Merging upstream version 1.66.0+dfsg1.

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

34 files changed, 815 insertions, 589 deletions

diff --git a/compiler/rustc_infer/src/infer/at.rs b/compiler/rustc_infer/src/infer/at.rs
index 00e238648..5ff3779fa 100644
--- a/compiler/rustc_infer/src/infer/at.rs
+++ b/compiler/rustc_infer/src/infer/at.rs
@@ -31,7 +31,7 @@ use rustc_middle::ty::relate::{Relate, TypeRelation};
 use rustc_middle::ty::{Const, ImplSubject};
 
 pub struct At<'a, 'tcx> {
-    pub infcx: &'a InferCtxt<'a, 'tcx>,
+    pub infcx: &'a InferCtxt<'tcx>,
     pub cause: &'a ObligationCause<'tcx>,
     pub param_env: ty::ParamEnv<'tcx>,
     /// Whether we should define opaque types
@@ -48,9 +48,9 @@ pub struct Trace<'a, 'tcx> {
     trace: TypeTrace<'tcx>,
 }
 
-impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
+impl<'tcx> InferCtxt<'tcx> {
     #[inline]
-    pub fn at(
+    pub fn at<'a>(
         &'a self,
         cause: &'a ObligationCause<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
@@ -66,7 +66,6 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             tcx: self.tcx,
             defining_use_anchor: self.defining_use_anchor,
             considering_regions: self.considering_regions,
-            in_progress_typeck_results: self.in_progress_typeck_results,
             inner: self.inner.clone(),
             skip_leak_check: self.skip_leak_check.clone(),
             lexical_region_resolutions: self.lexical_region_resolutions.clone(),
diff --git a/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs b/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs
index 9488d0a6c..a3ff70363 100644
--- a/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs
+++ b/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs
@@ -20,7 +20,7 @@ use rustc_data_structures::fx::FxHashMap;
 use rustc_index::vec::Idx;
 use smallvec::SmallVec;
 
-impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
+impl<'tcx> InferCtxt<'tcx> {
     /// Canonicalizes a query value `V`. When we canonicalize a query,
     /// we not only canonicalize unbound inference variables, but we
     /// *also* replace all free regions whatsoever. So for example a
@@ -316,7 +316,7 @@ impl CanonicalizeMode for CanonicalizeFreeRegionsOtherThanStatic {
 }
 
 struct Canonicalizer<'cx, 'tcx> {
-    infcx: &'cx InferCtxt<'cx, 'tcx>,
+    infcx: &'cx InferCtxt<'tcx>,
     tcx: TyCtxt<'tcx>,
     variables: SmallVec<[CanonicalVarInfo<'tcx>; 8]>,
     query_state: &'cx mut OriginalQueryValues<'tcx>,
@@ -521,7 +521,7 @@ impl<'cx, 'tcx> Canonicalizer<'cx, 'tcx> {
     /// `canonicalize_query` and `canonicalize_response`.
     fn canonicalize<V>(
         value: V,
-        infcx: &InferCtxt<'_, 'tcx>,
+        infcx: &InferCtxt<'tcx>,
         tcx: TyCtxt<'tcx>,
         canonicalize_region_mode: &dyn CanonicalizeMode,
         query_state: &mut OriginalQueryValues<'tcx>,
diff --git a/compiler/rustc_infer/src/infer/canonical/mod.rs b/compiler/rustc_infer/src/infer/canonical/mod.rs
index a9294a85e..06ca2534d 100644
--- a/compiler/rustc_infer/src/infer/canonical/mod.rs
+++ b/compiler/rustc_infer/src/infer/canonical/mod.rs
@@ -36,7 +36,7 @@ mod canonicalizer;
 pub mod query_response;
 mod substitute;
 
-impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
+impl<'tcx> InferCtxt<'tcx> {
     /// Creates a substitution S for the canonical value with fresh
     /// inference variables and applies it to the canonical value.
     /// Returns both the instantiated result *and* the substitution S.
diff --git a/compiler/rustc_infer/src/infer/canonical/query_response.rs b/compiler/rustc_infer/src/infer/canonical/query_response.rs
index 56e834898..a299a3e57 100644
--- a/compiler/rustc_infer/src/infer/canonical/query_response.rs
+++ b/compiler/rustc_infer/src/infer/canonical/query_response.rs
@@ -16,8 +16,8 @@ use crate::infer::nll_relate::{NormalizationStrategy, TypeRelating, TypeRelating
 use crate::infer::region_constraints::{Constraint, RegionConstraintData};
 use crate::infer::{InferCtxt, InferOk, InferResult, NllRegionVariableOrigin};
 use crate::traits::query::{Fallible, NoSolution};
-use crate::traits::TraitEngine;
 use crate::traits::{Obligation, ObligationCause, PredicateObligation};
+use crate::traits::{PredicateObligations, TraitEngine};
 use rustc_data_structures::captures::Captures;
 use rustc_index::vec::Idx;
 use rustc_index::vec::IndexVec;
@@ -32,7 +32,7 @@ use rustc_span::Span;
 use std::fmt::Debug;
 use std::iter;
 
-impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
+impl<'tcx> InferCtxt<'tcx> {
     /// This method is meant to be invoked as the final step of a canonical query
     /// implementation. It is given:
     ///
@@ -509,7 +509,7 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
         for &(a, b) in &query_response.value.opaque_types {
             let a = substitute_value(self.tcx, &result_subst, a);
             let b = substitute_value(self.tcx, &result_subst, b);
-            obligations.extend(self.handle_opaque_type(a, b, true, cause, param_env)?.obligations);
+            obligations.extend(self.at(cause, param_env).eq(a, b)?.obligations);
         }
 
         Ok(InferOk { value: result_subst, obligations })
@@ -677,7 +677,7 @@ pub fn make_query_region_constraints<'tcx>(
 }
 
 struct QueryTypeRelatingDelegate<'a, 'tcx> {
-    infcx: &'a InferCtxt<'a, 'tcx>,
+    infcx: &'a InferCtxt<'tcx>,
     obligations: &'a mut Vec<PredicateObligation<'tcx>>,
     param_env: ty::ParamEnv<'tcx>,
     cause: &'a ObligationCause<'tcx>,
@@ -741,17 +741,11 @@ impl<'tcx> TypeRelatingDelegate<'tcx> for QueryTypeRelatingDelegate<'_, 'tcx> {
         true
     }
 
-    fn register_opaque_type(
+    fn register_opaque_type_obligations(
         &mut self,
-        a: Ty<'tcx>,
-        b: Ty<'tcx>,
-        a_is_expected: bool,
+        obligations: PredicateObligations<'tcx>,
     ) -> Result<(), TypeError<'tcx>> {
-        self.obligations.extend(
-            self.infcx
-                .handle_opaque_type(a, b, a_is_expected, &self.cause, self.param_env)?
-                .obligations,
-        );
+        self.obligations.extend(obligations);
         Ok(())
     }
 }
diff --git a/compiler/rustc_infer/src/infer/combine.rs b/compiler/rustc_infer/src/infer/combine.rs
index c406df9e4..b5427f639 100644
--- a/compiler/rustc_infer/src/infer/combine.rs
+++ b/compiler/rustc_infer/src/infer/combine.rs
@@ -43,7 +43,7 @@ use rustc_span::{Span, DUMMY_SP};
 
 #[derive(Clone)]
 pub struct CombineFields<'infcx, 'tcx> {
-    pub infcx: &'infcx InferCtxt<'infcx, 'tcx>,
+    pub infcx: &'infcx InferCtxt<'tcx>,
     pub trace: TypeTrace<'tcx>,
     pub cause: Option<ty::relate::Cause>,
     pub param_env: ty::ParamEnv<'tcx>,
@@ -63,7 +63,7 @@ pub enum RelationDir {
     EqTo,
 }
 
-impl<'infcx, 'tcx> InferCtxt<'infcx, 'tcx> {
+impl<'tcx> InferCtxt<'tcx> {
     pub fn super_combine_tys<R>(
         &self,
         relation: &mut R,
@@ -147,11 +147,7 @@ impl<'infcx, 'tcx> InferCtxt<'infcx, 'tcx> {
                 ty::ConstKind::Infer(InferConst::Var(a_vid)),
                 ty::ConstKind::Infer(InferConst::Var(b_vid)),
             ) => {
-                self.inner
-                    .borrow_mut()
-                    .const_unification_table()
-                    .unify_var_var(a_vid, b_vid)
-                    .map_err(|e| const_unification_error(a_is_expected, e))?;
+                self.inner.borrow_mut().const_unification_table().union(a_vid, b_vid);
                 return Ok(a);
             }
 
@@ -246,21 +242,17 @@ impl<'infcx, 'tcx> InferCtxt<'infcx, 'tcx> {
         let value = ConstInferUnifier { infcx: self, span, param_env, for_universe, target_vid }
             .relate(ct, ct)?;
 
-        self.inner
-            .borrow_mut()
-            .const_unification_table()
-            .unify_var_value(
-                target_vid,
-                ConstVarValue {
-                    origin: ConstVariableOrigin {
-                        kind: ConstVariableOriginKind::ConstInference,
-                        span: DUMMY_SP,
-                    },
-                    val: ConstVariableValue::Known { value },
+        self.inner.borrow_mut().const_unification_table().union_value(
+            target_vid,
+            ConstVarValue {
+                origin: ConstVariableOrigin {
+                    kind: ConstVariableOriginKind::ConstInference,
+                    span: DUMMY_SP,
                 },
-            )
-            .map(|()| value)
-            .map_err(|e| const_unification_error(vid_is_expected, e))
+                val: ConstVariableValue::Known { value },
+            },
+        );
+        Ok(value)
     }
 
     fn unify_integral_variable(
@@ -460,7 +452,7 @@ impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> {
 }
 
 struct Generalizer<'cx, 'tcx> {
-    infcx: &'cx InferCtxt<'cx, 'tcx>,
+    infcx: &'cx InferCtxt<'tcx>,
 
     /// The span, used when creating new type variables and things.
     cause: &'cx ObligationCause<'tcx>,
@@ -742,9 +734,7 @@ impl<'tcx> TypeRelation<'tcx> for Generalizer<'_, 'tcx> {
                     }
                 }
             }
-            ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted }) => {
-                assert_eq!(promoted, ());
-
+            ty::ConstKind::Unevaluated(ty::UnevaluatedConst { def, substs }) => {
                 let substs = self.relate_with_variance(
                     ty::Variance::Invariant,
                     ty::VarianceDiagInfo::default(),
@@ -753,7 +743,7 @@ impl<'tcx> TypeRelation<'tcx> for Generalizer<'_, 'tcx> {
                 )?;
                 Ok(self.tcx().mk_const(ty::ConstS {
                     ty: c.ty(),
-                    kind: ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted }),
+                    kind: ty::ConstKind::Unevaluated(ty::UnevaluatedConst { def, substs }),
                 }))
             }
             _ => relate::super_relate_consts(self, c, c),
@@ -768,13 +758,6 @@ pub trait ConstEquateRelation<'tcx>: TypeRelation<'tcx> {
     fn const_equate_obligation(&mut self, a: ty::Const<'tcx>, b: ty::Const<'tcx>);
 }
 
-pub fn const_unification_error<'tcx>(
-    a_is_expected: bool,
-    (a, b): (ty::Const<'tcx>, ty::Const<'tcx>),
-) -> TypeError<'tcx> {
-    TypeError::ConstMismatch(ExpectedFound::new(a_is_expected, a, b))
-}
-
 fn int_unification_error<'tcx>(
     a_is_expected: bool,
     v: (ty::IntVarValue, ty::IntVarValue),
@@ -792,7 +775,7 @@ fn float_unification_error<'tcx>(
 }
 
 struct ConstInferUnifier<'cx, 'tcx> {
-    infcx: &'cx InferCtxt<'cx, 'tcx>,
+    infcx: &'cx InferCtxt<'tcx>,
 
     span: Span,
 
@@ -964,9 +947,7 @@ impl<'tcx> TypeRelation<'tcx> for ConstInferUnifier<'_, 'tcx> {
                     }
                 }
             }
-            ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted }) => {
-                assert_eq!(promoted, ());
-
+            ty::ConstKind::Unevaluated(ty::UnevaluatedConst { def, substs }) => {
                 let substs = self.relate_with_variance(
                     ty::Variance::Invariant,
                     ty::VarianceDiagInfo::default(),
@@ -976,7 +957,7 @@ impl<'tcx> TypeRelation<'tcx> for ConstInferUnifier<'_, 'tcx> {
 
                 Ok(self.tcx().mk_const(ty::ConstS {
                     ty: c.ty(),
-                    kind: ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted }),
+                    kind: ty::ConstKind::Unevaluated(ty::UnevaluatedConst { def, substs }),
                 }))
             }
             _ => relate::super_relate_consts(self, c, c),
diff --git a/compiler/rustc_infer/src/infer/equate.rs b/compiler/rustc_infer/src/infer/equate.rs
index 3b1798ca7..59728148a 100644
--- a/compiler/rustc_infer/src/infer/equate.rs
+++ b/compiler/rustc_infer/src/infer/equate.rs
@@ -110,6 +110,25 @@ impl<'tcx> TypeRelation<'tcx> for Equate<'_, '_, 'tcx> {
                         .obligations,
                 );
             }
+            // Optimization of GeneratorWitness relation since we know that all
+            // free regions are replaced with bound regions during construction.
+            // This greatly speeds up equating of GeneratorWitness.
+            (&ty::GeneratorWitness(a_types), &ty::GeneratorWitness(b_types)) => {
+                let a_types = infcx.tcx.anonymize_bound_vars(a_types);
+                let b_types = infcx.tcx.anonymize_bound_vars(b_types);
+                if a_types.bound_vars() == b_types.bound_vars() {
+                    let (a_types, b_types) = infcx.replace_bound_vars_with_placeholders(
+                        a_types.map_bound(|a_types| (a_types, b_types.skip_binder())),
+                    );
+                    for (a, b) in std::iter::zip(a_types, b_types) {
+                        self.relate(a, b)?;
+                    }
+                } else {
+                    return Err(ty::error::TypeError::Sorts(ty::relate::expected_found(
+                        self, a, b,
+                    )));
+                }
+            }
 
             _ => {
                 self.fields.infcx.super_combine_tys(self, a, b)?;
diff --git a/compiler/rustc_infer/src/infer/error_reporting/mod.rs b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
index eb5afe828..9ff703e52 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/mod.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
@@ -51,6 +51,7 @@ use super::{InferCtxt, RegionVariableOrigin, SubregionOrigin, TypeTrace, ValuePa
 
 use crate::infer;
 use crate::infer::error_reporting::nice_region_error::find_anon_type::find_anon_type;
+use crate::infer::ExpectedFound;
 use crate::traits::error_reporting::report_object_safety_error;
 use crate::traits::{
     IfExpressionCause, MatchExpressionArmCause, ObligationCause, ObligationCauseCode,
@@ -69,12 +70,12 @@ use rustc_middle::dep_graph::DepContext;
 use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::relate::{self, RelateResult, TypeRelation};
 use rustc_middle::ty::{
-    self, error::TypeError, Binder, List, Region, Subst, Ty, TyCtxt, TypeFoldable,
-    TypeSuperVisitable, TypeVisitable,
+    self, error::TypeError, Binder, List, Region, Ty, TyCtxt, TypeFoldable, TypeSuperVisitable,
+    TypeVisitable,
 };
 use rustc_span::{sym, symbol::kw, BytePos, DesugaringKind, Pos, Span};
 use rustc_target::spec::abi;
-use std::ops::ControlFlow;
+use std::ops::{ControlFlow, Deref};
 use std::{cmp, fmt, iter};
 
 mod note;
@@ -84,6 +85,31 @@ pub use need_type_info::TypeAnnotationNeeded;
 
 pub mod nice_region_error;
 
