Auto merge of #116455 - matthiaskrgr:rollup-p226a5u, r=matthiaskrgr

Rollup of 5 pull requests

Successful merges:

 - #116220 (stabilize `Option::as_`(`mut_`)`slice`)
 - #116288 (Add Span to various smir types)
 - #116415 (Move subtyper below reveal_all and change reveal_all)
 - #116428 (Add a note to duplicate diagnostics)
 - #116452 (Do not assert that hidden types don't have erased regions.)

r? `@ghost`
`@rustbot` modify labels: rollup

182 files changed, 762 insertions, 356 deletions

diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index b747a62b864..665b5d6adec 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -1376,16 +1376,16 @@ impl HandlerInner {
                 self.emitted_diagnostic_codes.insert(code.clone());
             }
 
-            let already_emitted = |this: &mut Self| {
+            let already_emitted = {
                 let mut hasher = StableHasher::new();
                 diagnostic.hash(&mut hasher);
                 let diagnostic_hash = hasher.finish();
-                !this.emitted_diagnostics.insert(diagnostic_hash)
+                !self.emitted_diagnostics.insert(diagnostic_hash)
             };
 
             // Only emit the diagnostic if we've been asked to deduplicate or
             // haven't already emitted an equivalent diagnostic.
-            if !(self.flags.deduplicate_diagnostics && already_emitted(self)) {
+            if !(self.flags.deduplicate_diagnostics && already_emitted) {
                 debug!(?diagnostic);
                 debug!(?self.emitted_diagnostics);
                 let already_emitted_sub = |sub: &mut SubDiagnostic| {
@@ -1401,6 +1401,11 @@ impl HandlerInner {
                 };
 
                 diagnostic.children.extract_if(already_emitted_sub).for_each(|_| {});
+                if already_emitted {
+                    diagnostic.note(
+                        "duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`",
+                    );
+                }
 
                 self.emitter.emit_diagnostic(diagnostic);
                 if diagnostic.is_error() {
diff --git a/compiler/rustc_hir_typeck/src/lib.rs b/compiler/rustc_hir_typeck/src/lib.rs
index 6873382c4ac..cd6adb345e7 100644
--- a/compiler/rustc_hir_typeck/src/lib.rs
+++ b/compiler/rustc_hir_typeck/src/lib.rs
@@ -5,7 +5,6 @@
 #![feature(box_patterns)]
 #![feature(min_specialization)]
 #![feature(control_flow_enum)]
-#![feature(option_as_slice)]
 #![recursion_limit = "256"]
 
 #[macro_use]
diff --git a/compiler/rustc_mir_transform/src/add_subtyping_projections.rs b/compiler/rustc_mir_transform/src/add_subtyping_projections.rs
index 1cc049d5a22..e5be7c0ca76 100644
--- a/compiler/rustc_mir_transform/src/add_subtyping_projections.rs
+++ b/compiler/rustc_mir_transform/src/add_subtyping_projections.rs
@@ -24,6 +24,11 @@ impl<'a, 'tcx> MutVisitor<'tcx> for SubTypeChecker<'a, 'tcx> {
         rvalue: &mut Rvalue<'tcx>,
         location: Location,
     ) {
+        // We don't need to do anything for deref temps as they are
+        // not part of the source code, but used for desugaring purposes.
+        if self.local_decls[place.local].is_deref_temp() {
+            return;
+        }
         let mut place_ty = place.ty(self.local_decls, self.tcx).ty;
         let mut rval_ty = rvalue.ty(self.local_decls, self.tcx);
         // Not erasing this causes `Free Regions` errors in validator,
@@ -48,7 +53,6 @@ impl<'a, 'tcx> MutVisitor<'tcx> for SubTypeChecker<'a, 'tcx> {
 // // gets transformed to
 // let temp: rval_ty = rval;
 // let place: place_ty = temp as place_ty;
-//
 pub fn subtype_finder<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
     let patch = MirPatch::new(body);
     let mut checker = SubTypeChecker { tcx, patcher: patch, local_decls: &body.local_decls };
diff --git a/compiler/rustc_mir_transform/src/lib.rs b/compiler/rustc_mir_transform/src/lib.rs
index 22381844d6d..c0a09b7a761 100644
--- a/compiler/rustc_mir_transform/src/lib.rs
+++ b/compiler/rustc_mir_transform/src/lib.rs
@@ -467,7 +467,6 @@ pub fn run_analysis_to_runtime_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'
 /// After this series of passes, no lifetime analysis based on borrowing can be done.
 fn run_analysis_cleanup_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
     let passes: &[&dyn MirPass<'tcx>] = &[
-        &add_subtyping_projections::Subtyper,
         &cleanup_post_borrowck::CleanupPostBorrowck,
         &remove_noop_landing_pads::RemoveNoopLandingPads,
         &simplify::SimplifyCfg::EarlyOpt,
@@ -483,6 +482,7 @@ fn run_runtime_lowering_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         // These next passes must be executed together
         &add_call_guards::CriticalCallEdges,
         &reveal_all::RevealAll, // has to be done before drop elaboration, since we need to drop opaque types, too.
+        &add_subtyping_projections::Subtyper, // calling this after reveal_all ensures that we don't deal with opaque types
         &elaborate_drops::ElaborateDrops,
         // This will remove extraneous landing pads which are no longer
         // necessary as well as well as forcing any call in a non-unwinding
diff --git a/compiler/rustc_mir_transform/src/reveal_all.rs b/compiler/rustc_mir_transform/src/reveal_all.rs
index 55f1eac6f84..1626cf3c035 100644
--- a/compiler/rustc_mir_transform/src/reveal_all.rs
+++ b/compiler/rustc_mir_transform/src/reveal_all.rs
@@ -46,16 +46,18 @@ impl<'tcx> MutVisitor<'tcx> for RevealAllVisitor<'tcx> {
                 .filter(|elem| !matches!(elem, ProjectionElem::OpaqueCast(_)))
                 .collect::<Vec<_>>(),
         );
+        self.super_place(place, _context, _location);
     }
 
