceKind::GenericArg {
@@ -456,33 +468,39 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     parent_name,
                 });
 
-                let args = fmt_printer(self, Namespace::TypeNS)
-                    .comma_sep(generic_args.iter().copied().map(|arg| {
-                        if arg.is_suggestable(self.tcx, true) {
-                            return arg;
-                        }
+                let args = if self.infcx.tcx.get_diagnostic_item(sym::iterator_collect_fn)
+                    == Some(generics_def_id)
+                {
+                    "Vec<_>".to_string()
+                } else {
+                    fmt_printer(self, Namespace::TypeNS)
+                        .comma_sep(generic_args.iter().copied().map(|arg| {
+                            if arg.is_suggestable(self.tcx, true) {
+                                return arg;
+                            }
 
-                        match arg.unpack() {
-                            GenericArgKind::Lifetime(_) => bug!("unexpected lifetime"),
-                            GenericArgKind::Type(_) => self
-                                .next_ty_var(TypeVariableOrigin {
-                                    span: rustc_span::DUMMY_SP,
-                                    kind: TypeVariableOriginKind::MiscVariable,
-                                })
-                                .into(),
-                            GenericArgKind::Const(arg) => self
-                                .next_const_var(
-                                    arg.ty(),
-                                    ConstVariableOrigin {
+                            match arg.unpack() {
+                                GenericArgKind::Lifetime(_) => bug!("unexpected lifetime"),
+                                GenericArgKind::Type(_) => self
+                                    .next_ty_var(TypeVariableOrigin {
                                         span: rustc_span::DUMMY_SP,
-                                        kind: ConstVariableOriginKind::MiscVariable,
-                                    },
-                                )
-                                .into(),
-                        }
-                    }))
-                    .unwrap()
-                    .into_buffer();
+                                        kind: TypeVariableOriginKind::MiscVariable,
+                                    })
+                                    .into(),
+                                GenericArgKind::Const(arg) => self
+                                    .next_const_var(
+                                        arg.ty(),
+                                        ConstVariableOrigin {
+                                            span: rustc_span::DUMMY_SP,
+                                            kind: ConstVariableOriginKind::MiscVariable,
+                                        },
+                                    )
+                                    .into(),
+                            }
+                        }))
+                        .unwrap()
+                        .into_buffer()
+                };
 
                 if !have_turbofish {
                     infer_subdiags.push(SourceKindSubdiag::GenericSuggestion {
@@ -520,7 +538,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                 ));
             }
             InferSourceKind::ClosureReturn { ty, data, should_wrap_expr } => {
-                let ty_info = ty_to_string(self, ty);
+                let ty_info = ty_to_string(self, ty, None);
                 multi_suggestions.push(SourceKindMultiSuggestion::new_closure_return(
                     ty_info,
                     data,
@@ -608,6 +626,7 @@ enum InferSourceKind<'tcx> {
         insert_span: Span,
         pattern_name: Option<Ident>,
         ty: Ty<'tcx>,
+        def_id: Option<DefId>,
     },
     ClosureArg {
         insert_span: Span,
@@ -661,8 +680,8 @@ impl<'tcx> InferSourceKind<'tcx> {
             | InferSourceKind::ClosureReturn { ty, .. } => {
                 if ty.is_closure() {
                     ("closure", closure_as_fn_str(infcx, ty))
-                } else if !ty.is_ty_infer() {
-                    ("normal", ty_to_string(infcx, ty))
+                } else if !ty.is_ty_or_numeric_infer() {
+                    ("normal", ty_to_string(infcx, ty, None))
                 } else {
                     ("other", String::new())
                 }
@@ -788,10 +807,18 @@ impl<'a, 'tcx> FindInferSourceVisitor<'a, 'tcx> {
     /// Uses `fn source_cost` to determine whether this inference source is preferable to
     /// previous sources. We generally prefer earlier sources.
     #[instrument(level = "debug", skip(self))]
-    fn update_infer_source(&mut self, new_source: InferSource<'tcx>) {
+    fn update_infer_source(&mut self, mut new_source: InferSource<'tcx>) {
         let cost = self.source_cost(&new_source) + self.attempt;
         debug!(?cost);
         self.attempt += 1;
+        if let Some(InferSource { kind: InferSourceKind::GenericArg { def_id: did, ..}, .. }) = self.infer_source
+            && let InferSourceKind::LetBinding { ref ty, ref mut def_id, ..} = new_source.kind
+            && ty.is_ty_or_numeric_infer()
+        {
+            // Customize the output so we talk about `let x: Vec<_> = iter.collect();` instead of
+            // `let x: _ = iter.collect();`, as this is a very common case.
+            *def_id = Some(did);
+        }
         if cost < self.infer_source_cost {
             self.infer_source_cost = cost;
             self.infer_source = Some(new_source);
@@ -852,7 +879,10 @@ impl<'a, 'tcx> FindInferSourceVisitor<'a, 'tcx> {
             match inner.unpack() {
                 GenericArgKind::Lifetime(_) => {}
                 GenericArgKind::Type(ty) => {
-                    if matches!(ty.kind(), ty::Opaque(..) | ty::Closure(..) | ty::Generator(..)) {
+                    if matches!(
+                        ty.kind(),
+                        ty::Alias(ty::Opaque, ..) | ty::Closure(..) | ty::Generator(..)
+                    ) {
                         // Opaque types can't be named by the user right now.
                         //
                         // Both the generic arguments of closures and generators can
@@ -1089,6 +1119,7 @@ impl<'a, 'tcx> Visitor<'tcx> for FindInferSourceVisitor<'a, 'tcx> {
                                 insert_span: local.pat.span.shrink_to_hi(),
                                 pattern_name: local.pat.simple_ident(),
                                 ty,
+                                def_id: None,
                             },
                         })
                     }
diff --git a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/find_anon_type.rs b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/find_anon_type.rs
index d8f540b74..39f4d5022 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/find_anon_type.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/find_anon_type.rs
@@ -96,8 +96,8 @@ impl<'tcx> Visitor<'tcx> for FindNestedTypeVisitor<'tcx> {
                 }
             }
 
-            hir::TyKind::Rptr(ref lifetime, _) => {
-                // the lifetime of the TyRptr
+            hir::TyKind::Ref(ref lifetime, _) => {
+                // the lifetime of the Ref
                 let hir_id = lifetime.hir_id;
                 match (self.tcx.named_region(hir_id), self.bound_region) {
                     // Find the index of the named region that was part of the
diff --git a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/mod.rs b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/mod.rs
index 8a0e332f9..59fb74eb5 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/mod.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/mod.rs
@@ -9,7 +9,7 @@ mod different_lifetimes;
 pub mod find_anon_type;
 mod mismatched_static_lifetime;
 mod named_anon_conflict;
-mod placeholder_error;
+pub(crate) mod placeholder_error;
 mod placeholder_relation;
 mod static_impl_trait;
 mod trait_impl_difference;
diff --git a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/named_anon_conflict.rs b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/named_anon_conflict.rs
index 3fe7c1598..4e13ec902 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/named_anon_conflict.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/named_anon_conflict.rs
@@ -1,8 +1,11 @@
 //! Error Reporting for Anonymous Region Lifetime Errors
 //! where one region is named and the other is anonymous.
-use crate::infer::error_reporting::nice_region_error::find_anon_type::find_anon_type;
 use crate::infer::error_reporting::nice_region_error::NiceRegionError;
-use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder, ErrorGuaranteed};
+use crate::{
+    errors::ExplicitLifetimeRequired,
+    infer::error_reporting::nice_region_error::find_anon_type::find_anon_type,
+};
+use rustc_errors::{DiagnosticBuilder, ErrorGuaranteed};
 use rustc_middle::ty;
 use rustc_span::symbol::kw;
 
@@ -86,31 +89,17 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
         {
             return None;
         }
-
-        let (error_var, span_label_var) = match param.pat.simple_ident() {
-            Some(simple_ident) => (
-                format!("the type of `{}`", simple_ident),
-                format!("the type of `{}`", simple_ident),
-            ),
-            None => ("parameter type".to_owned(), "type".to_owned()),
+        let named = named.to_string();
+        let err = match param.pat.simple_ident() {
+            Some(simple_ident) => ExplicitLifetimeRequired::WithIdent {
+                span,
+                simple_ident,
+                named,
+                new_ty_span,
+                new_ty,
+            },
+            None => ExplicitLifetimeRequired::WithParamType { span, named, new_ty_span, new_ty },
         };
-
-        let mut diag = struct_span_err!(
-            self.tcx().sess,
-            span,
-            E0621,
-            "explicit lifetime required in {}",
-            error_var
-        );
-
-        diag.span_label(span, format!("lifetime `{}` required", named));
-        diag.span_suggestion(
-            new_ty_span,
-            &format!("add explicit lifetime `{}` to {}", named, span_label_var),
-            new_ty,
-            Applicability::Unspecified,
-        );
-
-        Some(diag)
+        Some(self.tcx().sess.parse_sess.create_err(err))
     }
 }
diff --git a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/placeholder_error.rs b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/placeholder_error.rs
index 1f554c81e..99431567e 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/placeholder_error.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/placeholder_error.rs
@@ -1,10 +1,14 @@
+use crate::errors::{
+    ActualImplExpectedKind, ActualImplExpectedLifetimeKind, ActualImplExplNotes,
+    TraitPlaceholderMismatch, TyOrSig,
+};
 use crate::infer::error_reporting::nice_region_error::NiceRegionError;
 use crate::infer::lexical_region_resolve::RegionResolutionError;
 use crate::infer::ValuePairs;
 use crate::infer::{SubregionOrigin, TypeTrace};
 use crate::traits::{ObligationCause, ObligationCauseCode};
 use rustc_data_structures::intern::Interned;
-use rustc_errors::{Diagnostic, DiagnosticBuilder, ErrorGuaranteed};
+use rustc_errors::{DiagnosticBuilder, ErrorGuaranteed, IntoDiagnosticArg};
 use rustc_hir::def::Namespace;
 use rustc_hir::def_id::DefId;
 use rustc_middle::ty::error::ExpectedFound;
@@ -12,7 +16,43 @@ use rustc_middle::ty::print::{FmtPrinter, Print, RegionHighlightMode};
 use rustc_middle::ty::subst::SubstsRef;
 use rustc_middle::ty::{self, RePlaceholder, ReVar, Region, TyCtxt};
 
-use std::fmt::{self, Write};
+use std::fmt;
+
+// HACK(eddyb) maybe move this in a more central location.
+#[derive(Copy, Clone)]
+pub struct Highlighted<'tcx, T> {
+    tcx: TyCtxt<'tcx>,
+    highlight: RegionHighlightMode<'tcx>,
+    value: T,
+}
+
+impl<'tcx, T> IntoDiagnosticArg for Highlighted<'tcx, T>
+where
+    T: for<'a> Print<'tcx, FmtPrinter<'a, 'tcx>, Error = fmt::Error, Output = FmtPrinter<'a, 'tcx>>,
+{
+    fn into_diagnostic_arg(self) -> rustc_errors::DiagnosticArgValue<'static> {
+        rustc_errors::DiagnosticArgValue::Str(self.to_string().into())
+    }
+}
+
+impl<'tcx, T> Highlighted<'tcx, T> {
+    fn map<U>(self, f: impl FnOnce(T) -> U) -> Highlighted<'tcx, U> {
+        Highlighted { tcx: self.tcx, highlight: self.highlight, value: f(self.value) }
+    }
+}
+
+impl<'tcx, T> fmt::Display for Highlighted<'tcx, T>
+where
+    T: for<'a> Print<'tcx, FmtPrinter<'a, 'tcx>, Error = fmt::Error, Output = FmtPrinter<'a, 'tcx>>,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut printer = ty::print::FmtPrinter::new(self.tcx, Namespace::TypeNS);
+        printer.region_highlight_mode = self.highlight;
+
+        let s = self.value.print(printer)?.into_buffer();
+        f.write_str(&s)
+    }
+}
 
 impl<'tcx> NiceRegionError<'_, 'tcx> {
     /// When given a `ConcreteFailure` for a function with arguments containing a named region and
@@ -205,34 +245,27 @@ impl<'tcx> NiceRegionError<'_, 'tcx> {
         actual_substs: SubstsRef<'tcx>,
     ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
         let span = cause.span();
-        let msg = format!(
-            "implementation of `{}` is not general enough",
-            self.tcx().def_path_str(trait_def_id),
-        );
-        let mut err = self.tcx().sess.struct_span_err(span, &msg);
-
-        let leading_ellipsis = if let ObligationCauseCode::ItemObligation(def_id)
-        | ObligationCauseCode::ExprItemObligation(def_id, ..) =
-            *cause.code()
-        {
-            err.span_label(span, "doesn't satisfy where-clause");
-            err.span_label(
-                self.tcx().def_span(def_id),
-                &format!("due to a where-clause on `{}`...", self.tcx().def_path_str(def_id)),
-            );
-            true
-        } else {
-            err.span_label(span, &msg);
-            false
-        };
 
-        let expected_trait_ref = self.cx.resolve_vars_if_possible(ty::TraitRef {
-            def_id: trait_def_id,
-            substs: expected_substs,
-        });
-        let actual_trait_ref = self
+        let (leading_ellipsis, satisfy_span, where_span, dup_span, def_id) =
+            if let ObligationCauseCode::ItemObligation(def_id)
+            | ObligationCauseCode::ExprItemObligation(def_id, ..) = *cause.code()
+            {
+                (
+                    true,
+                    Some(span),
+                    Some(self.tcx().def_span(def_id)),
+                    None,
+                    self.tcx().def_path_str(def_id),
+                )
+            } else {
+                (false, None, None, Some(span), String::new())
+            };
+
+        let expected_trait_ref = self
             .cx
-            .resolve_vars_if_possible(ty::TraitRef { def_id: trait_def_id, substs: actual_substs });
+            .resolve_vars_if_possible(self.cx.tcx.mk_trait_ref(trait_def_id, expected_substs));
+        let actual_trait_ref =
+            self.cx.resolve_vars_if_possible(self.cx.tcx.mk_trait_ref(trait_def_id, actual_substs));
 
         // Search the expected and actual trait references to see (a)
         // whether the sub/sup placeholders appear in them (sometimes
@@ -286,8 +319,7 @@ impl<'tcx> NiceRegionError<'_, 'tcx> {
             ?expected_self_ty_has_vid,
         );
 
-        self.explain_actual_impl_that_was_found(
-            &mut err,
+        let actual_impl_expl_notes = self.explain_actual_impl_that_was_found(
             sub_placeholder,
             sup_placeholder,
             has_sub,
@@ -301,7 +333,15 @@ impl<'tcx> NiceRegionError<'_, 'tcx> {
             leading_ellipsis,
         );
 
-        err
+        self.tcx().sess.create_err(TraitPlaceholderMismatch {
+            span,
+            satisfy_span,
+            where_span,
+            dup_span,
+            def_id,
+            trait_def_id: self.tcx().def_path_str(trait_def_id),
+            actual_impl_expl_notes,
+        })
     }
 
     /// Add notes with details about the expected and actual trait refs, with attention to cases
@@ -311,7 +351,6 @@ impl<'tcx> NiceRegionError<'_, 'tcx> {
     /// due to the number of combinations we have to deal with.
     fn explain_actual_impl_that_was_found(
         &self,
-        err: &mut Diagnostic,
         sub_placeholder: Option<Region<'tcx>>,
         sup_placeholder: Option<Region<'tcx>>,
         has_sub: Option<usize>,
@@ -323,39 +362,7 @@ impl<'tcx> NiceRegionError<'_, 'tcx> {
         actual_has_vid: Option<usize>,
         any_self_ty_has_vid: bool,
         leading_ellipsis: bool,
-    ) {
-        // HACK(eddyb) maybe move this in a more central location.
-        #[derive(Copy, Clone)]
-        struct Highlighted<'tcx, T> {
-            tcx: TyCtxt<'tcx>,
-            highlight: RegionHighlightMode<'tcx>,
-            value: T,
-        }
-
-        impl<'tcx, T> Highlighted<'tcx, T> {
-            fn map<U>(self, f: impl FnOnce(T) -> U) -> Highlighted<'tcx, U> {
-                Highlighted { tcx: self.tcx, highlight: self.highlight, value: f(self.value) }
-            }
-        }
-
-        impl<'tcx, T> fmt::Display for Highlighted<'tcx, T>
-        where
-            T: for<'a> Print<
-                'tcx,
-                FmtPrinter<'a, 'tcx>,
-                Error = fmt::Error,
-                Output = FmtPrinter<'a, 'tcx>,
-            >,
-        {
-            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-                let mut printer = ty::print::FmtPrinter::new(self.tcx, Namespace::TypeNS);
-                printer.region_highlight_mode = self.highlight;
-
-                let s = self.value.print(printer)?.into_buffer();
-                f.write_str(&s)
-            }
-        }
-
+    ) -> Vec<ActualImplExplNotes<'tcx>> {
         // The weird thing here with the `maybe_highlighting_region` calls and the
         // the match inside is meant to be like this:
         //
@@ -363,7 +370,7 @@ impl<'tcx> NiceRegionError<'_, 'tcx> {
         //   in the types are about to print
         // - Meanwhile, the `maybe_highlighting_region` calls set up
         //   highlights so that, if they do appear, we will replace
-        //   them `'0` and whatever.  (This replacement takes place
+        //   them `'0` and whatever. (This replacement takes place
         //   inside the closure given to `maybe_highlighting_region`.)
         //
         // There is some duplication between the calls -- i.e., the
@@ -382,120 +389,110 @@ impl<'tcx> NiceRegionError<'_, 'tcx> {
         let mut expected_trait_ref = highlight_trait_ref(expected_trait_ref);
         expected_trait_ref.highlight.maybe_highlighting_region(sub_placeholder, has_sub);
         expected_trait_ref.highlight.maybe_highlighting_region(sup_placeholder, has_sup);
-        err.note(&{
-            let passive_voice = match (has_sub, has_sup) {
-                (Some(_), _) | (_, Some(_)) => any_self_ty_has_vid,
-                (None, None) => {
-                    expected_trait_ref.highlight.maybe_highlighting_region(vid, expected_has_vid);
-                    match expected_has_vid {
-                        Some(_) => true,
-                        None => any_self_ty_has_vid,
-                    }
-                }
-            };
 
-            let mut note = if same_self_type {
-                let mut self_ty = expected_trait_ref.map(|tr| tr.self_ty());
-                self_ty.highlight.maybe_highlighting_region(vid, actual_has_vid);
-
-                if self_ty.value.is_closure()
-                    && self.tcx().is_fn_trait(expected_trait_ref.value.def_id)
-                {
-                    let closure_sig = self_ty.map(|closure| {
-                        if let ty::Closure(_, substs) = closure.kind() {
-                            self.tcx().signature_unclosure(
-                                substs.as_closure().sig(),
-                                rustc_hir::Unsafety::Normal,
-                            )
-                        } else {
-                            bug!("type is not longer closure");
-                        }
-                    });
-
-                    format!(
-                        "{}closure with signature `{}` must implement `{}`",
-                        if leading_ellipsis { "..." } else { "" },
-                        closure_sig,
-                        expected_trait_ref.map(|tr| tr.print_only_trait_path()),
-                    )
-                } else {
-                    format!(
-                        "{}`{}` must implement `{}`",
-                        if leading_ellipsis { "..." } else { "" },
-                        self_ty,
-                        expected_trait_ref.map(|tr| tr.print_only_trait_path()),
-                    )
+        let passive_voice = match (has_sub, has_sup) {
+            (Some(_), _) | (_, Some(_)) => any_self_ty_has_vid,
+            (None, None) => {
+                expected_trait_ref.highlight.maybe_highlighting_region(vid, expected_has_vid);
+                match expected_has_vid {
+                    Some(_) => true,
+                    None => any_self_ty_has_vid,
                 }
-            } else if passive_voice {
-                format!(
-                    "{}`{}` would have to be implemented for the type `{}`",
-                    if leading_ellipsis { "..." } else { "" },
+            }
+        };
+
+        let (kind, ty_or_sig, trait_path) = if same_self_type {
+            let mut self_ty = expected_trait_ref.map(|tr| tr.self_ty());
+            self_ty.highlight.maybe_highlighting_region(vid, actual_has_vid);
+
+            if self_ty.value.is_closure() && self.tcx().is_fn_trait(expected_trait_ref.value.def_id)
+            {
+                let closure_sig = self_ty.map(|closure| {
+                    if let ty::Closure(_, substs) = closure.kind() {
+                        self.tcx().signature_unclosure(
+                            substs.as_closure().sig(),
+                            rustc_hir::Unsafety::Normal,
+                        )
+                    } else {
+                        bug!("type is not longer closure");
+                    }
+                });
+                (
+                    ActualImplExpectedKind::Signature,
+                    TyOrSig::ClosureSig(closure_sig),
                     expected_trait_ref.map(|tr| tr.print_only_trait_path()),
-                    expected_trait_ref.map(|tr| tr.self_ty()),
                 )
             } else {
-                format!(
-                    "{}`{}` must implement `{}`",
-                    if leading_ellipsis { "..." } else { "" },
-                    expected_trait_ref.map(|tr| tr.self_ty()),
+                (
+                    ActualImplExpectedKind::Other,
+                    TyOrSig::Ty(self_ty),
                     expected_trait_ref.map(|tr| tr.print_only_trait_path()),
                 )
-            };
+            }
+        } else if passive_voice {
+            (
+                ActualImplExpectedKind::Passive,
+                TyOrSig::Ty(expected_trait_ref.map(|tr| tr.self_ty())),
+                expected_trait_ref.map(|tr| tr.print_only_trait_path()),
+            )
+        } else {
+            (
+                ActualImplExpectedKind::Other,
+                TyOrSig::Ty(expected_trait_ref.map(|tr| tr.self_ty())),
+                expected_trait_ref.map(|tr| tr.print_only_trait_path()),
+            )
+        };
 
-            match (has_sub, has_sup) {
-                (Some(n1), Some(n2)) => {
-                    let _ = write!(
-                        note,
-                        ", for any two lifetimes `'{}` and `'{}`...",
-                        std::cmp::min(n1, n2),
-                        std::cmp::max(n1, n2),
-                    );
-                }
-                (Some(n), _) | (_, Some(n)) => {
-                    let _ = write!(note, ", for any lifetime `'{}`...", n,);
-                }
-                (None, None) => {
-                    if let Some(n) = expected_has_vid {
-                        let _ = write!(note, ", for some specific lifetime `'{}`...", n,);
-                    }
+        let (lt_kind, lifetime_1, lifetime_2) = match (has_sub, has_sup) {
+            (Some(n1), Some(n2)) => {
+                (ActualImplExpectedLifetimeKind::Two, std::cmp::min(n1, n2), std::cmp::max(n1, n2))
+            }
+            (Some(n), _) | (_, Some(n)) => (ActualImplExpectedLifetimeKind::Any, n, 0),
+            (None, None) => {
+                if let Some(n) = expected_has_vid {
+                    (ActualImplExpectedLifetimeKind::Some, n, 0)
+                } else {
+                    (ActualImplExpectedLifetimeKind::Nothing, 0, 0)
                 }
             }
+        };
 
-            note
-        });
+        let note_1 = ActualImplExplNotes::new_expected(
+            kind,
+            lt_kind,
+            leading_ellipsis,
+            ty_or_sig,
+            trait_path,
+            lifetime_1,
+            lifetime_2,
+        );
 
         let mut actual_trait_ref = highlight_trait_ref(actual_trait_ref);
         actual_trait_ref.highlight.maybe_highlighting_region(vid, actual_has_vid);
-        err.note(&{
-            let passive_voice = match actual_has_vid {
-                Some(_) => any_self_ty_has_vid,
-                None => true,
-            };
 
-            let mut note = if same_self_type {
-                format!(
-                    "...but it actually implements `{}`",
-                    actual_trait_ref.map(|tr| tr.print_only_trait_path()),
-                )
-            } else if passive_voice {
-                format!(
-                    "...but `{}` is actually implemented for the type `{}`",
-                    actual_trait_ref.map(|tr| tr.print_only_trait_path()),
-                    actual_trait_ref.map(|tr| tr.self_ty()),
-                )
-            } else {
-                format!(
-                    "...but `{}` actually implements `{}`",
-                    actual_trait_ref.map(|tr| tr.self_ty()),
-                    actual_trait_ref.map(|tr| tr.print_only_trait_path()),
-                )
-            };
+        let passive_voice = match actual_has_vid {
+            Some(_) => any_self_ty_has_vid,
+            None => true,
+        };
 
-            if let Some(n) = actual_has_vid {
-                let _ = write!(note, ", for some specific lifetime `'{}`", n);
+        let trait_path = actual_trait_ref.map(|tr| tr.print_only_trait_path());
+        let ty = actual_trait_ref.map(|tr| tr.self_ty()).to_string();
+        let has_lifetime = actual_has_vid.is_some();
+        let lifetime = actual_has_vid.unwrap_or_default();
+
+        let note_2 = if same_self_type {
+            ActualImplExplNotes::ButActuallyImplementsTrait { trait_path, has_lifetime, lifetime }
+        } else if passive_voice {
+            ActualImplExplNotes::ButActuallyImplementedForTy {
+                trait_path,
+                ty,
+                has_lifetime,
+                lifetime,
             }
+        } else {
+            ActualImplExplNotes::ButActuallyTyImplements { trait_path, ty, has_lifetime, lifetime }
+        };
 
-            note
-        });
+        vec![note_1, note_2]
     }
 }
diff --git a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/placeholder_relation.rs b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/placeholder_relation.rs
index c42240f21..9534bce54 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/placeholder_relation.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/placeholder_relation.rs
@@ -44,7 +44,7 @@ impl<'tcx> NiceRegionError<'_, 'tcx> {
                         );
                     }
                     (Some(sub_span), Some(sup_span), _, Some(sup_symbol)) => {
-                        err.span_note(sub_span, format!("the lifetime defined here..."));
+                        err.span_note(sub_span, "the lifetime defined here...");
                         err.span_note(
                             sup_span,
                             format!("...must outlive the lifetime `{sup_symbol}` defined here"),
@@ -55,17 +55,11 @@ impl<'tcx> NiceRegionError<'_, 'tcx> {
                             sub_span,
                             format!("the lifetime `{sub_symbol}` defined here..."),
                         );
-                        err.span_note(
-                            sup_span,
-                            format!("...must outlive the lifetime defined here"),
-                        );
+                        err.span_note(sup_span, "...must outlive the lifetime defined here");
                     }
                     (Some(sub_span), Some(sup_span), _, _) => {
-                        err.span_note(sub_span, format!("the lifetime defined here..."));
-                        err.span_note(
-                            sup_span,
-                            format!("...must outlive the lifetime defined here"),
-                        );
+                        err.span_note(sub_span, "the lifetime defined here...");
+                        err.span_note(sup_span, "...must outlive the lifetime defined here");
                     }
                     _ => {}
                 }
diff --git a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/static_impl_trait.rs b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/static_impl_trait.rs
index 09f9aa3c8..49ad3ce50 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/static_impl_trait.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/static_impl_trait.rs
@@ -1,20 +1,28 @@
 //! Error Reporting for static impl Traits.
 
+use crate::errors::{
+    ButCallingIntroduces, ButNeedsToSatisfy, DynTraitConstraintSuggestion, MoreTargeted,
+    ReqIntroducedLocations,
+};
 use crate::infer::error_reporting::nice_region_error::NiceRegionError;
 use crate::infer::lexical_region_resolve::RegionResolutionError;
 use crate::infer::{SubregionOrigin, TypeTrace};
 use crate::traits::{ObligationCauseCode, UnifyReceiverContext};
 use rustc_data_structures::fx::FxIndexSet;
-use rustc_errors::{struct_span_err, Applicability, Diagnostic, ErrorGuaranteed, MultiSpan};
+use rustc_errors::{AddToDiagnostic, Applicability, Diagnostic, ErrorGuaranteed, MultiSpan};
 use rustc_hir::def_id::DefId;
 use rustc_hir::intravisit::{walk_ty, Visitor};
-use rustc_hir::{self as hir, GenericBound, Item, ItemKind, Lifetime, LifetimeName, Node, TyKind};
+use rustc_hir::{
+    self as hir, GenericBound, GenericParamKind, Item, ItemKind, Lifetime, LifetimeName, Node,
+    TyKind,
+};
 use rustc_middle::ty::{
     self, AssocItemContainer, StaticLifetimeVisitor, Ty, TyCtxt, TypeSuperVisitable, TypeVisitor,
 };
 use rustc_span::symbol::Ident;
 use rustc_span::Span;
 
+use rustc_span::def_id::LocalDefId;
 use std::ops::ControlFlow;
 
 impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
@@ -49,46 +57,32 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
                     }
 
                     let param = self.find_param_with_region(*sup_r, *sub_r)?;
-                    let lifetime = if sup_r.has_name() {
-                        format!("lifetime `{}`", sup_r)
-                    } else {
-                        "an anonymous lifetime `'_`".to_string()
+                    let simple_ident = param.param.pat.simple_ident();
+
+                    let (has_impl_path, impl_path) = match ctxt.assoc_item.container {
+                        AssocItemContainer::TraitContainer => {
+                            let id = ctxt.assoc_item.container_id(tcx);
+                            (true, tcx.def_path_str(id))
+                        }
+                        AssocItemContainer::ImplContainer => (false, String::new()),
                     };
-                    let mut err = struct_span_err!(
-                        tcx.sess,
-                        cause.span,
-                        E0772,
-                        "{} has {} but calling `{}` introduces an implicit `'static` lifetime \
-                         requirement",
-                        param
-                            .param
-                            .pat
-                            .simple_ident()
-                            .map(|s| format!("`{}`", s))
-                            .unwrap_or_else(|| "`fn` parameter".to_string()),
-                        lifetime,
-                        ctxt.assoc_item.name,
-                    );
-                    err.span_label(param.param_ty_span, &format!("this data with {}...", lifetime));
-                    err.span_label(
-                        cause.span,
-                        &format!(
-                            "...is used and required to live as long as `'static` here \
-                             because of an implicit lifetime bound on the {}",
-                            match ctxt.assoc_item.container {
-                                AssocItemContainer::TraitContainer => {
-                                    let id = ctxt.assoc_item.container_id(tcx);
-                                    format!("`impl` of `{}`", tcx.def_path_str(id))
-                                }
-                                AssocItemContainer::ImplContainer => "inherent `impl`".to_string(),
-                            },
-                        ),
-                    );
+
+                    let mut err = self.tcx().sess.create_err(ButCallingIntroduces {
+                        param_ty_span: param.param_ty_span,
+                        cause_span: cause.span,
+                        has_param_name: simple_ident.is_some(),
+                        param_name: simple_ident.map(|x| x.to_string()).unwrap_or_default(),
+                        has_lifetime: sup_r.has_name(),
+                        lifetime: sup_r.to_string(),
+                        assoc_item: ctxt.assoc_item.name,
+                        has_impl_path,
+                        impl_path,
+                    });
                     if self.find_impl_on_dyn_trait(&mut err, param.param_ty, &ctxt) {
                         let reported = err.emit();
                         return Some(reported);
                     } else {
-                        err.cancel();
+                        err.cancel()
                     }
                 }
                 return None;
@@ -104,25 +98,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
         let sp = var_origin.span();
         let return_sp = sub_origin.span();
         let param = self.find_param_with_region(*sup_r, *sub_r)?;
-        let (lifetime_name, lifetime) = if sup_r.has_name() {
-            (sup_r.to_string(), format!("lifetime `{}`", sup_r))
-        } else {
-            ("'_".to_owned(), "an anonymous lifetime `'_`".to_string())
-        };
-        let param_name = param
-            .param
-            .pat
-            .simple_ident()
-            .map(|s| format!("`{}`", s))
-            .unwrap_or_else(|| "`fn` parameter".to_string());
-        let mut err = struct_span_err!(
-            tcx.sess,
-            sp,
-            E0759,
-            "{} has {} but it needs to satisfy a `'static` lifetime requirement",
-            param_name,
-            lifetime,
-        );
+        let lifetime_name = if sup_r.has_name() { sup_r.to_string() } else { "'_".to_owned() };
 
         let (mention_influencer, influencer_point) =
             if sup_origin.span().overlaps(param.param_ty_span) {
@@ -141,7 +117,6 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
             } else {
                 (!sup_origin.span().overlaps(return_sp), param.param_ty_span)
             };
-        err.span_label(influencer_point, &format!("this data with {}...", lifetime));
 
         debug!("try_report_static_impl_trait: param_info={:?}", param);
 
@@ -155,31 +130,19 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
         spans.dedup_by_key(|span| (span.lo(), span.hi()));
 
         // We try to make the output have fewer overlapping spans if possible.
-        let require_msg = if spans.is_empty() {
-            "...is used and required to live as long as `'static` here"
-        } else {
-            "...and is required to live as long as `'static` here"
-        };
         let require_span =
             if sup_origin.span().overlaps(return_sp) { sup_origin.span() } else { return_sp };
 
-        for span in &spans {
-            err.span_label(*span, "...is used here...");
-        }
-
-        if spans.iter().any(|sp| sp.overlaps(return_sp) || *sp > return_sp) {
-            // If any of the "captured here" labels appears on the same line or after
-            // `require_span`, we put it on a note to ensure the text flows by appearing
-            // always at the end.
-            err.span_note(require_span, require_msg);
+        let spans_empty = spans.is_empty();
+        let require_as_note = spans.iter().any(|sp| sp.overlaps(return_sp) || *sp > return_sp);
+        let bound = if let SubregionOrigin::RelateParamBound(_, _, Some(bound)) = sub_origin {
+            Some(*bound)
         } else {
-            // We don't need a note, it's already at the end, it can be shown as a `span_label`.
-            err.span_label(require_span, require_msg);
-        }
+            None
+        };
+
+        let mut subdiag = None;
 
-        if let SubregionOrigin::RelateParamBound(_, _, Some(bound)) = sub_origin {
-            err.span_note(*bound, "`'static` lifetime requirement introduced by this bound");
-        }
         if let SubregionOrigin::Subtype(box TypeTrace { cause, .. }) = sub_origin {
             if let ObligationCauseCode::ReturnValue(hir_id)
             | ObligationCauseCode::BlockTailExpression(hir_id) = cause.code()
@@ -187,33 +150,50 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
                 let parent_id = tcx.hir().get_parent_item(*hir_id);
                 if let Some(fn_decl) = tcx.hir().fn_decl_by_hir_id(parent_id.into()) {
                     let mut span: MultiSpan = fn_decl.output.span().into();
+                    let mut spans = Vec::new();
                     let mut add_label = true;
                     if let hir::FnRetTy::Return(ty) = fn_decl.output {
                         let mut v = StaticLifetimeVisitor(vec![], tcx.hir());
                         v.visit_ty(ty);
                         if !v.0.is_empty() {
                             span = v.0.clone().into();
-                            for sp in v.0 {
-                                span.push_span_label(sp, "`'static` requirement introduced here");
-                            }
+                            spans = v.0;
                             add_label = false;
                         }
                     }
-                    if add_label {
-                        span.push_span_label(
-                            fn_decl.output.span(),
-                            "requirement introduced by this return type",
-                        );
-                    }
-                    span.push_span_label(cause.span, "because of this returned expression");
-                    err.span_note(
+                    let fn_decl_span = fn_decl.output.span();
+
+                    subdiag = Some(ReqIntroducedLocations {
                         span,
-                        "`'static` lifetime requirement introduced by the return type",
-                    );
+                        spans,
+                        fn_decl_span,
+                        cause_span: cause.span,
+                        add_label,
+                    });
                 }
             }
         }
 
+        let diag = ButNeedsToSatisfy {
+            sp,
+            influencer_point,
+            spans: spans.clone(),
+            // If any of the "captured here" labels appears on the same line or after
+            // `require_span`, we put it on a note to ensure the text flows by appearing
+            // always at the end.
+            require_span_as_note: require_as_note.then_some(require_span),
+            // We don't need a note, it's already at the end, it can be shown as a `span_label`.
+            require_span_as_label: (!require_as_note).then_some(require_span),
+            req_introduces_loc: subdiag,
+
+            has_lifetime: sup_r.has_name(),
+            lifetime: sup_r.to_string(),
+            spans_empty,
+            bound,
+        };
+
+        let mut err = self.tcx().sess.create_err(diag);
+
         let fn_returns = tcx.return_type_impl_or_dyn_traits(anon_reg_sup.def_id);
 
         let mut override_error_code = None;
@@ -239,7 +219,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
             let mut v = TraitObjectVisitor(FxIndexSet::default());
             v.visit_ty(param.param_ty);
             if let Some((ident, self_ty)) =
-                self.get_impl_ident_and_self_ty_from_trait(item_def_id, &v.0)
+                NiceRegionError::get_impl_ident_and_self_ty_from_trait(tcx, item_def_id, &v.0)
                 && self.suggest_constrain_dyn_trait_in_impl(&mut err, &v.0, ident, self_ty)
             {
                 override_error_code = Some(ident.name);
@@ -247,12 +227,8 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
         }
         if let (Some(ident), true) = (override_error_code, fn_returns.is_empty()) {
             // Provide a more targeted error code and description.
-            err.code(rustc_errors::error_code!(E0772));
-            err.set_primary_message(&format!(
-                "{} has {} but calling `{}` introduces an implicit `'static` lifetime \
-                requirement",
-                param_name, lifetime, ident,
-            ));
+            let retarget_subdiag = MoreTargeted { ident };
+            retarget_subdiag.add_to_diagnostic(&mut err);
         }
 
         let arg = match param.param.pat.simple_ident() {
@@ -268,6 +244,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
             Some(arg),
             captures,
             Some((param.param_ty_span, param.param_ty.to_string())),
+            Some(anon_reg_sup.def_id),
         );
 
         let reported = err.emit();
@@ -283,6 +260,7 @@ pub fn suggest_new_region_bound(
     arg: Option<String>,
     captures: String,
     param: Option<(Span, String)>,
+    scope_def_id: Option<LocalDefId>,
 ) {
     debug!("try_report_static_impl_trait: fn_return={:?}", fn_returns);
     // FIXME: account for the need of parens in `&(dyn Trait + '_)`
@@ -309,19 +287,12 @@ pub fn suggest_new_region_bound(
                 let did = item_id.owner_id.to_def_id();
                 let ty = tcx.mk_opaque(did, ty::InternalSubsts::identity_for_item(tcx, did));
 
-                if let Some(span) = opaque
-                    .bounds
-                    .iter()
-                    .filter_map(|arg| match arg {
-                        GenericBound::Outlives(Lifetime {
-                            res: LifetimeName::Static,
-                            ident,
-                            ..
-                        }) => Some(ident.span),
-                        _ => None,
-                    })
-                    .next()
-                {
+                if let Some(span) = opaque.bounds.iter().find_map(|arg| match arg {
+                    GenericBound::Outlives(Lifetime {
+                        res: LifetimeName::Static, ident, ..
+                    }) => Some(ident.span),
+                    _ => None,
+                }) {
                     if let Some(explicit_static) = &explicit_static {
                         err.span_suggestion_verbose(
                             span,
@@ -330,7 +301,7 @@ pub fn suggest_new_region_bound(
                             Applicability::MaybeIncorrect,
                         );
                     }
-                    if let Some((param_span, param_ty)) = param.clone() {
+                    if let Some((param_span, ref param_ty)) = param {
                         err.span_suggestion_verbose(
                             param_span,
                             add_static_bound,
@@ -338,27 +309,78 @@ pub fn suggest_new_region_bound(
                             Applicability::MaybeIncorrect,
                         );
                     }
-                } else if opaque
-                    .bounds
-                    .iter()
-                    .filter_map(|arg| match arg {
-                        GenericBound::Outlives(Lifetime { ident, .. })
-                            if ident.name.to_string() == lifetime_name =>
-                        {
-                            Some(ident.span)
-                        }
-                        _ => None,
-                    })
-                    .next()
-                    .is_some()
-                {
+                } else if opaque.bounds.iter().any(|arg| match arg {
+                    GenericBound::Outlives(Lifetime { ident, .. })
+                        if ident.name.to_string() == lifetime_name =>
+                    {
+                        true
+                    }
+                    _ => false,
+                }) {
                 } else {
-                    err.span_suggestion_verbose(
-                        fn_return.span.shrink_to_hi(),
-                        &format!("{declare} `{ty}` {captures}, {explicit}",),
-                        &plus_lt,
-                        Applicability::MaybeIncorrect,
-                    );
+                    // get a lifetime name of existing named lifetimes if any
+                    let existing_lt_name = if let Some(id) = scope_def_id
+                        && let Some(generics) = tcx.hir().get_generics(id)
+                        && let named_lifetimes = generics
+                        .params
+                        .iter()
+                        .filter(|p| matches!(p.kind, GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit }))
+                        .map(|p| { if let hir::ParamName::Plain(name) = p.name {Some(name.to_string())} else {None}})
+                        .filter(|n| ! matches!(n, None))
+                        .collect::<Vec<_>>()
+                        && named_lifetimes.len() > 0 {
+                        named_lifetimes[0].clone()
+                    } else {
+                        None
+                    };
+                    let name = if let Some(name) = &existing_lt_name {
+                        format!("{}", name)
+                    } else {
+                        format!("'a")
+                    };
+                    // if there are more than one elided lifetimes in inputs, the explicit `'_` lifetime cannot be used.
+                    // introducing a new lifetime `'a` or making use of one from existing named lifetimes if any
+                    if let Some(id) = scope_def_id
+                        && let Some(generics) = tcx.hir().get_generics(id)
+                        && let mut spans_suggs = generics
+                            .params
+                            .iter()
+                            .filter(|p| p.is_elided_lifetime())
+                            .map(|p|
+                                  if p.span.hi() - p.span.lo() == rustc_span::BytePos(1) { // Ampersand (elided without '_)
+                                      (p.span.shrink_to_hi(),format!("{name} "))
+                                  } else { // Underscore (elided with '_)
+                                      (p.span, format!("{name}"))
+                                  }
+                            )
+                            .collect::<Vec<_>>()
+                        && spans_suggs.len() > 1
+                    {
+                        let use_lt =
+                        if existing_lt_name == None {
+                            spans_suggs.push((generics.span.shrink_to_hi(), format!("<{name}>")));
+                            format!("you can introduce a named lifetime parameter `{name}`")
+                        } else {
+                            // make use the existing named lifetime
+                            format!("you can use the named lifetime parameter `{name}`")
+                        };
+                        spans_suggs
+                            .push((fn_return.span.shrink_to_hi(), format!(" + {name} ")));
+                        err.multipart_suggestion_verbose(
+                            &format!(
+                                "{declare} `{ty}` {captures}, {use_lt}",
+                            ),
+                            spans_suggs,
+                            Applicability::MaybeIncorrect,
+                        );
+                    } else {
+                        err.span_suggestion_verbose(
+                            fn_return.span.shrink_to_hi(),
+                            &format!("{declare} `{ty}` {captures}, {explicit}",),
+                            &plus_lt,
+                            Applicability::MaybeIncorrect,
+                        );
+                    }
                 }
             }
             TyKind::TraitObject(_, lt, _) => {
@@ -403,66 +425,54 @@ pub fn suggest_new_region_bound(
 }
 
 impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
-    fn get_impl_ident_and_self_ty_from_trait(
-        &self,
+    pub fn get_impl_ident_and_self_ty_from_trait(
+        tcx: TyCtxt<'tcx>,
         def_id: DefId,
         trait_objects: &FxIndexSet<DefId>,
     ) -> Option<(Ident, &'tcx hir::Ty<'tcx>)> {
-        let tcx = self.tcx();
-        match tcx.hir().get_if_local(def_id) {
-            Some(Node::ImplItem(impl_item)) => {
-                match tcx.hir().find_by_def_id(tcx.hir().get_parent_item(impl_item.hir_id()).def_id)
+        match tcx.hir().get_if_local(def_id)? {
+            Node::ImplItem(impl_item) => {
+                let impl_did = tcx.hir().get_parent_item(impl_item.hir_id());
+                if let hir::OwnerNode::Item(Item {
+                    kind: ItemKind::Impl(hir::Impl { self_ty, .. }),
+                    ..
+                }) = tcx.hir().owner(impl_did)
                 {
-                    Some(Node::Item(Item {
-                        kind: ItemKind::Impl(hir::Impl { self_ty, .. }),
-                        ..
-                    })) => Some((impl_item.ident, self_ty)),
-                    _ => None,
+                    Some((impl_item.ident, self_ty))
+                } else {
+                    None
                 }
             }
-            Some(Node::TraitItem(trait_item)) => {
-                let trait_did = tcx.hir().get_parent_item(trait_item.hir_id());
-                match tcx.hir().find_by_def_id(trait_did.def_id) {
-                    Some(Node::Item(Item { kind: ItemKind::Trait(..), .. })) => {
-                        // The method being called is defined in the `trait`, but the `'static`
-                        // obligation comes from the `impl`. Find that `impl` so that we can point
-                        // at it in the suggestion.
-                        let trait_did = trait_did.to_def_id();
-                        match tcx
-                            .hir()
-                            .trait_impls(trait_did)
-                            .iter()
-                            .filter_map(|&impl_did| {
-                                match tcx.hir().get_if_local(impl_did.to_def_id()) {
-                                    Some(Node::Item(Item {
-                                        kind: ItemKind::Impl(hir::Impl { self_ty, .. }),
-                                        ..
-                                    })) if trait_objects.iter().all(|did| {
-                                        // FIXME: we should check `self_ty` against the receiver
-                                        // type in the `UnifyReceiver` context, but for now, use
-                                        // this imperfect proxy. This will fail if there are
-                                        // multiple `impl`s for the same trait like
-                                        // `impl Foo for Box<dyn Bar>` and `impl Foo for dyn Bar`.
-                                        // In that case, only the first one will get suggestions.
-                                        let mut traits = vec![];
-                                        let mut hir_v = HirTraitObjectVisitor(&mut traits, *did);
-                                        hir_v.visit_ty(self_ty);
-                                        !traits.is_empty()
-                                    }) =>
-                                    {
-                                        Some(self_ty)
-                                    }
-                                    _ => None,
-                                }
-                            })
-                            .next()
-                        {
-                            Some(self_ty) => Some((trait_item.ident, self_ty)),
-                            _ => None,
-                        }
+            Node::TraitItem(trait_item) => {
+                let trait_id = tcx.hir().get_parent_item(trait_item.hir_id());
+                debug_assert_eq!(tcx.def_kind(trait_id.def_id), hir::def::DefKind::Trait);
+                // The method being called is defined in the `trait`, but the `'static`
+                // obligation comes from the `impl`. Find that `impl` so that we can point
+                // at it in the suggestion.
+                let trait_did = trait_id.to_def_id();
+                tcx.hir().trait_impls(trait_did).iter().find_map(|&impl_did| {
+                    if let Node::Item(Item {
+                        kind: ItemKind::Impl(hir::Impl { self_ty, .. }),
+                        ..
+                    }) = tcx.hir().find_by_def_id(impl_did)?
+                        && trait_objects.iter().all(|did| {
+                            // FIXME: we should check `self_ty` against the receiver
+                            // type in the `UnifyReceiver` context, but for now, use
+                            // this imperfect proxy. This will fail if there are
+                            // multiple `impl`s for the same trait like
+                            // `impl Foo for Box<dyn Bar>` and `impl Foo for dyn Bar`.
+                            // In that case, only the first one will get suggestions.
+                            let mut traits = vec![];
+                            let mut hir_v = HirTraitObjectVisitor(&mut traits, *did);
+                            hir_v.visit_ty(self_ty);
+                            !traits.is_empty()
+                        })
+                    {
+                        Some((trait_item.ident, *self_ty))
+                    } else {
+                        None
                     }
-                    _ => None,
-                }
+                })
             }
             _ => None,
         }
@@ -493,7 +503,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
 
         // Get the `Ident` of the method being called and the corresponding `impl` (to point at
         // `Bar` in `impl Foo for dyn Bar {}` and the definition of the method being called).
-        let Some((ident, self_ty)) = self.get_impl_ident_and_self_ty_from_trait(instance.def_id(), &v.0) else {
+        let Some((ident, self_ty)) = NiceRegionError::get_impl_ident_and_self_ty_from_trait(tcx, instance.def_id(), &v.0) else {
             return false;
         };
 
@@ -513,21 +523,9 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
             let mut traits = vec![];
             let mut hir_v = HirTraitObjectVisitor(&mut traits, *found_did);
             hir_v.visit_ty(&self_ty);
-            for span in &traits {
-                let mut multi_span: MultiSpan = vec![*span].into();
-                multi_span
-                    .push_span_label(*span, "this has an implicit `'static` lifetime requirement");
-                multi_span.push_span_label(
-                    ident.span,
-                    "calling this method introduces the `impl`'s 'static` requirement",
-                );
-                err.span_note(multi_span, "the used `impl` has a `'static` requirement");
-                err.span_suggestion_verbose(
-                    span.shrink_to_hi(),
-                    "consider relaxing the implicit `'static` requirement",
-                    " + '_",
-                    Applicability::MaybeIncorrect,
-                );
+            for &span in &traits {
+                let subdiag = DynTraitConstraintSuggestion { span, ident };
+                subdiag.add_to_diagnostic(err);
                 suggested = true;
             }
         }
@@ -545,7 +543,7 @@ impl<'tcx> TypeVisitor<'tcx> for TraitObjectVisitor {
                 if let Some(def_id) = preds.principal_def_id() {
                     self.0.insert(def_id);
                 }
-                ControlFlow::CONTINUE
+                ControlFlow::Continue(())
             }
             _ => t.super_visit_with(self),
         }
diff --git a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/trait_impl_difference.rs b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/trait_impl_difference.rs
index 5d536e982..40c0c806e 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/trait_impl_difference.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/trait_impl_difference.rs
@@ -1,15 +1,17 @@
 //! Error Reporting for `impl` items that do not match the obligations from their `trait`.
 
+use crate::errors::{ConsiderBorrowingParamHelp, RelationshipHelp, TraitImplDiff};
 use crate::infer::error_reporting::nice_region_error::NiceRegionError;
 use crate::infer::lexical_region_resolve::RegionResolutionError;
-use crate::infer::Subtype;
+use crate::infer::{Subtype, ValuePairs};
 use crate::traits::ObligationCauseCode::CompareImplItemObligation;
-use rustc_errors::{ErrorGuaranteed, MultiSpan};
+use rustc_errors::ErrorGuaranteed;
 use rustc_hir as hir;
 use rustc_hir::def::Res;
 use rustc_hir::def_id::DefId;
 use rustc_hir::intravisit::Visitor;
 use rustc_middle::hir::nested_filter;
+use rustc_middle::ty::error::ExpectedFound;
 use rustc_middle::ty::print::RegionHighlightMode;
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeSuperVisitable, TypeVisitor};
 use rustc_span::Span;
@@ -22,22 +24,27 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
         let error = self.error.as_ref()?;
         debug!("try_report_impl_not_conforming_to_trait {:?}", error);
         if let RegionResolutionError::SubSupConflict(
-                _,
-                var_origin,
-                sub_origin,
-                _sub,
-                sup_origin,
-                _sup,
-                _,
-            ) = error.clone()
+            _,
+            var_origin,
+            sub_origin,
+            _sub,
+            sup_origin,
+            _sup,
+            _,
+        ) = error.clone()
             && let (Subtype(sup_trace), Subtype(sub_trace)) = (&sup_origin, &sub_origin)
-            && let sub_expected_found @ Some((sub_expected, sub_found)) = sub_trace.values.ty()
-            && let sup_expected_found @ Some(_) = sup_trace.values.ty()
             && let CompareImplItemObligation { trait_item_def_id, .. } = sub_trace.cause.code()
-            && sup_expected_found == sub_expected_found
+            && sub_trace.values == sup_trace.values
+            && let ValuePairs::Sigs(ExpectedFound { expected, found }) = sub_trace.values
         {
-            let guar =
-                self.emit_err(var_origin.span(), sub_expected, sub_found, *trait_item_def_id);
+            // FIXME(compiler-errors): Don't like that this needs `Ty`s, but
+            // all of the region highlighting machinery only deals with those.
+            let guar = self.emit_err(
+                var_origin.span(),
+                self.cx.tcx.mk_fn_ptr(ty::Binder::dummy(expected)),
+                self.cx.tcx.mk_fn_ptr(ty::Binder::dummy(found)),
+                *trait_item_def_id,
+            );
             return Some(guar);
         }
         None
@@ -51,10 +58,6 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
         trait_def_id: DefId,
     ) -> ErrorGuaranteed {
         let trait_sp = self.tcx().def_span(trait_def_id);
-        let mut err = self
-            .tcx()
-            .sess
-            .struct_span_err(sp, "`impl` item signature doesn't match `trait` item signature");
 
         // Mark all unnamed regions in the type with a number.
         // This diagnostic is called in response to lifetime errors, so be informative.
@@ -91,9 +94,6 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
         let found =
             self.cx.extract_inference_diagnostics_data(found.into(), Some(found_highlight)).name;
 
-        err.span_label(sp, &format!("found `{}`", found));
-        err.span_label(trait_sp, &format!("expected `{}`", expected));
-
         // Get the span of all the used type parameters in the method.
         let assoc_item = self.tcx().associated_item(trait_def_id);
         let mut visitor = TypeParamSpanVisitor { tcx: self.tcx(), types: vec![] };
@@ -110,26 +110,18 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
             }
             _ => {}
         }
-        let mut type_param_span: MultiSpan = visitor.types.to_vec().into();
-        for &span in &visitor.types {
-            type_param_span
-                .push_span_label(span, "consider borrowing this type parameter in the trait");
-        }
 
-        err.note(&format!("expected `{}`\n   found `{}`", expected, found));
-
-        err.span_help(
-            type_param_span,
-            "the lifetime requirements from the `impl` do not correspond to the requirements in \
-             the `trait`",
-        );
-        if visitor.types.is_empty() {
-            err.help(
-                "verify the lifetime relationships in the `trait` and `impl` between the `self` \
-                 argument, the other inputs and its output",
-            );
-        }
-        err.emit()
+        let diag = TraitImplDiff {
+            sp,
+            trait_sp,
+            note: (),
+            param_help: ConsiderBorrowingParamHelp { spans: visitor.types.to_vec() },
+            rel_help: visitor.types.is_empty().then_some(RelationshipHelp),
+            expected,
+            found,
+        };
+
+        self.tcx().sess.emit_err(diag)
     }
 }
 
@@ -147,7 +139,7 @@ impl<'tcx> Visitor<'tcx> for TypeParamSpanVisitor<'tcx> {
 
     fn visit_ty(&mut self, arg: &'tcx hir::Ty<'tcx>) {
         match arg.kind {
-            hir::TyKind::Rptr(_, ref mut_ty) => {
+            hir::TyKind::Ref(_, ref mut_ty) => {
                 // We don't want to suggest looking into borrowing `&T` or `&Self`.
                 hir::intravisit::walk_ty(self, mut_ty.ty);
                 return;
diff --git a/compiler/rustc_infer/src/infer/error_reporting/note.rs b/compiler/rustc_infer/src/infer/error_reporting/note.rs
index d2dffa4a0..b18cbd404 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/note.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/note.rs
@@ -2,11 +2,14 @@ use crate::errors::RegionOriginNote;
 use crate::infer::error_reporting::{note_and_explain_region, TypeErrCtxt};
 use crate::infer::{self, SubregionOrigin};
 use rustc_errors::{
-    fluent, struct_span_err, AddToDiagnostic, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
+    fluent, struct_span_err, AddToDiagnostic, Applicability, Diagnostic, DiagnosticBuilder,
+    ErrorGuaranteed,
 };
+use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_middle::traits::ObligationCauseCode;
 use rustc_middle::ty::error::TypeError;
-use rustc_middle::ty::{self, Region};
+use rustc_middle::ty::{self, IsSuggestable, Region};
+use rustc_span::symbol::kw;
 
 use super::ObligationCauseAsDiagArg;
 
@@ -22,29 +25,10 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             infer::Reborrow(span) => {
                 RegionOriginNote::Plain { span, msg: fluent::infer_reborrow }.add_to_diagnostic(err)
             }
-            infer::ReborrowUpvar(span, ref upvar_id) => {
-                let var_name = self.tcx.hir().name(upvar_id.var_path.hir_id);
-                RegionOriginNote::WithName {
-                    span,
-                    msg: fluent::infer_reborrow,
-                    name: &var_name.to_string(),
-                    continues: false,
-                }
-                .add_to_diagnostic(err);
-            }
             infer::RelateObjectBound(span) => {
                 RegionOriginNote::Plain { span, msg: fluent::infer_relate_object_bound }
                     .add_to_diagnostic(err);
             }
-            infer::DataBorrowed(ty, span) => {
-                RegionOriginNote::WithName {
-                    span,
-                    msg: fluent::infer_data_borrowed,
-                    name: &self.ty_to_string(ty),
-                    continues: false,
-                }
-                .add_to_diagnostic(err);
-            }
             infer::ReferenceOutlivesReferent(ty, span) => {
                 RegionOriginNote::WithName {
                     span,
@@ -159,33 +143,6 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                 );
                 err
             }
-            infer::ReborrowUpvar(span, ref upvar_id) => {
-                let var_name = self.tcx.hir().name(upvar_id.var_path.hir_id);
-                let mut err = struct_span_err!(
-                    self.tcx.sess,
-                    span,
-                    E0313,
-                    "lifetime of borrowed pointer outlives lifetime of captured variable `{}`...",
-                    var_name
-                );
-                note_and_explain_region(
-                    self.tcx,
-                    &mut err,
-                    "...the borrowed pointer is valid for ",
-                    sub,
-                    "...",
-                    None,
-                );
-                note_and_explain_region(
-                    self.tcx,
-                    &mut err,
-                    &format!("...but `{}` is only valid for ", var_name),
-                    sup,
-                    "",
-                    None,
-                );
-                err
-            }
             infer::RelateObjectBound(span) => {
                 let mut err = struct_span_err!(
                     self.tcx.sess,
@@ -261,32 +218,6 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                 );
                 err
             }
-            infer::DataBorrowed(ty, span) => {
-                let mut err = struct_span_err!(
-                    self.tcx.sess,
-                    span,
-                    E0490,
-                    "a value of type `{}` is borrowed for too long",
-                    self.ty_to_string(ty)
-                );
-                note_and_explain_region(
-                    self.tcx,
-                    &mut err,
-                    "the type is valid for ",
-                    sub,
-                    "",
-                    None,
-                );
-                note_and_explain_region(
-                    self.tcx,
-                    &mut err,
-                    "but the borrow lasts for ",
-                    sup,
-                    "",
-                    None,
-                );
-                err
-            }
             infer::ReferenceOutlivesReferent(ty, span) => {
                 let mut err = struct_span_err!(
                     self.tcx.sess,
@@ -313,55 +244,38 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                 );
                 err
             }
-            infer::CompareImplItemObligation { span, impl_item_def_id, trait_item_def_id } => self
-                .report_extra_impl_obligation(
+            infer::CompareImplItemObligation { span, impl_item_def_id, trait_item_def_id } => {
+                let mut err = self.report_extra_impl_obligation(
                     span,
                     impl_item_def_id,
                     trait_item_def_id,
                     &format!("`{}: {}`", sup, sub),
-                ),
+                );
+                // We should only suggest rewriting the `where` clause if the predicate is within that `where` clause
+                if let Some(generics) = self.tcx.hir().get_generics(impl_item_def_id)
+                    && generics.where_clause_span.contains(span)
+                {
+                    self.suggest_copy_trait_method_bounds(
+                        trait_item_def_id,
+                        impl_item_def_id,
+                        &mut err,
+                    );
+                }
+                err
+            }
             infer::CheckAssociatedTypeBounds { impl_item_def_id, trait_item_def_id, parent } => {
                 let mut err = self.report_concrete_failure(*parent, sub, sup);
-
                 let trait_item_span = self.tcx.def_span(trait_item_def_id);
                 let item_name = self.tcx.item_name(impl_item_def_id.to_def_id());
                 err.span_label(
                     trait_item_span,
                     format!("definition of `{}` from trait", item_name),
                 );
-
-                let trait_predicates = self.tcx.explicit_predicates_of(trait_item_def_id);
-                let impl_predicates = self.tcx.explicit_predicates_of(impl_item_def_id);
-
-                let impl_predicates: rustc_data_structures::fx::FxHashSet<_> =
-                    impl_predicates.predicates.into_iter().map(|(pred, _)| pred).collect();
-                let clauses: Vec<_> = trait_predicates
-                    .predicates
-                    .into_iter()
-                    .filter(|&(pred, _)| !impl_predicates.contains(pred))
-                    .map(|(pred, _)| format!("{}", pred))
-                    .collect();
-
-                if !clauses.is_empty() {
-                    let generics = self.tcx.hir().get_generics(impl_item_def_id).unwrap();
-                    let where_clause_span = generics.tail_span_for_predicate_suggestion();
-
-                    let suggestion = format!(
-                        "{} {}",
-                        generics.add_where_or_trailing_comma(),
-                        clauses.join(", "),
-                    );
-                    err.span_suggestion(
-                        where_clause_span,
-                        &format!(
-                            "try copying {} from the trait",
-                            if clauses.len() > 1 { "these clauses" } else { "this clause" }
-                        ),
-                        suggestion,
-                        rustc_errors::Applicability::MaybeIncorrect,
-                    );
-                }
-
+                self.suggest_copy_trait_method_bounds(
+                    trait_item_def_id,
+                    impl_item_def_id,
+                    &mut err,
+                );
                 err
             }
             infer::AscribeUserTypeProvePredicate(span) => {
@@ -388,6 +302,65 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         }
     }
 
+    pub fn suggest_copy_trait_method_bounds(
+        &self,
+        trait_item_def_id: DefId,
+        impl_item_def_id: LocalDefId,
+        err: &mut Diagnostic,
+    ) {
+        // FIXME(compiler-errors): Right now this is only being used for region
+        // predicate mismatches. Ideally, we'd use it for *all* predicate mismatches,
+        // but right now it's not really very smart when it comes to implicit `Sized`
+        // predicates and bounds on the trait itself.
+
+        let Some(impl_def_id) =
+            self.tcx.associated_item(impl_item_def_id).impl_container(self.tcx) else { return; };
+        let Some(trait_ref) = self
+            .tcx
+            .impl_trait_ref(impl_def_id)
+            else { return; };
+        let trait_substs = trait_ref
+            .subst_identity()
+            // Replace the explicit self type with `Self` for better suggestion rendering
+            .with_self_ty(self.tcx, self.tcx.mk_ty_param(0, kw::SelfUpper))
+            .substs;
+        let trait_item_substs =
+            ty::InternalSubsts::identity_for_item(self.tcx, impl_item_def_id.to_def_id())
+                .rebase_onto(self.tcx, impl_def_id, trait_substs);
+
+        let Ok(trait_predicates) = self
+            .tcx
+            .explicit_predicates_of(trait_item_def_id)
+            .instantiate_own(self.tcx, trait_item_substs)
+            .map(|(pred, _)| {
+                if pred.is_suggestable(self.tcx, false) {
+                    Ok(pred.to_string())
+                } else {
+                    Err(())
+                }
+            })
+            .collect::<Result<Vec<_>, ()>>() else { return; };
+
+        let Some(generics) = self.tcx.hir().get_generics(impl_item_def_id) else { return; };
+
+        if trait_predicates.is_empty() {
+            err.span_suggestion_verbose(
+                generics.where_clause_span,
+                "remove the `where` clause",
+                String::new(),
+                Applicability::MachineApplicable,
+            );
+        } else {
+            let space = if generics.where_clause_span.is_empty() { " " } else { "" };
+            err.span_suggestion_verbose(
+                generics.where_clause_span,
+                "copy the `where` clause predicates from the trait",
+                format!("{space}where {}", trait_predicates.join(", ")),
+                Applicability::MachineApplicable,
+            );
+        }
+    }
+
     pub(super) fn report_placeholder_failure(
         &self,
         placeholder_origin: SubregionOrigin<'tcx>,
diff --git a/compiler/rustc_infer/src/infer/error_reporting/note_region.rs b/compiler/rustc_infer/src/infer/error_reporting/note_region.rs
deleted file mode 100644
index 41b115f33..000000000
--- a/compiler/rustc_infer/src/infer/error_reporting/note_region.rs
+++ /dev/null
@@ -1,427 +0,0 @@
-use crate::errors::RegionOriginNote;
-use crate::infer::error_reporting::{note_and_explain_region, TypeErrCtxt};
-use crate::infer::{self, SubregionOrigin};
-use rustc_errors::{
-    fluent, struct_span_err, AddToDiagnostic, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
-};
-use rustc_middle::traits::ObligationCauseCode;
-use rustc_middle::ty::error::TypeError;
-use rustc_middle::ty::{self, Region};
-
-use super::ObligationCauseAsDiagArg;
-
-impl<'tcx> TypeErrCtxt<'_, 'tcx> {
-    pub(super) fn note_region_origin(&self, err: &mut Diagnostic, origin: &SubregionOrigin<'tcx>) {
-        match *origin {
-            infer::Subtype(ref trace) => RegionOriginNote::WithRequirement {
-                span: trace.cause.span,
-                requirement: ObligationCauseAsDiagArg(trace.cause.clone()),
-                expected_found: self.values_str(trace.values),
-            }
-            .add_to_diagnostic(err),
-            infer::Reborrow(span) => {
-                RegionOriginNote::Plain { span, msg: fluent::infer_reborrow }.add_to_diagnostic(err)
-            }
-            infer::ReborrowUpvar(span, ref upvar_id) => {
-                let var_name = self.tcx.hir().name(upvar_id.var_path.hir_id);
-                RegionOriginNote::WithName {
-                    span,
-                    msg: fluent::infer_reborrow,
-                    name: &var_name.to_string(),
-                    continues: false,
-                }
-                .add_to_diagnostic(err);
-            }
-            infer::RelateObjectBound(span) => {
-                RegionOriginNote::Plain { span, msg: fluent::infer_relate_object_bound }
-                    .add_to_diagnostic(err);
-            }
-            infer::DataBorrowed(ty, span) => {
-                RegionOriginNote::WithName {
-                    span,
-                    msg: fluent::infer_data_borrowed,
-                    name: &self.ty_to_string(ty),
-                    continues: false,
-                }
-                .add_to_diagnostic(err);
-            }
-            infer::ReferenceOutlivesReferent(ty, span) => {
-                RegionOriginNote::WithName {
-                    span,
-                    msg: fluent::infer_reference_outlives_referent,
-                    name: &self.ty_to_string(ty),
-                    continues: false,
-                }
-                .add_to_diagnostic(err);
-            }
-            infer::RelateParamBound(span, ty, opt_span) => {
-                RegionOriginNote::WithName {
-                    span,
-                    msg: fluent::infer_relate_param_bound,
-                    name: &self.ty_to_string(ty),
-                    continues: opt_span.is_some(),
-                }
-                .add_to_diagnostic(err);
-                if let Some(span) = opt_span {
-                    RegionOriginNote::Plain { span, msg: fluent::infer_relate_param_bound_2 }
-                        .add_to_diagnostic(err);
-                }
-            }
-            infer::RelateRegionParamBound(span) => {
-                RegionOriginNote::Plain { span, msg: fluent::infer_relate_region_param_bound }
-                    .add_to_diagnostic(err);
-            }
-            infer::CompareImplItemObligation { span, .. } => {
-                RegionOriginNote::Plain { span, msg: fluent::infer_compare_impl_item_obligation }
-                    .add_to_diagnostic(err);
-            }
-            infer::CheckAssociatedTypeBounds { ref parent, .. } => {
-                self.note_region_origin(err, &parent);
-            }
-            infer::AscribeUserTypeProvePredicate(span) => {
-                RegionOriginNote::Plain {
-                    span,
-                    msg: fluent::infer_ascribe_user_type_prove_predicate,
-                }
-                .add_to_diagnostic(err);
-            }
-        }
-    }
-
-    pub(super) fn report_concrete_failure(
-        &self,
-        origin: SubregionOrigin<'tcx>,
-        sub: Region<'tcx>,
-        sup: Region<'tcx>,
-    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
-        match origin {
-            infer::Subtype(box trace) => {
-                let terr = TypeError::RegionsDoesNotOutlive(sup, sub);
-                let mut err = self.report_and_explain_type_error(trace, terr);
-                match (*sub, *sup) {
-                    (ty::RePlaceholder(_), ty::RePlaceholder(_)) => {}
-                    (ty::RePlaceholder(_), _) => {
-                        note_and_explain_region(
-                            self.tcx,
-                            &mut err,
-                            "",
-                            sup,
-                            " doesn't meet the lifetime requirements",
-                            None,
-                        );
-                    }
-                    (_, ty::RePlaceholder(_)) => {
-                        note_and_explain_region(
-                            self.tcx,
-                            &mut err,
-                            "the required lifetime does not necessarily outlive ",
-                            sub,
-                            "",
-                            None,
-                        );
-                    }
-                    _ => {
-                        note_and_explain_region(self.tcx, &mut err, "", sup, "...", None);
-                        note_and_explain_region(
-                            self.tcx,
-                            &mut err,
-                            "...does not necessarily outlive ",
-                            sub,
-                            "",
-                            None,
-                        );
-                    }
-                }
-                err
-            }
-            infer::Reborrow(span) => {
-                let mut err = struct_span_err!(
-                    self.tcx.sess,
-                    span,
-                    E0312,
-                    "lifetime of reference outlives lifetime of borrowed content..."
-                );
-                note_and_explain_region(
-                    self.tcx,
-                    &mut err,
-                    "...the reference is valid for ",
-                    sub,
-                    "...",
-                    None,
-                );
-                note_and_explain_region(
-                    self.tcx,
-                    &mut err,
-                    "...but the borrowed content is only valid for ",
-                    sup,
-                    "",
-                    None,
-                );
-                err
-            }
-            infer::ReborrowUpvar(span, ref upvar_id) => {
-                let var_name = self.tcx.hir().name(upvar_id.var_path.hir_id);
-                let mut err = struct_span_err!(
-                    self.tcx.sess,
-                    span,
-                    E0313,
-                    "lifetime of borrowed pointer outlives lifetime of captured variable `{}`...",
-                    var_name
-                );
-                note_and_explain_region(
-                    self.tcx,
-                    &mut err,
-                    "...the borrowed pointer is valid for ",
-                    sub,
-                    "...",
-                    None,
-                );
-                note_and_explain_region(
-                    self.tcx,
-                    &mut err,
-                    &format!("...but `{}` is only valid for ", var_name),
-                    sup,
-                    "",
-                    None,
-                );
-                err
-            }
-            infer::RelateObjectBound(span) => {
-                let mut err = struct_span_err!(
-                    self.tcx.sess,
-                    span,
-                    E0476,
-                    "lifetime of the source pointer does not outlive lifetime bound of the \
-                     object type"
-                );
-                note_and_explain_region(
-                    self.tcx,
-                    &mut err,
-                    "object type is valid for ",
-                    sub,
-                    "",
-                    None,
-                );
-                note_and_explain_region(
-                    self.tcx,
-                    &mut err,
-                    "source pointer is only valid for ",
-                    sup,
-                    "",
-                    None,
-                );
-                err
-            }
-            infer::RelateParamBound(span, ty, opt_span) => {
-                let mut err = struct_span_err!(
-                    self.tcx.sess,
-                    span,
-                    E0477,
-                    "the type `{}` does not fulfill the required lifetime",
-                    self.ty_to_string(ty)
-                );
-                match *sub {
-                    ty::ReStatic => note_and_explain_region(
-                        self.tcx,
-                        &mut err,
-                        "type must satisfy ",
-                        sub,
-                        if opt_span.is_some() { " as required by this binding" } else { "" },
-                        opt_span,
-                    ),
-                    _ => note_and_explain_region(
-                        self.tcx,
-                        &mut err,
-                        "type must outlive ",
-                        sub,
-                        if opt_span.is_some() { " as required by this binding" } else { "" },
-                        opt_span,
-                    ),
-                }
-                err
-            }
-            infer::RelateRegionParamBound(span) => {
-                let mut err =
-                    struct_span_err!(self.tcx.sess, span, E0478, "lifetime bound not satisfied");
-                note_and_explain_region(
-                    self.tcx,
-                    &mut err,
-                    "lifetime parameter instantiated with ",
-                    sup,
-                    "",
-                    None,
-                );
-                note_and_explain_region(
-                    self.tcx,
-                    &mut err,
-                    "but lifetime parameter must outlive ",
-                    sub,
-                    "",
-                    None,
-                );
-                err
-            }
-            infer::DataBorrowed(ty, span) => {
-                let mut err = struct_span_err!(
-                    self.tcx.sess,
-                    span,
-                    E0490,
-                    "a value of type `{}` is borrowed for too long",
-                    self.ty_to_string(ty)
-                );
-                note_and_explain_region(
-                    self.tcx,
-                    &mut err,
-                    "the type is valid for ",
-                    sub,
-                    "",
-                    None,
-                );
-                note_and_explain_region(
-                    self.tcx,
-                    &mut err,
-                    "but the borrow lasts for ",
-                    sup,
-                    "",
-                    None,
-                );
-                err
-            }
-            infer::ReferenceOutlivesReferent(ty, span) => {
-                let mut err = struct_span_err!(
-                    self.tcx.sess,
-                    span,
-                    E0491,
-                    "in type `{}`, reference has a longer lifetime than the data it references",
-                    self.ty_to_string(ty)
-                );
-                note_and_explain_region(
-                    self.tcx,
-                    &mut err,
-                    "the pointer is valid for ",
-                    sub,
-                    "",
-                    None,
-                );
-                note_and_explain_region(
-                    self.tcx,
-                    &mut err,
-                    "but the referenced data is only valid for ",
-                    sup,
-                    "",
-                    None,
-                );
-                err
-            }
-            infer::CompareImplItemObligation { span, impl_item_def_id, trait_item_def_id } => self
-                .report_extra_impl_obligation(
-                    span,
-                    impl_item_def_id,
-                    trait_item_def_id,
-                    &format!("`{}: {}`", sup, sub),
-                ),
-            infer::CheckAssociatedTypeBounds { impl_item_def_id, trait_item_def_id, parent } => {
-                let mut err = self.report_concrete_failure(*parent, sub, sup);
-
-                let trait_item_span = self.tcx.def_span(trait_item_def_id);
-                let item_name = self.tcx.item_name(impl_item_def_id.to_def_id());
-                err.span_label(
-                    trait_item_span,
-                    format!("definition of `{}` from trait", item_name),
-                );
-
-                let trait_predicates = self.tcx.explicit_predicates_of(trait_item_def_id);
-                let impl_predicates = self.tcx.explicit_predicates_of(impl_item_def_id);
-
-                let impl_predicates: rustc_data_structures::fx::FxHashSet<_> =
-                    impl_predicates.predicates.into_iter().map(|(pred, _)| pred).collect();
-                let clauses: Vec<_> = trait_predicates
-                    .predicates
-                    .into_iter()
-                    .filter(|&(pred, _)| !impl_predicates.contains(pred))
-                    .map(|(pred, _)| format!("{}", pred))
-                    .collect();
-
-                if !clauses.is_empty() {
-                    let generics = self.tcx.hir().get_generics(impl_item_def_id).unwrap();
-                    let where_clause_span = generics.tail_span_for_predicate_suggestion();
-
-                    let suggestion = format!(
-                        "{} {}",
-                        generics.add_where_or_trailing_comma(),
-                        clauses.join(", "),
-                    );
-                    err.span_suggestion(
-                        where_clause_span,
-                        &format!(
-                            "try copying {} from the trait",
-                            if clauses.len() > 1 { "these clauses" } else { "this clause" }
-                        ),
-                        suggestion,
-                        rustc_errors::Applicability::MaybeIncorrect,
-                    );
-                }
-
-                err
-            }
-            infer::AscribeUserTypeProvePredicate(span) => {
-                let mut err =
-                    struct_span_err!(self.tcx.sess, span, E0478, "lifetime bound not satisfied");
-                note_and_explain_region(
-                    self.tcx,
-                    &mut err,
-                    "lifetime instantiated with ",
-                    sup,
-                    "",
-                    None,
-                );
-                note_and_explain_region(
-                    self.tcx,
-                    &mut err,
-                    "but lifetime must outlive ",
-                    sub,
-                    "",
-                    None,
-                );
-                err
-            }
-        }
-    }
-
-    pub(super) fn report_placeholder_failure(
-        &self,
-        placeholder_origin: SubregionOrigin<'tcx>,
-        sub: Region<'tcx>,
-        sup: Region<'tcx>,
-    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
-        // I can't think how to do better than this right now. -nikomatsakis
-        debug!(?placeholder_origin, ?sub, ?sup, "report_placeholder_failure");
-        match placeholder_origin {
-            infer::Subtype(box ref trace)
-                if matches!(
-                    &trace.cause.code().peel_derives(),
-                    ObligationCauseCode::BindingObligation(..)
-                        | ObligationCauseCode::ExprBindingObligation(..)
-                ) =>
-            {
-                // Hack to get around the borrow checker because trace.cause has an `Rc`.
-                if let ObligationCauseCode::BindingObligation(_, span)
-                | ObligationCauseCode::ExprBindingObligation(_, span, ..) =
-                    &trace.cause.code().peel_derives()
-                {
-                    let span = *span;
-                    let mut err = self.report_concrete_failure(placeholder_origin, sub, sup);
-                    err.span_note(span, "the lifetime requirement is introduced here");
-                    err
-                } else {
-                    unreachable!()
-                }
-            }
-            infer::Subtype(box trace) => {
-                let terr = TypeError::RegionsPlaceholderMismatch;
-                return self.report_and_explain_type_error(trace, terr);
-            }
-            _ => return self.report_concrete_failure(placeholder_origin, sub, sup),
-        }
-    }
-}
diff --git a/compiler/rustc_infer/src/infer/error_reporting/suggest.rs b/compiler/rustc_infer/src/infer/error_reporting/suggest.rs
index 73b5a2cc4..5b02956a1 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/suggest.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/suggest.rs
@@ -411,7 +411,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         span: Span,
     ) {
         let hir = self.tcx.hir();
-        let fn_hir_id = hir.get_parent_node(cause.body_id);
+        let fn_hir_id = hir.parent_id(cause.body_id);
         if let Some(node) = self.tcx.hir().find(fn_hir_id) &&
             let hir::Node::Item(hir::Item {
                     kind: hir::ItemKind::Fn(_sig, _, body_id), ..
@@ -486,12 +486,14 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             _ if self.same_type_modulo_infer(last_expr_ty, expected_ty) => {
                 StatementAsExpression::CorrectType
             }
-            (ty::Opaque(last_def_id, _), ty::Opaque(exp_def_id, _))
-                if last_def_id == exp_def_id =>
-            {
-                StatementAsExpression::CorrectType
-            }
-            (ty::Opaque(last_def_id, last_bounds), ty::Opaque(exp_def_id, exp_bounds)) => {
+            (
+                ty::Alias(ty::Opaque, ty::AliasTy { def_id: last_def_id, .. }),
+                ty::Alias(ty::Opaque, ty::AliasTy { def_id: exp_def_id, .. }),
+            ) if last_def_id == exp_def_id => StatementAsExpression::CorrectType,
+            (
+                ty::Alias(ty::Opaque, ty::AliasTy { def_id: last_def_id, substs: last_bounds, .. }),
+                ty::Alias(ty::Opaque, ty::AliasTy { def_id: exp_def_id, substs: exp_bounds, .. }),
+            ) => {
                 debug!(
                     "both opaque, likely future {:?} {:?} {:?} {:?}",
                     last_def_id, last_bounds, exp_def_id, exp_bounds
@@ -583,45 +585,42 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             let hir::StmtKind::Local(local) = &stmt.kind else { continue; };
             local.pat.walk(&mut find_compatible_candidates);
         }
-        match hir.find(hir.get_parent_node(blk.hir_id)) {
-            Some(hir::Node::Expr(hir::Expr { hir_id, .. })) => {
-                match hir.find(hir.get_parent_node(*hir_id)) {
-                    Some(hir::Node::Arm(hir::Arm { pat, .. })) => {
-                        pat.walk(&mut find_compatible_candidates);
-                    }
-                    Some(
-                        hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, _, body), .. })
-                        | hir::Node::ImplItem(hir::ImplItem {
-                            kind: hir::ImplItemKind::Fn(_, body),
-                            ..
-                        })
-                        | hir::Node::TraitItem(hir::TraitItem {
-                            kind: hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(body)),
-                            ..
-                        })
-                        | hir::Node::Expr(hir::Expr {
-                            kind: hir::ExprKind::Closure(hir::Closure { body, .. }),
-                            ..
-                        }),
-                    ) => {
-                        for param in hir.body(*body).params {
-                            param.pat.walk(&mut find_compatible_candidates);
-                        }
-                    }
-                    Some(hir::Node::Expr(hir::Expr {
-                        kind:
-                            hir::ExprKind::If(
-                                hir::Expr { kind: hir::ExprKind::Let(let_), .. },
-                                then_block,
-                                _,
-                            ),
+        match hir.find_parent(blk.hir_id) {
+            Some(hir::Node::Expr(hir::Expr { hir_id, .. })) => match hir.find_parent(*hir_id) {
+                Some(hir::Node::Arm(hir::Arm { pat, .. })) => {
+                    pat.walk(&mut find_compatible_candidates);
+                }
+                Some(
+                    hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, _, body), .. })
+                    | hir::Node::ImplItem(hir::ImplItem {
+                        kind: hir::ImplItemKind::Fn(_, body), ..
+                    })
+                    | hir::Node::TraitItem(hir::TraitItem {
+                        kind: hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(body)),
                         ..
-                    })) if then_block.hir_id == *hir_id => {
-                        let_.pat.walk(&mut find_compatible_candidates);
+                    })
+                    | hir::Node::Expr(hir::Expr {
+                        kind: hir::ExprKind::Closure(hir::Closure { body, .. }),
+                        ..
+                    }),
+                ) => {
+                    for param in hir.body(*body).params {
+                        param.pat.walk(&mut find_compatible_candidates);
                     }
-                    _ => {}
                 }
-            }
+                Some(hir::Node::Expr(hir::Expr {
+                    kind:
+                        hir::ExprKind::If(
+                            hir::Expr { kind: hir::ExprKind::Let(let_), .. },
+                            then_block,
+                            _,
+                        ),
+                    ..
+                })) if then_block.hir_id == *hir_id => {
+                    let_.pat.walk(&mut find_compatible_candidates);
+                }
+                _ => {}
+            },
             _ => {}
         }
 
diff --git a/compiler/rustc_infer/src/infer/freshen.rs b/compiler/rustc_infer/src/infer/freshen.rs
index f6946929b..8f53b1ccd 100644
--- a/compiler/rustc_infer/src/infer/freshen.rs
+++ b/compiler/rustc_infer/src/infer/freshen.rs
@@ -205,12 +205,11 @@ impl<'a, 'tcx> TypeFolder<'tcx> for TypeFreshener<'a, 'tcx> {
             | ty::Dynamic(..)
             | ty::Never
             | ty::Tuple(..)
-            | ty::Projection(..)
+            | ty::Alias(..)
             | ty::Foreign(..)
             | ty::Param(..)
             | ty::Closure(..)
-            | ty::GeneratorWitness(..)
-            | ty::Opaque(..) => t.super_fold_with(self),
+            | ty::GeneratorWitness(..) => t.super_fold_with(self),
 
             ty::Placeholder(..) | ty::Bound(..) => bug!("unexpected type {:?}", t),
         }
diff --git a/compiler/rustc_infer/src/infer/glb.rs b/compiler/rustc_infer/src/infer/glb.rs
index 7f27b35a5..21b68ce99 100644
--- a/compiler/rustc_infer/src/infer/glb.rs
+++ b/compiler/rustc_infer/src/infer/glb.rs
@@ -103,6 +103,11 @@ impl<'tcx> TypeRelation<'tcx> for Glb<'_, '_, 'tcx> {
     where
         T: Relate<'tcx>,
     {
+        // GLB of a binder and itself is just itself
+        if a == b {
+            return Ok(a);
+        }
+
         debug!("binders(a={:?}, b={:?})", a, b);
         if a.skip_binder().has_escaping_bound_vars() || b.skip_binder().has_escaping_bound_vars() {
             // When higher-ranked types are involved, computing the GLB is
diff --git a/compiler/rustc_infer/src/infer/lattice.rs b/compiler/rustc_infer/src/infer/lattice.rs
index eba65361a..4dbb4b4d7 100644
--- a/compiler/rustc_infer/src/infer/lattice.rs
+++ b/compiler/rustc_infer/src/infer/lattice.rs
@@ -78,7 +78,7 @@ where
         //
         // Example: if the LHS is a type variable, and RHS is
         // `Box<i32>`, then we current compare `v` to the RHS first,
-        // which will instantiate `v` with `Box<i32>`.  Then when `v`
+        // which will instantiate `v` with `Box<i32>`. Then when `v`
         // is compared to the LHS, we instantiate LHS with `Box<i32>`.
         // But if we did in reverse order, we would create a `v <:
         // LHS` (or vice versa) constraint and then instantiate
@@ -105,11 +105,13 @@ where
             Ok(v)
         }
 
-        (&ty::Opaque(a_def_id, _), &ty::Opaque(b_def_id, _)) if a_def_id == b_def_id => {
-            infcx.super_combine_tys(this, a, b)
-        }
-        (&ty::Opaque(did, ..), _) | (_, &ty::Opaque(did, ..))
-            if this.define_opaque_types() && did.is_local() =>
+        (
+            &ty::Alias(ty::Opaque, ty::AliasTy { def_id: a_def_id, .. }),
+            &ty::Alias(ty::Opaque, ty::AliasTy { def_id: b_def_id, .. }),
+        ) if a_def_id == b_def_id => infcx.super_combine_tys(this, a, b),
+        (&ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }), _)
+        | (_, &ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }))
+            if this.define_opaque_types() && def_id.is_local() =>
         {
             this.add_obligations(
                 infcx
diff --git a/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs b/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs
index ba990acfe..ce8aec804 100644
--- a/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs
+++ b/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs
@@ -52,7 +52,7 @@ pub struct LexicalRegionResolutions<'tcx> {
 
 #[derive(Copy, Clone, Debug)]
 pub(crate) enum VarValue<'tcx> {
-    /// Empty lifetime is for data that is never accessed.  We tag the
+    /// Empty lifetime is for data that is never accessed. We tag the
     /// empty lifetime with a universe -- the idea is that we don't
     /// want `exists<'a> { forall<'b> { 'b: 'a } }` to be satisfiable.
     /// Therefore, the `'empty` in a universe `U` is less than all
@@ -251,7 +251,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
                     VarValue::Empty(a_universe) => {
                         let b_data = var_values.value_mut(b_vid);
 
-                        let changed = (|| match *b_data {
+                        let changed = match *b_data {
                             VarValue::Empty(b_universe) => {
                                 // Empty regions are ordered according to the universe
                                 // they are associated with.
@@ -280,20 +280,20 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
                                 };
 
                                 if lub == cur_region {
-                                    return false;
+                                    false
+                                } else {
+                                    debug!(
+                                        "Expanding value of {:?} from {:?} to {:?}",
+                                        b_vid, cur_region, lub
+                                    );
+
+                                    *b_data = VarValue::Value(lub);
+                                    true
                                 }
-
-                                debug!(
-                                    "Expanding value of {:?} from {:?} to {:?}",
-                                    b_vid, cur_region, lub
-                                );
-
-                                *b_data = VarValue::Value(lub);
-                                true
                             }
 
                             VarValue::ErrorValue => false,
-                        })();
+                        };
 
                         if changed {
                             changes.push(b_vid);
@@ -488,7 +488,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
                         // If this empty region is from a universe that can
                         // name the placeholder, then the placeholder is
                         // larger; otherwise, the only ancestor is `'static`.
-                        if a_ui.can_name(placeholder.universe) { true } else { false }
+                        return a_ui.can_name(placeholder.universe);
                     }
                 }
             }
@@ -510,7 +510,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
         }
 
         // If both `a` and `b` are free, consult the declared
-        // relationships.  Note that this can be more precise than the
+        // relationships. Note that this can be more precise than the
         // `lub` relationship defined below, since sometimes the "lub"
         // is actually the `postdom_upper_bound` (see
         // `TransitiveRelation` for more details).
@@ -665,7 +665,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
         // conflicting regions to report to the user. As we walk, we
         // trip the flags from false to true, and if we find that
         // we've already reported an error involving any particular
-        // node we just stop and don't report the current error.  The
+        // node we just stop and don't report the current error. The
         // idea is to report errors that derive from independent
         // regions of the graph, but not those that derive from
         // overlapping locations.
@@ -702,26 +702,8 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
                     // Obtain the spans for all the places that can
                     // influence the constraints on this value for
                     // richer diagnostics in `static_impl_trait`.
-                    let influences: Vec<Span> = self
-                        .data
-                        .constraints
-                        .iter()
-                        .filter_map(|(constraint, origin)| match (constraint, origin) {
-                            (
-                                Constraint::VarSubVar(_, sup),
-                                SubregionOrigin::DataBorrowed(_, sp),
-                            ) if sup == &node_vid => Some(*sp),
-                            _ => None,
-                        })
-                        .collect();
-
-                    self.collect_error_for_expanding_node(
-                        graph,
-                        &mut dup_vec,
-                        node_vid,
-                        errors,
-                        influences,
-                    );
+
+                    self.collect_error_for_expanding_node(graph, &mut dup_vec, node_vid, errors);
                 }
             }
         }
@@ -775,7 +757,6 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
         dup_vec: &mut IndexVec<RegionVid, Option<RegionVid>>,
         node_idx: RegionVid,
         errors: &mut Vec<RegionResolutionError<'tcx>>,
-        influences: Vec<Span>,
     ) {
         // Errors in expanding nodes result from a lower-bound that is
         // not contained by an upper-bound.
@@ -830,7 +811,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
                         lower_bound.region,
                         upper_bound.origin.clone(),
                         upper_bound.region,
-                        influences,
+                        vec![],
                     ));
                     return;
                 }
diff --git a/compiler/rustc_infer/src/infer/lub.rs b/compiler/rustc_infer/src/infer/lub.rs
index 97ed4729b..c07ac1d3a 100644
--- a/compiler/rustc_infer/src/infer/lub.rs
+++ b/compiler/rustc_infer/src/infer/lub.rs
@@ -103,6 +103,11 @@ impl<'tcx> TypeRelation<'tcx> for Lub<'_, '_, 'tcx> {
     where
         T: Relate<'tcx>,
     {
+        // LUB of a binder and itself is just itself
+        if a == b {
+            return Ok(a);
+        }
+
         debug!("binders(a={:?}, b={:?})", a, b);
         if a.skip_binder().has_escaping_bound_vars() || b.skip_binder().has_escaping_bound_vars() {
             // When higher-ranked types are involved, computing the LUB is
diff --git a/compiler/rustc_infer/src/infer/mod.rs b/compiler/rustc_infer/src/infer/mod.rs
index 706cd4124..f0e42c1fc 100644
--- a/compiler/rustc_infer/src/infer/mod.rs
+++ b/compiler/rustc_infer/src/infer/mod.rs
@@ -361,6 +361,7 @@ pub enum ValuePairs<'tcx> {
     Terms(ExpectedFound<ty::Term<'tcx>>),
     TraitRefs(ExpectedFound<ty::TraitRef<'tcx>>),
     PolyTraitRefs(ExpectedFound<ty::PolyTraitRef<'tcx>>),
+    Sigs(ExpectedFound<ty::FnSig<'tcx>>),
 }
 
 impl<'tcx> ValuePairs<'tcx> {
@@ -409,12 +410,6 @@ pub enum SubregionOrigin<'tcx> {
     /// Creating a pointer `b` to contents of another reference
     Reborrow(Span),
 
-    /// Creating a pointer `b` to contents of an upvar
-    ReborrowUpvar(Span, ty::UpvarId),
-
-    /// Data with type `Ty<'tcx>` was borrowed
-    DataBorrowed(Ty<'tcx>, Span),
-
     /// (&'a &'b T) where a >= b
     ReferenceOutlivesReferent(Ty<'tcx>, Span),
 
@@ -690,6 +685,10 @@ impl<'tcx> InferCtxt<'tcx> {
             typeck_results: None,
             fallback_has_occurred: false,
             normalize_fn_sig: Box::new(|fn_sig| fn_sig),
+            autoderef_steps: Box::new(|ty| {
+                debug_assert!(false, "shouldn't be using autoderef_steps outside of typeck");
+                vec![(ty, vec![])]
+            }),
         }
     }
 
@@ -1106,7 +1105,7 @@ impl<'tcx> InferCtxt<'tcx> {
         self.tcx.mk_region(ty::ReVar(region_var))
     }
 
-    /// Return the universe that the region `r` was created in.  For
+    /// Return the universe that the region `r` was created in. For
     /// most regions (e.g., `'static`, named regions from the user,
     /// etc) this is the root universe U0. For inference variables or
     /// placeholders, however, it will return the universe which they
@@ -1340,6 +1339,12 @@ impl<'tcx> InferCtxt<'tcx> {
         var_infos
     }
 
+    #[instrument(level = "debug", skip(self), ret)]
+    pub fn take_opaque_types(&self) -> opaque_types::OpaqueTypeMap<'tcx> {
+        debug_assert_ne!(self.defining_use_anchor, DefiningAnchor::Error);
+        std::mem::take(&mut self.inner.borrow_mut().opaque_type_storage.opaque_types)
+    }
+
     pub fn ty_to_string(&self, t: Ty<'tcx>) -> String {
         self.resolve_vars_if_possible(t).to_string()
     }
@@ -1356,7 +1361,7 @@ impl<'tcx> InferCtxt<'tcx> {
     }
 
     /// Resolve any type variables found in `value` -- but only one
-    /// level.  So, if the variable `?X` is bound to some type
+    /// level. So, if the variable `?X` is bound to some type
     /// `Foo<?Y>`, then this would return `Foo<?Y>` (but `?Y` may
     /// itself be bound to a type).
     ///
@@ -1681,33 +1686,54 @@ impl<'tcx> InferCtxt<'tcx> {
 }
 
 impl<'tcx> TypeErrCtxt<'_, 'tcx> {
+    /// Processes registered region obliations and resolves regions, reporting
+    /// any errors if any were raised. Prefer using this function over manually
+    /// calling `resolve_regions_and_report_errors`.
+    pub fn check_region_obligations_and_report_errors(
+        &self,
+        generic_param_scope: LocalDefId,
+        outlives_env: &OutlivesEnvironment<'tcx>,
+    ) -> Result<(), ErrorGuaranteed> {
+        self.process_registered_region_obligations(
+            outlives_env.region_bound_pairs(),
+            outlives_env.param_env,
+        );
+
+        self.resolve_regions_and_report_errors(generic_param_scope, outlives_env)
+    }
+
     /// Process the region constraints and report any errors that
     /// result. After this, no more unification operations should be
     /// done -- or the compiler will panic -- but it is legal to use
     /// `resolve_vars_if_possible` as well as `fully_resolve`.
     ///
     /// Make sure to call [`InferCtxt::process_registered_region_obligations`]
-    /// first, or preferably use [`InferCtxt::check_region_obligations_and_report_errors`]
+    /// first, or preferably use [`TypeErrCtxt::check_region_obligations_and_report_errors`]
     /// to do both of these operations together.
     pub fn resolve_regions_and_report_errors(
         &self,
         generic_param_scope: LocalDefId,
         outlives_env: &OutlivesEnvironment<'tcx>,
-    ) -> Option<ErrorGuaranteed> {
+    ) -> Result<(), ErrorGuaranteed> {
         let errors = self.resolve_regions(outlives_env);
 
         if let None = self.tainted_by_errors() {
             // As a heuristic, just skip reporting region errors
             // altogether if other errors have been reported while
-            // this infcx was in use.  This is totally hokey but
+            // this infcx was in use. This is totally hokey but
             // otherwise we have a hard time separating legit region
             // errors from silly ones.
             self.report_region_errors(generic_param_scope, &errors);
         }
 
-        (!errors.is_empty()).then(|| {
-            self.tcx.sess.delay_span_bug(rustc_span::DUMMY_SP, "error should have been emitted")
-        })
+        if errors.is_empty() {
+            Ok(())
+        } else {
+            Err(self
+                .tcx
+                .sess
+                .delay_span_bug(rustc_span::DUMMY_SP, "error should have been emitted"))
+        }
     }
 
     // [Note-Type-error-reporting]
@@ -1924,7 +1950,7 @@ impl<'tcx> TypeTrace<'tcx> {
     ) -> TypeTrace<'tcx> {
         TypeTrace {
             cause: cause.clone(),
-            values: PolyTraitRefs(ExpectedFound::new(a_is_expected, a.into(), b.into())),
+            values: PolyTraitRefs(ExpectedFound::new(a_is_expected, a, b)),
         }
     }
 
@@ -1949,8 +1975,6 @@ impl<'tcx> SubregionOrigin<'tcx> {
             RelateParamBound(a, ..) => a,
             RelateRegionParamBound(a) => a,
             Reborrow(a) => a,
-            ReborrowUpvar(a, _) => a,
-            DataBorrowed(_, a) => a,
             ReferenceOutlivesReferent(_, a) => a,
             CompareImplItemObligation { span, .. } => span,
             AscribeUserTypeProvePredicate(span) => span,
@@ -2018,31 +2042,54 @@ fn replace_param_and_infer_substs_with_placeholder<'tcx>(
     tcx: TyCtxt<'tcx>,
     substs: SubstsRef<'tcx>,
 ) -> SubstsRef<'tcx> {
-    tcx.mk_substs(substs.iter().enumerate().map(|(idx, arg)| {
-        match arg.unpack() {
-            GenericArgKind::Type(_) if arg.has_non_region_param() || arg.has_non_region_infer() => {
-                tcx.mk_ty(ty::Placeholder(ty::PlaceholderType {
+    struct ReplaceParamAndInferWithPlaceholder<'tcx> {
+        tcx: TyCtxt<'tcx>,
+        idx: usize,
+    }
+
+    impl<'tcx> TypeFolder<'tcx> for ReplaceParamAndInferWithPlaceholder<'tcx> {
+        fn tcx(&self) -> TyCtxt<'tcx> {
+            self.tcx
+        }
+
+        fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
+            if let ty::Infer(_) = t.kind() {
+                self.tcx.mk_ty(ty::Placeholder(ty::PlaceholderType {
                     universe: ty::UniverseIndex::ROOT,
-                    name: ty::BoundVar::from_usize(idx),
+                    name: ty::BoundVar::from_usize({
+                        let idx = self.idx;
+                        self.idx += 1;
+                        idx
+                    }),
                 }))
-                .into()
+            } else {
+                t.super_fold_with(self)
             }
-            GenericArgKind::Const(ct) if ct.has_non_region_infer() || ct.has_non_region_param() => {
-                let ty = ct.ty();
-                // If the type references param or infer, replace that too...
+        }
+
+        fn fold_const(&mut self, c: ty::Const<'tcx>) -> ty::Const<'tcx> {
+            if let ty::ConstKind::Infer(_) = c.kind() {
+                let ty = c.ty();
+                // If the type references param or infer then ICE ICE ICE
                 if ty.has_non_region_param() || ty.has_non_region_infer() {
-                    bug!("const `{ct}`'s type should not reference params or types");
+                    bug!("const `{c}`'s type should not reference params or types");
                 }
-                tcx.mk_const(
+                self.tcx.mk_const(
                     ty::PlaceholderConst {
                         universe: ty::UniverseIndex::ROOT,
-                        name: ty::BoundVar::from_usize(idx),
+                        name: ty::BoundVar::from_usize({
+                            let idx = self.idx;
+                            self.idx += 1;
+                            idx
+                        }),
                     },
                     ty,
                 )
-                .into()
+            } else {
+                c.super_fold_with(self)
             }
-            _ => arg,
         }
-    }))
+    }
+
+    substs.fold_with(&mut ReplaceParamAndInferWithPlaceholder { tcx, idx: 0 })
 }
diff --git a/compiler/rustc_infer/src/infer/nll_relate/mod.rs b/compiler/rustc_infer/src/infer/nll_relate/mod.rs
index f6bc4db0d..f235cb5ab 100644
--- a/compiler/rustc_infer/src/infer/nll_relate/mod.rs
+++ b/compiler/rustc_infer/src/infer/nll_relate/mod.rs
@@ -275,13 +275,13 @@ where
     ///   `ProjectionEq(projection = ?U)`, `ProjectionEq(other_projection = ?U)`.
     fn relate_projection_ty(
         &mut self,
-        projection_ty: ty::ProjectionTy<'tcx>,
+        projection_ty: ty::AliasTy<'tcx>,
         value_ty: Ty<'tcx>,
     ) -> Ty<'tcx> {
         use rustc_span::DUMMY_SP;
 
         match *value_ty.kind() {
-            ty::Projection(other_projection_ty) => {
+            ty::Alias(ty::Projection, other_projection_ty) => {
                 let var = self.infcx.next_ty_var(TypeVariableOrigin {
                     kind: TypeVariableOriginKind::MiscVariable,
                     span: DUMMY_SP,
@@ -335,7 +335,9 @@ where
                 return Ok(value_ty);
             }
 
-            ty::Projection(projection_ty) if D::normalization() == NormalizationStrategy::Lazy => {
+            ty::Alias(ty::Projection, projection_ty)
+                if D::normalization() == NormalizationStrategy::Lazy =>
+            {
                 return Ok(self.relate_projection_ty(projection_ty, self.infcx.tcx.mk_ty_var(vid)));
             }
 
@@ -406,8 +408,8 @@ where
             }
         };
         let (a, b) = match (a.kind(), b.kind()) {
-            (&ty::Opaque(..), _) => (a, generalize(b, false)?),
-            (_, &ty::Opaque(..)) => (generalize(a, true)?, b),
+            (&ty::Alias(ty::Opaque, ..), _) => (a, generalize(b, false)?),
+            (_, &ty::Alias(ty::Opaque, ..)) => (generalize(a, true)?, b),
             _ => unreachable!(),
         };
         let cause = ObligationCause::dummy_with_span(self.delegate.span());
@@ -437,7 +439,7 @@ trait VidValuePair<'tcx>: Debug {
     fn value_ty(&self) -> Ty<'tcx>;
 
     /// Extract the scopes that apply to whichever side of the tuple
-    /// the vid was found on.  See the comment where this is called
+    /// the vid was found on. See the comment where this is called
     /// for more details on why we want them.
     fn vid_scopes<'r, D: TypeRelatingDelegate<'tcx>>(
         &self,
@@ -608,26 +610,30 @@ where
 
             (&ty::Infer(ty::TyVar(vid)), _) => self.relate_ty_var((vid, b)),
 
-            (&ty::Opaque(a_def_id, _), &ty::Opaque(b_def_id, _)) if a_def_id == b_def_id => {
-                infcx.super_combine_tys(self, a, b).or_else(|err| {
-                    self.tcx().sess.delay_span_bug(
-                        self.delegate.span(),
-                        "failure to relate an opaque to itself should result in an error later on",
-                    );
-                    if a_def_id.is_local() { self.relate_opaques(a, b) } else { Err(err) }
-                })
-            }
-            (&ty::Opaque(did, ..), _) | (_, &ty::Opaque(did, ..)) if did.is_local() => {
+            (
+                &ty::Alias(ty::Opaque, ty::AliasTy { def_id: a_def_id, .. }),
+                &ty::Alias(ty::Opaque, ty::AliasTy { def_id: b_def_id, .. }),
+            ) if a_def_id == b_def_id => infcx.super_combine_tys(self, a, b).or_else(|err| {
+                self.tcx().sess.delay_span_bug(
+                    self.delegate.span(),
+                    "failure to relate an opaque to itself should result in an error later on",
+                );
+                if a_def_id.is_local() { self.relate_opaques(a, b) } else { Err(err) }
+            }),
+            (&ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }), _)
+            | (_, &ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }))
+                if def_id.is_local() =>
+            {
                 self.relate_opaques(a, b)
             }
 
-            (&ty::Projection(projection_ty), _)
+            (&ty::Alias(ty::Projection, projection_ty), _)
                 if D::normalization() == NormalizationStrategy::Lazy =>
             {
                 Ok(self.relate_projection_ty(projection_ty, b))
             }
 
-            (_, &ty::Projection(projection_ty))
+            (_, &ty::Alias(ty::Projection, projection_ty))
                 if D::normalization() == NormalizationStrategy::Lazy =>
             {
                 Ok(self.relate_projection_ty(projection_ty, a))
@@ -825,7 +831,7 @@ where
 /// (these are not explicitly present in the ty representation right
 /// now). This visitor handles that: it descends the type, tracking
 /// binder depth, and finds late-bound regions targeting the
-/// `for<..`>.  For each of those, it creates an entry in
+/// `for<..`>. For each of those, it creates an entry in
 /// `bound_region_scope`.
 struct ScopeInstantiator<'me, 'tcx> {
     next_region: &'me mut dyn FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
@@ -843,7 +849,7 @@ impl<'me, 'tcx> TypeVisitor<'tcx> for ScopeInstantiator<'me, 'tcx> {
         t.super_visit_with(self);
         self.target_index.shift_out(1);
 
-        ControlFlow::CONTINUE
+        ControlFlow::Continue(())
     }
 
     fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
@@ -857,7 +863,7 @@ impl<'me, 'tcx> TypeVisitor<'tcx> for ScopeInstantiator<'me, 'tcx> {
             _ => {}
         }
 
-        ControlFlow::CONTINUE
+        ControlFlow::Continue(())
     }
 }
 
diff --git a/compiler/rustc_infer/src/infer/note.rs b/compiler/rustc_infer/src/infer/note.rs
deleted file mode 100644
index 2ccbd164f..000000000
--- a/compiler/rustc_infer/src/infer/note.rs
+++ /dev/null
@@ -1,203 +0,0 @@
-impl<'tcx> TypeErrCtxt<'_, 'tcx> {
-    fn note_error_origin(
-        &self,
-        err: &mut Diagnostic,
-        cause: &ObligationCause<'tcx>,
-        exp_found: Option<ty::error::ExpectedFound<Ty<'tcx>>>,
-        terr: TypeError<'tcx>,
-    ) {
-        match *cause.code() {
-            ObligationCauseCode::Pattern { origin_expr: true, span: Some(span), root_ty } => {
-                let ty = self.resolve_vars_if_possible(root_ty);
-                if !matches!(ty.kind(), ty::Infer(ty::InferTy::TyVar(_) | ty::InferTy::FreshTy(_)))
-                {
-                    // don't show type `_`
-                    if span.desugaring_kind() == Some(DesugaringKind::ForLoop)
-                        && let ty::Adt(def, substs) = ty.kind()
-                        && Some(def.did()) == self.tcx.get_diagnostic_item(sym::Option)
-                    {
-                        err.span_label(span, format!("this is an iterator with items of type `{}`", substs.type_at(0)));
-                    } else {
-                    err.span_label(span, format!("this expression has type `{}`", ty));
-                }
-                }
-                if let Some(ty::error::ExpectedFound { found, .. }) = exp_found
-                    && ty.is_box() && ty.boxed_ty() == found
-                    && let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span)
-                {
-                    err.span_suggestion(
-                        span,
-                        "consider dereferencing the boxed value",
-                        format!("*{}", snippet),
-                        Applicability::MachineApplicable,
-                    );
-                }
-            }
-            ObligationCauseCode::Pattern { origin_expr: false, span: Some(span), .. } => {
-                err.span_label(span, "expected due to this");
-            }
-            ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause {
-                arm_block_id,
-                arm_span,
-                arm_ty,
-                prior_arm_block_id,
-                prior_arm_span,
-                prior_arm_ty,
-                source,
-                ref prior_arms,
-                scrut_hir_id,
-                opt_suggest_box_span,
-                scrut_span,
-                ..
-            }) => match source {
-                hir::MatchSource::TryDesugar => {
-                    if let Some(ty::error::ExpectedFound { expected, .. }) = exp_found {
-                        let scrut_expr = self.tcx.hir().expect_expr(scrut_hir_id);
-                        let scrut_ty = if let hir::ExprKind::Call(_, args) = &scrut_expr.kind {
-                            let arg_expr = args.first().expect("try desugaring call w/out arg");
-                            self.typeck_results.as_ref().and_then(|typeck_results| {
-                                typeck_results.expr_ty_opt(arg_expr)
-                            })
-                        } else {
-                            bug!("try desugaring w/out call expr as scrutinee");
-                        };
-
-                        match scrut_ty {
-                            Some(ty) if expected == ty => {
-                                let source_map = self.tcx.sess.source_map();
-                                err.span_suggestion(
-                                    source_map.end_point(cause.span),
-                                    "try removing this `?`",
-                                    "",
-                                    Applicability::MachineApplicable,
-                                );
-                            }
-                            _ => {}
-                        }
-                    }
-                }
-                _ => {
-                    // `prior_arm_ty` can be `!`, `expected` will have better info when present.
-                    let t = self.resolve_vars_if_possible(match exp_found {
-                        Some(ty::error::ExpectedFound { expected, .. }) => expected,
-                        _ => prior_arm_ty,
-                    });
-                    let source_map = self.tcx.sess.source_map();
-                    let mut any_multiline_arm = source_map.is_multiline(arm_span);
-                    if prior_arms.len() <= 4 {
-                        for sp in prior_arms {
-                            any_multiline_arm |= source_map.is_multiline(*sp);
-                            err.span_label(*sp, format!("this is found to be of type `{}`", t));
-                        }
-                    } else if let Some(sp) = prior_arms.last() {
-                        any_multiline_arm |= source_map.is_multiline(*sp);
-                        err.span_label(
-                            *sp,
-                            format!("this and all prior arms are found to be of type `{}`", t),
-                        );
-                    }
-                    let outer_error_span = if any_multiline_arm {
-                        // Cover just `match` and the scrutinee expression, not
-                        // the entire match body, to reduce diagram noise.
-                        cause.span.shrink_to_lo().to(scrut_span)
-                    } else {
-                        cause.span
-                    };
-                    let msg = "`match` arms have incompatible types";
-                    err.span_label(outer_error_span, msg);
-                    self.suggest_remove_semi_or_return_binding(
-                        err,
-                        prior_arm_block_id,
-                        prior_arm_ty,
-                        prior_arm_span,
-                        arm_block_id,
-                        arm_ty,
-                        arm_span,
-                    );
-                    if let Some(ret_sp) = opt_suggest_box_span {
-                        // Get return type span and point to it.
-                        self.suggest_boxing_for_return_impl_trait(
-                            err,
-                            ret_sp,
-                            prior_arms.iter().chain(std::iter::once(&arm_span)).map(|s| *s),
-                        );
-                    }
-                }
-            },
-            ObligationCauseCode::IfExpression(box IfExpressionCause {
-                then_id,
-                else_id,
-                then_ty,
-                else_ty,
-                outer_span,
-                opt_suggest_box_span,
-            }) => {
-                let then_span = self.find_block_span_from_hir_id(then_id);
-                let else_span = self.find_block_span_from_hir_id(else_id);
-                err.span_label(then_span, "expected because of this");
-                if let Some(sp) = outer_span {
-                    err.span_label(sp, "`if` and `else` have incompatible types");
-                }
-                self.suggest_remove_semi_or_return_binding(
-                    err,
-                    Some(then_id),
-                    then_ty,
-                    then_span,
-                    Some(else_id),
-                    else_ty,
-                    else_span,
-                );
-                if let Some(ret_sp) = opt_suggest_box_span {
-                    self.suggest_boxing_for_return_impl_trait(
-                        err,
-                        ret_sp,
-                        [then_span, else_span].into_iter(),
-                    );
-                }
-            }
-            ObligationCauseCode::LetElse => {
-                err.help("try adding a diverging expression, such as `return` or `panic!(..)`");
-                err.help("...or use `match` instead of `let...else`");
-            }
-            _ => {
-                if let ObligationCauseCode::BindingObligation(_, span)
-                | ObligationCauseCode::ExprBindingObligation(_, span, ..)
-                = cause.code().peel_derives()
-                    && let TypeError::RegionsPlaceholderMismatch = terr
-                {
-                    err.span_note( * span,
-                    "the lifetime requirement is introduced here");
-                }
-            }
-        }
-    }
-}
-
-impl<'tcx> InferCtxt<'tcx> {
-    /// Given a [`hir::Block`], get the span of its last expression or
-    /// statement, peeling off any inner blocks.
-    pub fn find_block_span(&self, block: &'tcx hir::Block<'tcx>) -> Span {
-        let block = block.innermost_block();
-        if let Some(expr) = &block.expr {
-            expr.span
-        } else if let Some(stmt) = block.stmts.last() {
-            // possibly incorrect trailing `;` in the else arm
-            stmt.span
-        } else {
-            // empty block; point at its entirety
-            block.span
-        }
-    }
-
-    /// Given a [`hir::HirId`] for a block, get the span of its last expression
-    /// or statement, peeling off any inner blocks.
-    pub fn find_block_span_from_hir_id(&self, hir_id: hir::HirId) -> Span {
-        match self.tcx.hir().get(hir_id) {
-            hir::Node::Block(blk) => self.find_block_span(blk),
-            // The parser was in a weird state if either of these happen, but
-            // it's better not to panic.
-            hir::Node::Expr(e) => e.span,
-            _ => rustc_span::DUMMY_SP,
-        }
-    }
-}
diff --git a/compiler/rustc_infer/src/infer/opaque_types.rs b/compiler/rustc_infer/src/infer/opaque_types.rs
index 524f7a39e..c54c66eab 100644
--- a/compiler/rustc_infer/src/infer/opaque_types.rs
+++ b/compiler/rustc_infer/src/infer/opaque_types.rs
@@ -61,12 +61,14 @@ impl<'tcx> InferCtxt<'tcx> {
                 .as_local()
                 .map_or(false, |def_id| self.opaque_type_origin(def_id, span).is_some())
         };
-        let value = value.fold_with(&mut ty::fold::BottomUpFolder {
+        let value = value.fold_with(&mut BottomUpFolder {
             tcx: self.tcx,
             lt_op: |lt| lt,
             ct_op: |ct| ct,
             ty_op: |ty| match *ty.kind() {
-                ty::Opaque(def_id, _substs) if replace_opaque_type(def_id) => {
+                ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. })
+                    if replace_opaque_type(def_id) =>
+                {
                     let def_span = self.tcx.def_span(def_id);
                     let span = if span.contains(def_span) { def_span } else { span };
                     let code = traits::ObligationCauseCode::OpaqueReturnType(None);
@@ -104,13 +106,13 @@ impl<'tcx> InferCtxt<'tcx> {
         }
         let (a, b) = if a_is_expected { (a, b) } else { (b, a) };
         let process = |a: Ty<'tcx>, b: Ty<'tcx>, a_is_expected| match *a.kind() {
-            ty::Opaque(def_id, substs) if def_id.is_local() => {
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs, .. }) if def_id.is_local() => {
                 let def_id = def_id.expect_local();
                 let origin = match self.defining_use_anchor {
                     DefiningAnchor::Bind(_) => {
                         // Check that this is `impl Trait` type is
                         // declared by `parent_def_id` -- i.e., one whose
-                        // value we are inferring.  At present, this is
+                        // value we are inferring. At present, this is
                         // always true during the first phase of
                         // type-check, but not always true later on during
                         // NLL. Once we support named opaque types more fully,
@@ -147,18 +149,19 @@ impl<'tcx> InferCtxt<'tcx> {
                     DefiningAnchor::Bubble => self.opaque_ty_origin_unchecked(def_id, cause.span),
                     DefiningAnchor::Error => return None,
                 };
-                if let ty::Opaque(did2, _) = *b.kind() {
+                if let ty::Alias(ty::Opaque, ty::AliasTy { def_id: b_def_id, .. }) = *b.kind() {
                     // We could accept this, but there are various ways to handle this situation, and we don't
                     // want to make a decision on it right now. Likely this case is so super rare anyway, that
                     // no one encounters it in practice.
                     // It does occur however in `fn fut() -> impl Future<Output = i32> { async { 42 } }`,
                     // where it is of no concern, so we only check for TAITs.
-                    if let Some(OpaqueTyOrigin::TyAlias) =
-                        did2.as_local().and_then(|did2| self.opaque_type_origin(did2, cause.span))
+                    if let Some(OpaqueTyOrigin::TyAlias) = b_def_id
+                        .as_local()
+                        .and_then(|b_def_id| self.opaque_type_origin(b_def_id, cause.span))
                     {
                         self.tcx.sess.emit_err(OpaqueHiddenTypeDiag {
                             span: cause.span,
-                            hidden_type: self.tcx.def_span(did2),
+                            hidden_type: self.tcx.def_span(b_def_id),
                             opaque_type: self.tcx.def_span(def_id),
                         });
                     }
@@ -377,7 +380,7 @@ impl<'tcx> InferCtxt<'tcx> {
         };
         let item_kind = &self.tcx.hir().expect_item(def_id).kind;
 
-        let hir::ItemKind::OpaqueTy(hir::OpaqueTy { origin, ..  }) = item_kind else {
+        let hir::ItemKind::OpaqueTy(hir::OpaqueTy { origin, .. }) = item_kind else {
             span_bug!(
                 span,
                 "weird opaque type: {:#?}, {:#?}",
@@ -437,16 +440,16 @@ where
         t: &ty::Binder<'tcx, T>,
     ) -> ControlFlow<Self::BreakTy> {
         t.super_visit_with(self);
-        ControlFlow::CONTINUE
+        ControlFlow::Continue(())
     }
 
     fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
         match *r {
             // ignore bound regions, keep visiting
-            ty::ReLateBound(_, _) => ControlFlow::CONTINUE,
+            ty::ReLateBound(_, _) => ControlFlow::Continue(()),
             _ => {
                 (self.op)(r);
-                ControlFlow::CONTINUE
+                ControlFlow::Continue(())
             }
         }
     }
@@ -454,7 +457,7 @@ where
     fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
         // We're only interested in types involving regions
         if !ty.flags().intersects(ty::TypeFlags::HAS_FREE_REGIONS) {
-            return ControlFlow::CONTINUE;
+            return ControlFlow::Continue(());
         }
 
         match ty.kind() {
@@ -475,8 +478,8 @@ where
                 substs.as_generator().resume_ty().visit_with(self);
             }
 
-            ty::Opaque(def_id, ref substs) => {
-                // Skip lifetime paramters that are not captures.
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id, ref substs, .. }) => {
+                // Skip lifetime parameters that are not captures.
                 let variances = self.tcx.variances_of(*def_id);
 
                 for (v, s) in std::iter::zip(variances, substs.iter()) {
@@ -486,11 +489,11 @@ where
                 }
             }
 
-            ty::Projection(proj)
-                if self.tcx.def_kind(proj.item_def_id) == DefKind::ImplTraitPlaceholder =>
+            ty::Alias(ty::Projection, proj)
+                if self.tcx.def_kind(proj.def_id) == DefKind::ImplTraitPlaceholder =>
             {
-                // Skip lifetime paramters that are not captures.
-                let variances = self.tcx.variances_of(proj.item_def_id);
+                // Skip lifetime parameters that are not captures.
+                let variances = self.tcx.variances_of(proj.def_id);
 
                 for (v, s) in std::iter::zip(variances, proj.substs.iter()) {
                     if *v != ty::Variance::Bivariant {
@@ -504,7 +507,7 @@ where
             }
         }
 
-        ControlFlow::CONTINUE
+        ControlFlow::Continue(())
     }
 }
 
@@ -563,9 +566,9 @@ impl<'tcx> InferCtxt<'tcx> {
                     // We can't normalize associated types from `rustc_infer`,
                     // but we can eagerly register inference variables for them.
                     // FIXME(RPITIT): Don't replace RPITITs with inference vars.
-                    ty::Projection(projection_ty)
+                    ty::Alias(ty::Projection, projection_ty)
                         if !projection_ty.has_escaping_bound_vars()
-                            && tcx.def_kind(projection_ty.item_def_id)
+                            && tcx.def_kind(projection_ty.def_id)
                                 != DefKind::ImplTraitPlaceholder =>
                     {
                         self.infer_projection(
@@ -578,17 +581,16 @@ impl<'tcx> InferCtxt<'tcx> {
                     }
                     // Replace all other mentions of the same opaque type with the hidden type,
                     // as the bounds must hold on the hidden type after all.
-                    ty::Opaque(def_id2, substs2)
+                    ty::Alias(ty::Opaque, ty::AliasTy { def_id: def_id2, substs: substs2, .. })
                         if def_id.to_def_id() == def_id2 && substs == substs2 =>
                     {
                         hidden_ty
                     }
                     // FIXME(RPITIT): This can go away when we move to associated types
-                    ty::Projection(proj)
-                        if def_id.to_def_id() == proj.item_def_id && substs == proj.substs =>
-                    {
-                        hidden_ty
-                    }
+                    ty::Alias(
+                        ty::Projection,
+                        ty::AliasTy { def_id: def_id2, substs: substs2, .. },
+                    ) if def_id.to_def_id() == def_id2 && substs == substs2 => hidden_ty,
                     _ => ty,
                 },
                 lt_op: |lt| lt,
diff --git a/compiler/rustc_infer/src/infer/opaque_types/table.rs b/compiler/rustc_infer/src/infer/opaque_types/table.rs
index c146902d5..ae4b85c87 100644
--- a/compiler/rustc_infer/src/infer/opaque_types/table.rs
+++ b/compiler/rustc_infer/src/infer/opaque_types/table.rs
@@ -29,11 +29,6 @@ impl<'tcx> OpaqueTypeStorage<'tcx> {
         }
     }
 
-    #[instrument(level = "debug", ret)]
-    pub fn take_opaque_types(&mut self) -> OpaqueTypeMap<'tcx> {
-        std::mem::take(&mut self.opaque_types)
-    }
-
     #[inline]
     pub(crate) fn with_log<'a>(
         &'a mut self,
diff --git a/compiler/rustc_infer/src/infer/outlives/components.rs b/compiler/rustc_infer/src/infer/outlives/components.rs
index 14ee9f051..3d86279b0 100644
--- a/compiler/rustc_infer/src/infer/outlives/components.rs
+++ b/compiler/rustc_infer/src/infer/outlives/components.rs
@@ -3,9 +3,8 @@
 // RFC for reference.
 
 use rustc_data_structures::sso::SsoHashSet;
-use rustc_hir::def_id::DefId;
 use rustc_middle::ty::subst::{GenericArg, GenericArgKind};
-use rustc_middle::ty::{self, SubstsRef, Ty, TyCtxt, TypeVisitable};
+use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitable};
 use smallvec::{smallvec, SmallVec};
 
 #[derive(Debug)]
@@ -23,7 +22,7 @@ pub enum Component<'tcx> {
     // is not in a position to judge which is the best technique, so
     // we just product the projection as a component and leave it to
     // the consumer to decide (but see `EscapingProjection` below).
-    Projection(ty::ProjectionTy<'tcx>),
+    Alias(ty::AliasTy<'tcx>),
 
     // In the case where a projection has escaping regions -- meaning
     // regions bound within the type itself -- we always use
@@ -45,9 +44,7 @@ pub enum Component<'tcx> {
     // projection, so that implied bounds code can avoid relying on
     // them. This gives us room to improve the regionck reasoning in
     // the future without breaking backwards compat.
-    EscapingProjection(Vec<Component<'tcx>>),
-
-    Opaque(DefId, SubstsRef<'tcx>),
+    EscapingAlias(Vec<Component<'tcx>>),
 }
 
 /// Push onto `out` all the things that must outlive `'a` for the condition
@@ -123,17 +120,6 @@ fn compute_components<'tcx>(
                 out.push(Component::Param(p));
             }
 
-            // Ignore lifetimes found in opaque types. Opaque types can
-            // have lifetimes in their substs which their hidden type doesn't
-            // actually use. If we inferred that an opaque type is outlived by
-            // its parameter lifetimes, then we could prove that any lifetime
-            // outlives any other lifetime, which is unsound.
-            // See https://github.com/rust-lang/rust/issues/84305 for
-            // more details.
-            ty::Opaque(def_id, substs) => {
-                out.push(Component::Opaque(def_id, substs));
-            },
-
             // For projections, we prefer to generate an obligation like
             // `<P0 as Trait<P1...Pn>>::Foo: 'a`, because this gives the
             // regionck more ways to prove that it holds. However,
@@ -142,23 +128,23 @@ fn compute_components<'tcx>(
             // trait-ref. Therefore, if we see any higher-ranked regions,
             // we simply fallback to the most restrictive rule, which
             // requires that `Pi: 'a` for all `i`.
-            ty::Projection(ref data) => {
-                if !data.has_escaping_bound_vars() {
+            ty::Alias(_, alias_ty) => {
+                if !alias_ty.has_escaping_bound_vars() {
                     // best case: no escaping regions, so push the
                     // projection and skip the subtree (thus generating no
                     // constraints for Pi). This defers the choice between
                     // the rules OutlivesProjectionEnv,
                     // OutlivesProjectionTraitDef, and
                     // OutlivesProjectionComponents to regionck.
-                    out.push(Component::Projection(*data));
+                    out.push(Component::Alias(alias_ty));
                 } else {
                     // fallback case: hard code
-                    // OutlivesProjectionComponents.  Continue walking
+                    // OutlivesProjectionComponents. Continue walking
                     // through and constrain Pi.
                     let mut subcomponents = smallvec![];
                     let mut subvisited = SsoHashSet::new();
                     compute_components_recursive(tcx, ty.into(), &mut subcomponents, &mut subvisited);
-                    out.push(Component::EscapingProjection(subcomponents.into_iter().collect()));
+                    out.push(Component::EscapingAlias(subcomponents.into_iter().collect()));
                 }
             }
 
@@ -195,7 +181,7 @@ fn compute_components<'tcx>(
             ty::Error(_) => {
                 // (*) Function pointers and trait objects are both binders.
                 // In the RFC, this means we would add the bound regions to
-                // the "bound regions list".  In our representation, no such
+                // the "bound regions list". In our representation, no such
                 // list is maintained explicitly, because bound regions
                 // themselves can be readily identified.
                 compute_components_recursive(tcx, ty.into(), out, visited);
diff --git a/compiler/rustc_infer/src/infer/outlives/env.rs b/compiler/rustc_infer/src/infer/outlives/env.rs
index 33543135d..24e3c34dd 100644
--- a/compiler/rustc_infer/src/infer/outlives/env.rs
+++ b/compiler/rustc_infer/src/infer/outlives/env.rs
@@ -138,13 +138,9 @@ impl<'tcx> OutlivesEnvironmentBuilder<'tcx> {
                     self.region_bound_pairs
                         .insert(ty::OutlivesPredicate(GenericKind::Param(param_b), r_a));
                 }
-                OutlivesBound::RegionSubProjection(r_a, projection_b) => {
+                OutlivesBound::RegionSubAlias(r_a, alias_b) => {
                     self.region_bound_pairs
-                        .insert(ty::OutlivesPredicate(GenericKind::Projection(projection_b), r_a));
-                }
-                OutlivesBound::RegionSubOpaque(r_a, def_id, substs) => {
-                    self.region_bound_pairs
-                        .insert(ty::OutlivesPredicate(GenericKind::Opaque(def_id, substs), r_a));
+                        .insert(ty::OutlivesPredicate(GenericKind::Alias(alias_b), r_a));
                 }
                 OutlivesBound::RegionSubRegion(r_a, r_b) => {
                     if let (ReEarlyBound(_) | ReFree(_), ReVar(vid_b)) = (r_a.kind(), r_b.kind()) {
diff --git a/compiler/rustc_infer/src/infer/outlives/obligations.rs b/compiler/rustc_infer/src/infer/outlives/obligations.rs
index abb46ce3b..0194549a8 100644
--- a/compiler/rustc_infer/src/infer/outlives/obligations.rs
+++ b/compiler/rustc_infer/src/infer/outlives/obligations.rs
@@ -60,7 +60,6 @@
 //! imply that `'b: 'a`.
 
 use crate::infer::outlives::components::{push_outlives_components, Component};
-use crate::infer::outlives::env::OutlivesEnvironment;
 use crate::infer::outlives::env::RegionBoundPairs;
 use crate::infer::outlives::verify::VerifyBoundCx;
 use crate::infer::{
@@ -68,9 +67,6 @@ use crate::infer::{
 };
 use crate::traits::{ObligationCause, ObligationCauseCode};
 use rustc_data_structures::undo_log::UndoLogs;
-use rustc_errors::ErrorGuaranteed;
-use rustc_hir::def_id::DefId;
-use rustc_hir::def_id::LocalDefId;
 use rustc_middle::mir::ConstraintCategory;
 use rustc_middle::ty::subst::GenericArgKind;
 use rustc_middle::ty::{self, Region, SubstsRef, Ty, TyCtxt, TypeVisitable};
@@ -116,7 +112,7 @@ impl<'tcx> InferCtxt<'tcx> {
         std::mem::take(&mut self.inner.borrow_mut().region_obligations)
     }
 
-    /// NOTE: Prefer using [`InferCtxt::check_region_obligations_and_report_errors`]
+    /// NOTE: Prefer using `TypeErrCtxt::check_region_obligations_and_report_errors`
     /// instead of calling this directly.
     ///
     /// Process the region obligations that must be proven (during
@@ -170,22 +166,6 @@ impl<'tcx> InferCtxt<'tcx> {
             outlives.type_must_outlive(origin, sup_type, sub_region, category);
         }
     }
-
-    /// Processes registered region obliations and resolves regions, reporting
-    /// any errors if any were raised. Prefer using this function over manually
-    /// calling `resolve_regions_and_report_errors`.
-    pub fn check_region_obligations_and_report_errors(
-        &self,
-        generic_param_scope: LocalDefId,
-        outlives_env: &OutlivesEnvironment<'tcx>,
-    ) -> Option<ErrorGuaranteed> {
-        self.process_registered_region_obligations(
-            outlives_env.region_bound_pairs(),
-            outlives_env.param_env,
-        );
-
-        self.err_ctxt().resolve_regions_and_report_errors(generic_param_scope, outlives_env)
-    }
 }
 
 /// The `TypeOutlives` struct has the job of "lowering" a `T: 'a`
@@ -285,13 +265,8 @@ where
                 Component::Param(param_ty) => {
                     self.param_ty_must_outlive(origin, region, *param_ty);
                 }
-                Component::Opaque(def_id, substs) => {
-                    self.opaque_must_outlive(*def_id, substs, origin, region)
-                }
-                Component::Projection(projection_ty) => {
-                    self.projection_must_outlive(origin, region, *projection_ty);
-                }
-                Component::EscapingProjection(subcomponents) => {
+                Component::Alias(alias_ty) => self.alias_ty_must_outlive(origin, region, *alias_ty),
+                Component::EscapingAlias(subcomponents) => {
                     self.components_must_outlive(origin, &subcomponents, region, category);
                 }
                 Component::UnresolvedInferenceVariable(v) => {
@@ -307,78 +282,26 @@ where
         }
     }
 
+    #[instrument(level = "debug", skip(self))]
     fn param_ty_must_outlive(
         &mut self,
         origin: infer::SubregionOrigin<'tcx>,
         region: ty::Region<'tcx>,
         param_ty: ty::ParamTy,
     ) {
-        debug!(
-            "param_ty_must_outlive(region={:?}, param_ty={:?}, origin={:?})",
-            region, param_ty, origin
-        );
-
-        let generic = GenericKind::Param(param_ty);
         let verify_bound = self.verify_bound.param_bound(param_ty);
-        self.delegate.push_verify(origin, generic, region, verify_bound);
+        self.delegate.push_verify(origin, GenericKind::Param(param_ty), region, verify_bound);
     }
 
     #[instrument(level = "debug", skip(self))]
-    fn opaque_must_outlive(
+    fn alias_ty_must_outlive(
         &mut self,
-        def_id: DefId,
-        substs: SubstsRef<'tcx>,
         origin: infer::SubregionOrigin<'tcx>,
         region: ty::Region<'tcx>,
-    ) {
-        self.generic_must_outlive(
-            origin,
-            region,
-            GenericKind::Opaque(def_id, substs),
-            def_id,
-            substs,
-            true,
-            |ty| match *ty.kind() {
-                ty::Opaque(def_id, substs) => (def_id, substs),
-                _ => bug!("expected only projection types from env, not {:?}", ty),
-            },
-        );
-    }
-
-    #[instrument(level = "debug", skip(self))]
-    fn projection_must_outlive(
-        &mut self,
-        origin: infer::SubregionOrigin<'tcx>,
-        region: ty::Region<'tcx>,
-        projection_ty: ty::ProjectionTy<'tcx>,
-    ) {
-        self.generic_must_outlive(
-            origin,
-            region,
-            GenericKind::Projection(projection_ty),
-            projection_ty.item_def_id,
-            projection_ty.substs,
-            false,
-            |ty| match ty.kind() {
-                ty::Projection(projection_ty) => (projection_ty.item_def_id, projection_ty.substs),
-                _ => bug!("expected only projection types from env, not {:?}", ty),
-            },
-        );
-    }
-
-    #[instrument(level = "debug", skip(self, filter))]
-    fn generic_must_outlive(
-        &mut self,
-        origin: infer::SubregionOrigin<'tcx>,
-        region: ty::Region<'tcx>,
-        generic: GenericKind<'tcx>,
-        def_id: DefId,
-        substs: SubstsRef<'tcx>,
-        is_opaque: bool,
-        filter: impl Fn(Ty<'tcx>) -> (DefId, SubstsRef<'tcx>),
+        alias_ty: ty::AliasTy<'tcx>,
     ) {
         // An optimization for a common case with opaque types.
-        if substs.is_empty() {
+        if alias_ty.substs.is_empty() {
             return;
         }
 
@@ -388,7 +311,7 @@ where
         // particular). :) First off, we have to choose between using the
         // OutlivesProjectionEnv, OutlivesProjectionTraitDef, and
         // OutlivesProjectionComponent rules, any one of which is
-        // sufficient.  If there are no inference variables involved, it's
+        // sufficient. If there are no inference variables involved, it's
         // not hard to pick the right rule, but if there are, we're in a
         // bit of a catch 22: if we picked which rule we were going to
         // use, we could add constraints to the region inference graph
@@ -400,14 +323,14 @@ where
         // These are guaranteed to apply, no matter the inference
         // results.
         let trait_bounds: Vec<_> =
-            self.verify_bound.declared_region_bounds(def_id, substs).collect();
+            self.verify_bound.declared_bounds_from_definition(alias_ty).collect();
 
         debug!(?trait_bounds);
 