+/// A helper for building type related errors. The `typeck_results`
+/// field is only populated during an in-progress typeck.
+/// Get an instance by calling `InferCtxt::err` or `FnCtxt::infer_err`.
+pub struct TypeErrCtxt<'a, 'tcx> {
+    pub infcx: &'a InferCtxt<'tcx>,
+    pub typeck_results: Option<std::cell::Ref<'a, ty::TypeckResults<'tcx>>>,
+}
+
+impl TypeErrCtxt<'_, '_> {
+    /// This is just to avoid a potential footgun of accidentally
+    /// dropping `typeck_results` by calling `InferCtxt::err_ctxt`
+    #[deprecated(note = "you already have a `TypeErrCtxt`")]
+    #[allow(unused)]
+    pub fn err_ctxt(&self) -> ! {
+        bug!("called `err_ctxt` on `TypeErrCtxt`. Try removing the call");
+    }
+}
+
+impl<'tcx> Deref for TypeErrCtxt<'_, 'tcx> {
+    type Target = InferCtxt<'tcx>;
+    fn deref(&self) -> &InferCtxt<'tcx> {
+        &self.infcx
+    }
+}
+
 pub(super) fn note_and_explain_region<'tcx>(
     tcx: TyCtxt<'tcx>,
     err: &mut Diagnostic,
@@ -303,7 +329,38 @@ pub fn unexpected_hidden_region_diagnostic<'tcx>(
     err
 }
 
-impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
+impl<'tcx> InferCtxt<'tcx> {
+    pub fn get_impl_future_output_ty(&self, ty: Ty<'tcx>) -> Option<Binder<'tcx, Ty<'tcx>>> {
+        if let ty::Opaque(def_id, substs) = ty.kind() {
+            let future_trait = self.tcx.require_lang_item(LangItem::Future, None);
+            // Future::Output
+            let item_def_id = self.tcx.associated_item_def_ids(future_trait)[0];
+
+            let bounds = self.tcx.bound_explicit_item_bounds(*def_id);
+
+            for (predicate, _) in bounds.subst_iter_copied(self.tcx, substs) {
+                let output = predicate
+                    .kind()
+                    .map_bound(|kind| match kind {
+                        ty::PredicateKind::Projection(projection_predicate)
+                            if projection_predicate.projection_ty.item_def_id == item_def_id =>
+                        {
+                            projection_predicate.term.ty()
+                        }
+                        _ => None,
+                    })
+                    .transpose();
+                if output.is_some() {
+                    // We don't account for multiple `Future::Output = Ty` constraints.
+                    return output;
+                }
+            }
+        }
+        None
+    }
+}
+
+impl<'tcx> TypeErrCtxt<'_, 'tcx> {
     pub fn report_region_errors(
         &self,
         generic_param_scope: LocalDefId,
@@ -577,13 +634,13 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 {
                     // 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)
+                        && 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));
-                    }
+                    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
@@ -619,8 +676,8 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                         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.in_progress_typeck_results.and_then(|typeck_results| {
-                                typeck_results.borrow().expr_ty_opt(arg_expr)
+                            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");
@@ -726,10 +783,11 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             _ => {
                 if let ObligationCauseCode::BindingObligation(_, span)
                 | ObligationCauseCode::ExprBindingObligation(_, span, ..)
-                    = cause.code().peel_derives()
+                = cause.code().peel_derives()
                     && let TypeError::RegionsPlaceholderMismatch = terr
                 {
-                    err.span_note(*span, "the lifetime requirement is introduced here");
+                    err.span_note( * span,
+                    "the lifetime requirement is introduced here");
                 }
             }
         }
@@ -1653,8 +1711,114 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 ),
                 Mismatch::Fixed(s) => (s.into(), s.into(), None),
             };
-            match (&terr, expected == found) {
-                (TypeError::Sorts(values), extra) => {
+
+            enum Similar<'tcx> {
+                Adts { expected: ty::AdtDef<'tcx>, found: ty::AdtDef<'tcx> },
+                PrimitiveFound { expected: ty::AdtDef<'tcx>, found: Ty<'tcx> },
+                PrimitiveExpected { expected: Ty<'tcx>, found: ty::AdtDef<'tcx> },
+            }
+
+            let similarity = |ExpectedFound { expected, found }: ExpectedFound<Ty<'tcx>>| {
+                if let ty::Adt(expected, _) = expected.kind() && let Some(primitive) = found.primitive_symbol() {
+                    let path = self.tcx.def_path(expected.did()).data;
+                    let name = path.last().unwrap().data.get_opt_name();
+                    if name == Some(primitive) {
+                        return Some(Similar::PrimitiveFound { expected: *expected, found });
+                    }
+                } else if let Some(primitive) = expected.primitive_symbol() && let ty::Adt(found, _) = found.kind() {
+                    let path = self.tcx.def_path(found.did()).data;
+                    let name = path.last().unwrap().data.get_opt_name();
+                    if name == Some(primitive) {
+                        return Some(Similar::PrimitiveExpected { expected, found: *found });
+                    }
+                } else if let ty::Adt(expected, _) = expected.kind() && let ty::Adt(found, _) = found.kind() {
+                    if !expected.did().is_local() && expected.did().krate == found.did().krate {
+                        // Most likely types from different versions of the same crate
+                        // are in play, in which case this message isn't so helpful.
+                        // A "perhaps two different versions..." error is already emitted for that.
+                        return None;
+                    }
+                    let f_path = self.tcx.def_path(found.did()).data;
+                    let e_path = self.tcx.def_path(expected.did()).data;
+
+                    if let (Some(e_last), Some(f_last)) = (e_path.last(), f_path.last()) && e_last ==  f_last {
+                        return Some(Similar::Adts{expected: *expected, found: *found});
+                    }
+                }
+                None
+            };
+
+            match terr {
+                // If two types mismatch but have similar names, mention that specifically.
+                TypeError::Sorts(values) if let Some(s) = similarity(values) => {
+                    let diagnose_primitive =
+                        |prim: Ty<'tcx>,
+                         shadow: Ty<'tcx>,
+                         defid: DefId,
+                         diagnostic: &mut Diagnostic| {
+                            let name = shadow.sort_string(self.tcx);
+                            diagnostic.note(format!(
+                            "{prim} and {name} have similar names, but are actually distinct types"
+                        ));
+                            diagnostic
+                                .note(format!("{prim} is a primitive defined by the language"));
+                            let def_span = self.tcx.def_span(defid);
+                            let msg = if defid.is_local() {
+                                format!("{name} is defined in the current crate")
+                            } else {
+                                let crate_name = self.tcx.crate_name(defid.krate);
+                                format!("{name} is defined in crate `{crate_name}")
+                            };
+                            diagnostic.span_note(def_span, msg);
+                        };
+
+                    let diagnose_adts =
+                        |expected_adt : ty::AdtDef<'tcx>,
+                         found_adt: ty::AdtDef<'tcx>,
+                         diagnostic: &mut Diagnostic| {
+                            let found_name = values.found.sort_string(self.tcx);
+                            let expected_name = values.expected.sort_string(self.tcx);
+
+                            let found_defid = found_adt.did();
+                            let expected_defid = expected_adt.did();
+
+                            diagnostic.note(format!("{found_name} and {expected_name} have similar names, but are actually distinct types"));
+                            for (defid, name) in
+                                [(found_defid, found_name), (expected_defid, expected_name)]
+                            {
+                                let def_span = self.tcx.def_span(defid);
+
+                                let msg = if found_defid.is_local() && expected_defid.is_local() {
+                                    let module = self
+                                        .tcx
+                                        .parent_module_from_def_id(defid.expect_local())
+                                        .to_def_id();
+                                    let module_name = self.tcx.def_path(module).to_string_no_crate_verbose();
+                                    format!("{name} is defined in module `crate{module_name}` of the current crate")
+                                } else if defid.is_local() {
+                                    format!("{name} is defined in the current crate")
+                                } else {
+                                    let crate_name = self.tcx.crate_name(defid.krate);
+                                    format!("{name} is defined in crate `{crate_name}`")
+                                };
+                                diagnostic.span_note(def_span, msg);
+                            }
+                        };
+
+                    match s {
+                        Similar::Adts{expected, found} => {
+                            diagnose_adts(expected, found, diag)
+                        }
+                        Similar::PrimitiveFound{expected, found: prim} => {
+                            diagnose_primitive(prim, values.expected, expected.did(), diag)
+                        }
+                        Similar::PrimitiveExpected{expected: prim, found} => {
+                            diagnose_primitive(prim, values.found, found.did(), diag)
+                        }
+                    }
+                }
+                TypeError::Sorts(values) => {
+                    let extra = expected == found;
                     let sort_string = |ty: Ty<'tcx>| match (extra, ty.kind()) {
                         (true, ty::Opaque(def_id, _)) => {
                             let sm = self.tcx.sess.source_map();
@@ -1707,10 +1871,10 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                         );
                     }
                 }
-                (TypeError::ObjectUnsafeCoercion(_), _) => {
+                TypeError::ObjectUnsafeCoercion(_) => {
                     diag.note_unsuccessful_coercion(found, expected);
                 }
-                (_, _) => {
+                _ => {
                     debug!(
                         "note_type_err: exp_found={:?}, expected={:?} found={:?}",
                         exp_found, expected, found
@@ -1755,7 +1919,7 @@ impl<'a, 'tcx> InferCtxt<'a, '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
-        // librustc_typeck/check/compare_method.rs:compare_predicate_entailment) the latter
+        // rustc_hir_analysis/check/compare_method.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(|| {
@@ -1847,36 +2011,6 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         }
     }
 
-    pub fn get_impl_future_output_ty(&self, ty: Ty<'tcx>) -> Option<Binder<'tcx, Ty<'tcx>>> {
-        if let ty::Opaque(def_id, substs) = ty.kind() {
-            let future_trait = self.tcx.require_lang_item(LangItem::Future, None);
-            // Future::Output
-            let item_def_id = self.tcx.associated_item_def_ids(future_trait)[0];
-
-            let bounds = self.tcx.bound_explicit_item_bounds(*def_id);
-
-            for predicate in bounds.transpose_iter().map(|e| e.map_bound(|(p, _)| *p)) {
-                let predicate = predicate.subst(self.tcx, substs);
-                let output = predicate
-                    .kind()
-                    .map_bound(|kind| match kind {
-                        ty::PredicateKind::Projection(projection_predicate)
-                            if projection_predicate.projection_ty.item_def_id == item_def_id =>
-                        {
-                            projection_predicate.term.ty()
-                        }
-                        _ => None,
-                    })
-                    .transpose();
-                if output.is_some() {
-                    // We don't account for multiple `Future::Output = Ty` constraints.
-                    return output;
-                }
-            }
-        }
-        None
-    }
-
     /// A possible error is to forget to add `.await` when using futures:
     ///
     /// ```compile_fail,E0308
@@ -2051,8 +2185,22 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         exp_found: &ty::error::ExpectedFound<Ty<'tcx>>,
         diag: &mut Diagnostic,
     ) {
+        if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span)
+            && let Some(msg) = self.should_suggest_as_ref(exp_found.expected, exp_found.found)
+        {
+            diag.span_suggestion(
+                span,
+                msg,
+                // HACK: fix issue# 100605, suggesting convert from &Option<T> to Option<&T>, remove the extra `&`
+                format!("{}.as_ref()", snippet.trim_start_matches('&')),
+                Applicability::MachineApplicable,
+            );
+        }
+    }
+
+    pub fn should_suggest_as_ref(&self, expected: Ty<'tcx>, found: Ty<'tcx>) -> Option<&str> {
         if let (ty::Adt(exp_def, exp_substs), ty::Ref(_, found_ty, _)) =
-            (exp_found.expected.kind(), exp_found.found.kind())
+            (expected.kind(), found.kind())
         {
             if let ty::Adt(found_def, found_substs) = *found_ty.kind() {
                 if exp_def == &found_def {
@@ -2090,21 +2238,14 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                                 _ => show_suggestion = false,
                             }
                         }
-                        if let (Ok(snippet), true) =
-                            (self.tcx.sess.source_map().span_to_snippet(span), show_suggestion)
-                        {
-                            diag.span_suggestion(
-                                span,
-                                *msg,
-                                // HACK: fix issue# 100605, suggesting convert from &Option<T> to Option<&T>, remove the extra `&`
-                                format!("{}.as_ref()", snippet.trim_start_matches('&')),
-                                Applicability::MachineApplicable,
-                            );
+                        if show_suggestion {
+                            return Some(*msg);
                         }
                     }
                 }
             }
         }
+        None
     }
 
     pub fn report_and_explain_type_error(
@@ -2130,6 +2271,25 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 struct_span_err!(self.tcx.sess, span, E0580, "{}", failure_str)
             }
             FailureCode::Error0308(failure_str) => {
+                fn escape_literal(s: &str) -> String {
+                    let mut escaped = String::with_capacity(s.len());
+                    let mut chrs = s.chars().peekable();
+                    while let Some(first) = chrs.next() {
+                        match (first, chrs.peek()) {
+                            ('\\', Some(&delim @ '"') | Some(&delim @ '\'')) => {
+                                escaped.push('\\');
+                                escaped.push(delim);
+                                chrs.next();
+                            }
+                            ('"' | '\'', _) => {
+                                escaped.push('\\');
+                                escaped.push(first)
+                            }
+                            (c, _) => escaped.push(c),
+                        };
+                    }
+                    escaped
+                }
                 let mut err = struct_span_err!(self.tcx.sess, span, E0308, "{}", failure_str);
                 if let Some((expected, found)) = trace.values.ty() {
                     match (expected.kind(), found.kind()) {
@@ -2151,7 +2311,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                                 err.span_suggestion(
                                     span,
                                     "if you meant to write a `char` literal, use single quotes",
-                                    format!("'{}'", code),
+                                    format!("'{}'", escape_literal(code)),
                                     Applicability::MachineApplicable,
                                 );
                             }
@@ -2166,7 +2326,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                                     err.span_suggestion(
                                         span,
                                         "if you meant to write a `str` literal, use double quotes",
-                                        format!("\"{}\"", code),
+                                        format!("\"{}\"", escape_literal(code)),
                                         Applicability::MachineApplicable,
                                     );
                                 }
@@ -2317,7 +2477,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         origin: Option<SubregionOrigin<'tcx>>,
         bound_kind: GenericKind<'tcx>,
         sub: Region<'tcx>,
-    ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
+    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
         // Attempt to obtain the span of the parameter so we can
         // suggest adding an explicit lifetime bound to it.
         let generics = self.tcx.generics_of(generic_param_scope);
@@ -2333,7 +2493,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                         // 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);
+                        let 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
@@ -2374,6 +2534,9 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         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))
+            }
         };
 
         if let Some(SubregionOrigin::CompareImplItemObligation {
@@ -2453,7 +2616,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                             for h in self.tcx.hir().parent_iter(param.hir_id) {
                                 break 'origin match h.1 {
                                     Node::ImplItem(hir::ImplItem {
-                                        kind: hir::ImplItemKind::TyAlias(..),
+                                        kind: hir::ImplItemKind::Type(..),
                                         generics,
                                         ..
                                     })
@@ -2692,7 +2855,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     }
 }
 
-struct SameTypeModuloInfer<'a, 'tcx>(&'a InferCtxt<'a, 'tcx>);
+struct SameTypeModuloInfer<'a, 'tcx>(&'a InferCtxt<'tcx>);
 
 impl<'tcx> TypeRelation<'tcx> for SameTypeModuloInfer<'_, 'tcx> {
     fn tcx(&self) -> TyCtxt<'tcx> {
@@ -2779,7 +2942,7 @@ impl<'tcx> TypeRelation<'tcx> for SameTypeModuloInfer<'_, 'tcx> {
     }
 }
 
-impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
+impl<'tcx> InferCtxt<'tcx> {
     fn report_inference_failure(
         &self,
         var_origin: RegionVariableOrigin,
@@ -2967,7 +3130,7 @@ impl TyCategory {
     }
 }
 
-impl<'tcx> InferCtxt<'_, 'tcx> {
+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 {
@@ -2994,7 +3157,9 @@ impl<'tcx> InferCtxt<'_, 'tcx> {
             _ => rustc_span::DUMMY_SP,
         }
     }
+}
 
+impl<'tcx> TypeErrCtxt<'_, 'tcx> {
     /// Be helpful when the user wrote `{... expr; }` and taking the `;` off
     /// is enough to fix the error.
     pub fn could_remove_semicolon(
@@ -3011,7 +3176,7 @@ impl<'tcx> InferCtxt<'_, 'tcx> {
         let hir::StmtKind::Semi(ref last_expr) = last_stmt.kind else {
             return None;
         };
-        let last_expr_ty = self.in_progress_typeck_results?.borrow().expr_ty_opt(*last_expr)?;
+        let last_expr_ty = self.typeck_results.as_ref()?.expr_ty_opt(*last_expr)?;
         let needs_box = match (last_expr_ty.kind(), expected_ty.kind()) {
             _ if last_expr_ty.references_error() => return None,
             _ if self.same_type_modulo_infer(last_expr_ty, expected_ty) => {
@@ -3094,8 +3259,9 @@ impl<'tcx> InferCtxt<'_, 'tcx> {
         let mut find_compatible_candidates = |pat: &hir::Pat<'_>| {
             if let hir::PatKind::Binding(_, hir_id, ident, _) = &pat.kind
                 && let Some(pat_ty) = self
-                    .in_progress_typeck_results
-                    .and_then(|typeck_results| typeck_results.borrow().node_type_opt(*hir_id))
+                    .typeck_results
+                    .as_ref()
+                    .and_then(|typeck_results| typeck_results.node_type_opt(*hir_id))
             {
                 let pat_ty = self.resolve_vars_if_possible(pat_ty);
                 if self.same_type_modulo_infer(pat_ty, expected_ty)
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 cb2be9358..7b3178e61 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
@@ -2,8 +2,10 @@ use crate::errors::{
     AmbigousImpl, AmbigousReturn, AnnotationRequired, InferenceBadError, NeedTypeInfoInGenerator,
     SourceKindMultiSuggestion, SourceKindSubdiag,
 };
+use crate::infer::error_reporting::TypeErrCtxt;
 use crate::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use crate::infer::InferCtxt;
+use rustc_errors::IntoDiagnostic;
 use rustc_errors::{DiagnosticBuilder, ErrorGuaranteed, IntoDiagnosticArg};
 use rustc_hir as hir;
 use rustc_hir::def::Res;
@@ -15,10 +17,9 @@ use rustc_middle::hir::nested_filter;
 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
 use rustc_middle::ty::adjustment::{Adjust, Adjustment, AutoBorrow, AutoBorrowMutability};
 use rustc_middle::ty::print::{FmtPrinter, PrettyPrinter, Print, Printer};
-use rustc_middle::ty::subst::{GenericArg, GenericArgKind, Subst, SubstsRef};
 use rustc_middle::ty::{self, DefIdTree, InferConst};
+use rustc_middle::ty::{GenericArg, GenericArgKind, SubstsRef};
 use rustc_middle::ty::{IsSuggestable, Ty, TyCtxt, TypeckResults};
-use rustc_session::SessionDiagnostic;
 use rustc_span::symbol::{kw, Ident};
 use rustc_span::{BytePos, Span};
 use std::borrow::Cow;
@@ -151,7 +152,7 @@ impl UnderspecifiedArgKind {
     }
 }
 
-fn fmt_printer<'a, 'tcx>(infcx: &'a InferCtxt<'_, 'tcx>, ns: Namespace) -> FmtPrinter<'a, 'tcx> {
+fn fmt_printer<'a, 'tcx>(infcx: &'a InferCtxt<'tcx>, ns: Namespace) -> FmtPrinter<'a, 'tcx> {
     let mut printer = FmtPrinter::new(infcx.tcx, ns);
     let ty_getter = move |ty_vid| {
         if infcx.probe_ty_var(ty_vid).is_ok() {
@@ -182,7 +183,7 @@ fn fmt_printer<'a, 'tcx>(infcx: &'a InferCtxt<'_, 'tcx>, ns: Namespace) -> FmtPr
     printer
 }
 
-fn ty_to_string<'tcx>(infcx: &InferCtxt<'_, 'tcx>, ty: Ty<'tcx>) -> String {
+fn ty_to_string<'tcx>(infcx: &InferCtxt<'tcx>, ty: Ty<'tcx>) -> String {
     let printer = fmt_printer(infcx, Namespace::TypeNS);
     let ty = infcx.resolve_vars_if_possible(ty);
     match ty.kind() {
@@ -201,7 +202,7 @@ fn ty_to_string<'tcx>(infcx: &InferCtxt<'_, 'tcx>, ty: Ty<'tcx>) -> String {
 /// We don't want to directly use `ty_to_string` for closures as their type isn't really
 /// something users are familiar with. Directly printing the `fn_sig` of closures also
 /// doesn't work as they actually use the "rust-call" API.
-fn closure_as_fn_str<'tcx>(infcx: &InferCtxt<'_, 'tcx>, ty: Ty<'tcx>) -> String {
+fn closure_as_fn_str<'tcx>(infcx: &InferCtxt<'tcx>, ty: Ty<'tcx>) -> String {
     let ty::Closure(_, substs) = ty.kind() else { unreachable!() };
     let fn_sig = substs.as_closure().sig();
     let args = fn_sig
@@ -225,7 +226,7 @@ fn closure_as_fn_str<'tcx>(infcx: &InferCtxt<'_, 'tcx>, ty: Ty<'tcx>) -> String
     format!("fn({}){}", args, ret)
 }
 
-impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
+impl<'tcx> InferCtxt<'tcx> {
     /// Extracts data used by diagnostic for either types or constants
     /// which were stuck during inference.
     pub fn extract_inference_diagnostics_data(
@@ -317,7 +318,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         }
     }
 
-    /// Used as a fallback in [InferCtxt::emit_inference_failure_err]
+    /// Used as a fallback in [TypeErrCtxt::emit_inference_failure_err]
     /// in case we weren't able to get a better error.
     fn bad_inference_failure_err(
         &self,
@@ -364,7 +365,9 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             .into_diagnostic(&self.tcx.sess.parse_sess.span_diagnostic),
         }
     }
+}
 
+impl<'tcx> TypeErrCtxt<'_, 'tcx> {
     pub fn emit_inference_failure_err(
         &self,
         body_id: Option<hir::BodyId>,
@@ -376,14 +379,12 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         let arg = self.resolve_vars_if_possible(arg);
         let arg_data = self.extract_inference_diagnostics_data(arg, None);
 
-        let Some(typeck_results) = self.in_progress_typeck_results else {
+        let Some(typeck_results) = &self.typeck_results else {
             // If we don't have any typeck results we're outside
             // of a body, so we won't be able to get better info
             // here.
             return self.bad_inference_failure_err(failure_span, arg_data, error_code);
         };
-        let typeck_results = typeck_results.borrow();
-        let typeck_results = &typeck_results;
 
         let mut local_visitor = FindInferSourceVisitor::new(&self, typeck_results, arg);
         if let Some(body_id) = body_id {
@@ -435,6 +436,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 generics_def_id,
                 def_id: _,
                 generic_args,
+                have_turbofish,
             } => {
                 let generics = self.tcx.generics_of(generics_def_id);
                 let is_type = matches!(arg.unpack(), GenericArgKind::Type(_));
@@ -482,11 +484,13 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                     .unwrap()
                     .into_buffer();
 
-                infer_subdiags.push(SourceKindSubdiag::GenericSuggestion {
-                    span: insert_span,
-                    arg_count: generic_args.len(),
-                    args,
-                });
+                if !have_turbofish {
+                    infer_subdiags.push(SourceKindSubdiag::GenericSuggestion {
+                        span: insert_span,
+                        arg_count: generic_args.len(),
+                        args,
+                    });
+                }
             }
             InferSourceKind::FullyQualifiedMethodCall { receiver, successor, substs, def_id } => {
                 let printer = fmt_printer(self, Namespace::ValueNS);
@@ -560,7 +564,9 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             .into_diagnostic(&self.tcx.sess.parse_sess.span_diagnostic),
         }
     }
+}
 
+impl<'tcx> InferCtxt<'tcx> {
     pub fn need_type_info_err_in_generator(
         &self,
         kind: hir::GeneratorKind,
@@ -616,6 +622,7 @@ enum InferSourceKind<'tcx> {
         generics_def_id: DefId,
         def_id: DefId,
         generic_args: &'tcx [GenericArg<'tcx>],
+        have_turbofish: bool,
     },
     FullyQualifiedMethodCall {
         receiver: &'tcx Expr<'tcx>,
@@ -650,7 +657,7 @@ impl<'tcx> InferSource<'tcx> {
 }
 
 impl<'tcx> InferSourceKind<'tcx> {
-    fn ty_localized_msg(&self, infcx: &InferCtxt<'_, 'tcx>) -> (&'static str, String) {
+    fn ty_localized_msg(&self, infcx: &InferCtxt<'tcx>) -> (&'static str, String) {
         match *self {
             InferSourceKind::LetBinding { ty, .. }
             | InferSourceKind::ClosureArg { ty, .. }
@@ -676,6 +683,7 @@ struct InsertableGenericArgs<'tcx> {
     substs: SubstsRef<'tcx>,
     generics_def_id: DefId,
     def_id: DefId,
+    have_turbofish: bool,
 }
 
 /// A visitor which searches for the "best" spot to use in the inference error.
@@ -686,7 +694,7 @@ struct InsertableGenericArgs<'tcx> {
 /// While doing so, the currently best spot is stored in `infer_source`.
 /// For details on how we rank spots, see [Self::source_cost]
 struct FindInferSourceVisitor<'a, 'tcx> {
-    infcx: &'a InferCtxt<'a, 'tcx>,
+    infcx: &'a InferCtxt<'tcx>,
     typeck_results: &'a TypeckResults<'tcx>,
 
     target: GenericArg<'tcx>,
@@ -698,7 +706,7 @@ struct FindInferSourceVisitor<'a, 'tcx> {
 
 impl<'a, 'tcx> FindInferSourceVisitor<'a, 'tcx> {
     fn new(
-        infcx: &'a InferCtxt<'a, 'tcx>,
+        infcx: &'a InferCtxt<'tcx>,
         typeck_results: &'a TypeckResults<'tcx>,
         target: GenericArg<'tcx>,
     ) -> Self {
@@ -894,11 +902,18 @@ impl<'a, 'tcx> FindInferSourceVisitor<'a, 'tcx> {
             // impl is currently the `DefId` of `Output` in the trait definition
             // which makes this somewhat difficult and prevents us from just
             // using `self.path_inferred_subst_iter` here.
-            hir::ExprKind::Struct(&hir::QPath::Resolved(_self_ty, path), _, _) => {
-                if let Some(ty) = self.opt_node_type(expr.hir_id) {
-                    if let ty::Adt(_, substs) = ty.kind() {
-                        return Box::new(self.resolved_path_inferred_subst_iter(path, substs));
-                    }
+            hir::ExprKind::Struct(&hir::QPath::Resolved(_self_ty, path), _, _)
+            // FIXME(TaKO8Ki): Ideally we should support this. For that
+            // we have to map back from the self type to the
+            // type alias though. That's difficult.
+            //
+            // See the `need_type_info/issue-103053.rs` test for
+            // a example.
+            if !matches!(path.res, Res::Def(DefKind::TyAlias, _)) => {
+                if let Some(ty) = self.opt_node_type(expr.hir_id)
+                    && let ty::Adt(_, substs) = ty.kind()
+                {
+                    return Box::new(self.resolved_path_inferred_subst_iter(path, substs));
                 }
             }
             hir::ExprKind::MethodCall(segment, ..) => {
@@ -916,6 +931,7 @@ impl<'a, 'tcx> FindInferSourceVisitor<'a, 'tcx> {
                             substs,
                             generics_def_id: def_id,
                             def_id,
+                            have_turbofish: false,
                         }
                     };
                     return Box::new(insertable.into_iter());
@@ -933,6 +949,9 @@ impl<'a, 'tcx> FindInferSourceVisitor<'a, 'tcx> {
         substs: SubstsRef<'tcx>,
     ) -> impl Iterator<Item = InsertableGenericArgs<'tcx>> + 'a {
         let tcx = self.infcx.tcx;
+        let have_turbofish = path.segments.iter().any(|segment| {
+            segment.args.map_or(false, |args| args.args.iter().any(|arg| arg.is_ty_or_const()))
+        });
         // The last segment of a path often has `Res::Err` and the
         // correct `Res` is the one of the whole path.
         //
@@ -942,7 +961,7 @@ impl<'a, 'tcx> FindInferSourceVisitor<'a, 'tcx> {
             let generics_def_id = tcx.res_generics_def_id(path.res)?;
             let generics = tcx.generics_of(generics_def_id);
             if generics.has_impl_trait() {
-                None?
+                None?;
             }
             let insert_span =
                 path.segments.last().unwrap().ident.span.shrink_to_hi().with_hi(path.span.hi());
@@ -951,6 +970,7 @@ impl<'a, 'tcx> FindInferSourceVisitor<'a, 'tcx> {
                 substs,
                 generics_def_id,
                 def_id: path.res.def_id(),
+                have_turbofish,
             }
         };
 
@@ -970,6 +990,7 @@ impl<'a, 'tcx> FindInferSourceVisitor<'a, 'tcx> {
                     substs,
                     generics_def_id,
                     def_id: res.def_id(),
+                    have_turbofish,
                 })
             })
             .chain(last_segment_using_path_data)
@@ -998,7 +1019,13 @@ impl<'a, 'tcx> FindInferSourceVisitor<'a, 'tcx> {
                     }
                     let span = tcx.hir().span(segment.hir_id);
                     let insert_span = segment.ident.span.shrink_to_hi().with_hi(span.hi());
-                    InsertableGenericArgs { insert_span, substs, generics_def_id: def_id, def_id }
+                    InsertableGenericArgs {
+                        insert_span,
+                        substs,
+                        generics_def_id: def_id,
+                        def_id,
+                        have_turbofish: false,
+                    }
                 };
 
                 let parent_def_id = generics.parent.unwrap();
@@ -1021,7 +1048,7 @@ impl<'a, 'tcx> FindInferSourceVisitor<'a, 'tcx> {
                                     }
                                     // There cannot be inference variables in the self type,
                                     // so there's nothing for us to do here.
-                                    Res::SelfTy { .. } => {}
+                                    Res::SelfTyParam { .. } | Res::SelfTyAlias { .. } => {}
                                     _ => warn!(
                                         "unexpected path: def={:?} substs={:?} path={:?}",
                                         def, substs, path,
@@ -1121,7 +1148,13 @@ impl<'a, 'tcx> Visitor<'tcx> for FindInferSourceVisitor<'a, 'tcx> {
 
         for args in self.expr_inferred_subst_iter(expr) {
             debug!(?args);
-            let InsertableGenericArgs { insert_span, substs, generics_def_id, def_id } = args;
+            let InsertableGenericArgs {
+                insert_span,
+                substs,
+                generics_def_id,
+                def_id,
+                have_turbofish,
+            } = args;
             let generics = tcx.generics_of(generics_def_id);
             if let Some(argument_index) = generics
                 .own_substs(substs)
@@ -1144,6 +1177,7 @@ impl<'a, 'tcx> Visitor<'tcx> for FindInferSourceVisitor<'a, 'tcx> {
                         generics_def_id,
                         def_id,
                         generic_args,
+                        have_turbofish,
                     },
                 });
             }
diff --git a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/different_lifetimes.rs b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/different_lifetimes.rs
index 3a4320a9a..da0271a34 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/different_lifetimes.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/different_lifetimes.rs
@@ -11,7 +11,7 @@ use crate::infer::lexical_region_resolve::RegionResolutionError;
 use crate::infer::SubregionOrigin;
 use crate::infer::TyCtxt;
 
-use rustc_errors::AddSubdiagnostic;
+use rustc_errors::AddToDiagnostic;
 use rustc_errors::{Diagnostic, ErrorGuaranteed};
 use rustc_hir::Ty;
 use rustc_middle::ty::Region;
diff --git a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/mismatched_static_lifetime.rs b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/mismatched_static_lifetime.rs
index 1410e2b63..c5f2a1a3f 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/mismatched_static_lifetime.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/mismatched_static_lifetime.rs
@@ -2,7 +2,9 @@
 //! to hold.
 
 use crate::errors::{note_and_explain, IntroducesStaticBecauseUnmetLifetimeReq};
-use crate::errors::{ImplNote, MismatchedStaticLifetime, TraitSubdiag};
+use crate::errors::{
+    DoesNotOutliveStaticFromImpl, ImplicitStaticLifetimeSubdiag, MismatchedStaticLifetime,
+};
 use crate::infer::error_reporting::nice_region_error::NiceRegionError;
 use crate::infer::lexical_region_resolve::RegionResolutionError;
 use crate::infer::{SubregionOrigin, TypeTrace};
@@ -56,7 +58,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
             note_and_explain::SuffixKind::Continues,
         );
         let mut impl_span = None;
-        let mut trait_subdiags = Vec::new();
+        let mut implicit_static_lifetimes = Vec::new();
         if let Some(impl_node) = self.tcx().hir().get_if_local(*impl_def_id) {
             // If an impl is local, then maybe this isn't what they want. Try to
             // be as helpful as possible with implicit lifetimes.
@@ -90,10 +92,12 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
                 // Otherwise, point at all implicit static lifetimes
 
                 for span in &traits {
-                    trait_subdiags.push(TraitSubdiag::Note { span: *span });
+                    implicit_static_lifetimes
+                        .push(ImplicitStaticLifetimeSubdiag::Note { span: *span });
                     // It would be nice to put this immediately under the above note, but they get
                     // pushed to the end.
-                    trait_subdiags.push(TraitSubdiag::Sugg { span: span.shrink_to_hi() });
+                    implicit_static_lifetimes
+                        .push(ImplicitStaticLifetimeSubdiag::Sugg { span: span.shrink_to_hi() });
                 }
             }
         } else {
@@ -105,8 +109,10 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
             cause_span: cause.span,
             unmet_lifetime_reqs: multispan_subdiag,
             expl,
-            impl_note: ImplNote { impl_span },
-            trait_subdiags,
+            does_not_outlive_static_from_impl: impl_span
+                .map(|span| DoesNotOutliveStaticFromImpl::Spanned { span })
+                .unwrap_or(DoesNotOutliveStaticFromImpl::Unspanned),
+            implicit_static_lifetimes,
         };
         let reported = self.tcx().sess.emit_err(err);
         Some(reported)
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 53d9acf7d..aaf5a7af0 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
@@ -1,6 +1,6 @@
+use crate::infer::error_reporting::TypeErrCtxt;
 use crate::infer::lexical_region_resolve::RegionResolutionError;
 use crate::infer::lexical_region_resolve::RegionResolutionError::*;
-use crate::infer::InferCtxt;
 use rustc_errors::{DiagnosticBuilder, ErrorGuaranteed};
 use rustc_middle::ty::{self, TyCtxt};
 use rustc_span::source_map::Span;
@@ -19,34 +19,34 @@ pub use find_anon_type::find_anon_type;
 pub use static_impl_trait::{suggest_new_region_bound, HirTraitObjectVisitor, TraitObjectVisitor};
 pub use util::find_param_with_region;
 
-impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
-    pub fn try_report_nice_region_error(&self, error: &RegionResolutionError<'tcx>) -> bool {
+impl<'cx, 'tcx> TypeErrCtxt<'cx, 'tcx> {
+    pub fn try_report_nice_region_error(&'cx self, error: &RegionResolutionError<'tcx>) -> bool {
         NiceRegionError::new(self, error.clone()).try_report().is_some()
     }
 }
 
 pub struct NiceRegionError<'cx, 'tcx> {
-    infcx: &'cx InferCtxt<'cx, 'tcx>,
+    cx: &'cx TypeErrCtxt<'cx, 'tcx>,
     error: Option<RegionResolutionError<'tcx>>,
     regions: Option<(Span, ty::Region<'tcx>, ty::Region<'tcx>)>,
 }
 
 impl<'cx, 'tcx> NiceRegionError<'cx, 'tcx> {
-    pub fn new(infcx: &'cx InferCtxt<'cx, 'tcx>, error: RegionResolutionError<'tcx>) -> Self {
-        Self { infcx, error: Some(error), regions: None }
+    pub fn new(cx: &'cx TypeErrCtxt<'cx, 'tcx>, error: RegionResolutionError<'tcx>) -> Self {
+        Self { cx, error: Some(error), regions: None }
     }
 
     pub fn new_from_span(
-        infcx: &'cx InferCtxt<'cx, 'tcx>,
+        cx: &'cx TypeErrCtxt<'cx, 'tcx>,
         span: Span,
         sub: ty::Region<'tcx>,
         sup: ty::Region<'tcx>,
     ) -> Self {
-        Self { infcx, error: None, regions: Some((span, sub, sup)) }
+        Self { cx, error: None, regions: Some((span, sub, sup)) }
     }
 
     fn tcx(&self) -> TyCtxt<'tcx> {
-        self.infcx.tcx
+        self.cx.tcx
     }
 
     pub fn try_report_from_nll(&self) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
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 d4db07512..a58516829 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
@@ -226,12 +226,12 @@ impl<'tcx> NiceRegionError<'_, 'tcx> {
             false
         };
 
-        let expected_trait_ref = self.infcx.resolve_vars_if_possible(ty::TraitRef {
+        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
-            .infcx
+            .cx
             .resolve_vars_if_possible(ty::TraitRef { def_id: trait_def_id, substs: actual_substs });
 
         // Search the expected and actual trait references to see (a)
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 ae56bea6f..9bf755d7f 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
@@ -185,8 +185,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
             | ObligationCauseCode::BlockTailExpression(hir_id) = cause.code()
             {
                 let parent_id = tcx.hir().get_parent_item(*hir_id);
-                let parent_id = tcx.hir().local_def_id_to_hir_id(parent_id);
-                if let Some(fn_decl) = tcx.hir().fn_decl_by_hir_id(parent_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 add_label = true;
                     if let hir::FnRetTy::Return(ty) = fn_decl.output {
@@ -287,8 +286,8 @@ pub fn suggest_new_region_bound(
 ) {
     debug!("try_report_static_impl_trait: fn_return={:?}", fn_returns);
     // FIXME: account for the need of parens in `&(dyn Trait + '_)`
-    let consider = "consider changing the";
-    let declare = "to declare that the";
+    let consider = "consider changing";
+    let declare = "to declare that";
     let explicit = format!("you can add an explicit `{}` lifetime bound", lifetime_name);
     let explicit_static =
         arg.map(|arg| format!("explicit `'static` bound to the lifetime of {}", arg));
@@ -306,6 +305,10 @@ pub fn suggest_new_region_bound(
                     return;
                 };
 
+                // Get the identity type for this RPIT
+                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()
@@ -322,7 +325,7 @@ pub fn suggest_new_region_bound(
                     if let Some(explicit_static) = &explicit_static {
                         err.span_suggestion_verbose(
                             span,
-                            &format!("{} `impl Trait`'s {}", consider, explicit_static),
+                            &format!("{consider} `{ty}`'s {explicit_static}"),
                             &lifetime_name,
                             Applicability::MaybeIncorrect,
                         );
@@ -352,12 +355,7 @@ pub fn suggest_new_region_bound(
                 } else {
                     err.span_suggestion_verbose(
                         fn_return.span.shrink_to_hi(),
-                        &format!(
-                            "{declare} `impl Trait` {captures}, {explicit}",
-                            declare = declare,
-                            captures = captures,
-                            explicit = explicit,
-                        ),
+                        &format!("{declare} `{ty}` {captures}, {explicit}",),
                         &plus_lt,
                         Applicability::MaybeIncorrect,
                     );
@@ -368,7 +366,7 @@ pub fn suggest_new_region_bound(
                     err.span_suggestion_verbose(
                         fn_return.span.shrink_to_hi(),
                         &format!(
-                            "{declare} trait object {captures}, {explicit}",
+                            "{declare} the trait object {captures}, {explicit}",
                             declare = declare,
                             captures = captures,
                             explicit = explicit,
@@ -385,7 +383,7 @@ pub fn suggest_new_region_bound(
                     if let Some(explicit_static) = &explicit_static {
                         err.span_suggestion_verbose(
                             lt.span,
-                            &format!("{} trait object's {}", consider, explicit_static),
+                            &format!("{} the trait object's {}", consider, explicit_static),
                             &lifetime_name,
                             Applicability::MaybeIncorrect,
                         );
@@ -415,7 +413,8 @@ impl<'a, 'tcx> NiceRegionError<'a, '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())) {
+                match tcx.hir().find_by_def_id(tcx.hir().get_parent_item(impl_item.hir_id()).def_id)
+                {
                     Some(Node::Item(Item {
                         kind: ItemKind::Impl(hir::Impl { self_ty, .. }),
                         ..
@@ -425,7 +424,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
             }
             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) {
+                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
@@ -486,7 +485,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
             tcx,
             ctxt.param_env,
             ctxt.assoc_item.def_id,
-            self.infcx.resolve_vars_if_possible(ctxt.substs),
+            self.cx.resolve_vars_if_possible(ctxt.substs),
         ) else {
             return false;
         };
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 a6a39d062..5d536e982 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
@@ -84,12 +84,12 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
 
         let expected_highlight = HighlightBuilder::build(self.tcx(), expected);
         let expected = self
-            .infcx
+            .cx
             .extract_inference_diagnostics_data(expected.into(), Some(expected_highlight))
             .name;
         let found_highlight = HighlightBuilder::build(self.tcx(), found);
         let found =
-            self.infcx.extract_inference_diagnostics_data(found.into(), Some(found_highlight)).name;
+            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));
@@ -156,7 +156,8 @@ impl<'tcx> Visitor<'tcx> for TypeParamSpanVisitor<'tcx> {
                 [segment]
                     if matches!(
                         segment.res,
-                        Res::SelfTy { trait_: _, alias_to: _ }
+                        Res::SelfTyParam { .. }
+                            | Res::SelfTyAlias { .. }
                             | Res::Def(hir::def::DefKind::TyParam, _)
                     ) =>
                 {
diff --git a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/util.rs b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/util.rs
index 3e9d491af..f1461d701 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/util.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/util.rs
@@ -130,7 +130,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
             let ret_ty = fn_ty.fn_sig(self.tcx()).output();
             let span = hir_sig.decl.output.span();
             let future_output = if hir_sig.header.is_async() {
-                ret_ty.map_bound(|ty| self.infcx.get_impl_future_output_ty(ty)).transpose()
+                ret_ty.map_bound(|ty| self.cx.get_impl_future_output_ty(ty)).transpose()
             } else {
                 None
             };
diff --git a/compiler/rustc_infer/src/infer/error_reporting/note.rs b/compiler/rustc_infer/src/infer/error_reporting/note.rs
index adaa47c01..41b115f33 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/note.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/note.rs
@@ -1,8 +1,8 @@
 use crate::errors::RegionOriginNote;
-use crate::infer::error_reporting::note_and_explain_region;
-use crate::infer::{self, InferCtxt, SubregionOrigin};
+use crate::infer::error_reporting::{note_and_explain_region, TypeErrCtxt};
+use crate::infer::{self, SubregionOrigin};
 use rustc_errors::{
-    fluent, struct_span_err, AddSubdiagnostic, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
+    fluent, struct_span_err, AddToDiagnostic, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
 };
 use rustc_middle::traits::ObligationCauseCode;
 use rustc_middle::ty::error::TypeError;
@@ -10,7 +10,7 @@ use rustc_middle::ty::{self, Region};
 
 use super::ObligationCauseAsDiagArg;
 
-impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
+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 {
@@ -19,26 +19,27 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 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::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,
+                    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 }
+                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,
+                    msg: fluent::infer_data_borrowed,
                     name: &self.ty_to_string(ty),
                     continues: false,
                 }
@@ -47,7 +48,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             infer::ReferenceOutlivesReferent(ty, span) => {
                 RegionOriginNote::WithName {
                     span,
-                    msg: fluent::infer::reference_outlives_referent,
+                    msg: fluent::infer_reference_outlives_referent,
                     name: &self.ty_to_string(ty),
                     continues: false,
                 }
@@ -56,22 +57,22 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             infer::RelateParamBound(span, ty, opt_span) => {
                 RegionOriginNote::WithName {
                     span,
-                    msg: fluent::infer::relate_param_bound,
+                    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 }
+                    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 }
+                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 }
+                RegionOriginNote::Plain { span, msg: fluent::infer_compare_impl_item_obligation }
                     .add_to_diagnostic(err);
             }
             infer::CheckAssociatedTypeBounds { ref parent, .. } => {
@@ -80,7 +81,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             infer::AscribeUserTypeProvePredicate(span) => {
                 RegionOriginNote::Plain {
                     span,
-                    msg: fluent::infer::ascribe_user_type_prove_predicate,
+                    msg: fluent::infer_ascribe_user_type_prove_predicate,
                 }
                 .add_to_diagnostic(err);
             }
diff --git a/compiler/rustc_infer/src/infer/freshen.rs b/compiler/rustc_infer/src/infer/freshen.rs
index fee15afc7..ff5d1a05a 100644
--- a/compiler/rustc_infer/src/infer/freshen.rs
+++ b/compiler/rustc_infer/src/infer/freshen.rs
@@ -38,7 +38,7 @@ use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable, TypeVi
 use std::collections::hash_map::Entry;
 
 pub struct TypeFreshener<'a, 'tcx> {
-    infcx: &'a InferCtxt<'a, 'tcx>,
+    infcx: &'a InferCtxt<'tcx>,
     ty_freshen_count: u32,
     const_freshen_count: u32,
     ty_freshen_map: FxHashMap<ty::InferTy, Ty<'tcx>>,
@@ -47,7 +47,7 @@ pub struct TypeFreshener<'a, 'tcx> {
 }
 
 impl<'a, 'tcx> TypeFreshener<'a, 'tcx> {
-    pub fn new(infcx: &'a InferCtxt<'a, 'tcx>, keep_static: bool) -> TypeFreshener<'a, 'tcx> {
+    pub fn new(infcx: &'a InferCtxt<'tcx>, keep_static: bool) -> TypeFreshener<'a, 'tcx> {
         TypeFreshener {
             infcx,
             ty_freshen_count: 0,
diff --git a/compiler/rustc_infer/src/infer/fudge.rs b/compiler/rustc_infer/src/infer/fudge.rs
index 2f0eadce6..6dd6c4e1f 100644
--- a/compiler/rustc_infer/src/infer/fudge.rs
+++ b/compiler/rustc_infer/src/infer/fudge.rs
@@ -43,7 +43,7 @@ struct VariableLengths {
     region_constraints_len: usize,
 }
 
-impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
+impl<'tcx> InferCtxt<'tcx> {
     fn variable_lengths(&self) -> VariableLengths {
         let mut inner = self.inner.borrow_mut();
         VariableLengths {
@@ -167,7 +167,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
 }
 
 pub struct InferenceFudger<'a, 'tcx> {
-    infcx: &'a InferCtxt<'a, 'tcx>,
+    infcx: &'a InferCtxt<'tcx>,
     type_vars: (Range<TyVid>, Vec<TypeVariableOrigin>),
     int_vars: Range<IntVid>,
     float_vars: Range<FloatVid>,
diff --git a/compiler/rustc_infer/src/infer/glb.rs b/compiler/rustc_infer/src/infer/glb.rs
index 1570a08f3..6ffefcb7a 100644
--- a/compiler/rustc_infer/src/infer/glb.rs
+++ b/compiler/rustc_infer/src/infer/glb.rs
@@ -113,7 +113,7 @@ impl<'tcx> TypeRelation<'tcx> for Glb<'_, '_, 'tcx> {
 }
 
 impl<'combine, 'infcx, 'tcx> LatticeDir<'infcx, 'tcx> for Glb<'combine, 'infcx, 'tcx> {
-    fn infcx(&self) -> &'infcx InferCtxt<'infcx, 'tcx> {
+    fn infcx(&self) -> &'infcx InferCtxt<'tcx> {
         self.fields.infcx
     }
 
diff --git a/compiler/rustc_infer/src/infer/higher_ranked/mod.rs b/compiler/rustc_infer/src/infer/higher_ranked/mod.rs
index 0ce271c0e..28c87a115 100644
--- a/compiler/rustc_infer/src/infer/higher_ranked/mod.rs
+++ b/compiler/rustc_infer/src/infer/higher_ranked/mod.rs
@@ -59,7 +59,7 @@ impl<'a, 'tcx> CombineFields<'a, 'tcx> {
     }
 }
 
-impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
+impl<'tcx> InferCtxt<'tcx> {
     /// Replaces all bound variables (lifetimes, types, and constants) bound by
     /// `binder` with placeholder variables in a new universe. This means that the
     /// new placeholders can only be named by inference variables created after
@@ -114,7 +114,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     pub fn leak_check(
         &self,
         overly_polymorphic: bool,
-        snapshot: &CombinedSnapshot<'_, 'tcx>,
+        snapshot: &CombinedSnapshot<'tcx>,
     ) -> RelateResult<'tcx, ()> {
         // If the user gave `-Zno-leak-check`, or we have been
         // configured to skip the leak check, then skip the leak check
diff --git a/compiler/rustc_infer/src/infer/lattice.rs b/compiler/rustc_infer/src/infer/lattice.rs
index 1e3293efa..eba65361a 100644
--- a/compiler/rustc_infer/src/infer/lattice.rs
+++ b/compiler/rustc_infer/src/infer/lattice.rs
@@ -31,7 +31,7 @@ use rustc_middle::ty::{self, Ty};
 /// GLB moves "down" the lattice (to smaller values); LUB moves
 /// "up" the lattice (to bigger values).
 pub trait LatticeDir<'f, 'tcx>: TypeRelation<'tcx> {
-    fn infcx(&self) -> &'f InferCtxt<'f, 'tcx>;
+    fn infcx(&self) -> &'f InferCtxt<'tcx>;
 
     fn cause(&self) -> &ObligationCause<'tcx>;
 
diff --git a/compiler/rustc_infer/src/infer/lub.rs b/compiler/rustc_infer/src/infer/lub.rs
index 9f96d52c8..d6e56fcb7 100644
--- a/compiler/rustc_infer/src/infer/lub.rs
+++ b/compiler/rustc_infer/src/infer/lub.rs
@@ -119,7 +119,7 @@ impl<'tcx> ConstEquateRelation<'tcx> for Lub<'_, '_, 'tcx> {
 }
 
 impl<'combine, 'infcx, 'tcx> LatticeDir<'infcx, 'tcx> for Lub<'combine, 'infcx, 'tcx> {
-    fn infcx(&self) -> &'infcx InferCtxt<'infcx, 'tcx> {
+    fn infcx(&self) -> &'infcx InferCtxt<'tcx> {
         self.fields.infcx
     }
 
diff --git a/compiler/rustc_infer/src/infer/mod.rs b/compiler/rustc_infer/src/infer/mod.rs
index 3abed1221..ffb020398 100644
--- a/compiler/rustc_infer/src/infer/mod.rs
+++ b/compiler/rustc_infer/src/infer/mod.rs
@@ -35,10 +35,11 @@ use rustc_middle::ty::{ConstVid, FloatVid, IntVid, TyVid};
 use rustc_span::symbol::Symbol;
 use rustc_span::{Span, DUMMY_SP};
 
-use std::cell::{Cell, Ref, RefCell};
+use std::cell::{Cell, RefCell};
 use std::fmt;
 
 use self::combine::CombineFields;
+use self::error_reporting::TypeErrCtxt;
 use self::free_regions::RegionRelations;
 use self::lexical_region_resolve::LexicalRegionResolutions;
 use self::outlives::env::OutlivesEnvironment;
@@ -252,7 +253,7 @@ pub enum DefiningAnchor {
     Error,
 }
 
-pub struct InferCtxt<'a, 'tcx> {
+pub struct InferCtxt<'tcx> {
     pub tcx: TyCtxt<'tcx>,
 
     /// The `DefId` of the item in whose context we are performing inference or typeck.
@@ -272,12 +273,6 @@ pub struct InferCtxt<'a, 'tcx> {
     /// solving is left to borrowck instead.
     pub considering_regions: bool,
 
-    /// During type-checking/inference of a body, `in_progress_typeck_results`
-    /// contains a reference to the typeck results being built up, which are
-    /// used for reading closure kinds/signatures as they are inferred,
-    /// and for error reporting logic to read arbitrary node types.
-    pub in_progress_typeck_results: Option<&'a RefCell<ty::TypeckResults<'tcx>>>,
-
     pub inner: RefCell<InferCtxtInner<'tcx>>,
 
     /// If set, this flag causes us to skip the 'leak check' during
@@ -340,7 +335,7 @@ pub struct InferCtxt<'a, 'tcx> {
     universe: Cell<ty::UniverseIndex>,
 
     normalize_fn_sig_for_diagnostic:
-        Option<Lrc<dyn Fn(&InferCtxt<'_, 'tcx>, ty::PolyFnSig<'tcx>) -> ty::PolyFnSig<'tcx>>>,
+        Option<Lrc<dyn Fn(&InferCtxt<'tcx>, ty::PolyFnSig<'tcx>) -> ty::PolyFnSig<'tcx>>>,
 }
 
 /// See the `error_reporting` module for more details.
@@ -551,16 +546,13 @@ impl<'tcx> fmt::Display for FixupError<'tcx> {
     }
 }
 
-/// A temporary returned by `tcx.infer_ctxt()`. This is necessary
-/// for multiple `InferCtxt` to share the same `in_progress_typeck_results`
-/// without using `Rc` or something similar.
+/// Used to configure inference contexts before their creation
 pub struct InferCtxtBuilder<'tcx> {
     tcx: TyCtxt<'tcx>,
     defining_use_anchor: DefiningAnchor,
     considering_regions: bool,
-    fresh_typeck_results: Option<RefCell<ty::TypeckResults<'tcx>>>,
     normalize_fn_sig_for_diagnostic:
-        Option<Lrc<dyn Fn(&InferCtxt<'_, 'tcx>, ty::PolyFnSig<'tcx>) -> ty::PolyFnSig<'tcx>>>,
+        Option<Lrc<dyn Fn(&InferCtxt<'tcx>, ty::PolyFnSig<'tcx>) -> ty::PolyFnSig<'tcx>>>,
 }
 
 pub trait TyCtxtInferExt<'tcx> {
@@ -573,26 +565,17 @@ impl<'tcx> TyCtxtInferExt<'tcx> for TyCtxt<'tcx> {
             tcx: self,
             defining_use_anchor: DefiningAnchor::Error,
             considering_regions: true,
-            fresh_typeck_results: None,
             normalize_fn_sig_for_diagnostic: None,
         }
     }
 }
 
 impl<'tcx> InferCtxtBuilder<'tcx> {
-    /// Used only by `rustc_typeck` during body type-checking/inference,
-    /// will initialize `in_progress_typeck_results` with fresh `TypeckResults`.
-    /// Will also change the scope for opaque type defining use checks to the given owner.
-    pub fn with_fresh_in_progress_typeck_results(mut self, table_owner: LocalDefId) -> Self {
-        self.fresh_typeck_results = Some(RefCell::new(ty::TypeckResults::new(table_owner)));
-        self.with_opaque_type_inference(DefiningAnchor::Bind(table_owner))
-    }
-
     /// Whenever the `InferCtxt` should be able to handle defining uses of opaque types,
     /// you need to call this function. Otherwise the opaque type will be treated opaquely.
     ///
     /// It is only meant to be called in two places, for typeck
-    /// (via `with_fresh_in_progress_typeck_results`) and for the inference context used
+    /// (via `Inherited::build`) and for the inference context used
     /// in mir borrowck.
     pub fn with_opaque_type_inference(mut self, defining_use_anchor: DefiningAnchor) -> Self {
         self.defining_use_anchor = defining_use_anchor;
@@ -606,7 +589,7 @@ impl<'tcx> InferCtxtBuilder<'tcx> {
 
     pub fn with_normalize_fn_sig_for_diagnostic(
         mut self,
-        fun: Lrc<dyn Fn(&InferCtxt<'_, 'tcx>, ty::PolyFnSig<'tcx>) -> ty::PolyFnSig<'tcx>>,
+        fun: Lrc<dyn Fn(&InferCtxt<'tcx>, ty::PolyFnSig<'tcx>) -> ty::PolyFnSig<'tcx>>,
     ) -> Self {
         self.normalize_fn_sig_for_diagnostic = Some(fun);
         self
@@ -619,36 +602,30 @@ impl<'tcx> InferCtxtBuilder<'tcx> {
     /// `V` and a substitution `S`. This substitution `S` maps from
     /// the bound values in `C` to their instantiated values in `V`
     /// (in other words, `S(C) = V`).
-    pub fn enter_with_canonical<T, R>(
+    pub fn build_with_canonical<T>(
         &mut self,
         span: Span,
         canonical: &Canonical<'tcx, T>,
-        f: impl for<'a> FnOnce(InferCtxt<'a, 'tcx>, T, CanonicalVarValues<'tcx>) -> R,
-    ) -> R
+    ) -> (InferCtxt<'tcx>, T, CanonicalVarValues<'tcx>)
     where
         T: TypeFoldable<'tcx>,
     {
-        self.enter(|infcx| {
-            let (value, subst) =
-                infcx.instantiate_canonical_with_fresh_inference_vars(span, canonical);
-            f(infcx, value, subst)
-        })
+        let infcx = self.build();
+        let (value, subst) = infcx.instantiate_canonical_with_fresh_inference_vars(span, canonical);
+        (infcx, value, subst)
     }
 
-    pub fn enter<R>(&mut self, f: impl for<'a> FnOnce(InferCtxt<'a, 'tcx>) -> R) -> R {
+    pub fn build(&mut self) -> InferCtxt<'tcx> {
         let InferCtxtBuilder {
             tcx,
             defining_use_anchor,
             considering_regions,
-            ref fresh_typeck_results,
             ref normalize_fn_sig_for_diagnostic,
         } = *self;
-        let in_progress_typeck_results = fresh_typeck_results.as_ref();
-        f(InferCtxt {
+        InferCtxt {
             tcx,
             defining_use_anchor,
             considering_regions,
-            in_progress_typeck_results,
             inner: RefCell::new(InferCtxtInner::new()),
             lexical_region_resolutions: RefCell::new(None),
             selection_cache: Default::default(),
@@ -663,7 +640,7 @@ impl<'tcx> InferCtxtBuilder<'tcx> {
             normalize_fn_sig_for_diagnostic: normalize_fn_sig_for_diagnostic
                 .as_ref()
                 .map(|f| f.clone()),
-        })
+        }
     }
 }
 
@@ -675,7 +652,7 @@ impl<'tcx, T> InferOk<'tcx, T> {
     /// Extracts `value`, registering any obligations into `fulfill_cx`.
     pub fn into_value_registering_obligations(
         self,
-        infcx: &InferCtxt<'_, 'tcx>,
+        infcx: &InferCtxt<'tcx>,
         fulfill_cx: &mut dyn TraitEngine<'tcx>,
     ) -> T {
         let InferOk { value, obligations } = self;
@@ -691,29 +668,34 @@ impl<'tcx> InferOk<'tcx, ()> {
 }
 
 #[must_use = "once you start a snapshot, you should always consume it"]
-pub struct CombinedSnapshot<'a, 'tcx> {
+pub struct CombinedSnapshot<'tcx> {
     undo_snapshot: Snapshot<'tcx>,
     region_constraints_snapshot: RegionSnapshot,
     universe: ty::UniverseIndex,
     was_in_snapshot: bool,
-    _in_progress_typeck_results: Option<Ref<'a, ty::TypeckResults<'tcx>>>,
 }
 
-impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
+impl<'tcx> InferCtxt<'tcx> {
+    /// Creates a `TypeErrCtxt` for emitting various inference errors.
+    /// During typeck, use `FnCtxt::infer_err` instead.
+    pub fn err_ctxt(&self) -> TypeErrCtxt<'_, 'tcx> {
+        TypeErrCtxt { infcx: self, typeck_results: None }
+    }
+
     /// calls `tcx.try_unify_abstract_consts` after
     /// canonicalizing the consts.
     #[instrument(skip(self), level = "debug")]
     pub fn try_unify_abstract_consts(
         &self,
-        a: ty::Unevaluated<'tcx, ()>,
-        b: ty::Unevaluated<'tcx, ()>,
+        a: ty::UnevaluatedConst<'tcx>,
+        b: ty::UnevaluatedConst<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
     ) -> bool {
         // Reject any attempt to unify two unevaluated constants that contain inference
         // variables, since inference variables in queries lead to ICEs.
-        if a.substs.has_infer_types_or_consts()
-            || b.substs.has_infer_types_or_consts()
-            || param_env.has_infer_types_or_consts()
+        if a.substs.has_non_region_infer()
+            || b.substs.has_non_region_infer()
+            || param_env.has_non_region_infer()
         {
             debug!("a or b or param_env contain infer vars in its substs -> cannot unify");
             return false;
@@ -738,7 +720,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     /// if this is not a type variable.
     ///
     /// No attempt is made to resolve `ty`.
-    pub fn type_var_origin(&'a self, ty: Ty<'tcx>) -> Option<TypeVariableOrigin> {
+    pub fn type_var_origin(&self, ty: Ty<'tcx>) -> Option<TypeVariableOrigin> {
         match *ty.kind() {
             ty::Infer(ty::TyVar(vid)) => {
                 Some(*self.inner.borrow_mut().type_variables().var_origin(vid))
@@ -779,7 +761,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         vars
     }
 
-    fn combine_fields(
+    fn combine_fields<'a>(
         &'a self,
         trace: TypeTrace<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
@@ -821,7 +803,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         result
     }
 
-    fn start_snapshot(&self) -> CombinedSnapshot<'a, 'tcx> {
+    fn start_snapshot(&self) -> CombinedSnapshot<'tcx> {
         debug!("start_snapshot()");
 
         let in_snapshot = self.in_snapshot.replace(true);
@@ -833,22 +815,16 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             region_constraints_snapshot: inner.unwrap_region_constraints().start_snapshot(),
             universe: self.universe(),
             was_in_snapshot: in_snapshot,
-            // Borrow typeck results "in progress" (i.e., during typeck)
-            // to ban writes from within a snapshot to them.
-            _in_progress_typeck_results: self
-                .in_progress_typeck_results
-                .map(|typeck_results| typeck_results.borrow()),
         }
     }
 
     #[instrument(skip(self, snapshot), level = "debug")]
-    fn rollback_to(&self, cause: &str, snapshot: CombinedSnapshot<'a, 'tcx>) {
+    fn rollback_to(&self, cause: &str, snapshot: CombinedSnapshot<'tcx>) {
         let CombinedSnapshot {
             undo_snapshot,
             region_constraints_snapshot,
             universe,
             was_in_snapshot,
-            _in_progress_typeck_results,
         } = snapshot;
 
         self.in_snapshot.set(was_in_snapshot);
@@ -860,13 +836,12 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     }
 
     #[instrument(skip(self, snapshot), level = "debug")]
-    fn commit_from(&self, snapshot: CombinedSnapshot<'a, 'tcx>) {
+    fn commit_from(&self, snapshot: CombinedSnapshot<'tcx>) {
         let CombinedSnapshot {
             undo_snapshot,
             region_constraints_snapshot: _,
             universe: _,
             was_in_snapshot,
-            _in_progress_typeck_results,
         } = snapshot;
 
         self.in_snapshot.set(was_in_snapshot);
@@ -878,7 +853,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     #[instrument(skip(self, f), level = "debug")]
     pub fn commit_if_ok<T, E, F>(&self, f: F) -> Result<T, E>
     where
-        F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> Result<T, E>,
+        F: FnOnce(&CombinedSnapshot<'tcx>) -> Result<T, E>,
     {
         let snapshot = self.start_snapshot();
         let r = f(&snapshot);
@@ -898,7 +873,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     #[instrument(skip(self, f), level = "debug")]
     pub fn probe<R, F>(&self, f: F) -> R
     where
-        F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> R,
+        F: FnOnce(&CombinedSnapshot<'tcx>) -> R,
     {
         let snapshot = self.start_snapshot();
         let r = f(&snapshot);
@@ -910,7 +885,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     #[instrument(skip(self, f), level = "debug")]
     pub fn probe_maybe_skip_leak_check<R, F>(&self, should_skip: bool, f: F) -> R
     where
-        F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> R,
+        F: FnOnce(&CombinedSnapshot<'tcx>) -> R,
     {
         let snapshot = self.start_snapshot();
         let was_skip_leak_check = self.skip_leak_check.get();
@@ -930,7 +905,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     /// - `Some(false)` -- if there are `'a: 'b` constraints but none involve placeholders
     pub fn region_constraints_added_in_snapshot(
         &self,
-        snapshot: &CombinedSnapshot<'a, 'tcx>,
+        snapshot: &CombinedSnapshot<'tcx>,
     ) -> Option<bool> {
         self.inner
             .borrow_mut()
@@ -938,7 +913,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             .region_constraints_added_in_snapshot(&snapshot.undo_snapshot)
     }
 
-    pub fn opaque_types_added_in_snapshot(&self, snapshot: &CombinedSnapshot<'a, 'tcx>) -> bool {
+    pub fn opaque_types_added_in_snapshot(&self, snapshot: &CombinedSnapshot<'tcx>) -> bool {
         self.inner.borrow().undo_log.opaque_types_in_snapshot(&snapshot.undo_snapshot)
     }
 
@@ -1175,8 +1150,8 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     /// 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 which
-    /// they are associated.
+    /// placeholders, however, it will return the universe which they
+    /// are associated.
     pub fn universe_of_region(&self, r: ty::Region<'tcx>) -> ty::UniverseIndex {
         self.inner.borrow_mut().unwrap_region_constraints().universe(r)
     }
@@ -1308,7 +1283,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         assert!(old_value.is_none());
     }
 
-    /// Process the region constraints and return any any errors that
+    /// Process the region constraints and return 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`.
@@ -1342,32 +1317,6 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
 
         errors
     }
-
-    /// 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`]
-    /// to do both of these operations together.
-    pub fn resolve_regions_and_report_errors(
-        &self,
-        generic_param_scope: LocalDefId,
-        outlives_env: &OutlivesEnvironment<'tcx>,
-    ) {
-        let errors = self.resolve_regions(outlives_env);
-
-        if !self.is_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
-            // otherwise we have a hard time separating legit region
-            // errors from silly ones.
-            self.report_region_errors(generic_param_scope, &errors);
-        }
-    }
-
     /// Obtains (and clears) the current set of region
     /// constraints. The inference context is still usable: further
     /// unifications will simply add new constraints.
@@ -1520,60 +1469,12 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
          * except during the writeback phase.
          */
 
-        resolve::fully_resolve(self, value)
-    }
-
-    // [Note-Type-error-reporting]
-    // An invariant is that anytime the expected or actual type is Error (the special
-    // error type, meaning that an error occurred when typechecking this expression),
-    // this is a derived error. The error cascaded from another error (that was already
-    // reported), so it's not useful to display it to the user.
-    // The following methods implement this logic.
-    // They check if either the actual or expected type is Error, and don't print the error
-    // in this case. The typechecker should only ever report type errors involving mismatched
-    // types using one of these methods, and should not call span_err directly for such
-    // errors.
-
-    pub fn type_error_struct_with_diag<M>(
-        &self,
-        sp: Span,
-        mk_diag: M,
-        actual_ty: Ty<'tcx>,
-    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>
-    where
-        M: FnOnce(String) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>,
-    {
-        let actual_ty = self.resolve_vars_if_possible(actual_ty);
-        debug!("type_error_struct_with_diag({:?}, {:?})", sp, actual_ty);
-
-        let mut err = mk_diag(self.ty_to_string(actual_ty));
-
-        // Don't report an error if actual type is `Error`.
-        if actual_ty.references_error() {
-            err.downgrade_to_delayed_bug();
-        }
-
-        err
-    }
-
-    pub fn report_mismatched_types(
-        &self,
-        cause: &ObligationCause<'tcx>,
-        expected: Ty<'tcx>,
-        actual: Ty<'tcx>,
-        err: TypeError<'tcx>,
-    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
-        self.report_and_explain_type_error(TypeTrace::types(cause, true, expected, actual), err)
-    }
-
-    pub fn report_mismatched_consts(
-        &self,
-        cause: &ObligationCause<'tcx>,
-        expected: ty::Const<'tcx>,
-        actual: ty::Const<'tcx>,
-        err: TypeError<'tcx>,
-    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
-        self.report_and_explain_type_error(TypeTrace::consts(cause, true, expected, actual), err)
+        let value = resolve::fully_resolve(self, value);
+        assert!(
+            value.as_ref().map_or(true, |value| !value.needs_infer()),
+            "`{value:?}` is not fully resolved"
+        );
+        value
     }
 
     pub fn replace_bound_vars_with_fresh_vars<T>(
@@ -1590,7 +1491,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         }
 
         struct ToFreshVars<'a, 'tcx> {
-            infcx: &'a InferCtxt<'a, 'tcx>,
+            infcx: &'a InferCtxt<'tcx>,
             span: Span,
             lbrct: LateBoundRegionConversionTime,
             map: FxHashMap<ty::BoundVar, ty::GenericArg<'tcx>>,
@@ -1690,7 +1591,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     pub fn try_const_eval_resolve(
         &self,
         param_env: ty::ParamEnv<'tcx>,
-        unevaluated: ty::Unevaluated<'tcx, ()>,
+        unevaluated: ty::UnevaluatedConst<'tcx>,
         ty: Ty<'tcx>,
         span: Option<Span>,
     ) -> Result<ty::Const<'tcx>, ErrorHandled> {
@@ -1725,7 +1626,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     pub fn const_eval_resolve(
         &self,
         mut param_env: ty::ParamEnv<'tcx>,
-        unevaluated: ty::Unevaluated<'tcx, ()>,
+        unevaluated: ty::UnevaluatedConst<'tcx>,
         span: Option<Span>,
     ) -> EvalToValTreeResult<'tcx> {
         let mut substs = self.resolve_vars_if_possible(unevaluated.substs);
@@ -1733,7 +1634,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
 
         // Postpone the evaluation of constants whose substs depend on inference
         // variables
-        if substs.has_infer_types_or_consts() {
+        if substs.has_non_region_infer() {
             let ac = AbstractConst::new(self.tcx, unevaluated);
             match ac {
                 Ok(None) => {
@@ -1756,8 +1657,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         debug!(?param_env_erased);
         debug!(?substs_erased);
 
-        let unevaluated =
-            ty::Unevaluated { def: unevaluated.def, substs: substs_erased, promoted: () };
+        let unevaluated = ty::UnevaluatedConst { def: unevaluated.def, substs: substs_erased };
 
         // The return value is the evaluated value which doesn't contain any reference to inference
         // variables, thus we don't need to substitute back the original values.
@@ -1816,6 +1716,86 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     }
 }
 
+impl<'tcx> TypeErrCtxt<'_, 'tcx> {
+    /// 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`]
+    /// to do both of these operations together.
+    pub fn resolve_regions_and_report_errors(
+        &self,
+        generic_param_scope: LocalDefId,
+        outlives_env: &OutlivesEnvironment<'tcx>,
+    ) {
+        let errors = self.resolve_regions(outlives_env);
+
+        if !self.is_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
+            // otherwise we have a hard time separating legit region
+            // errors from silly ones.
+            self.report_region_errors(generic_param_scope, &errors);
+        }
+    }
+
+    // [Note-Type-error-reporting]
+    // An invariant is that anytime the expected or actual type is Error (the special
+    // error type, meaning that an error occurred when typechecking this expression),
+    // this is a derived error. The error cascaded from another error (that was already
+    // reported), so it's not useful to display it to the user.
+    // The following methods implement this logic.
+    // They check if either the actual or expected type is Error, and don't print the error
+    // in this case. The typechecker should only ever report type errors involving mismatched
+    // types using one of these methods, and should not call span_err directly for such
+    // errors.
+
+    pub fn type_error_struct_with_diag<M>(
+        &self,
+        sp: Span,
+        mk_diag: M,
+        actual_ty: Ty<'tcx>,
+    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>
+    where
+        M: FnOnce(String) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>,
+    {
+        let actual_ty = self.resolve_vars_if_possible(actual_ty);
+        debug!("type_error_struct_with_diag({:?}, {:?})", sp, actual_ty);
+
+        let mut err = mk_diag(self.ty_to_string(actual_ty));
+
+        // Don't report an error if actual type is `Error`.
+        if actual_ty.references_error() {
+            err.downgrade_to_delayed_bug();
+        }
+
+        err
+    }
+
+    pub fn report_mismatched_types(
+        &self,
+        cause: &ObligationCause<'tcx>,
+        expected: Ty<'tcx>,
+        actual: Ty<'tcx>,
+        err: TypeError<'tcx>,
+    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
+        self.report_and_explain_type_error(TypeTrace::types(cause, true, expected, actual), err)
+    }
+
+    pub fn report_mismatched_consts(
+        &self,
+        cause: &ObligationCause<'tcx>,
+        expected: ty::Const<'tcx>,
+        actual: ty::Const<'tcx>,
+        err: TypeError<'tcx>,
+    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
+        self.report_and_explain_type_error(TypeTrace::consts(cause, true, expected, actual), err)
+    }
+}
+
 /// Helper for `ty_or_const_infer_var_changed` (see comment on that), currently
 /// used only for `traits::fulfill`'s list of `stalled_on` inference variables.
 #[derive(Copy, Clone, Debug)]
@@ -1885,7 +1865,7 @@ impl<'tcx> TypeFolder<'tcx> for InferenceLiteralEraser<'tcx> {
 }
 
 struct ShallowResolver<'a, 'tcx> {
-    infcx: &'a InferCtxt<'a, 'tcx>,
+    infcx: &'a InferCtxt<'tcx>,
 }
 
 impl<'a, 'tcx> TypeFolder<'tcx> for ShallowResolver<'a, 'tcx> {
@@ -2072,21 +2052,17 @@ fn replace_param_and_infer_substs_with_placeholder<'tcx>(
 ) -> SubstsRef<'tcx> {
     tcx.mk_substs(substs.iter().enumerate().map(|(idx, arg)| {
         match arg.unpack() {
-            GenericArgKind::Type(_)
-                if arg.has_param_types_or_consts() || arg.has_infer_types_or_consts() =>
-            {
+            GenericArgKind::Type(_) if arg.has_non_region_param() || arg.has_non_region_infer() => {
                 tcx.mk_ty(ty::Placeholder(ty::PlaceholderType {
                     universe: ty::UniverseIndex::ROOT,
                     name: ty::BoundVar::from_usize(idx),
                 }))
                 .into()
             }
-            GenericArgKind::Const(ct)
-                if ct.has_infer_types_or_consts() || ct.has_param_types_or_consts() =>
-            {
+            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...
-                if ty.has_param_types_or_consts() || ty.has_infer_types_or_consts() {
+                if ty.has_non_region_param() || ty.has_non_region_infer() {
                     bug!("const `{ct}`'s type should not reference params or types");
                 }
                 tcx.mk_const(ty::ConstS {
diff --git a/compiler/rustc_infer/src/infer/nll_relate/mod.rs b/compiler/rustc_infer/src/infer/nll_relate/mod.rs
index 00fc442d3..600f94f09 100644
--- a/compiler/rustc_infer/src/infer/nll_relate/mod.rs
+++ b/compiler/rustc_infer/src/infer/nll_relate/mod.rs
@@ -25,7 +25,9 @@ use crate::infer::combine::ConstEquateRelation;
 use crate::infer::InferCtxt;
 use crate::infer::{ConstVarValue, ConstVariableValue};
 use crate::infer::{TypeVariableOrigin, TypeVariableOriginKind};
+use crate::traits::PredicateObligation;
 use rustc_data_structures::fx::FxHashMap;
+use rustc_middle::traits::ObligationCause;
 use rustc_middle::ty::error::TypeError;
 use rustc_middle::ty::relate::{self, Relate, RelateResult, TypeRelation};
 use rustc_middle::ty::visit::{TypeSuperVisitable, TypeVisitable, TypeVisitor};
@@ -44,7 +46,7 @@ pub struct TypeRelating<'me, 'tcx, D>
 where
     D: TypeRelatingDelegate<'tcx>,
 {
-    infcx: &'me InferCtxt<'me, 'tcx>,
+    infcx: &'me InferCtxt<'tcx>,
 
     /// Callback to use when we deduce an outlives relationship.
     delegate: D,
@@ -91,11 +93,9 @@ pub trait TypeRelatingDelegate<'tcx> {
     );
 
     fn const_equate(&mut self, a: ty::Const<'tcx>, b: ty::Const<'tcx>);
-    fn register_opaque_type(
+    fn register_opaque_type_obligations(
         &mut self,
-        a: Ty<'tcx>,
-        b: Ty<'tcx>,
-        a_is_expected: bool,
+        obligations: Vec<PredicateObligation<'tcx>>,
     ) -> Result<(), TypeError<'tcx>>;
 
     /// Creates a new universe index. Used when instantiating placeholders.
@@ -149,11 +149,7 @@ impl<'me, 'tcx, D> TypeRelating<'me, 'tcx, D>
 where
     D: TypeRelatingDelegate<'tcx>,
 {
-    pub fn new(
-        infcx: &'me InferCtxt<'me, 'tcx>,
-        delegate: D,
-        ambient_variance: ty::Variance,
-    ) -> Self {
+    pub fn new(infcx: &'me InferCtxt<'tcx>, delegate: D, ambient_variance: ty::Variance) -> Self {
         Self {
             infcx,
             delegate,
@@ -357,7 +353,7 @@ where
             // In NLL, we don't have type inference variables
             // floating around, so we can do this rather imprecise
             // variant of the occurs-check.
-            assert!(!generalized_ty.has_infer_types_or_consts());
+            assert!(!generalized_ty.has_non_region_infer());
         }
 
         self.infcx.inner.borrow_mut().type_variables().instantiate(vid, generalized_ty);
@@ -418,7 +414,12 @@ where
             (_, &ty::Opaque(..)) => (generalize(a, true)?, b),
             _ => unreachable!(),
         };
-        self.delegate.register_opaque_type(a, b, true)?;
+        let cause = ObligationCause::dummy_with_span(self.delegate.span());
+        let obligations = self
+            .infcx
+            .handle_opaque_type(a, b, true, &cause, self.delegate.param_env())?
+            .obligations;
+        self.delegate.register_opaque_type_obligations(obligations)?;
         trace!(a = ?a.kind(), b = ?b.kind(), "opaque type instantiated");
         Ok(a)
     }
@@ -867,7 +868,7 @@ struct TypeGeneralizer<'me, 'tcx, D>
 where
     D: TypeRelatingDelegate<'tcx>,
 {
-    infcx: &'me InferCtxt<'me, 'tcx>,
+    infcx: &'me InferCtxt<'tcx>,
 
     delegate: &'me mut D,
 
diff --git a/compiler/rustc_infer/src/infer/opaque_types.rs b/compiler/rustc_infer/src/infer/opaque_types.rs
index 8c9ddf866..a982f11f7 100644
--- a/compiler/rustc_infer/src/infer/opaque_types.rs
+++ b/compiler/rustc_infer/src/infer/opaque_types.rs
@@ -1,14 +1,16 @@
 use crate::errors::OpaqueHiddenTypeDiag;
 use crate::infer::{DefiningAnchor, InferCtxt, InferOk};
 use crate::traits;
+use hir::def::DefKind;
 use hir::def_id::{DefId, LocalDefId};
 use hir::{HirId, OpaqueTyOrigin};
 use rustc_data_structures::sync::Lrc;
 use rustc_data_structures::vec_map::VecMap;
 use rustc_hir as hir;
 use rustc_middle::traits::ObligationCause;
+use rustc_middle::ty::error::{ExpectedFound, TypeError};
 use rustc_middle::ty::fold::BottomUpFolder;
-use rustc_middle::ty::subst::{GenericArgKind, Subst};
+use rustc_middle::ty::GenericArgKind;
 use rustc_middle::ty::{
     self, OpaqueHiddenType, OpaqueTypeKey, Ty, TyCtxt, TypeFoldable, TypeSuperVisitable,
     TypeVisitable, TypeVisitor,
@@ -40,7 +42,7 @@ pub struct OpaqueTypeDecl<'tcx> {
     pub origin: hir::OpaqueTyOrigin,
 }
 
-impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
+impl<'tcx> InferCtxt<'tcx> {
     /// This is a backwards compatibility hack to prevent breaking changes from
     /// lazy TAIT around RPIT handling.
     pub fn replace_opaque_types_with_inference_vars<T: TypeFoldable<'tcx>>(
@@ -101,7 +103,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             return Ok(InferOk { value: (), obligations: vec![] });
         }
         let (a, b) = if a_is_expected { (a, b) } else { (b, a) };
-        let process = |a: Ty<'tcx>, b: Ty<'tcx>| match *a.kind() {
+        let process = |a: Ty<'tcx>, b: Ty<'tcx>, a_is_expected| match *a.kind() {
             ty::Opaque(def_id, substs) if def_id.is_local() => {
                 let def_id = def_id.expect_local();
                 let origin = match self.defining_use_anchor {
@@ -167,25 +169,18 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                     param_env,
                     b,
                     origin,
+                    a_is_expected,
                 ))
             }
             _ => None,
         };
-        if let Some(res) = process(a, b) {
+        if let Some(res) = process(a, b, true) {
             res
-        } else if let Some(res) = process(b, a) {
+        } else if let Some(res) = process(b, a, false) {
             res
         } else {
-            // Rerun equality check, but this time error out due to
-            // different types.
-            match self.at(cause, param_env).define_opaque_types(false).eq(a, b) {
-                Ok(_) => span_bug!(
-                    cause.span,
-                    "opaque types are never equal to anything but themselves: {:#?}",
-                    (a.kind(), b.kind())
-                ),
-                Err(e) => Err(e),
-            }
+            let (a, b) = self.resolve_vars_if_possible((a, b));
+            Err(TypeError::Sorts(ExpectedFound::new(true, a, b)))
         }
     }
 
@@ -518,15 +513,16 @@ impl UseKind {
     }
 }
 
-impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
+impl<'tcx> InferCtxt<'tcx> {
     #[instrument(skip(self), level = "debug")]
-    pub fn register_hidden_type(
+    fn register_hidden_type(
         &self,
         opaque_type_key: OpaqueTypeKey<'tcx>,
         cause: ObligationCause<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
         hidden_ty: Ty<'tcx>,
         origin: hir::OpaqueTyOrigin,
+        a_is_expected: bool,
     ) -> InferResult<'tcx, ()> {
         let tcx = self.tcx;
         let OpaqueTypeKey { def_id, substs } = opaque_type_key;
@@ -545,21 +541,24 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             origin,
         );
         if let Some(prev) = prev {
-            obligations = self.at(&cause, param_env).eq(prev, hidden_ty)?.obligations;
+            obligations =
+                self.at(&cause, param_env).eq_exp(a_is_expected, prev, hidden_ty)?.obligations;
         }
 
         let item_bounds = tcx.bound_explicit_item_bounds(def_id.to_def_id());
 
-        for predicate in item_bounds.transpose_iter().map(|e| e.map_bound(|(p, _)| *p)) {
-            debug!(?predicate);
-            let predicate = predicate.subst(tcx, substs);
-
+        for (predicate, _) in item_bounds.subst_iter_copied(tcx, substs) {
             let predicate = predicate.fold_with(&mut BottomUpFolder {
                 tcx,
                 ty_op: |ty| match *ty.kind() {
                     // We can't normalize associated types from `rustc_infer`,
                     // but we can eagerly register inference variables for them.
-                    ty::Projection(projection_ty) if !projection_ty.has_escaping_bound_vars() => {
+                    // FIXME(RPITIT): Don't replace RPITITs with inference vars.
+                    ty::Projection(projection_ty)
+                        if !projection_ty.has_escaping_bound_vars()
+                            && tcx.def_kind(projection_ty.item_def_id)
+                                != DefKind::ImplTraitPlaceholder =>
+                    {
                         self.infer_projection(
                             param_env,
                             projection_ty,
@@ -575,6 +574,12 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                     {
                         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,
                 },
                 lt_op: |lt| lt,
@@ -623,7 +628,7 @@ fn may_define_opaque_type(tcx: TyCtxt<'_>, def_id: LocalDefId, opaque_hir_id: hi
     let scope = tcx.hir().get_defining_scope(opaque_hir_id);
     // We walk up the node tree until we hit the root or the scope of the opaque type.
     while hir_id != scope && hir_id != hir::CRATE_HIR_ID {
-        hir_id = tcx.hir().local_def_id_to_hir_id(tcx.hir().get_parent_item(hir_id));
+        hir_id = tcx.hir().get_parent_item(hir_id).into();
     }
     // Syntactically, we are allowed to define the concrete type if:
     let res = hir_id == scope;
diff --git a/compiler/rustc_infer/src/infer/outlives/components.rs b/compiler/rustc_infer/src/infer/outlives/components.rs
index b2d7f4a66..14ee9f051 100644
--- a/compiler/rustc_infer/src/infer/outlives/components.rs
+++ b/compiler/rustc_infer/src/infer/outlives/components.rs
@@ -3,8 +3,9 @@
 // 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, Ty, TyCtxt, TypeVisitable};
+use rustc_middle::ty::{self, SubstsRef, Ty, TyCtxt, TypeVisitable};
 use smallvec::{smallvec, SmallVec};
 
 #[derive(Debug)]
@@ -45,6 +46,8 @@ pub enum Component<'tcx> {
     // 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>),
 }
 
 /// Push onto `out` all the things that must outlive `'a` for the condition
@@ -120,6 +123,17 @@ 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,
@@ -168,7 +182,6 @@ fn compute_components<'tcx>(
             ty::Float(..) |       // OutlivesScalar
             ty::Never |           // ...
             ty::Adt(..) |         // OutlivesNominalType
-            ty::Opaque(..) |      // OutlivesNominalType (ish)
             ty::Foreign(..) |     // OutlivesNominalType
             ty::Str |             // OutlivesScalar (ish)
             ty::Slice(..) |       // ...
diff --git a/compiler/rustc_infer/src/infer/outlives/env.rs b/compiler/rustc_infer/src/infer/outlives/env.rs
index 9922b156e..33543135d 100644
--- a/compiler/rustc_infer/src/infer/outlives/env.rs
+++ b/compiler/rustc_infer/src/infer/outlives/env.rs
@@ -87,9 +87,9 @@ impl<'tcx> OutlivesEnvironment<'tcx> {
     }
 
     /// Create a new `OutlivesEnvironment` with extra outlives bounds.
-    pub fn with_bounds<'a>(
+    pub fn with_bounds(
         param_env: ty::ParamEnv<'tcx>,
-        infcx: Option<&InferCtxt<'a, 'tcx>>,
+        infcx: Option<&InferCtxt<'tcx>>,
         extra_bounds: impl IntoIterator<Item = OutlivesBound<'tcx>>,
     ) -> Self {
         let mut builder = Self::builder(param_env);
@@ -108,7 +108,7 @@ impl<'tcx> OutlivesEnvironment<'tcx> {
     }
 }
 
-impl<'a, 'tcx> OutlivesEnvironmentBuilder<'tcx> {
+impl<'tcx> OutlivesEnvironmentBuilder<'tcx> {
     #[inline]
     #[instrument(level = "debug")]
     fn build(self) -> OutlivesEnvironment<'tcx> {
@@ -125,7 +125,7 @@ impl<'a, 'tcx> OutlivesEnvironmentBuilder<'tcx> {
     /// contain inference variables, it must be supplied, in which
     /// case we will register "givens" on the inference context. (See
     /// `RegionConstraintData`.)
-    fn add_outlives_bounds<I>(&mut self, infcx: Option<&InferCtxt<'a, 'tcx>>, outlives_bounds: I)
+    fn add_outlives_bounds<I>(&mut self, infcx: Option<&InferCtxt<'tcx>>, outlives_bounds: I)
     where
         I: IntoIterator<Item = OutlivesBound<'tcx>>,
     {
@@ -142,6 +142,10 @@ impl<'a, 'tcx> OutlivesEnvironmentBuilder<'tcx> {
                     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));
+                }
                 OutlivesBound::RegionSubRegion(r_a, r_b) => {
                     if let (ReEarlyBound(_) | ReFree(_), ReVar(vid_b)) = (r_a.kind(), r_b.kind()) {
                         infcx
diff --git a/compiler/rustc_infer/src/infer/outlives/obligations.rs b/compiler/rustc_infer/src/infer/outlives/obligations.rs
index 5bd1774f6..6ca884799 100644
--- a/compiler/rustc_infer/src/infer/outlives/obligations.rs
+++ b/compiler/rustc_infer/src/infer/outlives/obligations.rs
@@ -68,13 +68,14 @@ use crate::infer::{
 };
 use crate::traits::{ObligationCause, ObligationCauseCode};
 use rustc_data_structures::undo_log::UndoLogs;
+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, Ty, TyCtxt, TypeVisitable};
+use rustc_middle::ty::{self, Region, SubstsRef, Ty, TyCtxt, TypeVisitable};
 use smallvec::smallvec;
 
-impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
+impl<'tcx> InferCtxt<'tcx> {
     /// Registers that the given region obligation must be resolved
     /// from within the scope of `body_id`. These regions are enqueued
     /// and later processed by regionck, when full type information is
@@ -182,7 +183,7 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
             outlives_env.param_env,
         );
 
-        self.resolve_regions_and_report_errors(generic_param_scope, outlives_env)
+        self.err_ctxt().resolve_regions_and_report_errors(generic_param_scope, outlives_env)
     }
 }
 
@@ -283,6 +284,9 @@ 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);
                 }
@@ -314,17 +318,69 @@ where
         );
 
         let generic = GenericKind::Param(param_ty);
-        let verify_bound = self.verify_bound.generic_bound(generic);
+        let verify_bound = self.verify_bound.param_bound(param_ty);
         self.delegate.push_verify(origin, generic, region, verify_bound);
     }
 
     #[instrument(level = "debug", skip(self))]
+    fn opaque_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>),
+    ) {
+        // An optimization for a common case with opaque types.
+        if substs.is_empty() {
+            return;
+        }
+
         // This case is thorny for inference. The fundamental problem is
         // that there are many cases where we have choice, and inference
         // doesn't like choice (the current region inference in
@@ -343,16 +399,15 @@ where
         // These are guaranteed to apply, no matter the inference
         // results.
         let trait_bounds: Vec<_> =
-            self.verify_bound.projection_declared_bounds_from_trait(projection_ty).collect();
+            self.verify_bound.declared_region_bounds(def_id, substs).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.projection_approx_declared_bounds_from_env(projection_ty);
-        debug!("projection_must_outlive: approx_env_bounds={:?}", approx_env_bounds);
+        let mut approx_env_bounds = self.verify_bound.approx_declared_bounds_from_env(generic);
+        debug!(?approx_env_bounds);
 
         // Remove outlives bounds that we get from the environment but
         // which are also deducible from the trait. This arises (cc
@@ -366,14 +421,8 @@ 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();
-            match *bound.0.kind() {
-                ty::Projection(projection_ty) => self
-                    .verify_bound
-                    .projection_declared_bounds_from_trait(projection_ty)
-                    .all(|r| r != bound.1),
-
-                _ => panic!("expected only projection types from env, not {:?}", bound.0),
-            }
+            let (def_id, substs) = filter(bound.0);
+            self.verify_bound.declared_region_bounds(def_id, substs).all(|r| r != bound.1)
         });
 
         // If declared bounds list is empty, the only applicable rule is
@@ -390,29 +439,11 @@ 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 = projection_ty.needs_infer();
-        if approx_env_bounds.is_empty() && trait_bounds.is_empty() && needs_infer {
-            debug!("projection_must_outlive: no declared bounds");
-
-            let constraint = origin.to_constraint_category();
-            for k in projection_ty.substs {
-                match k.unpack() {
-                    GenericArgKind::Lifetime(lt) => {
-                        self.delegate.push_sub_region_constraint(
-                            origin.clone(),
-                            region,
-                            lt,
-                            constraint,
-                        );
-                    }
-                    GenericArgKind::Type(ty) => {
-                        self.type_must_outlive(origin.clone(), ty, region, constraint);
-                    }
-                    GenericArgKind::Const(_) => {
-                        // Const parameters don't impose constraints.
-                    }
-                }
-            }
+        let needs_infer = substs.needs_infer();
+        if approx_env_bounds.is_empty() && trait_bounds.is_empty() && (needs_infer || is_opaque) {
+            debug!("no declared bounds");
+
+            self.substs_must_outlive(substs, origin, region);
 
             return;
         }
@@ -442,8 +473,8 @@ where
                 .all(|b| b == Some(trait_bounds[0]))
         {
             let unique_bound = trait_bounds[0];
-            debug!("projection_must_outlive: unique trait bound = {:?}", unique_bound);
-            debug!("projection_must_outlive: unique declared bound appears in trait ref");
+            debug!(?unique_bound);
+            debug!("unique declared bound appears in trait ref");
             let category = origin.to_constraint_category();
             self.delegate.push_sub_region_constraint(origin, region, unique_bound, category);
             return;
@@ -454,14 +485,45 @@ 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 generic = GenericKind::Projection(projection_ty);
-        let verify_bound = self.verify_bound.generic_bound(generic);
+        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);
     }
+
+    fn substs_must_outlive(
+        &mut self,
+        substs: SubstsRef<'tcx>,
+        origin: infer::SubregionOrigin<'tcx>,
+        region: ty::Region<'tcx>,
+    ) {
+        let constraint = origin.to_constraint_category();
+        for k in substs {
+            match k.unpack() {
+                GenericArgKind::Lifetime(lt) => {
+                    self.delegate.push_sub_region_constraint(
+                        origin.clone(),
+                        region,
+                        lt,
+                        constraint,
+                    );
+                }
+                GenericArgKind::Type(ty) => {
+                    self.type_must_outlive(origin.clone(), ty, region, constraint);
+                }
+                GenericArgKind::Const(_) => {
+                    // Const parameters don't impose constraints.
+                }
+            }
+        }
+    }
 }
 
-impl<'cx, 'tcx> TypeOutlivesDelegate<'tcx> for &'cx InferCtxt<'cx, 'tcx> {
+impl<'cx, 'tcx> TypeOutlivesDelegate<'tcx> for &'cx InferCtxt<'tcx> {
     fn push_sub_region_constraint(
         &mut self,
         origin: SubregionOrigin<'tcx>,
diff --git a/compiler/rustc_infer/src/infer/outlives/verify.rs b/compiler/rustc_infer/src/infer/outlives/verify.rs
index 752334950..f470b2eb8 100644
--- a/compiler/rustc_infer/src/infer/outlives/verify.rs
+++ b/compiler/rustc_infer/src/infer/outlives/verify.rs
@@ -2,11 +2,10 @@ 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 rustc_data_structures::captures::Captures;
 use rustc_data_structures::sso::SsoHashSet;
 use rustc_hir::def_id::DefId;
-use rustc_middle::ty::subst::{GenericArg, Subst};
-use rustc_middle::ty::{self, EarlyBinder, OutlivesPredicate, Ty, TyCtxt};
+use rustc_middle::ty::GenericArg;
+use rustc_middle::ty::{self, EarlyBinder, OutlivesPredicate, SubstsRef, Ty, TyCtxt};
 
 use smallvec::smallvec;
 
@@ -38,20 +37,8 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
         Self { tcx, region_bound_pairs, implicit_region_bound, param_env }
     }
 
-    /// Returns a "verify bound" that encodes what we know about
-    /// `generic` and the regions it outlives.
-    pub fn generic_bound(&self, generic: GenericKind<'tcx>) -> VerifyBound<'tcx> {
-        let mut visited = SsoHashSet::new();
-        match generic {
-            GenericKind::Param(param_ty) => self.param_bound(param_ty),
-            GenericKind::Projection(projection_ty) => {
-                self.projection_bound(projection_ty, &mut visited)
-            }
-        }
-    }
-
     #[instrument(level = "debug", skip(self))]
-    fn param_bound(&self, param_ty: ty::ParamTy) -> VerifyBound<'tcx> {
+    pub fn param_bound(&self, param_ty: ty::ParamTy) -> VerifyBound<'tcx> {
         // Start with anything like `T: 'a` we can scrape from the
         // environment. If the environment contains something like
         // `for<'a> T: 'a`, then we know that `T` outlives everything.
@@ -105,41 +92,31 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
     /// the clause from the environment only applies if `'0 = 'a`,
     /// which we don't know yet. But we would still include `'b` in
     /// this list.
-    pub fn projection_approx_declared_bounds_from_env(
+    pub fn approx_declared_bounds_from_env(
         &self,
-        projection_ty: ty::ProjectionTy<'tcx>,
+        generic: GenericKind<'tcx>,
     ) -> Vec<ty::Binder<'tcx, ty::OutlivesPredicate<Ty<'tcx>, ty::Region<'tcx>>>> {
-        let projection_ty = GenericKind::Projection(projection_ty).to_ty(self.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)
     }
 
-    /// Searches the where-clauses in scope for regions that
-    /// `projection_ty` is known to outlive. Currently requires an
-    /// exact match.
-    pub fn projection_declared_bounds_from_trait(
+    #[instrument(level = "debug", skip(self, visited))]
+    pub fn projection_opaque_bounds(
         &self,
-        projection_ty: ty::ProjectionTy<'tcx>,
-    ) -> impl Iterator<Item = ty::Region<'tcx>> + 'cx + Captures<'tcx> {
-        self.declared_projection_bounds_from_trait(projection_ty)
-    }
-
-    pub fn projection_bound(
-        &self,
-        projection_ty: ty::ProjectionTy<'tcx>,
+        generic: GenericKind<'tcx>,
+        def_id: DefId,
+        substs: SubstsRef<'tcx>,
         visited: &mut SsoHashSet<GenericArg<'tcx>>,
     ) -> VerifyBound<'tcx> {
-        debug!("projection_bound(projection_ty={:?})", projection_ty);
-
-        let projection_ty_as_ty =
-            self.tcx.mk_projection(projection_ty.item_def_id, projection_ty.substs);
+        let generic_ty = generic.to_ty(self.tcx);
 
         // Search the env for where clauses like `P: 'a`.
-        let env_bounds = self
-            .projection_approx_declared_bounds_from_env(projection_ty)
+        let projection_opaque_bounds = self
+            .approx_declared_bounds_from_env(generic)
             .into_iter()
             .map(|binder| {
-                if let Some(ty::OutlivesPredicate(ty, r)) = binder.no_bound_vars() && ty == projection_ty_as_ty {
+                if let Some(ty::OutlivesPredicate(ty, r)) = binder.no_bound_vars() && ty == generic_ty {
                     // Micro-optimize if this is an exact match (this
                     // occurs often when there are no region variables
                     // involved).
@@ -149,21 +126,19 @@ 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
-            .projection_declared_bounds_from_trait(projection_ty)
-            .map(|r| VerifyBound::OutlivedBy(r));
+        let trait_bounds =
+            self.declared_region_bounds(def_id, substs).map(|r| VerifyBound::OutlivedBy(r));
 
         // see the extensive comment in projection_must_outlive
         let recursive_bound = {
             let mut components = smallvec![];
-            let ty = self.tcx.mk_projection(projection_ty.item_def_id, projection_ty.substs);
-            compute_components_recursive(self.tcx, ty.into(), &mut components, visited);
+            compute_components_recursive(self.tcx, generic_ty.into(), &mut components, visited);
             self.bound_from_components(&components, visited)
         };
 
-        VerifyBound::AnyBound(env_bounds.chain(trait_bounds).collect()).or(recursive_bound)
+        VerifyBound::AnyBound(projection_opaque_bounds.chain(trait_bounds).collect())
+            .or(recursive_bound)
     }
 
     fn bound_from_components(
@@ -195,7 +170,18 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
         match *component {
             Component::Region(lt) => VerifyBound::OutlivedBy(lt),
             Component::Param(param_ty) => self.param_bound(param_ty),
-            Component::Projection(projection_ty) => self.projection_bound(projection_ty, visited),
+            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) => {
                 self.bound_from_components(components, visited)
             }
@@ -293,30 +279,6 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
     /// }
     /// ```
     ///
-    /// then this function would return `'x`. This is subject to the
-    /// limitations around higher-ranked bounds described in
-    /// `region_bounds_declared_on_associated_item`.
-    fn declared_projection_bounds_from_trait(
-        &self,
-        projection_ty: ty::ProjectionTy<'tcx>,
-    ) -> impl Iterator<Item = ty::Region<'tcx>> + 'cx + Captures<'tcx> {
-        debug!("projection_bounds(projection_ty={:?})", projection_ty);
-        let tcx = self.tcx;
-        self.region_bounds_declared_on_associated_item(projection_ty.item_def_id)
-            .map(move |r| EarlyBinder(r).subst(tcx, projection_ty.substs))
-    }
-
-    /// Given the `DefId` of an associated item, returns any region
-    /// bounds attached to that associated item from the trait definition.
-    ///
-    /// For example:
-    ///
-    /// ```rust
-    /// trait Foo<'a> {
-    ///     type Bar: 'a;
-    /// }
-    /// ```
-    ///
     /// If we were given the `DefId` of `Foo::Bar`, we would return
     /// `'a`. You could then apply the substitutions from the
     /// projection to convert this into your namespace. This also
@@ -336,17 +298,20 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
     ///
     /// This is for simplicity, and because we are not really smart
     /// enough to cope with such bounds anywhere.
-    fn region_bounds_declared_on_associated_item(
+    pub fn declared_region_bounds(
         &self,
-        assoc_item_def_id: DefId,
+        def_id: DefId,
+        substs: SubstsRef<'tcx>,
     ) -> impl Iterator<Item = ty::Region<'tcx>> {
         let tcx = self.tcx;
-        let bounds = tcx.item_bounds(assoc_item_def_id);
+        let bounds = tcx.item_bounds(def_id);
+        trace!("{:#?}", bounds);
         bounds
             .into_iter()
             .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))
     }
 
     /// 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 b45a6514d..9f12bc972 100644
--- a/compiler/rustc_infer/src/infer/projection.rs
+++ b/compiler/rustc_infer/src/infer/projection.rs
@@ -6,7 +6,7 @@ use crate::traits::{Obligation, PredicateObligation};
 use super::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use super::InferCtxt;
 
-impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
+impl<'tcx> InferCtxt<'tcx> {
     /// Instead of normalizing an associated type projection,
     /// this function generates an inference variable and registers
     /// an obligation that this inference variable must be the result
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 397efe6ee..90858e307 100644
--- a/compiler/rustc_infer/src/infer/region_constraints/leak_check.rs
+++ b/compiler/rustc_infer/src/infer/region_constraints/leak_check.rs
@@ -66,7 +66,7 @@ impl<'tcx> RegionConstraintCollector<'_, 'tcx> {
         tcx: TyCtxt<'tcx>,
         overly_polymorphic: bool,
         max_universe: ty::UniverseIndex,
-        snapshot: &CombinedSnapshot<'_, 'tcx>,
+        snapshot: &CombinedSnapshot<'tcx>,
     ) -> RelateResult<'tcx, ()> {
         debug!(
             "leak_check(max_universe={:?}, snapshot.universe={:?}, overly_polymorphic={:?})",
diff --git a/compiler/rustc_infer/src/infer/region_constraints/mod.rs b/compiler/rustc_infer/src/infer/region_constraints/mod.rs
index e43d28ee5..67b3da687 100644
--- a/compiler/rustc_infer/src/infer/region_constraints/mod.rs
+++ b/compiler/rustc_infer/src/infer/region_constraints/mod.rs
@@ -12,8 +12,10 @@ 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};
@@ -168,6 +170,7 @@ pub struct Verify<'tcx> {
 pub enum GenericKind<'tcx> {
     Param(ty::ParamTy),
     Projection(ty::ProjectionTy<'tcx>),
+    Opaque(DefId, SubstsRef<'tcx>),
 }
 
 /// Describes the things that some `GenericKind` value `G` is known to
@@ -747,6 +750,9 @@ impl<'tcx> fmt::Debug for GenericKind<'tcx> {
         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()))
+            }),
         }
     }
 }
@@ -756,6 +762,9 @@ impl<'tcx> fmt::Display for GenericKind<'tcx> {
         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()))
+            }),
         }
     }
 }
@@ -765,6 +774,7 @@ impl<'tcx> GenericKind<'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),
         }
     }
 }
diff --git a/compiler/rustc_infer/src/infer/resolve.rs b/compiler/rustc_infer/src/infer/resolve.rs
index 3d99f0958..4db4ff238 100644
--- a/compiler/rustc_infer/src/infer/resolve.rs
+++ b/compiler/rustc_infer/src/infer/resolve.rs
@@ -1,6 +1,5 @@
 use super::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use super::{FixupError, FixupResult, InferCtxt, Span};
-use rustc_middle::mir;
 use rustc_middle::ty::fold::{FallibleTypeFolder, TypeFolder, TypeSuperFoldable};
 use rustc_middle::ty::visit::{TypeSuperVisitable, TypeVisitor};
 use rustc_middle::ty::{self, Const, InferConst, Ty, TyCtxt, TypeFoldable, TypeVisitable};
@@ -16,12 +15,12 @@ use std::ops::ControlFlow;
 /// useful for printing messages etc but also required at various
 /// points for correctness.
 pub struct OpportunisticVarResolver<'a, 'tcx> {
-    infcx: &'a InferCtxt<'a, 'tcx>,
+    infcx: &'a InferCtxt<'tcx>,
 }
 
 impl<'a, 'tcx> OpportunisticVarResolver<'a, 'tcx> {
     #[inline]
-    pub fn new(infcx: &'a InferCtxt<'a, 'tcx>) -> Self {
+    pub fn new(infcx: &'a InferCtxt<'tcx>) -> Self {
         OpportunisticVarResolver { infcx }
     }
 }
@@ -32,7 +31,7 @@ impl<'a, 'tcx> TypeFolder<'tcx> for OpportunisticVarResolver<'a, 'tcx> {
     }
 
     fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
-        if !t.has_infer_types_or_consts() {
+        if !t.has_non_region_infer() {
             t // micro-optimize -- if there is nothing in this type that this fold affects...
         } else {
             let t = self.infcx.shallow_resolve(t);
@@ -41,17 +40,13 @@ impl<'a, 'tcx> TypeFolder<'tcx> for OpportunisticVarResolver<'a, 'tcx> {
     }
 
     fn fold_const(&mut self, ct: Const<'tcx>) -> Const<'tcx> {
-        if !ct.has_infer_types_or_consts() {
+        if !ct.has_non_region_infer() {
             ct // micro-optimize -- if there is nothing in this const that this fold affects...
         } else {
             let ct = self.infcx.shallow_resolve(ct);
             ct.super_fold_with(self)
         }
     }
-
-    fn fold_mir_const(&mut self, constant: mir::ConstantKind<'tcx>) -> mir::ConstantKind<'tcx> {
-        constant.super_fold_with(self)
-    }
 }
 
 /// The opportunistic region resolver opportunistically resolves regions
@@ -62,11 +57,11 @@ impl<'a, 'tcx> TypeFolder<'tcx> for OpportunisticVarResolver<'a, 'tcx> {
 /// If you want to resolve type and const variables as well, call
 /// [InferCtxt::resolve_vars_if_possible] first.
 pub struct OpportunisticRegionResolver<'a, 'tcx> {
-    infcx: &'a InferCtxt<'a, 'tcx>,
+    infcx: &'a InferCtxt<'tcx>,
 }
 
 impl<'a, 'tcx> OpportunisticRegionResolver<'a, 'tcx> {
-    pub fn new(infcx: &'a InferCtxt<'a, 'tcx>) -> Self {
+    pub fn new(infcx: &'a InferCtxt<'tcx>) -> Self {
         OpportunisticRegionResolver { infcx }
     }
 }
@@ -116,11 +111,11 @@ impl<'a, 'tcx> TypeFolder<'tcx> for OpportunisticRegionResolver<'a, 'tcx> {
 /// It does not construct the fully resolved type (which might
 /// involve some hashing and so forth).
 pub struct UnresolvedTypeFinder<'a, 'tcx> {
-    infcx: &'a InferCtxt<'a, 'tcx>,
+    infcx: &'a InferCtxt<'tcx>,
 }
 
 impl<'a, 'tcx> UnresolvedTypeFinder<'a, 'tcx> {
-    pub fn new(infcx: &'a InferCtxt<'a, 'tcx>) -> Self {
+    pub fn new(infcx: &'a InferCtxt<'tcx>) -> Self {
         UnresolvedTypeFinder { infcx }
     }
 }
@@ -167,7 +162,7 @@ impl<'a, 'tcx> TypeVisitor<'tcx> for UnresolvedTypeFinder<'a, 'tcx> {
 /// Full type resolution replaces all type and region variables with
 /// their concrete results. If any variable cannot be replaced (never unified, etc)
 /// then an `Err` result is returned.
-pub fn fully_resolve<'a, 'tcx, T>(infcx: &InferCtxt<'a, 'tcx>, value: T) -> FixupResult<'tcx, T>
+pub fn fully_resolve<'tcx, T>(infcx: &InferCtxt<'tcx>, value: T) -> FixupResult<'tcx, T>
 where
     T: TypeFoldable<'tcx>,
 {
@@ -177,7 +172,7 @@ where
 // N.B. This type is not public because the protocol around checking the
 // `err` field is not enforceable otherwise.
 struct FullTypeResolver<'a, 'tcx> {
-    infcx: &'a InferCtxt<'a, 'tcx>,
+    infcx: &'a InferCtxt<'tcx>,
 }
 
 impl<'a, 'tcx> FallibleTypeFolder<'tcx> for FullTypeResolver<'a, 'tcx> {
diff --git a/compiler/rustc_infer/src/infer/sub.rs b/compiler/rustc_infer/src/infer/sub.rs
index b7eab5d43..97354ba5d 100644
--- a/compiler/rustc_infer/src/infer/sub.rs
+++ b/compiler/rustc_infer/src/infer/sub.rs
@@ -2,9 +2,7 @@ use super::combine::{CombineFields, RelationDir};
 use super::SubregionOrigin;
 
 use crate::infer::combine::ConstEquateRelation;
-use crate::infer::{TypeVariableOrigin, TypeVariableOriginKind};
 use crate::traits::Obligation;
-use rustc_middle::ty::error::{ExpectedFound, TypeError};
 use rustc_middle::ty::relate::{Cause, Relate, RelateResult, TypeRelation};
 use rustc_middle::ty::visit::TypeVisitable;
 use rustc_middle::ty::TyVar;
@@ -12,8 +10,8 @@ use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt};
 use std::mem;
 
 /// Ensures `a` is made a subtype of `b`. Returns `a` on success.
-pub struct Sub<'combine, 'infcx, 'tcx> {
-    fields: &'combine mut CombineFields<'infcx, 'tcx>,
+pub struct Sub<'combine, 'a, 'tcx> {
+    fields: &'combine mut CombineFields<'a, 'tcx>,
     a_is_expected: bool,
 }
 
@@ -130,39 +128,36 @@ impl<'tcx> TypeRelation<'tcx> for Sub<'_, '_, 'tcx> {
             (&ty::Opaque(did, ..), _) | (_, &ty::Opaque(did, ..))
                 if self.fields.define_opaque_types && did.is_local() =>
             {
-                let mut generalize = |ty, ty_is_expected| {
-                    let var = infcx.next_ty_var_id_in_universe(
-                        TypeVariableOrigin {
-                            kind: TypeVariableOriginKind::MiscVariable,
-                            span: self.fields.trace.cause.span,
-                        },
-                        ty::UniverseIndex::ROOT,
-                    );
-                    self.fields.instantiate(ty, RelationDir::SubtypeOf, var, ty_is_expected)?;
-                    Ok(infcx.tcx.mk_ty_var(var))
-                };
-                let (a, b) = if self.a_is_expected { (a, b) } else { (b, a) };
-                let (ga, gb) = match (a.kind(), b.kind()) {
-                    (&ty::Opaque(..), _) => (a, generalize(b, true)?),
-                    (_, &ty::Opaque(..)) => (generalize(a, false)?, b),
-                    _ => unreachable!(),
-                };
                 self.fields.obligations.extend(
                     infcx
-                        .handle_opaque_type(ga, gb, true, &self.fields.trace.cause, self.param_env())
-                        // Don't leak any generalized type variables out of this
-                        // subtyping relation in the case of a type error.
-                        .map_err(|err| {
-                            let (ga, gb) = self.fields.infcx.resolve_vars_if_possible((ga, gb));
-                            if let TypeError::Sorts(sorts) = err && sorts.expected == ga && sorts.found == gb {
-                                TypeError::Sorts(ExpectedFound { expected: a, found: b })
-                            } else {
-                                err
-                            }
-                        })?
+                        .handle_opaque_type(
+                            a,
+                            b,
+                            self.a_is_expected,
+                            &self.fields.trace.cause,
+                            self.param_env(),
+                        )?
                         .obligations,
                 );
-                Ok(ga)
+                Ok(a)
+            }
+            // Optimization of GeneratorWitness relation since we know that all
+            // free regions are replaced with bound regions during construction.
+            // This greatly speeds up subtyping of GeneratorWitness.
+            (&ty::GeneratorWitness(a_types), &ty::GeneratorWitness(b_types)) => {
+                let a_types = infcx.tcx.anonymize_bound_vars(a_types);
+                let b_types = infcx.tcx.anonymize_bound_vars(b_types);
+                if a_types.bound_vars() == b_types.bound_vars() {
+                    let (a_types, b_types) = infcx.replace_bound_vars_with_placeholders(
+                        a_types.map_bound(|a_types| (a_types, b_types.skip_binder())),
+                    );
+                    for (a, b) in std::iter::zip(a_types, b_types) {
+                        self.relate(a, b)?;
+                    }
+                    Ok(a)
+                } else {
+                    Err(ty::error::TypeError::Sorts(ty::relate::expected_found(self, a, b)))
+                }
             }
 
             _ => {