     #[inline]
-    fn visit_constant(&mut self, constant: &mut ConstOperand<'tcx>, _: Location) {
+    fn visit_constant(&mut self, constant: &mut ConstOperand<'tcx>, location: Location) {
         // We have to use `try_normalize_erasing_regions` here, since it's
         // possible that we visit impossible-to-satisfy where clauses here,
         // see #91745
         if let Ok(c) = self.tcx.try_normalize_erasing_regions(self.param_env, constant.const_) {
             constant.const_ = c;
         }
+        self.super_constant(constant, location);
     }
 
     #[inline]
diff --git a/compiler/rustc_smir/src/rustc_smir/mod.rs b/compiler/rustc_smir/src/rustc_smir/mod.rs
index c6c97ce35e8..7d1122c2fd2 100644
--- a/compiler/rustc_smir/src/rustc_smir/mod.rs
+++ b/compiler/rustc_smir/src/rustc_smir/mod.rs
@@ -15,7 +15,7 @@ use rustc_middle::mir::interpret::{alloc_range, AllocId};
 use rustc_middle::ty::{self, Ty, TyCtxt, Variance};
 use rustc_span::def_id::{CrateNum, DefId, LOCAL_CRATE};
 use rustc_target::abi::FieldIdx;
-use stable_mir::mir::{CopyNonOverlapping, UserTypeProjection, VariantIdx};
+use stable_mir::mir::{CopyNonOverlapping, Statement, UserTypeProjection, VariantIdx};
 use stable_mir::ty::{FloatTy, GenericParamDef, IntTy, Movability, RigidTy, Span, TyKind, UintTy};
 use stable_mir::{self, opaque, Context};
 use tracing::debug;
@@ -106,7 +106,14 @@ impl<'tcx> Context for Tables<'tcx> {
                         .collect(),
                 })
                 .collect(),
-            locals: mir.local_decls.iter().map(|decl| self.intern_ty(decl.ty)).collect(),
+            locals: mir
+                .local_decls
+                .iter()
+                .map(|decl| stable_mir::mir::LocalDecl {
+                    ty: self.intern_ty(decl.ty),
+                    span: decl.source_info.span.stable(self),
+                })
+                .collect(),
         }
     }
 
@@ -223,41 +230,64 @@ pub(crate) trait Stable<'tcx> {
 impl<'tcx> Stable<'tcx> for mir::Statement<'tcx> {
     type T = stable_mir::mir::Statement;
     fn stable(&self, tables: &mut Tables<'tcx>) -> Self::T {
-        use rustc_middle::mir::StatementKind::*;
-        match &self.kind {
-            Assign(assign) => {
-                stable_mir::mir::Statement::Assign(assign.0.stable(tables), assign.1.stable(tables))
-            }
-            FakeRead(fake_read_place) => stable_mir::mir::Statement::FakeRead(
-                fake_read_place.0.stable(tables),
-                fake_read_place.1.stable(tables),
+        Statement { kind: self.kind.stable(tables), span: self.source_info.span.stable(tables) }
+    }
+}
+
+impl<'tcx> Stable<'tcx> for mir::StatementKind<'tcx> {
+    type T = stable_mir::mir::StatementKind;
+    fn stable(&self, tables: &mut Tables<'tcx>) -> