diff --git a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
index 18cf6f64fbc03..2b0c0e939f59b 100644
--- a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
@@ -229,7 +229,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 seen_spans.insert(move_span);
             }
 
-            use_spans.var_path_only_subdiag(&mut err, desired_action);
+            use_spans.var_path_only_subdiag(self.dcx(), &mut err, desired_action);
 
             if !is_loop_move {
                 err.span_label(
@@ -291,18 +291,24 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             if needs_note {
                 if let Some(local) = place.as_local() {
                     let span = self.body.local_decls[local].source_info.span;
-                    err.subdiagnostic(crate::session_diagnostics::TypeNoCopy::Label {
-                        is_partial_move,
-                        ty,
-                        place: &note_msg,
-                        span,
-                    });
+                    err.subdiagnostic(
+                        self.dcx(),
+                        crate::session_diagnostics::TypeNoCopy::Label {
+                            is_partial_move,
+                            ty,
+                            place: &note_msg,
+                            span,
+                        },
+                    );
                 } else {
-                    err.subdiagnostic(crate::session_diagnostics::TypeNoCopy::Note {
-                        is_partial_move,
-                        ty,
-                        place: &note_msg,
-                    });
+                    err.subdiagnostic(
+                        self.dcx(),
+                        crate::session_diagnostics::TypeNoCopy::Note {
+                            is_partial_move,
+                            ty,
+                            place: &note_msg,
+                        },
+                    );
                 };
             }
 
@@ -557,7 +563,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             E0381,
             "{used} binding {desc}{isnt_initialized}"
         );
-        use_spans.var_path_only_subdiag(&mut err, desired_action);
+        use_spans.var_path_only_subdiag(self.dcx(), &mut err, desired_action);
 
         if let InitializationRequiringAction::PartialAssignment
         | InitializationRequiringAction::Assignment = desired_action
@@ -848,9 +854,13 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             &value_msg,
         );
 
-        borrow_spans.var_path_only_subdiag(&mut err, crate::InitializationRequiringAction::Borrow);
+        borrow_spans.var_path_only_subdiag(
+            self.dcx(),
+            &mut err,
+            crate::InitializationRequiringAction::Borrow,
+        );
 
-        move_spans.var_subdiag(None, &mut err, None, |kind, var_span| {
+        move_spans.var_subdiag(self.dcx(), &mut err, None, |kind, var_span| {
             use crate::session_diagnostics::CaptureVarCause::*;
             match kind {
                 hir::ClosureKind::Coroutine(_) => MoveUseInCoroutine { var_span },
@@ -895,7 +905,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             borrow_span,
             &self.describe_any_place(borrow.borrowed_place.as_ref()),
         );
-        borrow_spans.var_subdiag(None, &mut err, Some(borrow.kind), |kind, var_span| {
+        borrow_spans.var_subdiag(self.dcx(), &mut err, Some(borrow.kind), |kind, var_span| {
             use crate::session_diagnostics::CaptureVarCause::*;
             let place = &borrow.borrowed_place;
             let desc_place = self.describe_any_place(place.as_ref());
@@ -1043,7 +1053,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                         "mutably borrow",
                     );
                     borrow_spans.var_subdiag(
-                        None,
+                        self.dcx(),
                         &mut err,
                         Some(BorrowKind::Mut { kind: MutBorrowKind::ClosureCapture }),
                         |kind, var_span| {
@@ -1131,22 +1141,31 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         };
 
         if issued_spans == borrow_spans {
-            borrow_spans.var_subdiag(None, &mut err, Some(gen_borrow_kind), |kind, var_span| {
-                use crate::session_diagnostics::CaptureVarCause::*;
-                match kind {
-                    hir::ClosureKind::Coroutine(_) => BorrowUsePlaceCoroutine {
-                        place: desc_place,
-                        var_span,
-                        is_single_var: false,
-                    },
-                    hir::ClosureKind::Closure | hir::ClosureKind::CoroutineClosure(_) => {
-                        BorrowUsePlaceClosure { place: desc_place, var_span, is_single_var: false }
+            borrow_spans.var_subdiag(
+                self.dcx(),
+                &mut err,
+                Some(gen_borrow_kind),
+                |kind, var_span| {
+                    use crate::session_diagnostics::CaptureVarCause::*;
+                    match kind {
+                        hir::ClosureKind::Coroutine(_) => BorrowUsePlaceCoroutine {
+                            place: desc_place,
+                            var_span,
+                            is_single_var: false,
+                        },
+                        hir::ClosureKind::Closure | hir::ClosureKind::CoroutineClosure(_) => {
+                            BorrowUsePlaceClosure {
+                                place: desc_place,
+                                var_span,
+                                is_single_var: false,
+                            }
+                        }
                     }
-                }
-            });
+                },
+            );
         } else {
             issued_spans.var_subdiag(
-                Some(self.dcx()),
+                self.dcx(),
                 &mut err,
                 Some(issued_borrow.kind),
                 |kind, var_span| {
@@ -1165,7 +1184,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             );
 
             borrow_spans.var_subdiag(
-                Some(self.dcx()),
+                self.dcx(),
                 &mut err,
                 Some(gen_borrow_kind),
                 |kind, var_span| {
@@ -2217,7 +2236,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             err.span_label(borrow_span, "borrowed value does not live long enough");
             err.span_label(drop_span, format!("`{name}` dropped here while still borrowed"));
 
-            borrow_spans.args_subdiag(&mut err, |args_span| {
+            borrow_spans.args_subdiag(self.dcx(), &mut err, |args_span| {
                 crate::session_diagnostics::CaptureArgLabel::Capture {
                     is_within: borrow_spans.for_coroutine(),
                     args_span,
@@ -2476,7 +2495,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             None,
         );
 
-        borrow_spans.args_subdiag(&mut err, |args_span| {
+        borrow_spans.args_subdiag(self.dcx(), &mut err, |args_span| {
             crate::session_diagnostics::CaptureArgLabel::Capture {
                 is_within: borrow_spans.for_coroutine(),
                 args_span,
@@ -2935,7 +2954,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     "assign",
                 );
 
-                loan_spans.var_subdiag(None, &mut err, Some(loan.kind), |kind, var_span| {
+                loan_spans.var_subdiag(self.dcx(), &mut err, Some(loan.kind), |kind, var_span| {
                     use crate::session_diagnostics::CaptureVarCause::*;
                     match kind {
                         hir::ClosureKind::Coroutine(_) => BorrowUseInCoroutine { var_span },
@@ -2953,7 +2972,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 
         let mut err = self.cannot_assign_to_borrowed(span, loan_span, &descr_place);
 
-        loan_spans.var_subdiag(None, &mut err, Some(loan.kind), |kind, var_span| {
+        loan_spans.var_subdiag(self.dcx(), &mut err, Some(loan.kind), |kind, var_span| {
             use crate::session_diagnostics::CaptureVarCause::*;
             match kind {
                 hir::ClosureKind::Coroutine(_) => BorrowUseInCoroutine { var_span },
diff --git a/compiler/rustc_borrowck/src/diagnostics/mod.rs b/compiler/rustc_borrowck/src/diagnostics/mod.rs
index 59f3aa706edea..4ca854c857de9 100644
--- a/compiler/rustc_borrowck/src/diagnostics/mod.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/mod.rs
@@ -124,7 +124,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     if let ty::Closure(did, _) = self.body.local_decls[closure].ty.kind() {
                         let did = did.expect_local();
                         if let Some((span, hir_place)) = self.infcx.tcx.closure_kind_origin(did) {
-                            diag.eager_subdiagnostic(
+                            diag.subdiagnostic(
                                 self.dcx(),
                                 OnClosureNote::InvokedTwice {
                                     place_name: &ty::place_to_string_for_capture(
@@ -146,7 +146,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             if let ty::Closure(did, _) = self.body.local_decls[target].ty.kind() {
                 let did = did.expect_local();
                 if let Some((span, hir_place)) = self.infcx.tcx.closure_kind_origin(did) {
-                    diag.eager_subdiagnostic(
+                    diag.subdiagnostic(
                         self.dcx(),
                         OnClosureNote::MovedTwice {
                             place_name: &ty::place_to_string_for_capture(self.infcx.tcx, hir_place),
@@ -587,11 +587,12 @@ impl UseSpans<'_> {
     /// Add a span label to the arguments of the closure, if it exists.
     pub(super) fn args_subdiag(
         self,
+        dcx: &rustc_errors::DiagCtxt,
         err: &mut Diagnostic,
         f: impl FnOnce(Span) -> CaptureArgLabel,
     ) {
         if let UseSpans::ClosureUse { args_span, .. } = self {
-            err.subdiagnostic(f(args_span));
+            err.subdiagnostic(dcx, f(args_span));
         }
     }
 
@@ -599,6 +600,7 @@ impl UseSpans<'_> {
     /// only adds label to the `path_span`
     pub(super) fn var_path_only_subdiag(
         self,
+        dcx: &rustc_errors::DiagCtxt,
         err: &mut Diagnostic,
         action: crate::InitializationRequiringAction,
     ) {
@@ -607,20 +609,26 @@ impl UseSpans<'_> {
         if let UseSpans::ClosureUse { closure_kind, path_span, .. } = self {
             match closure_kind {
                 hir::ClosureKind::Coroutine(_) => {
-                    err.subdiagnostic(match action {
-                        Borrow => BorrowInCoroutine { path_span },
-                        MatchOn | Use => UseInCoroutine { path_span },
-                        Assignment => AssignInCoroutine { path_span },
-                        PartialAssignment => AssignPartInCoroutine { path_span },
-                    });
+                    err.subdiagnostic(
+                        dcx,
+                        match action {
+                            Borrow => BorrowInCoroutine { path_span },
+                            MatchOn | Use => UseInCoroutine { path_span },
+                            Assignment => AssignInCoroutine { path_span },
+                            PartialAssignment => AssignPartInCoroutine { path_span },
+                        },
+                    );
                 }
                 hir::ClosureKind::Closure | hir::ClosureKind::CoroutineClosure(_) => {
-                    err.subdiagnostic(match action {
-                        Borrow => BorrowInClosure { path_span },
-                        MatchOn | Use => UseInClosure { path_span },
-                        Assignment => AssignInClosure { path_span },
-                        PartialAssignment => AssignPartInClosure { path_span },
-                    });
+                    err.subdiagnostic(
+                        dcx,
+                        match action {
+                            Borrow => BorrowInClosure { path_span },
+                            MatchOn | Use => UseInClosure { path_span },
+                            Assignment => AssignInClosure { path_span },
+                            PartialAssignment => AssignPartInClosure { path_span },
+                        },
+                    );
                 }
             }
         }
@@ -629,32 +637,32 @@ impl UseSpans<'_> {
     /// Add a subdiagnostic to the use of the captured variable, if it exists.
     pub(super) fn var_subdiag(
         self,
-        dcx: Option<&rustc_errors::DiagCtxt>,
+        dcx: &rustc_errors::DiagCtxt,
         err: &mut Diagnostic,
         kind: Option<rustc_middle::mir::BorrowKind>,
         f: impl FnOnce(hir::ClosureKind, Span) -> CaptureVarCause,
     ) {
         if let UseSpans::ClosureUse { closure_kind, capture_kind_span, path_span, .. } = self {
             if capture_kind_span != path_span {
-                err.subdiagnostic(match kind {
-                    Some(kd) => match kd {
-                        rustc_middle::mir::BorrowKind::Shared
-                        | rustc_middle::mir::BorrowKind::Fake => {
-                            CaptureVarKind::Immut { kind_span: capture_kind_span }
-                        }
+                err.subdiagnostic(
+                    dcx,
+                    match kind {
+                        Some(kd) => match kd {
+                            rustc_middle::mir::BorrowKind::Shared
+                            | rustc_middle::mir::BorrowKind::Fake => {
+                                CaptureVarKind::Immut { kind_span: capture_kind_span }
+                            }
 
-                        rustc_middle::mir::BorrowKind::Mut { .. } => {
-                            CaptureVarKind::Mut { kind_span: capture_kind_span }
-                        }
+                            rustc_middle::mir::BorrowKind::Mut { .. } => {
+                                CaptureVarKind::Mut { kind_span: capture_kind_span }
+                            }
+                        },
+                        None => CaptureVarKind::Move { kind_span: capture_kind_span },
                     },
-                    None => CaptureVarKind::Move { kind_span: capture_kind_span },
-                });
+                );
             };
             let diag = f(closure_kind, path_span);
-            match dcx {
-                Some(hd) => err.eager_subdiagnostic(hd, diag),
-                None => err.subdiagnostic(diag),
-            };
+            err.subdiagnostic(dcx, diag);
         }
     }
 
@@ -1025,26 +1033,33 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 CallKind::FnCall { fn_trait_id, .. }
                     if Some(fn_trait_id) == self.infcx.tcx.lang_items().fn_once_trait() =>
                 {
-                    err.subdiagnostic(CaptureReasonLabel::Call {
-                        fn_call_span,
-                        place_name: &place_name,
-                        is_partial,
-                        is_loop_message,
-                    });
-                    err.subdiagnostic(CaptureReasonNote::FnOnceMoveInCall { var_span });
+                    err.subdiagnostic(
+                        self.dcx(),
+                        CaptureReasonLabel::Call {
+                            fn_call_span,
+                            place_name: &place_name,
+                            is_partial,
+                            is_loop_message,
+                        },
+                    );
+                    err.subdiagnostic(self.dcx(), CaptureReasonNote::FnOnceMoveInCall { var_span });
                 }
                 CallKind::Operator { self_arg, .. } => {
                     let self_arg = self_arg.unwrap();
-                    err.subdiagnostic(CaptureReasonLabel::OperatorUse {
-                        fn_call_span,
-                        place_name: &place_name,
-                        is_partial,
-                        is_loop_message,
-                    });
+                    err.subdiagnostic(
+                        self.dcx(),
+                        CaptureReasonLabel::OperatorUse {
+                            fn_call_span,
+                            place_name: &place_name,
+                            is_partial,
+                            is_loop_message,
+                        },
+                    );
                     if self.fn_self_span_reported.insert(fn_span) {
-                        err.subdiagnostic(CaptureReasonNote::LhsMoveByOperator {
-                            span: self_arg.span,
-                        });
+                        err.subdiagnostic(
+                            self.dcx(),
+                            CaptureReasonNote::LhsMoveByOperator { span: self_arg.span },
+                        );
                     }
                 }
                 CallKind::Normal { self_arg, desugaring, method_did, method_args } => {
@@ -1061,11 +1076,14 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                         );
 