         // Compute the bounds we can derive from the environment. This
         // is an "approximate" match -- in some cases, these bounds
         // may not apply.
-        let mut approx_env_bounds = self.verify_bound.approx_declared_bounds_from_env(generic);
+        let mut approx_env_bounds = self.verify_bound.approx_declared_bounds_from_env(alias_ty);
         debug!(?approx_env_bounds);
 
         // Remove outlives bounds that we get from the environment but
@@ -422,8 +345,8 @@ where
             // If the declaration is `trait Trait<'b> { type Item: 'b; }`, then `projection_declared_bounds_from_trait`
             // will be invoked with `['b => ^1]` and so we will get `^1` returned.
             let bound = bound_outlives.skip_binder();
-            let (def_id, substs) = filter(bound.0);
-            self.verify_bound.declared_region_bounds(def_id, substs).all(|r| r != bound.1)
+            let ty::Alias(_, alias_ty) = bound.0.kind() else { bug!("expected AliasTy") };
+            self.verify_bound.declared_bounds_from_definition(*alias_ty).all(|r| r != bound.1)
         });
 
         // If declared bounds list is empty, the only applicable rule is
@@ -440,12 +363,12 @@ where
         // the problem is to add `T: 'r`, which isn't true. So, if there are no
         // inference variables, we use a verify constraint instead of adding
         // edges, which winds up enforcing the same condition.
-        let needs_infer = substs.needs_infer();
-        if approx_env_bounds.is_empty() && trait_bounds.is_empty() && (needs_infer || is_opaque) {
+        if approx_env_bounds.is_empty()
+            && trait_bounds.is_empty()
+            && (alias_ty.needs_infer() || alias_ty.kind(self.tcx) == ty::Opaque)
+        {
             debug!("no declared bounds");
-
-            self.substs_must_outlive(substs, origin, region);
-
+            self.substs_must_outlive(alias_ty.substs, origin, region);
             return;
         }
 
@@ -486,14 +409,9 @@ where
         // projection outlive; in some cases, this may add insufficient
         // edges into the inference graph, leading to inference failures
         // even though a satisfactory solution exists.
-        let verify_bound = self.verify_bound.projection_opaque_bounds(
-            generic,
-            def_id,
-            substs,
-            &mut Default::default(),
-        );
-        debug!("projection_must_outlive: pushing {:?}", verify_bound);
-        self.delegate.push_verify(origin, generic, region, verify_bound);
+        let verify_bound = self.verify_bound.alias_bound(alias_ty, &mut Default::default());
+        debug!("alias_must_outlive: pushing {:?}", verify_bound);
+        self.delegate.push_verify(origin, GenericKind::Alias(alias_ty), region, verify_bound);
     }
 
     fn substs_must_outlive(
diff --git a/compiler/rustc_infer/src/infer/outlives/verify.rs b/compiler/rustc_infer/src/infer/outlives/verify.rs
index f470b2eb8..94de9bc2d 100644
--- a/compiler/rustc_infer/src/infer/outlives/verify.rs
+++ b/compiler/rustc_infer/src/infer/outlives/verify.rs
@@ -1,11 +1,10 @@
 use crate::infer::outlives::components::{compute_components_recursive, Component};
 use crate::infer::outlives::env::RegionBoundPairs;
 use crate::infer::region_constraints::VerifyIfEq;
-use crate::infer::{GenericKind, VerifyBound};
+use crate::infer::VerifyBound;
 use rustc_data_structures::sso::SsoHashSet;
-use rustc_hir::def_id::DefId;
 use rustc_middle::ty::GenericArg;
-use rustc_middle::ty::{self, EarlyBinder, OutlivesPredicate, SubstsRef, Ty, TyCtxt};
+use rustc_middle::ty::{self, OutlivesPredicate, Ty, TyCtxt};
 
 use smallvec::smallvec;
 
@@ -94,29 +93,26 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
     /// this list.
     pub fn approx_declared_bounds_from_env(
         &self,
-        generic: GenericKind<'tcx>,
+        alias_ty: ty::AliasTy<'tcx>,
     ) -> Vec<ty::Binder<'tcx, ty::OutlivesPredicate<Ty<'tcx>, ty::Region<'tcx>>>> {
-        let projection_ty = generic.to_ty(self.tcx);
-        let erased_projection_ty = self.tcx.erase_regions(projection_ty);
-        self.declared_generic_bounds_from_env_for_erased_ty(erased_projection_ty)
+        let erased_alias_ty = self.tcx.erase_regions(alias_ty.to_ty(self.tcx));
+        self.declared_generic_bounds_from_env_for_erased_ty(erased_alias_ty)
     }
 
     #[instrument(level = "debug", skip(self, visited))]
-    pub fn projection_opaque_bounds(
+    pub fn alias_bound(
         &self,
-        generic: GenericKind<'tcx>,
-        def_id: DefId,
-        substs: SubstsRef<'tcx>,
+        alias_ty: ty::AliasTy<'tcx>,
         visited: &mut SsoHashSet<GenericArg<'tcx>>,
     ) -> VerifyBound<'tcx> {
-        let generic_ty = generic.to_ty(self.tcx);
+        let alias_ty_as_ty = alias_ty.to_ty(self.tcx);
 
         // Search the env for where clauses like `P: 'a`.
-        let projection_opaque_bounds = self
-            .approx_declared_bounds_from_env(generic)
+        let env_bounds = self
+            .approx_declared_bounds_from_env(alias_ty)
             .into_iter()
             .map(|binder| {
-                if let Some(ty::OutlivesPredicate(ty, r)) = binder.no_bound_vars() && ty == generic_ty {
+                if let Some(ty::OutlivesPredicate(ty, r)) = binder.no_bound_vars() && ty == alias_ty_as_ty {
                     // Micro-optimize if this is an exact match (this
                     // occurs often when there are no region variables
                     // involved).
@@ -126,19 +122,19 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
                     VerifyBound::IfEq(verify_if_eq_b)
                 }
             });
-        // Extend with bounds that we can find from the trait.
-        let trait_bounds =
-            self.declared_region_bounds(def_id, substs).map(|r| VerifyBound::OutlivedBy(r));
+
+        // Extend with bounds that we can find from the definition.
+        let definition_bounds =
+            self.declared_bounds_from_definition(alias_ty).map(|r| VerifyBound::OutlivedBy(r));
 
         // see the extensive comment in projection_must_outlive
         let recursive_bound = {
             let mut components = smallvec![];
-            compute_components_recursive(self.tcx, generic_ty.into(), &mut components, visited);
+            compute_components_recursive(self.tcx, alias_ty_as_ty.into(), &mut components, visited);
             self.bound_from_components(&components, visited)
         };
 
-        VerifyBound::AnyBound(projection_opaque_bounds.chain(trait_bounds).collect())
-            .or(recursive_bound)
+        VerifyBound::AnyBound(env_bounds.chain(definition_bounds).collect()).or(recursive_bound)
     }
 
     fn bound_from_components(
@@ -149,10 +145,8 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
         let mut bounds = components
             .iter()
             .map(|component| self.bound_from_single_component(component, visited))
-            .filter(|bound| {
-                // Remove bounds that must hold, since they are not interesting.
-                !bound.must_hold()
-            });
+            // Remove bounds that must hold, since they are not interesting.
+            .filter(|bound| !bound.must_hold());
 
         match (bounds.next(), bounds.next()) {
             (Some(first), None) => first,
@@ -170,19 +164,8 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
         match *component {
             Component::Region(lt) => VerifyBound::OutlivedBy(lt),
             Component::Param(param_ty) => self.param_bound(param_ty),
-            Component::Opaque(did, substs) => self.projection_opaque_bounds(
-                GenericKind::Opaque(did, substs),
-                did,
-                substs,
-                visited,
-            ),
-            Component::Projection(projection_ty) => self.projection_opaque_bounds(
-                GenericKind::Projection(projection_ty),
-                projection_ty.item_def_id,
-                projection_ty.substs,
-                visited,
-            ),
-            Component::EscapingProjection(ref components) => {
+            Component::Alias(alias_ty) => self.alias_bound(alias_ty, visited),
+            Component::EscapingAlias(ref components) => {
                 self.bound_from_components(components, visited)
             }
             Component::UnresolvedInferenceVariable(v) => {
@@ -298,20 +281,18 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
     ///
     /// This is for simplicity, and because we are not really smart
     /// enough to cope with such bounds anywhere.
-    pub fn declared_region_bounds(
+    pub fn declared_bounds_from_definition(
         &self,
-        def_id: DefId,
-        substs: SubstsRef<'tcx>,
+        alias_ty: ty::AliasTy<'tcx>,
     ) -> impl Iterator<Item = ty::Region<'tcx>> {
         let tcx = self.tcx;
-        let bounds = tcx.item_bounds(def_id);
-        trace!("{:#?}", bounds);
+        let bounds = tcx.item_bounds(alias_ty.def_id);
+        trace!("{:#?}", bounds.0);
         bounds
-            .into_iter()
+            .subst_iter(tcx, alias_ty.substs)
             .filter_map(|p| p.to_opt_type_outlives())
             .filter_map(|p| p.no_bound_vars())
-            .map(|b| b.1)
-            .map(move |r| EarlyBinder(r).subst(tcx, substs))
+            .map(|OutlivesPredicate(_, r)| r)
     }
 
     /// Searches through a predicate list for a predicate `T: 'a`.
diff --git a/compiler/rustc_infer/src/infer/projection.rs b/compiler/rustc_infer/src/infer/projection.rs
index eb6deee29..4667d99ff 100644
--- a/compiler/rustc_infer/src/infer/projection.rs
+++ b/compiler/rustc_infer/src/infer/projection.rs
@@ -16,12 +16,12 @@ impl<'tcx> InferCtxt<'tcx> {
     pub fn infer_projection(
         &self,
         param_env: ty::ParamEnv<'tcx>,
-        projection_ty: ty::ProjectionTy<'tcx>,
+        projection_ty: ty::AliasTy<'tcx>,
         cause: ObligationCause<'tcx>,
         recursion_depth: usize,
         obligations: &mut Vec<PredicateObligation<'tcx>>,
     ) -> Ty<'tcx> {
-        let def_id = projection_ty.item_def_id;
+        let def_id = projection_ty.def_id;
         let ty_var = self.next_ty_var(TypeVariableOrigin {
             kind: TypeVariableOriginKind::NormalizeProjectionType,
             span: self.tcx.def_span(def_id),
diff --git a/compiler/rustc_infer/src/infer/region_constraints/leak_check.rs b/compiler/rustc_infer/src/infer/region_constraints/leak_check.rs
index 22b4bbb17..c46edc33f 100644
--- a/compiler/rustc_infer/src/infer/region_constraints/leak_check.rs
+++ b/compiler/rustc_infer/src/infer/region_constraints/leak_check.rs
@@ -357,15 +357,13 @@ impl<'tcx> SccUniverse<'tcx> {
 }
 
 rustc_index::newtype_index! {
-    struct LeakCheckNode {
-        DEBUG_FORMAT = "LeakCheckNode({})"
-    }
+    #[debug_format = "LeakCheckNode({})"]
+    struct LeakCheckNode {}
 }
 
 rustc_index::newtype_index! {
-    struct LeakCheckScc {
-        DEBUG_FORMAT = "LeakCheckScc({})"
-    }
+    #[debug_format = "LeakCheckScc({})"]
+    struct LeakCheckScc {}
 }
 
 /// Represents the graph of constraints. For each `R1: R2` constraint we create
diff --git a/compiler/rustc_infer/src/infer/region_constraints/mod.rs b/compiler/rustc_infer/src/infer/region_constraints/mod.rs
index 985c5d360..0428481b7 100644
--- a/compiler/rustc_infer/src/infer/region_constraints/mod.rs
+++ b/compiler/rustc_infer/src/infer/region_constraints/mod.rs
@@ -12,10 +12,8 @@ use rustc_data_structures::intern::Interned;
 use rustc_data_structures::sync::Lrc;
 use rustc_data_structures::undo_log::UndoLogs;
 use rustc_data_structures::unify as ut;
-use rustc_hir::def_id::DefId;
 use rustc_index::vec::IndexVec;
 use rustc_middle::infer::unify_key::{RegionVidKey, UnifiedRegion};
-use rustc_middle::ty::subst::SubstsRef;
 use rustc_middle::ty::ReStatic;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_middle::ty::{ReLateBound, ReVar};
@@ -169,8 +167,7 @@ pub struct Verify<'tcx> {
 #[derive(Copy, Clone, PartialEq, Eq, Hash, TypeFoldable, TypeVisitable)]
 pub enum GenericKind<'tcx> {
     Param(ty::ParamTy),
-    Projection(ty::ProjectionTy<'tcx>),
-    Opaque(DefId, SubstsRef<'tcx>),
+    Alias(ty::AliasTy<'tcx>),
 }
 
 /// Describes the things that some `GenericKind` value `G` is known to
@@ -749,10 +746,7 @@ impl<'tcx> fmt::Debug for GenericKind<'tcx> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match *self {
             GenericKind::Param(ref p) => write!(f, "{:?}", p),
-            GenericKind::Projection(ref p) => write!(f, "{:?}", p),
-            GenericKind::Opaque(def_id, substs) => ty::tls::with(|tcx| {
-                write!(f, "{}", tcx.def_path_str_with_substs(def_id, tcx.lift(substs).unwrap()))
-            }),
+            GenericKind::Alias(ref p) => write!(f, "{:?}", p),
         }
     }
 }
@@ -761,10 +755,7 @@ impl<'tcx> fmt::Display for GenericKind<'tcx> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match *self {
             GenericKind::Param(ref p) => write!(f, "{}", p),
-            GenericKind::Projection(ref p) => write!(f, "{}", p),
-            GenericKind::Opaque(def_id, substs) => ty::tls::with(|tcx| {
-                write!(f, "{}", tcx.def_path_str_with_substs(def_id, tcx.lift(substs).unwrap()))
-            }),
+            GenericKind::Alias(ref p) => write!(f, "{}", p),
         }
     }
 }
@@ -773,8 +764,7 @@ impl<'tcx> GenericKind<'tcx> {
     pub fn to_ty(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
         match *self {
             GenericKind::Param(ref p) => p.to_ty(tcx),
-            GenericKind::Projection(ref p) => tcx.mk_projection(p.item_def_id, p.substs),
-            GenericKind::Opaque(def_id, substs) => tcx.mk_opaque(def_id, substs),
+            GenericKind::Alias(ref p) => p.to_ty(tcx),
         }
     }
 }
diff --git a/compiler/rustc_infer/src/infer/resolve.rs b/compiler/rustc_infer/src/infer/resolve.rs
index 8671f8d45..65b90aa3d 100644
--- a/compiler/rustc_infer/src/infer/resolve.rs
+++ b/compiler/rustc_infer/src/infer/resolve.rs
@@ -147,7 +147,7 @@ impl<'a, 'tcx> TypeVisitor<'tcx> for UnresolvedTypeOrConstFinder<'a, 'tcx> {
         } else if !t.has_non_region_infer() {
             // All const/type variables in inference types must already be resolved,
             // no need to visit the contents.
-            ControlFlow::CONTINUE
+            ControlFlow::Continue(())
         } else {
             // Otherwise, keep visiting.
             t.super_visit_with(self)
@@ -178,7 +178,7 @@ impl<'a, 'tcx> TypeVisitor<'tcx> for UnresolvedTypeOrConstFinder<'a, 'tcx> {
         } else if !ct.has_non_region_infer() {
             // All const/type variables in inference types must already be resolved,
             // no need to visit the contents.
-            ControlFlow::CONTINUE
+            ControlFlow::Continue(())
         } else {
             // Otherwise, keep visiting.
             ct.super_visit_with(self)
diff --git a/compiler/rustc_infer/src/infer/sub.rs b/compiler/rustc_infer/src/infer/sub.rs
index 2c6987cc3..bd38b52ba 100644
--- a/compiler/rustc_infer/src/infer/sub.rs
+++ b/compiler/rustc_infer/src/infer/sub.rs
@@ -130,12 +130,16 @@ impl<'tcx> TypeRelation<'tcx> for Sub<'_, '_, 'tcx> {
                 Ok(self.tcx().ty_error_with_guaranteed(e))
             }
 
-            (&ty::Opaque(a_def_id, _), &ty::Opaque(b_def_id, _)) if a_def_id == b_def_id => {
+            (
+                &ty::Alias(ty::Opaque, ty::AliasTy { def_id: a_def_id, .. }),
+                &ty::Alias(ty::Opaque, ty::AliasTy { def_id: b_def_id, .. }),
+            ) if a_def_id == b_def_id => {
                 self.fields.infcx.super_combine_tys(self, a, b)?;
                 Ok(a)
             }
-            (&ty::Opaque(did, ..), _) | (_, &ty::Opaque(did, ..))
-                if self.fields.define_opaque_types && did.is_local() =>
+            (&ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }), _)
+            | (_, &ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }))
+                if self.fields.define_opaque_types && def_id.is_local() =>
             {
                 self.fields.obligations.extend(
                     infcx
@@ -213,6 +217,11 @@ impl<'tcx> TypeRelation<'tcx> for Sub<'_, '_, 'tcx> {
     where
         T: Relate<'tcx>,
     {
+        // A binder is always a subtype of itself if it's structually equal to itself
+        if a == b {
+            return Ok(a);
+        }
+
         self.fields.higher_ranked_sub(a, b, self.a_is_expected)?;
         Ok(a)
     }
diff --git a/compiler/rustc_infer/src/infer/type_variable.rs b/compiler/rustc_infer/src/infer/type_variable.rs
index 7ff086452..263c6a47d 100644
--- a/compiler/rustc_infer/src/infer/type_variable.rs
+++ b/compiler/rustc_infer/src/infer/type_variable.rs
@@ -433,7 +433,7 @@ impl<'tcx> ut::UnifyValue for TypeVariableValue<'tcx> {
     fn unify_values(value1: &Self, value2: &Self) -> Result<Self, ut::NoError> {
         match (value1, value2) {
             // We never equate two type variables, both of which
-            // have known types.  Instead, we recursively equate
+            // have known types. Instead, we recursively equate
             // those types.
             (&TypeVariableValue::Known { .. }, &TypeVariableValue::Known { .. }) => {
                 bug!("equating two type variables, both of which have known types")
diff --git a/compiler/rustc_infer/src/infer/undo_log.rs b/compiler/rustc_infer/src/infer/undo_log.rs
index 611961ab1..955c54e85 100644
--- a/compiler/rustc_infer/src/infer/undo_log.rs
+++ b/compiler/rustc_infer/src/infer/undo_log.rs
@@ -87,18 +87,12 @@ impl<'tcx> Rollback<UndoLog<'tcx>> for InferCtxtInner<'tcx> {
 
 /// The combined undo log for all the various unification tables. For each change to the storage
 /// for any kind of inference variable, we record an UndoLog entry in the vector here.
-#[derive(Clone)]
+#[derive(Clone, Default)]
 pub(crate) struct InferCtxtUndoLogs<'tcx> {
     logs: Vec<UndoLog<'tcx>>,
     num_open_snapshots: usize,
 }
 
-impl Default for InferCtxtUndoLogs<'_> {
-    fn default() -> Self {
-        Self { logs: Default::default(), num_open_snapshots: Default::default() }
-    }
-}
-
 /// The UndoLogs trait defines how we undo a particular kind of action (of type T). We can undo any
 /// action that is convertible into an UndoLog (per the From impls above).
 impl<'tcx, T> UndoLogs<T> for InferCtxtUndoLogs<'tcx>