                         let func = tcx.def_path_str(method_did);
-                        err.subdiagnostic(CaptureReasonNote::FuncTakeSelf {
-                            func,
-                            place_name: place_name.clone(),
-                            span: self_arg.span,
-                        });
+                        err.subdiagnostic(
+                            self.dcx(),
+                            CaptureReasonNote::FuncTakeSelf {
+                                func,
+                                place_name: place_name.clone(),
+                                span: self_arg.span,
+                            },
+                        );
                     }
                     let parent_did = tcx.parent(method_did);
                     let parent_self_ty =
@@ -1079,7 +1097,10 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                         matches!(tcx.get_diagnostic_name(def_id), Some(sym::Option | sym::Result))
                     });
                     if is_option_or_result && maybe_reinitialized_locations_is_empty {
-                        err.subdiagnostic(CaptureReasonLabel::BorrowContent { var_span });
+                        err.subdiagnostic(
+                            self.dcx(),
+                            CaptureReasonLabel::BorrowContent { var_span },
+                        );
                     }
                     if let Some((CallDesugaringKind::ForLoopIntoIter, _)) = desugaring {
                         let ty = moved_place.ty(self.body, tcx).ty;
@@ -1093,18 +1114,24 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                             _ => false,
                         };
                         if suggest {
-                            err.subdiagnostic(CaptureReasonSuggest::IterateSlice {
-                                ty,
-                                span: move_span.shrink_to_lo(),
-                            });
+                            err.subdiagnostic(
+                                self.dcx(),
+                                CaptureReasonSuggest::IterateSlice {
+                                    ty,
+                                    span: move_span.shrink_to_lo(),
+                                },
+                            );
                         }
 
-                        err.subdiagnostic(CaptureReasonLabel::ImplicitCall {
-                            fn_call_span,
-                            place_name: &place_name,
-                            is_partial,
-                            is_loop_message,
-                        });
+                        err.subdiagnostic(
+                            self.dcx(),
+                            CaptureReasonLabel::ImplicitCall {
+                                fn_call_span,
+                                place_name: &place_name,
+                                is_partial,
+                                is_loop_message,
+                            },
+                        );
                         // If the moved place was a `&mut` ref, then we can
                         // suggest to reborrow it where it was moved, so it
                         // will still be valid by the time we get to the usage.
@@ -1128,19 +1155,25 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                         }
                     } else {
                         if let Some((CallDesugaringKind::Await, _)) = desugaring {
-                            err.subdiagnostic(CaptureReasonLabel::Await {
-                                fn_call_span,
-                                place_name: &place_name,
-                                is_partial,
-                                is_loop_message,
-                            });
+                            err.subdiagnostic(
+                                self.dcx(),
+                                CaptureReasonLabel::Await {
+                                    fn_call_span,
+                                    place_name: &place_name,
+                                    is_partial,
+                                    is_loop_message,
+                                },
+                            );
                         } else {
-                            err.subdiagnostic(CaptureReasonLabel::MethodCall {
-                                fn_call_span,
-                                place_name: &place_name,
-                                is_partial,
-                                is_loop_message,
-                            });
+                            err.subdiagnostic(
+                                self.dcx(),
+                                CaptureReasonLabel::MethodCall {
+                                    fn_call_span,
+                                    place_name: &place_name,
+                                    is_partial,
+                                    is_loop_message,
+                                },
+                            );
                         }
                         // Erase and shadow everything that could be passed to the new infcx.
                         let ty = moved_place.ty(self.body, tcx).ty;
@@ -1155,7 +1188,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                             )
                             && self.infcx.can_eq(self.param_env, ty, self_ty)
                         {
-                            err.eager_subdiagnostic(
+                            err.subdiagnostic(
                                 self.dcx(),
                                 CaptureReasonSuggest::FreshReborrow {
                                     span: move_span.shrink_to_hi(),
@@ -1239,17 +1272,20 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             }
         } else {
             if move_span != span || is_loop_message {
-                err.subdiagnostic(CaptureReasonLabel::MovedHere {
-                    move_span,
-                    is_partial,
-                    is_move_msg,
-                    is_loop_message,
-                });
+                err.subdiagnostic(
+                    self.dcx(),
+                    CaptureReasonLabel::MovedHere {
+                        move_span,
+                        is_partial,
+                        is_move_msg,
+                        is_loop_message,
+                    },
+                );
             }
             // If the move error occurs due to a loop, don't show
             // another message for the same span
             if !is_loop_message {
-                move_spans.var_subdiag(None, err, None, |kind, var_span| match kind {
+                move_spans.var_subdiag(self.dcx(), err, None, |kind, var_span| match kind {
                     hir::ClosureKind::Coroutine(_) => {
                         CaptureVarCause::PartialMoveUseInCoroutine { var_span, is_partial }
                     }
diff --git a/compiler/rustc_borrowck/src/diagnostics/move_errors.rs b/compiler/rustc_borrowck/src/diagnostics/move_errors.rs
index 126a50c91b494..dad20690d02cc 100644
--- a/compiler/rustc_borrowck/src/diagnostics/move_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/move_errors.rs
@@ -448,12 +448,15 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                         None => "value".to_string(),
                     };
 
-                    err.subdiagnostic(crate::session_diagnostics::TypeNoCopy::Label {
-                        is_partial_move: false,
-                        ty: place_ty,
-                        place: &place_desc,
-                        span,
-                    });
+                    err.subdiagnostic(
+                        self.dcx(),
+                        crate::session_diagnostics::TypeNoCopy::Label {
+                            is_partial_move: false,
+                            ty: place_ty,
+                            place: &place_desc,
+                            span,
+                        },
+                    );
                 } else {
                     binds_to.sort();
                     binds_to.dedup();
@@ -475,14 +478,17 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                     Some(desc) => format!("`{desc}`"),
                     None => "value".to_string(),
                 };
-                err.subdiagnostic(crate::session_diagnostics::TypeNoCopy::Label {
-                    is_partial_move: false,
-                    ty: place_ty,
-                    place: &place_desc,
-                    span,
-                });
+                err.subdiagnostic(
+                    self.dcx(),
+                    crate::session_diagnostics::TypeNoCopy::Label {
+                        is_partial_move: false,
+                        ty: place_ty,
+                        place: &place_desc,
+                        span,
+                    },
+                );
 
-                use_spans.args_subdiag(err, |args_span| {
+                use_spans.args_subdiag(self.dcx(), err, |args_span| {
                     crate::session_diagnostics::CaptureArgLabel::MoveOutPlace {
                         place: place_desc,
                         args_span,
@@ -580,12 +586,15 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
 
             if binds_to.len() == 1 {
                 let place_desc = &format!("`{}`", self.local_names[*local].unwrap());
-                err.subdiagnostic(crate::session_diagnostics::TypeNoCopy::Label {
-                    is_partial_move: false,
-                    ty: bind_to.ty,
-                    place: place_desc,
-                    span: binding_span,
-                });
+                err.subdiagnostic(
+                    self.dcx(),
+                    crate::session_diagnostics::TypeNoCopy::Label {
+                        is_partial_move: false,
+                        ty: bind_to.ty,
+                        place: place_desc,
+                        span: binding_span,
+                    },
+                );
             }
         }
 
diff --git a/compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs b/compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs
index 65643e93d27c1..514e9c39eb440 100644
--- a/compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs
@@ -229,7 +229,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                 }
                 if suggest {
                     borrow_spans.var_subdiag(
-                        None,
+                        self.dcx(),
                         &mut err,
                         Some(mir::BorrowKind::Mut { kind: mir::MutBorrowKind::Default }),
                         |_kind, var_span| {
diff --git a/compiler/rustc_borrowck/src/diagnostics/region_errors.rs b/compiler/rustc_borrowck/src/diagnostics/region_errors.rs
index 7529ec53a9869..e8effd5c1633a 100644
--- a/compiler/rustc_borrowck/src/diagnostics/region_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/region_errors.rs
@@ -616,13 +616,13 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                 let upvars_map = self.infcx.tcx.upvars_mentioned(def_id).unwrap();
                 let upvar_def_span = self.infcx.tcx.hir().span(def_hir);
                 let upvar_span = upvars_map.get(&def_hir).unwrap().span;
-                diag.subdiagnostic(VarHereDenote::Defined { span: upvar_def_span });
-                diag.subdiagnostic(VarHereDenote::Captured { span: upvar_span });
+                diag.subdiagnostic(self.dcx(), VarHereDenote::Defined { span: upvar_def_span });
+                diag.subdiagnostic(self.dcx(), VarHereDenote::Captured { span: upvar_span });
             }
         }
 
         if let Some(fr_span) = self.give_region_a_name(*outlived_fr).unwrap().span() {
-            diag.subdiagnostic(VarHereDenote::FnMutInferred { span: fr_span });
+            diag.subdiagnostic(self.dcx(), VarHereDenote::FnMutInferred { span: fr_span });
         }
 
         self.suggest_move_on_borrowing_closure(&mut diag);
@@ -788,7 +788,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
             },
         };
 
-        diag.subdiagnostic(err_category);
+        diag.subdiagnostic(self.dcx(), err_category);
 
         self.add_static_impl_trait_suggestion(&mut diag, *fr, fr_name, *outlived_fr);
         self.suggest_adding_lifetime_params(&mut diag, *fr, *outlived_fr);
@@ -979,7 +979,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                     ident.span,
                     "calling this method introduces the `impl`'s `'static` requirement",
                 );
-                err.subdiagnostic(RequireStaticErr::UsedImpl { multi_span });
+                err.subdiagnostic(self.dcx(), RequireStaticErr::UsedImpl { multi_span });
                 err.span_suggestion_verbose(
                     span.shrink_to_hi(),
                     "consider relaxing the implicit `'static` requirement",
diff --git a/compiler/rustc_codegen_cranelift/src/lib.rs b/compiler/rustc_codegen_cranelift/src/lib.rs
index 7c432e9c59051..7e2e1f7c6ac07 100644
--- a/compiler/rustc_codegen_cranelift/src/lib.rs
+++ b/compiler/rustc_codegen_cranelift/src/lib.rs
@@ -233,11 +233,11 @@ impl CodegenBackend for CraneliftCodegenBackend {
         ongoing_codegen: Box<dyn Any>,
         sess: &Session,
         _outputs: &OutputFilenames,
-    ) -> Result<(CodegenResults, FxIndexMap<WorkProductId, WorkProduct>), ErrorGuaranteed> {
-        Ok(ongoing_codegen
+    ) -> (CodegenResults, FxIndexMap<WorkProductId, WorkProduct>) {
+        ongoing_codegen
             .downcast::<driver::aot::OngoingCodegen>()
             .unwrap()
-            .join(sess, self.config.borrow().as_ref().unwrap()))
+            .join(sess, self.config.borrow().as_ref().unwrap())
     }
 
     fn link(
diff --git a/compiler/rustc_codegen_gcc/src/errors.rs b/compiler/rustc_codegen_gcc/src/errors.rs
index cc0fbe46dcc11..79eb4406b8a33 100644
--- a/compiler/rustc_codegen_gcc/src/errors.rs
+++ b/compiler/rustc_codegen_gcc/src/errors.rs
@@ -122,7 +122,7 @@ impl<G: EmissionGuarantee> IntoDiagnostic<'_, G> for TargetFeatureDisableOrEnabl
             diag.span(span);
         };
         if let Some(missing_features) = self.missing_features {
-            diag.subdiagnostic(missing_features);
+            diag.subdiagnostic(dcx, missing_features);
         }
         diag.arg("features", self.features.join(", "));
         diag
diff --git a/compiler/rustc_codegen_gcc/src/lib.rs b/compiler/rustc_codegen_gcc/src/lib.rs
index 863b6333bcc29..09ce059476ec7 100644
--- a/compiler/rustc_codegen_gcc/src/lib.rs
+++ b/compiler/rustc_codegen_gcc/src/lib.rs
@@ -217,13 +217,11 @@ impl CodegenBackend for GccCodegenBackend {
         Box::new(res)
     }
 
-    fn join_codegen(&self, ongoing_codegen: Box<dyn Any>, sess: &Session, _outputs: &OutputFilenames) -> Result<(CodegenResults, FxIndexMap<WorkProductId, WorkProduct>), ErrorGuaranteed> {
-        let (codegen_results, work_products) = ongoing_codegen
+    fn join_codegen(&self, ongoing_codegen: Box<dyn Any>, sess: &Session, _outputs: &OutputFilenames) -> (CodegenResults, FxIndexMap<WorkProductId, WorkProduct>) {
+        ongoing_codegen
             .downcast::<rustc_codegen_ssa::back::write::OngoingCodegen<GccCodegenBackend>>()
             .expect("Expected GccCodegenBackend's OngoingCodegen, found Box<Any>")
-            .join(sess);
-
-        Ok((codegen_results, work_products))
+            .join(sess)
     }
 
     fn link(&self, sess: &Session, codegen_results: CodegenResults, outputs: &OutputFilenames) -> Result<(), ErrorGuaranteed> {
diff --git a/compiler/rustc_codegen_llvm/src/errors.rs b/compiler/rustc_codegen_llvm/src/errors.rs
index 587c5e9e8d235..87e3774068bcd 100644
--- a/compiler/rustc_codegen_llvm/src/errors.rs
+++ b/compiler/rustc_codegen_llvm/src/errors.rs
@@ -131,7 +131,7 @@ impl<G: EmissionGuarantee> IntoDiagnostic<'_, G> for TargetFeatureDisableOrEnabl
             diag.span(span);
         };
         if let Some(missing_features) = self.missing_features {
-            diag.subdiagnostic(missing_features);
+            diag.subdiagnostic(dcx, missing_features);
         }
         diag.arg("features", self.features.join(", "));
         diag
diff --git a/compiler/rustc_codegen_llvm/src/lib.rs b/compiler/rustc_codegen_llvm/src/lib.rs
index e688e84db61a5..35210b0b2e86d 100644
--- a/compiler/rustc_codegen_llvm/src/lib.rs
+++ b/compiler/rustc_codegen_llvm/src/lib.rs
@@ -369,7 +369,7 @@ impl CodegenBackend for LlvmCodegenBackend {
         ongoing_codegen: Box<dyn Any>,
         sess: &Session,
         outputs: &OutputFilenames,
-    ) -> Result<(CodegenResults, FxIndexMap<WorkProductId, WorkProduct>), ErrorGuaranteed> {
+    ) -> (CodegenResults, FxIndexMap<WorkProductId, WorkProduct>) {
         let (codegen_results, work_products) = ongoing_codegen
             .downcast::<rustc_codegen_ssa::back::write::OngoingCodegen<LlvmCodegenBackend>>()
             .expect("Expected LlvmCodegenBackend's OngoingCodegen, found Box<Any>")
@@ -382,7 +382,7 @@ impl CodegenBackend for LlvmCodegenBackend {
             });
         }
 
-        Ok((codegen_results, work_products))
+        (codegen_results, work_products)
     }
 
     fn link(
diff --git a/compiler/rustc_codegen_ssa/src/traits/backend.rs b/compiler/rustc_codegen_ssa/src/traits/backend.rs
index 8e9907ed8bb03..cb1feff13363e 100644
--- a/compiler/rustc_codegen_ssa/src/traits/backend.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/backend.rs
@@ -102,7 +102,7 @@ pub trait CodegenBackend {
         ongoing_codegen: Box<dyn Any>,
         sess: &Session,
         outputs: &OutputFilenames,
-    ) -> Result<(CodegenResults, FxIndexMap<WorkProductId, WorkProduct>), ErrorGuaranteed>;
+    ) -> (CodegenResults, FxIndexMap<WorkProductId, WorkProduct>);
 
     /// This is called on the returned `CodegenResults` from `join_codegen`
     fn link(
diff --git a/compiler/rustc_const_eval/src/transform/check_consts/ops.rs b/compiler/rustc_const_eval/src/transform/check_consts/ops.rs
index 0c93cfaa54647..25ddd5e85f9f3 100644
--- a/compiler/rustc_const_eval/src/transform/check_consts/ops.rs
+++ b/compiler/rustc_const_eval/src/transform/check_consts/ops.rs
@@ -131,7 +131,7 @@ impl<'tcx> NonConstOp<'tcx> for FnCallNonConst<'tcx> {
                         // FIXME(effects) revisit this
                         if !tcx.is_const_trait_impl_raw(data.impl_def_id) {
                             let span = tcx.def_span(data.impl_def_id);
-                            err.subdiagnostic(errors::NonConstImplNote { span });
+                            err.subdiagnostic(tcx.dcx(), errors::NonConstImplNote { span });
                         }
                     }
                 }
diff --git a/compiler/rustc_error_messages/src/lib.rs b/compiler/rustc_error_messages/src/lib.rs
index a1abe8fd4f306..f91b6655f6399 100644
--- a/compiler/rustc_error_messages/src/lib.rs
+++ b/compiler/rustc_error_messages/src/lib.rs
@@ -263,14 +263,10 @@ pub enum SubdiagnosticMessage {
     /// Translatable message which has already been translated eagerly.
     ///
     /// Some diagnostics have repeated subdiagnostics where the same interpolated variables would
-    /// be instantiated multiple times with different values. As translation normally happens
-    /// immediately prior to emission, after the diagnostic and subdiagnostic derive logic has run,
-    /// the setting of diagnostic arguments in the derived code will overwrite previous variable
-    /// values and only the final value will be set when translation occurs - resulting in
-    /// incorrect diagnostics. Eager translation results in translation for a subdiagnostic
-    /// happening immediately after the subdiagnostic derive's logic has been run. This variant
-    /// stores messages which have been translated eagerly.
-    Eager(Cow<'static, str>),
+    /// be instantiated multiple times with different values. These subdiagnostics' messages
+    /// are translated when they are added to the parent diagnostic, producing this variant of
+    /// `DiagnosticMessage`.
+    Translated(Cow<'static, str>),
     /// Identifier of a Fluent message. Instances of this variant are generated by the
     /// `Subdiagnostic` derive.
     FluentIdentifier(FluentId),
@@ -307,19 +303,15 @@ impl From<Cow<'static, str>> for SubdiagnosticMessage {
 pub enum DiagnosticMessage {
     /// Non-translatable diagnostic message.
     Str(Cow<'static, str>),
-    /// Translatable message which has already been translated eagerly.
+    /// Translatable message which has been already translated.
     ///
     /// Some diagnostics have repeated subdiagnostics where the same interpolated variables would
-    /// be instantiated multiple times with different values. As translation normally happens
-    /// immediately prior to emission, after the diagnostic and subdiagnostic derive logic has run,
-    /// the setting of diagnostic arguments in the derived code will overwrite previous variable
-    /// values and only the final value will be set when translation occurs - resulting in
-    /// incorrect diagnostics. Eager translation results in translation for a subdiagnostic
-    /// happening immediately after the subdiagnostic derive's logic has been run. This variant
-    /// stores messages which have been translated eagerly.
-    Eager(Cow<'static, str>),
+    /// be instantiated multiple times with different values. These subdiagnostics' messages
+    /// are translated when they are added to the parent diagnostic, producing this variant of
+    /// `DiagnosticMessage`.
+    Translated(Cow<'static, str>),
     /// Identifier for a Fluent message (with optional attribute) corresponding to the diagnostic
-    /// message.
+    /// message. Yet to be translated.
     ///
     /// <https://projectfluent.org/fluent/guide/hello.html>
     /// <https://projectfluent.org/fluent/guide/attributes.html>
@@ -336,7 +328,7 @@ impl DiagnosticMessage {
     pub fn with_subdiagnostic_message(&self, sub: SubdiagnosticMessage) -> Self {
         let attr = match sub {
             SubdiagnosticMessage::Str(s) => return DiagnosticMessage::Str(s),
-            SubdiagnosticMessage::Eager(s) => return DiagnosticMessage::Eager(s),
+            SubdiagnosticMessage::Translated(s) => return DiagnosticMessage::Translated(s),
             SubdiagnosticMessage::FluentIdentifier(id) => {
                 return DiagnosticMessage::FluentIdentifier(id, None);
             }
@@ -345,7 +337,7 @@ impl DiagnosticMessage {
 
         match self {
             DiagnosticMessage::Str(s) => DiagnosticMessage::Str(s.clone()),
-            DiagnosticMessage::Eager(s) => DiagnosticMessage::Eager(s.clone()),
+            DiagnosticMessage::Translated(s) => DiagnosticMessage::Translated(s.clone()),
             DiagnosticMessage::FluentIdentifier(id, _) => {
                 DiagnosticMessage::FluentIdentifier(id.clone(), Some(attr))
             }
@@ -354,7 +346,7 @@ impl DiagnosticMessage {
 
     pub fn as_str(&self) -> Option<&str> {
         match self {
-            DiagnosticMessage::Eager(s) | DiagnosticMessage::Str(s) => Some(s),
+            DiagnosticMessage::Translated(s) | DiagnosticMessage::Str(s) => Some(s),
             DiagnosticMessage::FluentIdentifier(_, _) => None,
         }
     }
@@ -396,7 +388,7 @@ impl Into<SubdiagnosticMessage> for DiagnosticMessage {
     fn into(self) -> SubdiagnosticMessage {
         match self {
             DiagnosticMessage::Str(s) => SubdiagnosticMessage::Str(s),
-            DiagnosticMessage::Eager(s) => SubdiagnosticMessage::Eager(s),
+            DiagnosticMessage::Translated(s) => SubdiagnosticMessage::Translated(s),
             DiagnosticMessage::FluentIdentifier(id, None) => {
                 SubdiagnosticMessage::FluentIdentifier(id)
             }
diff --git a/compiler/rustc_errors/src/diagnostic.rs b/compiler/rustc_errors/src/diagnostic.rs
index 91a8ec3b794b0..034636bea4818 100644
--- a/compiler/rustc_errors/src/diagnostic.rs
+++ b/compiler/rustc_errors/src/diagnostic.rs
@@ -851,18 +851,11 @@ impl Diagnostic {
         self
     }
 
-    /// Add a subdiagnostic from a type that implements `Subdiagnostic` (see
-    /// [rustc_macros::Subdiagnostic]).
-    pub fn subdiagnostic(&mut self, subdiagnostic: impl AddToDiagnostic) -> &mut Self {
-        subdiagnostic.add_to_diagnostic(self);
-        self
-    }
-
     /// Add a subdiagnostic from a type that implements `Subdiagnostic` (see
     /// [rustc_macros::Subdiagnostic]). Performs eager translation of any translatable messages
     /// used in the subdiagnostic, so suitable for use with repeated messages (i.e. re-use of
     /// interpolated variables).
-    pub fn eager_subdiagnostic(
+    pub fn subdiagnostic(
         &mut self,
         dcx: &crate::DiagCtxt,
         subdiagnostic: impl AddToDiagnostic,
@@ -918,7 +911,7 @@ impl Diagnostic {
     /// Helper function that takes a `SubdiagnosticMessage` and returns a `DiagnosticMessage` by
     /// combining it with the primary message of the diagnostic (if translatable, otherwise it just
     /// passes the user's string along).
-    fn subdiagnostic_message_to_diagnostic_message(
+    pub(crate) fn subdiagnostic_message_to_diagnostic_message(
         &self,
         attr: impl Into<SubdiagnosticMessage>,
     ) -> DiagnosticMessage {
diff --git a/compiler/rustc_errors/src/diagnostic_builder.rs b/compiler/rustc_errors/src/diagnostic_builder.rs
index e484bef0e0bc9..0572df69ca947 100644
--- a/compiler/rustc_errors/src/diagnostic_builder.rs
+++ b/compiler/rustc_errors/src/diagnostic_builder.rs
@@ -404,9 +404,6 @@ impl<'a, G: EmissionGuarantee> DiagnosticBuilder<'a, G> {
         name: impl Into<Cow<'static, str>>, arg: impl IntoDiagnosticArg,
     ));
     forward!((subdiagnostic, with_subdiagnostic)(
-        subdiagnostic: impl crate::AddToDiagnostic,
-    ));
-    forward!((eager_subdiagnostic, with_eager_subdiagnostic)(
         dcx: &DiagCtxt,
         subdiagnostic: impl crate::AddToDiagnostic,
     ));
diff --git a/compiler/rustc_errors/src/emitter.rs b/compiler/rustc_errors/src/emitter.rs
index afb1b854e7258..e09c041c1d063 100644
--- a/compiler/rustc_errors/src/emitter.rs
+++ b/compiler/rustc_errors/src/emitter.rs
@@ -10,6 +10,7 @@
 use rustc_span::source_map::SourceMap;
 use rustc_span::{FileLines, FileName, SourceFile, Span};
 
+use crate::error::TranslateError;
 use crate::snippet::{
     Annotation, AnnotationColumn, AnnotationType, Line, MultilineAnnotation, Style, StyledString,
 };
@@ -559,6 +560,18 @@ pub struct SilentEmitter {
     pub fatal_note: String,
 }
 
+pub fn silent_translate<'a>(
+    message: &'a DiagnosticMessage,
+) -> Result<Cow<'_, str>, TranslateError<'_>> {
+    match message {
+        DiagnosticMessage::Str(msg) | DiagnosticMessage::Translated(msg) => Ok(Cow::Borrowed(msg)),
+        DiagnosticMessage::FluentIdentifier(identifier, _) => {
+            // Any value works here.
+            Ok(identifier.clone())
+        }
+    }
+}
+
 impl Translate for SilentEmitter {
     fn fluent_bundle(&self) -> Option<&Lrc<FluentBundle>> {
         None
@@ -567,6 +580,16 @@ impl Translate for SilentEmitter {
     fn fallback_fluent_bundle(&self) -> &FluentBundle {
         panic!("silent emitter attempted to translate message")
     }
+
+    // Override `translate_message` for the silent emitter because eager translation of
+    // subdiagnostics result in a call to this.
+    fn translate_message<'a>(
+        &'a self,
+        message: &'a DiagnosticMessage,
+        _: &'a FluentArgs<'_>,
+    ) -> Result<Cow<'_, str>, TranslateError<'_>> {
+        silent_translate(message)
+    }
 }
 
 impl Emitter for SilentEmitter {
diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index b9b257856e678..064ea8d75163e 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -643,7 +643,8 @@ impl DiagCtxt {
         message: DiagnosticMessage,
         args: impl Iterator<Item = DiagnosticArg<'a>>,
     ) -> SubdiagnosticMessage {
-        SubdiagnosticMessage::Eager(Cow::from(self.eagerly_translate_to_string(message, args)))
+        let inner = self.inner.borrow();
+        inner.eagerly_translate(message, args)
     }
 
     /// Translate `message` eagerly with `args` to `String`.
@@ -653,8 +654,7 @@ impl DiagCtxt {
         args: impl Iterator<Item = DiagnosticArg<'a>>,
     ) -> String {
         let inner = self.inner.borrow();
-        let args = crate::translation::to_fluent_args(args);
-        inner.emitter.translate_message(&message, &args).map_err(Report::new).unwrap().to_string()
+        inner.eagerly_translate_to_string(message, args)
     }
 
     // This is here to not allow mutation of flags;
@@ -1464,6 +1464,25 @@ impl DiagCtxtInner {
             .or_else(|| self.delayed_bugs.get(0).map(|(_, guar)| guar).copied())
     }
 
+    /// Translate `message` eagerly with `args` to `SubdiagnosticMessage::Eager`.
+    pub fn eagerly_translate<'a>(
+        &self,
+        message: DiagnosticMessage,
+        args: impl Iterator<Item = DiagnosticArg<'a>>,
+    ) -> SubdiagnosticMessage {
+        SubdiagnosticMessage::Translated(Cow::from(self.eagerly_translate_to_string(message, args)))
+    }
+
+    /// Translate `message` eagerly with `args` to `String`.
+    pub fn eagerly_translate_to_string<'a>(
+        &self,
+        message: DiagnosticMessage,
+        args: impl Iterator<Item = DiagnosticArg<'a>>,
+    ) -> String {
+        let args = crate::translation::to_fluent_args(args);
+        self.emitter.translate_message(&message, &args).map_err(Report::new).unwrap().to_string()
+    }
+
     fn flush_delayed(&mut self) {
         if self.delayed_bugs.is_empty() {
             return;
@@ -1502,15 +1521,22 @@ impl DiagCtxtInner {
             }
 
             let mut bug =
-                if backtrace || self.ice_file.is_none() { bug.decorate() } else { bug.inner };
+                if backtrace || self.ice_file.is_none() { bug.decorate(self) } else { bug.inner };
 
             // "Undelay" the delayed bugs (into plain `Bug`s).
             if bug.level != DelayedBug {
                 // NOTE(eddyb) not panicking here because we're already producing
                 // an ICE, and the more information the merrier.
-                bug.subdiagnostic(InvalidFlushedDelayedDiagnosticLevel {
+                let subdiag = InvalidFlushedDelayedDiagnosticLevel {
                     span: bug.span.primary_span().unwrap(),
                     level: bug.level,
+                };
+                // FIXME: Cannot use `Diagnostic::subdiagnostic` which takes `DiagCtxt`, but it
+                // just uses `DiagCtxtInner` functions.
+                subdiag.add_to_diagnostic_with(&mut bug, |diag, msg| {
+                    let args = diag.args();
+                    let msg = diag.subdiagnostic_message_to_diagnostic_message(msg);
+                    self.eagerly_translate(msg, args)
                 });
             }
             bug.level = Bug;
@@ -1545,25 +1571,35 @@ impl DelayedDiagnostic {
         DelayedDiagnostic { inner: diagnostic, note: backtrace }
     }
 
-    fn decorate(mut self) -> Diagnostic {
+    fn decorate(mut self, dcx: &DiagCtxtInner) -> Diagnostic {
+        // FIXME: Cannot use `Diagnostic::subdiagnostic` which takes `DiagCtxt`, but it
+        // just uses `DiagCtxtInner` functions.
+        let subdiag_with = |diag: &mut Diagnostic, msg| {
+            let args = diag.args();
+            let msg = diag.subdiagnostic_message_to_diagnostic_message(msg);
+            dcx.eagerly_translate(msg, args)
+        };
+
         match self.note.status() {
             BacktraceStatus::Captured => {
                 let inner = &self.inner;
-                self.inner.subdiagnostic(DelayedAtWithNewline {
+                let subdiag = DelayedAtWithNewline {
                     span: inner.span.primary_span().unwrap_or(DUMMY_SP),
                     emitted_at: inner.emitted_at.clone(),
                     note: self.note,
-                });
+                };
+                subdiag.add_to_diagnostic_with(&mut self.inner, subdiag_with);
             }
             // Avoid the needless newline when no backtrace has been captured,
             // the display impl should just be a single line.
             _ => {
                 let inner = &self.inner;
-                self.inner.subdiagnostic(DelayedAtWithoutNewline {
+                let subdiag = DelayedAtWithoutNewline {
                     span: inner.span.primary_span().unwrap_or(DUMMY_SP),
                     emitted_at: inner.emitted_at.clone(),
                     note: self.note,
-                });
+                };
+                subdiag.add_to_diagnostic_with(&mut self.inner, subdiag_with);
             }
         }
 
@@ -1709,15 +1745,15 @@ impl Level {
 }
 
 // FIXME(eddyb) this doesn't belong here AFAICT, should be moved to callsite.
-pub fn add_elided_lifetime_in_path_suggestion(
+pub fn add_elided_lifetime_in_path_suggestion<E: EmissionGuarantee>(
     source_map: &SourceMap,
-    diag: &mut Diagnostic,
+    diag: &mut DiagnosticBuilder<'_, E>,
     n: usize,
     path_span: Span,
     incl_angl_brckt: bool,
     insertion_span: Span,
 ) {
-    diag.subdiagnostic(ExpectedLifetimeParameter { span: path_span, count: n });
+    diag.subdiagnostic(diag.dcx, ExpectedLifetimeParameter { span: path_span, count: n });
     if !source_map.is_span_accessible(insertion_span) {
         // Do not try to suggest anything if generated by a proc-macro.
         return;
@@ -1726,11 +1762,10 @@ pub fn add_elided_lifetime_in_path_suggestion(
     let suggestion =
         if incl_angl_brckt { format!("<{anon_lts}>") } else { format!("{anon_lts}, ") };
 
-    diag.subdiagnostic(IndicateAnonymousLifetime {
-        span: insertion_span.shrink_to_hi(),
-        count: n,
-        suggestion,
-    });
+    diag.subdiagnostic(
+        diag.dcx,
+        IndicateAnonymousLifetime { span: insertion_span.shrink_to_hi(), count: n, suggestion },
+    );
 }
 
 pub fn report_ambiguity_error<'a, G: EmissionGuarantee>(
diff --git a/compiler/rustc_errors/src/translation.rs b/compiler/rustc_errors/src/translation.rs
index 5bdac367d55e7..5f074dbbbad30 100644
--- a/compiler/rustc_errors/src/translation.rs
+++ b/compiler/rustc_errors/src/translation.rs
@@ -2,7 +2,7 @@ use crate::error::{TranslateError, TranslateErrorKind};
 use crate::snippet::Style;
 use crate::{DiagnosticArg, DiagnosticMessage, FluentBundle};
 use rustc_data_structures::sync::Lrc;
-use rustc_error_messages::FluentArgs;
+pub use rustc_error_messages::FluentArgs;
 use std::borrow::Cow;
 use std::env;
 use std::error::Report;
@@ -61,7 +61,7 @@ pub trait Translate {
     ) -> Result<Cow<'_, str>, TranslateError<'_>> {
         trace!(?message, ?args);
         let (identifier, attr) = match message {
-            DiagnosticMessage::Str(msg) | DiagnosticMessage::Eager(msg) => {
+            DiagnosticMessage::Str(msg) | DiagnosticMessage::Translated(msg) => {
                 return Ok(Cow::Borrowed(msg));
             }
             DiagnosticMessage::FluentIdentifier(identifier, attr) => (identifier, attr),
diff --git a/compiler/rustc_expand/src/mbe/diagnostics.rs b/compiler/rustc_expand/src/mbe/diagnostics.rs
index be4b6399e12da..e7197c5768b4d 100644
--- a/compiler/rustc_expand/src/mbe/diagnostics.rs
+++ b/compiler/rustc_expand/src/mbe/diagnostics.rs
@@ -7,7 +7,7 @@ use crate::mbe::{
 use rustc_ast::token::{self, Token, TokenKind};
 use rustc_ast::tokenstream::TokenStream;
 use rustc_ast_pretty::pprust;
-use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, DiagnosticMessage};
+use rustc_errors::{Applicability, DiagCtxt, Diagnostic, DiagnosticBuilder, DiagnosticMessage};
 use rustc_parse::parser::{Parser, Recovery};
 use rustc_span::source_map::SourceMap;
 use rustc_span::symbol::Ident;
@@ -58,7 +58,7 @@ pub(super) fn failed_to_match_macro<'cx>(
         err.span_label(cx.source_map().guess_head_span(def_span), "when calling this macro");
     }
 
-    annotate_doc_comment(&mut err, sess.source_map(), span);
+    annotate_doc_comment(cx.sess.dcx(), &mut err, sess.source_map(), span);
 
     if let Some(span) = remaining_matcher.span() {
         err.span_note(span, format!("while trying to match {remaining_matcher}"));
@@ -311,12 +311,17 @@ enum ExplainDocComment {
     },
 }
 
-pub(super) fn annotate_doc_comment(err: &mut Diagnostic, sm: &SourceMap, span: Span) {
+pub(super) fn annotate_doc_comment(
+    dcx: &DiagCtxt,
+    err: &mut Diagnostic,
+    sm: &SourceMap,
+    span: Span,
+) {
     if let Ok(src) = sm.span_to_snippet(span) {
         if src.starts_with("///") || src.starts_with("/**") {
-            err.subdiagnostic(ExplainDocComment::Outer { span });
+            err.subdiagnostic(dcx, ExplainDocComment::Outer { span });
         } else if src.starts_with("//!") || src.starts_with("/*!") {
-            err.subdiagnostic(ExplainDocComment::Inner { span });
+            err.subdiagnostic(dcx, ExplainDocComment::Inner { span });
         }
     }
 }
diff --git a/compiler/rustc_expand/src/mbe/macro_rules.rs b/compiler/rustc_expand/src/mbe/macro_rules.rs
index 83e0f870c8a25..c82609503c18a 100644
--- a/compiler/rustc_expand/src/mbe/macro_rules.rs
+++ b/compiler/rustc_expand/src/mbe/macro_rules.rs
@@ -454,7 +454,7 @@ pub fn compile_declarative_macro(
                 let sp = token.span.substitute_dummy(def.span);
                 let mut err = sess.dcx().struct_span_err(sp, s);
                 err.span_label(sp, msg);
-                annotate_doc_comment(&mut err, sess.source_map(), sp);
+                annotate_doc_comment(sess.dcx(), &mut err, sess.source_map(), sp);
                 err.emit();
                 return dummy_syn_ext();
             }
diff --git a/compiler/rustc_hir_typeck/src/_match.rs b/compiler/rustc_hir_typeck/src/_match.rs
index b0caf45b40afe..d1e95db1de0cc 100644
--- a/compiler/rustc_hir_typeck/src/_match.rs
+++ b/compiler/rustc_hir_typeck/src/_match.rs
@@ -260,7 +260,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         let semi = expr.span.shrink_to_hi().with_hi(semi_span.hi());
         let sugg = crate::errors::RemoveSemiForCoerce { expr: expr.span, ret, semi };
-        diag.subdiagnostic(sugg);
+        diag.subdiagnostic(self.dcx(), sugg);
     }
 
     /// When the previously checked expression (the scrutinee) diverges,
diff --git a/compiler/rustc_hir_typeck/src/cast.rs b/compiler/rustc_hir_typeck/src/cast.rs
index 9a8f287ec14f7..042dd576c5b9b 100644
--- a/compiler/rustc_hir_typeck/src/cast.rs
+++ b/compiler/rustc_hir_typeck/src/cast.rs
@@ -993,19 +993,25 @@ impl<'a, 'tcx> CastCheck<'tcx> {
             if let Some((deref_ty, _)) = derefed {
                 // Give a note about what the expr derefs to.
                 if deref_ty != self.expr_ty.peel_refs() {
-                    err.subdiagnostic(errors::DerefImplsIsEmpty {
-                        span: self.expr_span,
-                        deref_ty: fcx.ty_to_string(deref_ty),
-                    });
+                    err.subdiagnostic(
+                        fcx.dcx(),
+                        errors::DerefImplsIsEmpty {
+                            span: self.expr_span,
+                            deref_ty: fcx.ty_to_string(deref_ty),
+                        },
+                    );
                 }
 
                 // Create a multipart suggestion: add `!` and `.is_empty()` in
                 // place of the cast.
-                err.subdiagnostic(errors::UseIsEmpty {
-                    lo: self.expr_span.shrink_to_lo(),
-                    hi: self.span.with_lo(self.expr_span.hi()),
-                    expr_ty: fcx.ty_to_string(self.expr_ty),
-                });
+                err.subdiagnostic(
+                    fcx.dcx(),
+                    errors::UseIsEmpty {
+                        lo: self.expr_span.shrink_to_lo(),
+                        hi: self.span.with_lo(self.expr_span.hi()),
+                        expr_ty: fcx.ty_to_string(self.expr_ty),
+                    },
+                );
             }
         }
     }
diff --git a/compiler/rustc_hir_typeck/src/expr.rs b/compiler/rustc_hir_typeck/src/expr.rs
index 949fbb65dbd49..ed19d00d64119 100644
--- a/compiler/rustc_hir_typeck/src/expr.rs
+++ b/compiler/rustc_hir_typeck/src/expr.rs
@@ -396,7 +396,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         if let Some(sp) =
                             tcx.sess.parse_sess.ambiguous_block_expr_parse.borrow().get(&sp)
                         {
-                            err.subdiagnostic(ExprParenthesesNeeded::surrounding(*sp));
+                            err.subdiagnostic(self.dcx(), ExprParenthesesNeeded::surrounding(*sp));
                         }
                         oprnd_t = Ty::new_error(tcx, err.emit());
                     }
@@ -2048,7 +2048,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 .shrink_to_hi()
                 .to(range_end.span);
 
-            err.subdiagnostic(TypeMismatchFruTypo { expr_span: range_start.span, fru_span, expr });
+            err.subdiagnostic(
+                self.dcx(),
+                TypeMismatchFruTypo { expr_span: range_start.span, fru_span, expr },
+            );
         }
     }
 
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
index 3bce8a1dd4500..dd527666d5555 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
@@ -1269,7 +1269,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         {
             // The user provided `ptr::null()`, but the function expects
             // `ptr::null_mut()`.
-            err.subdiagnostic(SuggestPtrNullMut { span: arg.span });
+            err.subdiagnostic(self.dcx(), SuggestPtrNullMut { span: arg.span });
         }
     }
 
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
index 8b6f263b1a746..c1a32a1afa3cf 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
@@ -458,13 +458,16 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             // but those checks need to be a bit more delicate and the benefit is diminishing.
             if self.can_eq(self.param_env, found_ty_inner, peeled) && error_tys_equate_as_ref {
                 let sugg = prefix_wrap(".as_ref()");
-                err.subdiagnostic(errors::SuggestConvertViaMethod {
-                    span: expr.span.shrink_to_hi(),
-                    sugg,
-                    expected,
-                    found,
-                    borrow_removal_span,
-                });
+                err.subdiagnostic(
+                    self.dcx(),
+                    errors::SuggestConvertViaMethod {
+                        span: expr.span.shrink_to_hi(),
+                        sugg,
+                        expected,
+                        found,
+                        borrow_removal_span,
+                    },
+                );
                 return true;
             } else if let Some((deref_ty, _)) =
                 self.autoderef(expr.span, found_ty_inner).silence_errors().nth(1)
@@ -472,13 +475,16 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 && error_tys_equate_as_ref
             {
                 let sugg = prefix_wrap(".as_deref()");
-                err.subdiagnostic(errors::SuggestConvertViaMethod {
-                    span: expr.span.shrink_to_hi(),
-                    sugg,
-                    expected,
-                    found,
-                    borrow_removal_span,
-                });
+                err.subdiagnostic(
+                    self.dcx(),
+                    errors::SuggestConvertViaMethod {
+                        span: expr.span.shrink_to_hi(),
+                        sugg,
+                        expected,
+                        found,
+                        borrow_removal_span,
+                    },
+                );
                 return true;
             } else if let ty::Adt(adt, _) = found_ty_inner.peel_refs().kind()
                 && Some(adt.did()) == self.tcx.lang_items().string()
@@ -565,7 +571,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     end: span.shrink_to_hi(),
                 },
             };
-            err.subdiagnostic(suggest_boxing);
+            err.subdiagnostic(self.dcx(), suggest_boxing);
 
             true
         } else {
@@ -799,29 +805,35 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         match &fn_decl.output {
             &hir::FnRetTy::DefaultReturn(span) if expected.is_unit() && !can_suggest => {
                 // `fn main()` must return `()`, do not suggest changing return type
-                err.subdiagnostic(errors::ExpectedReturnTypeLabel::Unit { span });
+                err.subdiagnostic(self.dcx(), errors::ExpectedReturnTypeLabel::Unit { span });
                 return true;
             }
             &hir::FnRetTy::DefaultReturn(span) if expected.is_unit() => {
                 if let Some(found) = found.make_suggestable(self.tcx, false) {
-                    err.subdiagnostic(errors::AddReturnTypeSuggestion::Add {
-                        span,
-                        found: found.to_string(),
-                    });
+                    err.subdiagnostic(
+                        self.dcx(),
+                        errors::AddReturnTypeSuggestion::Add { span, found: found.to_string() },
+                    );
                     return true;
                 } else if let ty::Closure(_, args) = found.kind()
                     // FIXME(compiler-errors): Get better at printing binders...
                     && let closure = args.as_closure()
                     && closure.sig().is_suggestable(self.tcx, false)
                 {
-                    err.subdiagnostic(errors::AddReturnTypeSuggestion::Add {
-                        span,
-                        found: closure.print_as_impl_trait().to_string(),
-                    });
+                    err.subdiagnostic(
+                        self.dcx(),
+                        errors::AddReturnTypeSuggestion::Add {
+                            span,
+                            found: closure.print_as_impl_trait().to_string(),
+                        },
+                    );
                     return true;
                 } else {
                     // FIXME: if `found` could be `impl Iterator` we should suggest that.
-                    err.subdiagnostic(errors::AddReturnTypeSuggestion::MissingHere { span });
+                    err.subdiagnostic(
+                        self.dcx(),
+                        errors::AddReturnTypeSuggestion::MissingHere { span },
+                    );
                     return true;
                 }
             }
@@ -843,16 +855,22 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     debug!(?found);
                     if found.is_suggestable(self.tcx, false) {
                         if term.span.is_empty() {
-                            err.subdiagnostic(errors::AddReturnTypeSuggestion::Add {
-                                span: term.span,
-                                found: found.to_string(),
-                            });
+                            err.subdiagnostic(
+                                self.dcx(),
+                                errors::AddReturnTypeSuggestion::Add {
+                                    span: term.span,
+                                    found: found.to_string(),
+                                },
+                            );
                             return true;
                         } else {
-                            err.subdiagnostic(errors::ExpectedReturnTypeLabel::Other {
-                                span: term.span,
-                                expected,
-                            });
+                            err.subdiagnostic(
+                                self.dcx(),
+                                errors::ExpectedReturnTypeLabel::Other {
+                                    span: term.span,
+                                    expected,
+                                },
+                            );
                         }
                     }
                 } else {
@@ -867,10 +885,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     let ty = self.normalize(hir_ty.span, ty);
                     let ty = self.tcx.instantiate_bound_regions_with_erased(ty);
                     if self.can_coerce(expected, ty) {
-                        err.subdiagnostic(errors::ExpectedReturnTypeLabel::Other {
-                            span: hir_ty.span,
-                            expected,
-                        });
+                        err.subdiagnostic(
+                            self.dcx(),
+                            errors::ExpectedReturnTypeLabel::Other { span: hir_ty.span, expected },
+                        );
                         self.try_suggest_return_impl_trait(err, expected, ty, fn_id);
                         return true;
                     }
@@ -1106,7 +1124,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let sp = self.tcx.sess.source_map().start_point(expr.span).with_parent(None);
         if let Some(sp) = self.tcx.sess.parse_sess.ambiguous_block_expr_parse.borrow().get(&sp) {
             // `{ 42 } &&x` (#61475) or `{ 42 } && if x { 1 } else { 0 }`
-            err.subdiagnostic(ExprParenthesesNeeded::surrounding(*sp));
+            err.subdiagnostic(self.dcx(), ExprParenthesesNeeded::surrounding(*sp));
             true
         } else {
             false
@@ -1220,7 +1238,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 } else {
                     return false;
                 };
-                diag.subdiagnostic(subdiag);
+                diag.subdiagnostic(self.dcx(), subdiag);
                 return true;
             }
         }
diff --git a/compiler/rustc_hir_typeck/src/method/suggest.rs b/compiler/rustc_hir_typeck/src/method/suggest.rs
index f39b496154b46..4151298b42f0a 100644
--- a/compiler/rustc_hir_typeck/src/method/suggest.rs
+++ b/compiler/rustc_hir_typeck/src/method/suggest.rs
@@ -3269,19 +3269,22 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     if impls_trait(trait_info.def_id) {
                         self.suggest_valid_traits(err, vec![trait_info.def_id], false);
                     } else {
-                        err.subdiagnostic(CandidateTraitNote {
-                            span: self.tcx.def_span(trait_info.def_id),
-                            trait_name: self.tcx.def_path_str(trait_info.def_id),
-                            item_name,
-                            action_or_ty: if trait_missing_method {
-                                "NONE".to_string()
-                            } else {
-                                param_type.map_or_else(
-                                    || "implement".to_string(), // FIXME: it might only need to be imported into scope, not implemented.
-                                    ToString::to_string,
-                                )
+                        err.subdiagnostic(
+                            self.dcx(),
+                            CandidateTraitNote {
+                                span: self.tcx.def_span(trait_info.def_id),
+                                trait_name: self.tcx.def_path_str(trait_info.def_id),
+                                item_name,
+                                action_or_ty: if trait_missing_method {
+                                    "NONE".to_string()
+                                } else {
+                                    param_type.map_or_else(
+                                        || "implement".to_string(), // FIXME: it might only need to be imported into scope, not implemented.
+                                        ToString::to_string,
+                                    )
+                                },
                             },
-                        });
+                        );
                     }
                 }
                 trait_infos => {
diff --git a/compiler/rustc_hir_typeck/src/op.rs b/compiler/rustc_hir_typeck/src/op.rs
index 9a8444e6a2bcd..929b3557f5242 100644
--- a/compiler/rustc_hir_typeck/src/op.rs
+++ b/compiler/rustc_hir_typeck/src/op.rs
@@ -824,7 +824,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         // If the previous expression was a block expression, suggest parentheses
                         // (turning this into a binary subtraction operation instead.)
                         // for example, `{2} - 2` -> `({2}) - 2` (see src\test\ui\parser\expr-as-stmt.rs)
-                        err.subdiagnostic(ExprParenthesesNeeded::surrounding(*sp));
+                        err.subdiagnostic(self.dcx(), ExprParenthesesNeeded::surrounding(*sp));
                     } else {
                         match actual.kind() {
                             Uint(_) if op == hir::UnOp::Neg => {
diff --git a/compiler/rustc_infer/src/infer/error_reporting/mod.rs b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
index 8f06a5eeb5f43..9bfaeb5ee32b6 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/mod.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
@@ -845,7 +845,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                         arm_ty,
                         arm_span,
                     ) {
-                        err.subdiagnostic(subdiag);
+                        err.subdiagnostic(self.dcx(), subdiag);
                     }
                     if let Some(ret_sp) = opt_suggest_box_span {
                         // Get return type span and point to it.
@@ -882,7 +882,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     else_ty,
                     else_span,
                 ) {
-                    err.subdiagnostic(subdiag);
+                    err.subdiagnostic(self.dcx(), subdiag);
                 }
                 // don't suggest wrapping either blocks in `if .. {} else {}`
                 let is_empty_arm = |id| {
diff --git a/compiler/rustc_infer/src/infer/error_reporting/note.rs b/compiler/rustc_infer/src/infer/error_reporting/note.rs
index 02200d6a4aaf5..50ac6235debc0 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/note.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/note.rs
@@ -342,7 +342,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                 trait_predicates: trait_predicates.join(", "),
             }
         };
-        err.subdiagnostic(suggestion);
+        err.subdiagnostic(self.dcx(), suggestion);
     }
 
     pub(super) fn report_placeholder_failure(
diff --git a/compiler/rustc_infer/src/infer/error_reporting/suggest.rs b/compiler/rustc_infer/src/infer/error_reporting/suggest.rs
index f49369c5a237c..15834c7841336 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/suggest.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/suggest.rs
@@ -84,7 +84,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             start_sp: return_sp.with_hi(return_sp.lo() + BytePos(4)),
             end_sp: return_sp.shrink_to_hi(),
         };
-        err.subdiagnostic(sugg);
+        err.subdiagnostic(self.dcx(), sugg);
 
         let mut starts = Vec::new();
         let mut ends = Vec::new();
@@ -93,7 +93,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             ends.push(span.shrink_to_hi());
         }
         let sugg = SuggestBoxingForReturnImplTrait::BoxReturnExpr { starts, ends };
-        err.subdiagnostic(sugg);
+        err.subdiagnostic(self.dcx(), sugg);
     }
 
     pub(super) fn suggest_tuple_pattern(
@@ -138,7 +138,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                             span_low: cause.span.shrink_to_lo(),
                             span_high: cause.span.shrink_to_hi(),
                         };
-                        diag.subdiagnostic(sugg);
+                        diag.subdiagnostic(self.dcx(), sugg);
                     }
                     _ => {
                         // More than one matching variant.
@@ -147,7 +147,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                             cause_span: cause.span,
                             compatible_variants,
                         };
-                        diag.subdiagnostic(sugg);
+                        diag.subdiagnostic(self.dcx(), sugg);
                     }
                 }
             }
@@ -219,9 +219,10 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             },
             (_, Some(ty)) if self.same_type_modulo_infer(exp_found.expected, ty) => {
                 // FIXME: Seems like we can't have a suggestion and a note with different spans in a single subdiagnostic
-                diag.subdiagnostic(ConsiderAddingAwait::FutureSugg {
-                    span: exp_span.shrink_to_hi(),
-                });
+                diag.subdiagnostic(
+                    self.dcx(),
+                    ConsiderAddingAwait::FutureSugg { span: exp_span.shrink_to_hi() },
+                );
                 Some(ConsiderAddingAwait::FutureSuggNote { span: exp_span })
             }
             (Some(ty), _) if self.same_type_modulo_infer(ty, exp_found.found) => match cause.code()
@@ -249,7 +250,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             _ => None,
         };
         if let Some(subdiag) = subdiag {
-            diag.subdiagnostic(subdiag);
+            diag.subdiagnostic(self.dcx(), subdiag);
         }
     }
 
@@ -285,7 +286,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                         } else {
                             return;
                         };
-                        diag.subdiagnostic(suggestion);
+                        diag.subdiagnostic(self.dcx(), suggestion);
                     }
                 }
             }
@@ -325,15 +326,15 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     (true, false) => FunctionPointerSuggestion::UseRef { span, fn_name },
                     (false, true) => FunctionPointerSuggestion::RemoveRef { span, fn_name },
                     (true, true) => {
-                        diag.subdiagnostic(FnItemsAreDistinct);
+                        diag.subdiagnostic(self.dcx(), FnItemsAreDistinct);
                         FunctionPointerSuggestion::CastRef { span, fn_name, sig: *sig }
                     }
                     (false, false) => {
-                        diag.subdiagnostic(FnItemsAreDistinct);
+                        diag.subdiagnostic(self.dcx(), FnItemsAreDistinct);
                         FunctionPointerSuggestion::Cast { span, fn_name, sig: *sig }
                     }
                 };
-                diag.subdiagnostic(sugg);
+                diag.subdiagnostic(self.dcx(), sugg);
             }
             (ty::FnDef(did1, args1), ty::FnDef(did2, args2)) => {
                 let expected_sig =
@@ -342,7 +343,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     &(self.normalize_fn_sig)(self.tcx.fn_sig(*did2).instantiate(self.tcx, args2));
 
                 if self.same_type_modulo_infer(*expected_sig, *found_sig) {
-                    diag.subdiagnostic(FnUniqTypes);
+                    diag.subdiagnostic(self.dcx(), FnUniqTypes);
                 }
 
                 if !self.same_type_modulo_infer(*found_sig, *expected_sig)
@@ -371,7 +372,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     }
                 };
 
-                diag.subdiagnostic(sug);
+                diag.subdiagnostic(self.dcx(), sug);
             }
             (ty::FnDef(did, args), ty::FnPtr(sig)) => {
                 let expected_sig =
@@ -390,7 +391,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     format!("{fn_name} as {found_sig}")
                 };
 
-                diag.subdiagnostic(FnConsiderCasting { casting });
+                diag.subdiagnostic(self.dcx(), FnConsiderCasting { casting });
             }
             _ => {
                 return;
@@ -822,7 +823,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         let diag = self.consider_returning_binding_diag(blk, expected_ty);
         match diag {
             Some(diag) => {
-                err.subdiagnostic(diag);
+                err.subdiagnostic(self.dcx(), diag);
                 true
             }
             None => false,
diff --git a/compiler/rustc_interface/src/queries.rs b/compiler/rustc_interface/src/queries.rs
index 2a4eefb7f771b..211bcb9da94db 100644
--- a/compiler/rustc_interface/src/queries.rs
+++ b/compiler/rustc_interface/src/queries.rs
@@ -259,7 +259,7 @@ pub struct Linker {
 impl Linker {
     pub fn link(self, sess: &Session, codegen_backend: &dyn CodegenBackend) -> Result<()> {
         let (codegen_results, work_products) =
-            codegen_backend.join_codegen(self.ongoing_codegen, sess, &self.output_filenames)?;
+            codegen_backend.join_codegen(self.ongoing_codegen, sess, &self.output_filenames);
 
         sess.compile_status()?;
 
diff --git a/compiler/rustc_lint/src/lints.rs b/compiler/rustc_lint/src/lints.rs
index da59ffebdc5a9..c204c67fc1f7c 100644
--- a/compiler/rustc_lint/src/lints.rs
+++ b/compiler/rustc_lint/src/lints.rs
@@ -1757,7 +1757,7 @@ impl<'a> DecorateLint<'a, ()> for UnusedDef<'_, '_> {
             diag.note(note.to_string());
         }
         if let Some(sugg) = self.suggestion {
-            diag.subdiagnostic(sugg);
+            diag.subdiagnostic(diag.dcx, sugg);
         }
     }
 
diff --git a/compiler/rustc_macros/src/diagnostics/diagnostic_builder.rs b/compiler/rustc_macros/src/diagnostics/diagnostic_builder.rs
index 85bb9584a0575..ae481efb263df 100644
--- a/compiler/rustc_macros/src/diagnostics/diagnostic_builder.rs
+++ b/compiler/rustc_macros/src/diagnostics/diagnostic_builder.rs
@@ -331,44 +331,7 @@ impl DiagnosticDeriveVariantBuilder {
                 }
             }
             (Meta::Path(_), "subdiagnostic") => {
-                if FieldInnerTy::from_type(&info.binding.ast().ty).will_iterate() {
-                    let DiagnosticDeriveKind::Diagnostic = self.kind else {
-                        // No eager translation for lints.
-                        return Ok(quote! { diag.subdiagnostic(#binding); });
-                    };
-                    return Ok(quote! { diag.eager_subdiagnostic(dcx, #binding); });
-                } else {
-                    return Ok(quote! { diag.subdiagnostic(#binding); });
-                }
-            }
-            (Meta::List(meta_list), "subdiagnostic") => {
-                let err = || {
-                    span_err(
-                        meta_list.span().unwrap(),
-                        "`eager` is the only supported nested attribute for `subdiagnostic`",
-                    )
-                    .emit();
-                };
-
-                let Ok(p): Result<Path, _> = meta_list.parse_args() else {
-                    err();
-                    return Ok(quote! {});
-                };
-
-                if !p.is_ident("eager") {
-                    err();
-                    return Ok(quote! {});
-                }
-
-                match &self.kind {
-                    DiagnosticDeriveKind::Diagnostic => {}
-                    DiagnosticDeriveKind::LintDiagnostic => {
-                        throw_invalid_attr!(attr, |diag| {
-                            diag.help("eager subdiagnostics are not supported on lints")
-                        })
-                    }
-                };
-                return Ok(quote! { diag.eager_subdiagnostic(dcx, #binding); });
+                return Ok(quote! { diag.subdiagnostic(diag.dcx, #binding); });
             }
             _ => (),
         }
diff --git a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
index 692f4511bb807..a0235f20a0570 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
@@ -1109,7 +1109,7 @@ fn report_non_exhaustive_match<'p, 'tcx>(
 
     let all_arms_have_guards = arms.iter().all(|arm_id| thir[*arm_id].guard.is_some());
     if !is_empty_match && all_arms_have_guards {
-        err.subdiagnostic(NonExhaustiveMatchAllArmsGuarded);
+        err.subdiagnostic(cx.tcx.dcx(), NonExhaustiveMatchAllArmsGuarded);
     }
     if let Some((span, sugg)) = suggestion {
         err.span_suggestion_verbose(span, msg, sugg, Applicability::HasPlaceholders);
diff --git a/compiler/rustc_mir_transform/src/errors.rs b/compiler/rustc_mir_transform/src/errors.rs
index 30de40e226c33..ff4918df9a262 100644
--- a/compiler/rustc_mir_transform/src/errors.rs
+++ b/compiler/rustc_mir_transform/src/errors.rs
@@ -270,7 +270,7 @@ impl<'a> DecorateLint<'a, ()> for MustNotSupend<'_, '_> {
     fn decorate_lint<'b>(self, diag: &'b mut rustc_errors::DiagnosticBuilder<'a, ()>) {
         diag.span_label(self.yield_sp, fluent::_subdiag::label);
         if let Some(reason) = self.reason {
-            diag.subdiagnostic(reason);
+            diag.subdiagnostic(diag.dcx, reason);
         }
         diag.span_help(self.src_sp, fluent::_subdiag::help);
         diag.arg("pre", self.pre);
diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index 69518287f38ec..ce0421ef62dd7 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -2350,7 +2350,7 @@ impl<'a> Parser<'a> {
         let mut err = self.dcx().struct_span_err(span, msg);
         let sp = self.sess.source_map().start_point(self.token.span);
         if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&sp) {
-            err.subdiagnostic(ExprParenthesesNeeded::surrounding(*sp));
+            err.subdiagnostic(self.dcx(), ExprParenthesesNeeded::surrounding(*sp));
         }
         err.span_label(span, "expected expression");
 
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index 2424b6c130d23..20b9581f2ef27 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -1433,7 +1433,7 @@ impl<'a> Parser<'a> {
                     // If the input is something like `if a { 1 } else { 2 } | if a { 3 } else { 4 }`
                     // then suggest parens around the lhs.
                     if let Some(sp) = this.sess.ambiguous_block_expr_parse.borrow().get(&lo) {
-                        err.subdiagnostic(ExprParenthesesNeeded::surrounding(*sp));
+                        err.subdiagnostic(this.dcx(), ExprParenthesesNeeded::surrounding(*sp));
                     }
                     err
                 })
diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index a0605b8a44c3a..e7b9076bd3c8f 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -1933,7 +1933,7 @@ impl<'a> Parser<'a> {
         if self.token.kind == token::Not {
             if let Err(mut err) = self.unexpected::<FieldDef>() {
                 // Encounter the macro invocation
-                err.subdiagnostic(MacroExpandsToAdtField { adt_ty });
+                err.subdiagnostic(self.dcx(), MacroExpandsToAdtField { adt_ty });
                 return Err(err);
             }
         }
@@ -2352,10 +2352,13 @@ impl<'a> Parser<'a> {
                             .into_iter()
                             .any(|s| self.prev_token.is_ident_named(s));
 
-                        err.subdiagnostic(errors::FnTraitMissingParen {
-                            span: self.prev_token.span,
-                            machine_applicable,
-                        });
+                        err.subdiagnostic(
+                            self.dcx(),
+                            errors::FnTraitMissingParen {
+                                span: self.prev_token.span,
+                                machine_applicable,
+                            },
+                        );
                     }
                     return Err(err);
                 }
diff --git a/compiler/rustc_parse/src/parser/pat.rs b/compiler/rustc_parse/src/parser/pat.rs
index 12260ec95a5b9..75fc013d3e6fe 100644
--- a/compiler/rustc_parse/src/parser/pat.rs
+++ b/compiler/rustc_parse/src/parser/pat.rs
@@ -843,7 +843,7 @@ impl<'a> Parser<'a> {
 
         let sp = self.sess.source_map().start_point(self.token.span);
         if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&sp) {
-            err.subdiagnostic(ExprParenthesesNeeded::surrounding(*sp));
+            err.subdiagnostic(self.dcx(), ExprParenthesesNeeded::surrounding(*sp));
         }
 
         Err(err)
diff --git a/compiler/rustc_resolve/src/diagnostics.rs b/compiler/rustc_resolve/src/diagnostics.rs
index d91a865e38aba..737481c78db68 100644
--- a/compiler/rustc_resolve/src/diagnostics.rs
+++ b/compiler/rustc_resolve/src/diagnostics.rs
@@ -403,9 +403,12 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
         }
 
         if let Some(suggestion) = suggestion {
-            err.subdiagnostic(ChangeImportBindingSuggestion { span: binding_span, suggestion });
+            err.subdiagnostic(
+                self.dcx(),
+                ChangeImportBindingSuggestion { span: binding_span, suggestion },
+            );
         } else {
-            err.subdiagnostic(ChangeImportBinding { span: binding_span });
+            err.subdiagnostic(self.dcx(), ChangeImportBinding { span: binding_span });
         }
     }
 
@@ -1430,17 +1433,17 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
         );
 
         if macro_kind == MacroKind::Bang && ident.name == sym::macro_rules {
-            err.subdiagnostic(MaybeMissingMacroRulesName { span: ident.span });
+            err.subdiagnostic(self.dcx(), MaybeMissingMacroRulesName { span: ident.span });
             return;
         }
 
         if macro_kind == MacroKind::Derive && (ident.name == sym::Send || ident.name == sym::Sync) {
-            err.subdiagnostic(ExplicitUnsafeTraits { span: ident.span, ident });
+            err.subdiagnostic(self.dcx(), ExplicitUnsafeTraits { span: ident.span, ident });
             return;
         }
 
         if self.macro_names.contains(&ident.normalize_to_macros_2_0()) {
-            err.subdiagnostic(AddedMacroUse);
+            err.subdiagnostic(self.dcx(), AddedMacroUse);
             return;
         }
 
@@ -1450,10 +1453,13 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
             let span = self.def_span(def_id);
             let source_map = self.tcx.sess.source_map();
             let head_span = source_map.guess_head_span(span);
-            err.subdiagnostic(ConsiderAddingADerive {
-                span: head_span.shrink_to_lo(),
-                suggestion: "#[derive(Default)]\n".to_string(),
-            });
+            err.subdiagnostic(
+                self.dcx(),
+                ConsiderAddingADerive {
+                    span: head_span.shrink_to_lo(),
+                    suggestion: "#[derive(Default)]\n".to_string(),
+                },
+            );
         }
         for ns in [Namespace::MacroNS, Namespace::TypeNS, Namespace::ValueNS] {
             if let Ok(binding) = self.early_resolve_ident_in_lexical_scope(
diff --git a/compiler/rustc_resolve/src/imports.rs b/compiler/rustc_resolve/src/imports.rs
index 30fb35238c3c7..dcd01b9b33417 100644
--- a/compiler/rustc_resolve/src/imports.rs
+++ b/compiler/rustc_resolve/src/imports.rs
@@ -1262,12 +1262,12 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                             // exclude decl_macro
                             if self.get_macro_by_def_id(def_id).macro_rules =>
                         {
-                            err.subdiagnostic(ConsiderAddingMacroExport {
+                            err.subdiagnostic(self.dcx(), ConsiderAddingMacroExport {
                                 span: binding.span,
                             });
                         }
                         _ => {
-                            err.subdiagnostic(ConsiderMarkingAsPub {
+                            err.subdiagnostic(self.dcx(), ConsiderMarkingAsPub {
                                 span: import.span,
                                 ident,
                             });
diff --git a/compiler/rustc_resolve/src/late/diagnostics.rs b/compiler/rustc_resolve/src/late/diagnostics.rs
index cb3b95a443416..f71f7ccecabb8 100644
--- a/compiler/rustc_resolve/src/late/diagnostics.rs
+++ b/compiler/rustc_resolve/src/late/diagnostics.rs
@@ -1111,11 +1111,14 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                 Side::Start => (segment.ident.span.between(range.span), " @ ".into()),
                 Side::End => (range.span.to(segment.ident.span), format!("{} @ ..", segment.ident)),
             };
-            err.subdiagnostic(errors::UnexpectedResUseAtOpInSlicePatWithRangeSugg {
-                span,
-                ident: segment.ident,
-                snippet,
-            });
+            err.subdiagnostic(
+                self.r.dcx(),
+                errors::UnexpectedResUseAtOpInSlicePatWithRangeSugg {
+                    span,
+                    ident: segment.ident,
+                    snippet,
+                },
+            );
         }
 
         enum Side {
@@ -1207,10 +1210,13 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
         });
 
         if let Some(param) = param {
-            err.subdiagnostic(errors::UnexpectedResChangeTyToConstParamSugg {
-                span: param.shrink_to_lo(),
-                applicability,
-            });
+            err.subdiagnostic(
+                self.r.dcx(),
+                errors::UnexpectedResChangeTyToConstParamSugg {
+                    span: param.shrink_to_lo(),
+                    applicability,
+                },
+            );
         }
     }
 
diff --git a/compiler/rustc_session/src/parse.rs b/compiler/rustc_session/src/parse.rs
index 288e0a5ca6f30..701c5bf375f6e 100644
--- a/compiler/rustc_session/src/parse.rs
+++ b/compiler/rustc_session/src/parse.rs
@@ -173,21 +173,21 @@ pub fn add_feature_diagnostics_for_issue(
     feature_from_cli: bool,
 ) {
     if let Some(n) = find_feature_issue(feature, issue) {
-        err.subdiagnostic(FeatureDiagnosticForIssue { n });
+        err.subdiagnostic(sess.dcx(), FeatureDiagnosticForIssue { n });
     }
 
     // #23973: do not suggest `#![feature(...)]` if we are in beta/stable
     if sess.parse_sess.unstable_features.is_nightly_build() {
         if feature_from_cli {
-            err.subdiagnostic(CliFeatureDiagnosticHelp { feature });
+            err.subdiagnostic(sess.dcx(), CliFeatureDiagnosticHelp { feature });
         } else {
-            err.subdiagnostic(FeatureDiagnosticHelp { feature });
+            err.subdiagnostic(sess.dcx(), FeatureDiagnosticHelp { feature });
         }
 
         if sess.opts.unstable_opts.ui_testing {
-            err.subdiagnostic(SuggestUpgradeCompiler::ui_testing());
+            err.subdiagnostic(sess.dcx(), SuggestUpgradeCompiler::ui_testing());
         } else if let Some(suggestion) = SuggestUpgradeCompiler::new() {
-            err.subdiagnostic(suggestion);
+            err.subdiagnostic(sess.dcx(), suggestion);
         }
     }
 }
diff --git a/compiler/rustc_target/src/spec/base/apple/mod.rs b/compiler/rustc_target/src/spec/base/apple/mod.rs
index afd60b40c3be1..aee5d60626e31 100644
--- a/compiler/rustc_target/src/spec/base/apple/mod.rs
+++ b/compiler/rustc_target/src/spec/base/apple/mod.rs
@@ -17,6 +17,7 @@ pub enum Arch {
     Arm64e,
     Arm64_32,
     I386,
+    I386_sim,
     I686,
     X86_64,
     X86_64h,
@@ -34,7 +35,7 @@ impl Arch {
             Arm64 | Arm64_macabi | Arm64_sim => "arm64",
             Arm64e => "arm64e",
             Arm64_32 => "arm64_32",
-            I386 => "i386",
+            I386 | I386_sim => "i386",
             I686 => "i686",
             X86_64 | X86_64_sim | X86_64_macabi => "x86_64",
             X86_64h => "x86_64h",
@@ -45,7 +46,7 @@ impl Arch {
         Cow::Borrowed(match self {
             Armv7k | Armv7s => "arm",
             Arm64 | Arm64e | Arm64_32 | Arm64_macabi | Arm64_sim => "aarch64",
-            I386 | I686 => "x86",
+            I386 | I386_sim | I686 => "x86",
             X86_64 | X86_64_sim | X86_64_macabi | X86_64h => "x86_64",
         })
     }
@@ -54,9 +55,7 @@ impl Arch {
         match self {
             Armv7k | Armv7s | Arm64 | Arm64e | Arm64_32 | I386 | I686 | X86_64 | X86_64h => "",
             X86_64_macabi | Arm64_macabi => "macabi",
-            // x86_64-apple-ios is a simulator target, even though it isn't
-            // declared that way in the target like the other ones...
-            Arm64_sim | X86_64_sim => "sim",
+            I386_sim | Arm64_sim | X86_64_sim => "sim",
         }
     }
 
@@ -70,7 +69,7 @@ impl Arch {
             // Only macOS 10.12+ is supported, which means
             // all x86_64/x86 CPUs must be running at least penryn
             // https://github.com/llvm/llvm-project/blob/01f924d0e37a5deae51df0d77e10a15b63aa0c0f/clang/lib/Driver/ToolChains/Arch/X86.cpp#L79-L82
-            I386 | I686 => "penryn",
+            I386 | I386_sim | I686 => "penryn",
             X86_64 | X86_64_sim => "penryn",
             X86_64_macabi => "penryn",
             // Note: `core-avx2` is slightly more advanced than `x86_64h`, see
@@ -85,7 +84,7 @@ impl Arch {
     fn stack_probes(self) -> StackProbeType {
         match self {
             Armv7k | Armv7s => StackProbeType::None,
-            Arm64 | Arm64e | Arm64_32 | I386 | I686 | X86_64 | X86_64h | X86_64_sim
+            Arm64 | Arm64e | Arm64_32 | I386 | I386_sim | I686 | X86_64 | X86_64h | X86_64_sim
             | X86_64_macabi | Arm64_macabi | Arm64_sim => StackProbeType::Inline,
         }
     }
@@ -302,8 +301,8 @@ fn link_env_remove(arch: Arch, os: &'static str) -> StaticCow<[StaticCow<str>]>
         // Otherwise if cross-compiling for a different OS/SDK, remove any part
         // of the linking environment that's wrong and reversed.
         match arch {
-            Armv7k | Armv7s | Arm64 | Arm64e | Arm64_32 | I386 | I686 | X86_64 | X86_64_sim
-            | X86_64h | Arm64_sim => {
+            Armv7k | Armv7s | Arm64 | Arm64e | Arm64_32 | I386 | I386_sim | I686 | X86_64
+            | X86_64_sim | X86_64h | Arm64_sim => {
                 cvs!["MACOSX_DEPLOYMENT_TARGET"]
             }
             X86_64_macabi | Arm64_macabi => cvs!["IPHONEOS_DEPLOYMENT_TARGET"],
diff --git a/compiler/rustc_target/src/spec/targets/i386_apple_ios.rs b/compiler/rustc_target/src/spec/targets/i386_apple_ios.rs
index a221538b9022f..d78acdbd1aad5 100644
--- a/compiler/rustc_target/src/spec/targets/i386_apple_ios.rs
+++ b/compiler/rustc_target/src/spec/targets/i386_apple_ios.rs
@@ -2,7 +2,9 @@ use crate::spec::base::apple::{ios_sim_llvm_target, opts, Arch};
 use crate::spec::{Target, TargetOptions};
 
 pub fn target() -> Target {
-    let arch = Arch::I386;
+    // i386-apple-ios is a simulator target, even though it isn't declared
+    // that way in the target name like the other ones...
+    let arch = Arch::I386_sim;
     Target {
         // Clang automatically chooses a more specific target based on
         // IPHONEOS_DEPLOYMENT_TARGET.
diff --git a/compiler/rustc_target/src/spec/targets/x86_64_apple_ios.rs b/compiler/rustc_target/src/spec/targets/x86_64_apple_ios.rs
index 55165ea4ec68c..5b34390141e0e 100644
--- a/compiler/rustc_target/src/spec/targets/x86_64_apple_ios.rs
+++ b/compiler/rustc_target/src/spec/targets/x86_64_apple_ios.rs
@@ -2,6 +2,8 @@ use crate::spec::base::apple::{ios_sim_llvm_target, opts, Arch};
 use crate::spec::{SanitizerSet, Target, TargetOptions};
 
 pub fn target() -> Target {
+    // x86_64-apple-ios is a simulator target, even though it isn't declared
+    // that way in the target name like the other ones...
     let arch = Arch::X86_64_sim;
     let mut base = opts("ios", arch);
     base.supported_sanitizers = SanitizerSet::ADDRESS | SanitizerSet::THREAD;
diff --git a/compiler/rustc_target/src/spec/targets/x86_64_apple_tvos.rs b/compiler/rustc_target/src/spec/targets/x86_64_apple_tvos.rs
index 20b0161255314..95033699f1af3 100644
--- a/compiler/rustc_target/src/spec/targets/x86_64_apple_tvos.rs
+++ b/compiler/rustc_target/src/spec/targets/x86_64_apple_tvos.rs
@@ -2,6 +2,8 @@ use crate::spec::base::apple::{opts, tvos_sim_llvm_target, Arch};
 use crate::spec::{Target, TargetOptions};
 
 pub fn target() -> Target {
+    // x86_64-apple-tvos is a simulator target, even though it isn't declared
+    // that way in the target name like the other ones...
     let arch = Arch::X86_64_sim;
     Target {
         llvm_target: tvos_sim_llvm_target(arch).into(),
diff --git a/compiler/rustc_trait_selection/src/solve/inspect/analyse.rs b/compiler/rustc_trait_selection/src/solve/inspect/analyse.rs
index 47f207e1d75c1..c5d4ce33d8617 100644
--- a/compiler/rustc_trait_selection/src/solve/inspect/analyse.rs
+++ b/compiler/rustc_trait_selection/src/solve/inspect/analyse.rs
@@ -223,8 +223,10 @@ impl<'tcx> InferCtxt<'tcx> {
         goal: Goal<'tcx, ty::Predicate<'tcx>>,
         visitor: &mut V,
     ) -> ControlFlow<V::BreakTy> {
-        let (_, proof_tree) = self.evaluate_root_goal(goal, GenerateProofTree::Yes);
-        let proof_tree = proof_tree.unwrap();
-        visitor.visit_goal(&InspectGoal::new(self, 0, &proof_tree))
+        self.probe(|_| {
+            let (_, proof_tree) = self.evaluate_root_goal(goal, GenerateProofTree::Yes);
+            let proof_tree = proof_tree.unwrap();
+            visitor.visit_goal(&InspectGoal::new(self, 0, &proof_tree))
+        })
     }
 }
diff --git a/compiler/rustc_trait_selection/src/traits/coherence.rs b/compiler/rustc_trait_selection/src/traits/coherence.rs
index e48bd437f59c5..f663f02f87289 100644
--- a/compiler/rustc_trait_selection/src/traits/coherence.rs
+++ b/compiler/rustc_trait_selection/src/traits/coherence.rs
@@ -8,23 +8,21 @@ use crate::infer::outlives::env::OutlivesEnvironment;
 use crate::infer::InferOk;
 use crate::regions::InferCtxtRegionExt;
 use crate::solve::inspect::{InspectGoal, ProofTreeInferCtxtExt, ProofTreeVisitor};
-use crate::solve::{deeply_normalize_for_diagnostics, inspect};
-use crate::traits::engine::TraitEngineExt;
-use crate::traits::query::evaluate_obligation::InferCtxtExt;
+use crate::solve::{deeply_normalize_for_diagnostics, inspect, FulfillmentCtxt};
+use crate::traits::engine::TraitEngineExt as _;
 use crate::traits::select::IntercrateAmbiguityCause;
 use crate::traits::structural_normalize::StructurallyNormalizeExt;
 use crate::traits::NormalizeExt;
 use crate::traits::SkipLeakCheck;
 use crate::traits::{
-    Obligation, ObligationCause, ObligationCtxt, PredicateObligation, PredicateObligations,
-    SelectionContext,
+    Obligation, ObligationCause, PredicateObligation, PredicateObligations, SelectionContext,
 };
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_errors::Diagnostic;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
 use rustc_infer::infer::{DefineOpaqueTypes, InferCtxt, TyCtxtInferExt};
-use rustc_infer::traits::{util, TraitEngine};
+use rustc_infer::traits::{util, TraitEngine, TraitEngineExt};
 use rustc_middle::traits::query::NoSolution;
 use rustc_middle::traits::solve::{CandidateSource, Certainty, Goal};
 use rustc_middle::traits::specialization_graph::OverlapMode;
@@ -310,29 +308,35 @@ fn equate_impl_headers<'tcx>(
 fn impl_intersection_has_impossible_obligation<'a, 'cx, 'tcx>(
     selcx: &mut SelectionContext<'cx, 'tcx>,
     obligations: &'a [PredicateObligation<'tcx>],
-) -> Option<&'a PredicateObligation<'tcx>> {
+) -> Option<PredicateObligation<'tcx>> {
     let infcx = selcx.infcx;
 
-    obligations.iter().find(|obligation| {
-        let evaluation_result = if infcx.next_trait_solver() {
-            infcx.evaluate_obligation(obligation)
-        } else {
+    if infcx.next_trait_solver() {
+        let mut fulfill_cx = FulfillmentCtxt::new(infcx);
+        fulfill_cx.register_predicate_obligations(infcx, obligations.iter().cloned());
+
+        // We only care about the obligations that are *definitely* true errors.
+        // Ambiguities do not prove the disjointness of two impls.
+        let mut errors = fulfill_cx.select_where_possible(infcx);
+        errors.pop().map(|err| err.obligation)
+    } else {
+        obligations.iter().cloned().find(|obligation| {
             // We use `evaluate_root_obligation` to correctly track intercrate
             // ambiguity clauses. We cannot use this in the new solver.
-            selcx.evaluate_root_obligation(obligation)
-        };
-
-        match evaluation_result {
-            Ok(result) => !result.may_apply(),
-            // If overflow occurs, we need to conservatively treat the goal as possibly holding,
-            // since there can be instantiations of this goal that don't overflow and result in
-            // success. This isn't much of a problem in the old solver, since we treat overflow
-            // fatally (this still can be encountered: <https://github.com/rust-lang/rust/issues/105231>),
-            // but in the new solver, this is very important for correctness, since overflow
-            // *must* be treated as ambiguity for completeness.
-            Err(_overflow) => false,
-        }
-    })
+            let evaluation_result = selcx.evaluate_root_obligation(obligation);
+
+            match evaluation_result {
+                Ok(result) => !result.may_apply(),
+                // If overflow occurs, we need to conservatively treat the goal as possibly holding,
+                // since there can be instantiations of this goal that don't overflow and result in
+                // success. This isn't much of a problem in the old solver, since we treat overflow
+                // fatally (this still can be encountered: <https://github.com/rust-lang/rust/issues/105231>),
+                // but in the new solver, this is very important for correctness, since overflow
+                // *must* be treated as ambiguity for completeness.
+                Err(_overflow) => false,
+            }
+        })
+    }
 }
 
 /// Check if both impls can be satisfied by a common type by considering whether
@@ -522,15 +526,13 @@ fn try_prove_negated_where_clause<'tcx>(
     // Without this, we over-eagerly register coherence ambiguity candidates when
     // impl candidates do exist.
     let ref infcx = root_infcx.fork_with_intercrate(false);
-    let ocx = ObligationCtxt::new(infcx);
-
-    ocx.register_obligation(Obligation::new(
-        infcx.tcx,
-        ObligationCause::dummy(),
-        param_env,
-        negative_predicate,
-    ));
-    if !ocx.select_all_or_error().is_empty() {
+    let mut fulfill_cx = FulfillmentCtxt::new(infcx);
+
+    fulfill_cx.register_predicate_obligation(
+        infcx,
+        Obligation::new(infcx.tcx, ObligationCause::dummy(), param_env, negative_predicate),
+    );
+    if !fulfill_cx.select_all_or_error(infcx).is_empty() {
         return false;
     }
 
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
index 7de13bf0c0299..0472981086e84 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
@@ -4558,11 +4558,14 @@ fn hint_missing_borrow<'tcx>(
     }
 
     if !to_borrow.is_empty() {
-        err.subdiagnostic(errors::AdjustSignatureBorrow::Borrow { to_borrow });
+        err.subdiagnostic(infcx.dcx(), errors::AdjustSignatureBorrow::Borrow { to_borrow });
     }
 
     if !remove_borrow.is_empty() {
-        err.subdiagnostic(errors::AdjustSignatureBorrow::RemoveBorrow { remove_borrow });
+        err.subdiagnostic(
+            infcx.dcx(),
+            errors::AdjustSignatureBorrow::RemoveBorrow { remove_borrow },
+        );
     }
 }
 
diff --git a/library/alloc/src/vec/into_iter.rs b/library/alloc/src/vec/into_iter.rs
index 63d8fe19ac35c..dfd42ca06193a 100644
--- a/library/alloc/src/vec/into_iter.rs
+++ b/library/alloc/src/vec/into_iter.rs
@@ -11,7 +11,7 @@ use core::iter::{
     TrustedRandomAccessNoCoerce,
 };
 use core::marker::PhantomData;
-use core::mem::{self, ManuallyDrop, MaybeUninit, SizedTypeProperties};
+use core::mem::{ManuallyDrop, MaybeUninit, SizedTypeProperties};
 use core::num::NonZero;
 #[cfg(not(no_global_oom_handling))]
 use core::ops::Deref;
@@ -200,27 +200,23 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
 
     #[inline]
     fn next(&mut self) -> Option<T> {
-        if T::IS_ZST {
-            if self.ptr.as_ptr() == self.end as *mut _ {
-                None
-            } else {
-                // `ptr` has to stay where it is to remain aligned, so we reduce the length by 1 by
-                // reducing the `end`.
-                self.end = self.end.wrapping_byte_sub(1);
-
-                // Make up a value of this ZST.
-                Some(unsafe { mem::zeroed() })
+        let ptr = if T::IS_ZST {
+            if self.ptr.as_ptr() == self.end as *mut T {
+                return None;
             }
+            // `ptr` has to stay where it is to remain aligned, so we reduce the length by 1 by
+            // reducing the `end`.
+            self.end = self.end.wrapping_byte_sub(1);
+            self.ptr
         } else {
             if self.ptr == non_null!(self.end, T) {
-                None
-            } else {
-                let old = self.ptr;
-                self.ptr = unsafe { old.add(1) };
-
-                Some(unsafe { ptr::read(old.as_ptr()) })
+                return None;
             }
-        }
+            let old = self.ptr;
+            self.ptr = unsafe { old.add(1) };
+            old
+        };
+        Some(unsafe { ptr.read() })
     }
 
     #[inline]
@@ -305,7 +301,7 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
         // Also note the implementation of `Self: TrustedRandomAccess` requires
         // that `T: Copy` so reading elements from the buffer doesn't invalidate
         // them for `Drop`.
-        unsafe { if T::IS_ZST { mem::zeroed() } else { self.ptr.add(i).read() } }
+        unsafe { self.ptr.add(i).read() }
     }
 }
 
@@ -314,23 +310,22 @@ impl<T, A: Allocator> DoubleEndedIterator for IntoIter<T, A> {
     #[inline]
     fn next_back(&mut self) -> Option<T> {
         if T::IS_ZST {
-            if self.end as *mut _ == self.ptr.as_ptr() {
-                None
-            } else {
-                // See above for why 'ptr.offset' isn't used
-                self.end = self.end.wrapping_byte_sub(1);
-
-                // Make up a value of this ZST.
-                Some(unsafe { mem::zeroed() })
+            if self.ptr.as_ptr() == self.end as *mut _ {
+                return None;
             }
+            // See above for why 'ptr.offset' isn't used
+            self.end = self.end.wrapping_byte_sub(1);
+            // Note that even though this is next_back() we're reading from `self.ptr`, not
+            // `self.end`. We track our length using the byte offset from `self.ptr` to `self.end`,
+            // so the end pointer may not be suitably aligned for T.
+            Some(unsafe { ptr::read(self.ptr.as_ptr()) })
         } else {
-            if non_null!(self.end, T) == self.ptr {
-                None
-            } else {
-                let new_end = unsafe { non_null!(self.end, T).sub(1) };
-                *non_null!(mut self.end, T) = new_end;
-
-                Some(unsafe { ptr::read(new_end.as_ptr()) })
+            if self.ptr == non_null!(self.end, T) {
+                return None;
+            }
+            unsafe {
+                self.end = self.end.sub(1);
+                Some(ptr::read(self.end))
             }
         }
     }
diff --git a/src/bootstrap/src/core/build_steps/dist.rs b/src/bootstrap/src/core/build_steps/dist.rs
index 6d56492e41b56..d43acf6f299dd 100644
--- a/src/bootstrap/src/core/build_steps/dist.rs
+++ b/src/bootstrap/src/core/build_steps/dist.rs
@@ -398,10 +398,11 @@ impl Step for Rustc {
             let host = compiler.host;
             let src = builder.sysroot(compiler);
 
-            // Copy rustc/rustdoc binaries
+            // Copy rustc binary
+            builder.install(&src.join("bin").join("rustc"), &image.join("bin"), 0o755);
             t!(fs::create_dir_all(image.join("bin")));
-            builder.cp_r(&src.join("bin"), &image.join("bin"));
 
+            // If enabled, copy rustdoc binary
             if builder
                 .config
                 .tools
diff --git a/src/bootstrap/src/core/build_steps/install.rs b/src/bootstrap/src/core/build_steps/install.rs
index 1c565e7f7cc06..0225f8f24a5ef 100644
--- a/src/bootstrap/src/core/build_steps/install.rs
+++ b/src/bootstrap/src/core/build_steps/install.rs
@@ -95,7 +95,7 @@ fn install_sh(
     }
 
     let datadir = prefix.join(default_path(&builder.config.datadir, "share"));
-    let docdir = prefix.join(default_path(&builder.config.docdir, "share/doc/rust"));
+    let docdir = prefix.join(default_path(&builder.config.docdir, &format!("share/doc/{package}")));
     let mandir = prefix.join(default_path(&builder.config.mandir, "share/man"));
     let libdir = prefix.join(default_path(&builder.config.libdir, "lib"));
     let bindir = prefix.join(&builder.config.bindir); // Default in config.rs
diff --git a/src/bootstrap/src/core/config/tests.rs b/src/bootstrap/src/core/config/tests.rs
index 0ae466eca7d7c..6ac573c68df18 100644
--- a/src/bootstrap/src/core/config/tests.rs
+++ b/src/bootstrap/src/core/config/tests.rs
@@ -11,9 +11,15 @@ use std::{
 };
 
 fn parse(config: &str) -> Config {
-    Config::parse_inner(&["check".to_owned(), "--config=/does/not/exist".to_owned()], |&_| {
-        toml::from_str(config).unwrap()
-    })
+    let config = format!("{config} \r\n build.rustc = \"/does-not-exists\" ");
+    Config::parse_inner(
+        &[
+            "check".to_owned(),
+            "--config=/does/not/exist".to_owned(),
+            "--skip-stage0-validation".to_owned(),
+        ],
+        |&_| toml::from_str(&config).unwrap(),
+    )
 }
 
 #[test]
diff --git a/src/bootstrap/src/core/download.rs b/src/bootstrap/src/core/download.rs
index e63d60feff125..b4ae3578ce317 100644
--- a/src/bootstrap/src/core/download.rs
+++ b/src/bootstrap/src/core/download.rs
@@ -399,6 +399,7 @@ impl Config {
             self.fix_bin_or_dylib(&cargo_clippy.with_file_name(exe("clippy-driver", host)));
         }
 
+        self.create(&clippy_stamp, date);
         cargo_clippy
     }
 
diff --git a/src/tools/miri/src/diagnostics.rs b/src/tools/miri/src/diagnostics.rs
index 19b29a4181984..d7d357657f6c9 100644
--- a/src/tools/miri/src/diagnostics.rs
+++ b/src/tools/miri/src/diagnostics.rs
@@ -504,7 +504,7 @@ pub fn report_msg<'tcx>(
         let is_local = machine.is_local(frame_info);
         // No span for non-local frames and the first frame (which is the error site).
         if is_local && idx > 0 {
-            err.eager_subdiagnostic(err.dcx, frame_info.as_note(machine.tcx));
+            err.subdiagnostic(err.dcx, frame_info.as_note(machine.tcx));
         } else {
             let sm = sess.source_map();
             let span = sm.span_to_embeddable_string(frame_info.span);
diff --git a/src/tools/rustfmt/src/parse/session.rs b/src/tools/rustfmt/src/parse/session.rs
index f0af401d3da4b..cff025cf2ab3a 100644
--- a/src/tools/rustfmt/src/parse/session.rs
+++ b/src/tools/rustfmt/src/parse/session.rs
@@ -1,3 +1,4 @@
+use std::borrow::Cow;
 use std::path::Path;
 use std::sync::atomic::{AtomicBool, Ordering};
 
@@ -40,6 +41,16 @@ impl Translate for SilentEmitter {
     fn fallback_fluent_bundle(&self) -> &rustc_errors::FluentBundle {
         panic!("silent emitter attempted to translate a diagnostic");
     }
+
+    // Override `translate_message` for the silent emitter because eager translation of
+    // subdiagnostics result in a call to this.
+    fn translate_message<'a>(
+        &'a self,
+        message: &'a rustc_errors::DiagnosticMessage,
+        _: &'a rustc_errors::translation::FluentArgs<'_>,
+    ) -> Result<Cow<'_, str>, rustc_errors::error::TranslateError<'_>> {
+        rustc_errors::emitter::silent_translate(message)
+    }
 }
 
 impl Emitter for SilentEmitter {
diff --git a/tests/codegen/vec-iter.rs b/tests/codegen/vec-iter.rs
index 0282791e9d169..4e2068587510c 100644
--- a/tests/codegen/vec-iter.rs
+++ b/tests/codegen/vec-iter.rs
@@ -32,9 +32,9 @@ pub fn vec_iter_is_empty_nonnull(it: &vec::IntoIter<u8>) -> bool {
     it.is_empty()
 }
 
-// CHECK-LABEL: @vec_iter_next
+// CHECK-LABEL: @vec_iter_next_nonnull
 #[no_mangle]
-pub fn vec_iter_next(it: &mut vec::IntoIter<u8>) -> Option<u8> {
+pub fn vec_iter_next_nonnull(it: &mut vec::IntoIter<u8>) -> Option<u8> {
     // CHECK: load ptr
     // CHECK-SAME: !nonnull
     // CHECK-SAME: !noundef
@@ -44,3 +44,16 @@ pub fn vec_iter_next(it: &mut vec::IntoIter<u8>) -> Option<u8> {
     // CHECK: ret
     it.next()
 }
+
+// CHECK-LABEL: @vec_iter_next_back_nonnull
+#[no_mangle]
+pub fn vec_iter_next_back_nonnull(it: &mut vec::IntoIter<u8>) -> Option<u8> {
+    // CHECK: load ptr
+    // CHECK-SAME: !nonnull
+    // CHECK-SAME: !noundef
+    // CHECK: load ptr
+    // CHECK-SAME: !nonnull
+    // CHECK-SAME: !noundef
+    // CHECK: ret
+    it.next_back()
+}
diff --git a/tests/run-make-fulldeps/hotplug_codegen_backend/the_backend.rs b/tests/run-make-fulldeps/hotplug_codegen_backend/the_backend.rs
index 9e0a7ba63d05f..28a1e27cccccd 100644
--- a/tests/run-make-fulldeps/hotplug_codegen_backend/the_backend.rs
+++ b/tests/run-make-fulldeps/hotplug_codegen_backend/the_backend.rs
@@ -49,11 +49,11 @@ impl CodegenBackend for TheBackend {
         ongoing_codegen: Box<dyn Any>,
         _sess: &Session,
         _outputs: &OutputFilenames,
-    ) -> Result<(CodegenResults, FxIndexMap<WorkProductId, WorkProduct>), ErrorGuaranteed> {
+    ) -> (CodegenResults, FxIndexMap<WorkProductId, WorkProduct>) {
         let codegen_results = ongoing_codegen
             .downcast::<CodegenResults>()
             .expect("in join_codegen: ongoing_codegen is not a CodegenResults");
-        Ok((*codegen_results, FxIndexMap::default()))
+        (*codegen_results, FxIndexMap::default())
     }
 
     fn link(
diff --git a/tests/ui-fulldeps/session-diagnostic/diagnostic-derive.rs b/tests/ui-fulldeps/session-diagnostic/diagnostic-derive.rs
index d3cfd28082d61..6cc6fdfc0eb2b 100644
--- a/tests/ui-fulldeps/session-diagnostic/diagnostic-derive.rs
+++ b/tests/ui-fulldeps/session-diagnostic/diagnostic-derive.rs
@@ -701,7 +701,7 @@ struct RawIdentDiagnosticArg {
 #[diag(no_crate_example)]
 struct SubdiagnosticBad {
     #[subdiagnostic(bad)]
-    //~^ ERROR `eager` is the only supported nested attribute for `subdiagnostic`
+    //~^ ERROR `#[subdiagnostic(...)]` is not a valid attribute
     note: Note,
 }
 
@@ -717,7 +717,7 @@ struct SubdiagnosticBadStr {
 #[diag(no_crate_example)]
 struct SubdiagnosticBadTwice {
     #[subdiagnostic(bad, bad)]
-    //~^ ERROR `eager` is the only supported nested attribute for `subdiagnostic`
+    //~^ ERROR `#[subdiagnostic(...)]` is not a valid attribute
     note: Note,
 }
 
@@ -725,7 +725,7 @@ struct SubdiagnosticBadTwice {
 #[diag(no_crate_example)]
 struct SubdiagnosticBadLitStr {
     #[subdiagnostic("bad")]
-    //~^ ERROR `eager` is the only supported nested attribute for `subdiagnostic`
+    //~^ ERROR `#[subdiagnostic(...)]` is not a valid attribute
     note: Note,
 }
 
@@ -739,8 +739,9 @@ struct SubdiagnosticEagerLint {
 
 #[derive(Diagnostic)]
 #[diag(no_crate_example)]
-struct SubdiagnosticEagerCorrect {
+struct SubdiagnosticEagerFormerlyCorrect {
     #[subdiagnostic(eager)]
+    //~^ ERROR `#[subdiagnostic(...)]` is not a valid attribute
     note: Note,
 }
 
@@ -761,6 +762,7 @@ pub(crate) struct SubdiagnosticWithSuggestion {
 #[diag(no_crate_example)]
 struct SubdiagnosticEagerSuggestion {
     #[subdiagnostic(eager)]
+    //~^ ERROR `#[subdiagnostic(...)]` is not a valid attribute
     sub: SubdiagnosticWithSuggestion,
 }
 
diff --git a/tests/ui-fulldeps/session-diagnostic/diagnostic-derive.stderr b/tests/ui-fulldeps/session-diagnostic/diagnostic-derive.stderr
index 2032b8a972a3b..f2dbc718c7627 100644
--- a/tests/ui-fulldeps/session-diagnostic/diagnostic-derive.stderr
+++ b/tests/ui-fulldeps/session-diagnostic/diagnostic-derive.stderr
@@ -468,11 +468,11 @@ LL | #[label]
    |
    = help: `#[label]` and `#[suggestion]` can only be applied to fields
 
-error: `eager` is the only supported nested attribute for `subdiagnostic`
-  --> $DIR/diagnostic-derive.rs:703:7
+error: `#[subdiagnostic(...)]` is not a valid attribute
+  --> $DIR/diagnostic-derive.rs:703:5
    |
 LL |     #[subdiagnostic(bad)]
-   |       ^^^^^^^^^^^^^
+   |     ^
 
 error: `#[subdiagnostic = ...]` is not a valid attribute
   --> $DIR/diagnostic-derive.rs:711:5
@@ -480,40 +480,50 @@ error: `#[subdiagnostic = ...]` is not a valid attribute
 LL |     #[subdiagnostic = "bad"]
    |     ^
 
-error: `eager` is the only supported nested attribute for `subdiagnostic`
-  --> $DIR/diagnostic-derive.rs:719:7
+error: `#[subdiagnostic(...)]` is not a valid attribute
+  --> $DIR/diagnostic-derive.rs:719:5
    |
 LL |     #[subdiagnostic(bad, bad)]
-   |       ^^^^^^^^^^^^^
+   |     ^
 
-error: `eager` is the only supported nested attribute for `subdiagnostic`
-  --> $DIR/diagnostic-derive.rs:727:7
+error: `#[subdiagnostic(...)]` is not a valid attribute
+  --> $DIR/diagnostic-derive.rs:727:5
    |
 LL |     #[subdiagnostic("bad")]
-   |       ^^^^^^^^^^^^^
+   |     ^
 
 error: `#[subdiagnostic(...)]` is not a valid attribute
   --> $DIR/diagnostic-derive.rs:735:5
    |
 LL |     #[subdiagnostic(eager)]
    |     ^
+
+error: `#[subdiagnostic(...)]` is not a valid attribute
+  --> $DIR/diagnostic-derive.rs:743:5
    |
-   = help: eager subdiagnostics are not supported on lints
+LL |     #[subdiagnostic(eager)]
+   |     ^
+
+error: `#[subdiagnostic(...)]` is not a valid attribute
+  --> $DIR/diagnostic-derive.rs:764:5
+   |
+LL |     #[subdiagnostic(eager)]
+   |     ^
 
 error: expected at least one string literal for `code(...)`
-  --> $DIR/diagnostic-derive.rs:793:23
+  --> $DIR/diagnostic-derive.rs:795:23
    |
 LL |     #[suggestion(code())]
    |                       ^
 
 error: `code(...)` must contain only string literals
-  --> $DIR/diagnostic-derive.rs:801:23
+  --> $DIR/diagnostic-derive.rs:803:23
    |
 LL |     #[suggestion(code(foo))]
    |                       ^^^
 
 error: `#[suggestion(...)]` is not a valid attribute
-  --> $DIR/diagnostic-derive.rs:825:5
+  --> $DIR/diagnostic-derive.rs:827:5
    |
 LL |     #[suggestion(no_crate_suggestion, code = "")]
    |     ^
@@ -529,13 +539,13 @@ LL | #[diag = "E0123"]
    |        ^ maybe a missing crate `core`?
 
 error[E0433]: failed to resolve: maybe a missing crate `core`?
-  --> $DIR/diagnostic-derive.rs:801:23
+  --> $DIR/diagnostic-derive.rs:803:23
    |
 LL |     #[suggestion(code(foo))]
    |                       ^^^ maybe a missing crate `core`?
 
 error[E0433]: failed to resolve: maybe a missing crate `core`?
-  --> $DIR/diagnostic-derive.rs:810:25
+  --> $DIR/diagnostic-derive.rs:812:25
    |
 LL |     #[suggestion(code = 3)]
    |                         ^ maybe a missing crate `core`?
@@ -601,7 +611,7 @@ LL | #[diag(nonsense, code = E0123)]
    |        ^^^^^^^^ not found in `crate::fluent_generated`
 
 error[E0425]: cannot find value `__code_34` in this scope
-  --> $DIR/diagnostic-derive.rs:807:10
+  --> $DIR/diagnostic-derive.rs:809:10
    |
 LL | #[derive(Diagnostic)]
    |          ^^^^^^^^^^ not found in this scope
@@ -622,7 +632,7 @@ note: required by a bound in `DiagnosticBuilder::<'a, G>::arg`
   --> $COMPILER_DIR/rustc_errors/src/diagnostic_builder.rs:LL:CC
    = note: this error originates in the macro `forward` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: aborting due to 84 previous errors
+error: aborting due to 86 previous errors
 
 Some errors have detailed explanations: E0277, E0425, E0433.
 For more information about an error, try `rustc --explain E0277`.
diff --git a/tests/ui/coherence/coherent-due-to-fulfill.rs b/tests/ui/coherence/coherent-due-to-fulfill.rs
new file mode 100644
index 0000000000000..084f9be0a8c3f
--- /dev/null
+++ b/tests/ui/coherence/coherent-due-to-fulfill.rs
@@ -0,0 +1,20 @@
+//@ compile-flags: -Znext-solver=coherence
+//@ check-pass
+
+trait Mirror {
+    type Assoc;
+}
+impl<T> Mirror for T {
+    type Assoc = T;
+}
+
+trait Foo {}
+trait Bar {}
+
+// self type starts out as `?0` but is constrained to `()`
+// due to the where clause below. Because `(): Bar` does not
+// hold in intercrate mode, we can prove the impls disjoint.
+impl<T> Foo for T where (): Mirror<Assoc = T> {}
+impl<T> Foo for T where T: Bar {}
+
+fn main() {}
diff --git a/tests/ui/coherence/incoherent-even-though-we-fulfill.rs b/tests/ui/coherence/incoherent-even-though-we-fulfill.rs
new file mode 100644
index 0000000000000..b3c9cf328c21c
--- /dev/null
+++ b/tests/ui/coherence/incoherent-even-though-we-fulfill.rs
@@ -0,0 +1,22 @@
+//@ compile-flags: -Znext-solver=coherence
+
+trait Mirror {
+    type Assoc;
+}
+impl<T> Mirror for T {
+    type Assoc = T;
+}
+
+trait Foo {}
+
+// Even though using fulfillment in coherence allows us to figure out that
+// `?T = ()`, we still treat it as incoherent because `(): Iterator` may be
+// added upstream.
+impl<T> Foo for T where (): Mirror<Assoc = T> {}
+//~^ NOTE first implementation here
+impl<T> Foo for T where T: Iterator {}
+//~^ ERROR conflicting implementations of trait `Foo` for type `()`
+//~| NOTE conflicting implementation for `()`
+//~| NOTE upstream crates may add a new impl of trait `std::iter::Iterator` for type `()` in future versions
+
+fn main() {}
diff --git a/tests/ui/coherence/incoherent-even-though-we-fulfill.stderr b/tests/ui/coherence/incoherent-even-though-we-fulfill.stderr
new file mode 100644
index 0000000000000..b16465d201140
--- /dev/null
+++ b/tests/ui/coherence/incoherent-even-though-we-fulfill.stderr
@@ -0,0 +1,14 @@
+error[E0119]: conflicting implementations of trait `Foo` for type `()`
+  --> $DIR/incoherent-even-though-we-fulfill.rs:17:1
+   |
+LL | impl<T> Foo for T where (): Mirror<Assoc = T> {}
+   | --------------------------------------------- first implementation here
+LL |
+LL | impl<T> Foo for T where T: Iterator {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `()`
+   |
+   = note: upstream crates may add a new impl of trait `std::iter::Iterator` for type `()` in future versions
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0119`.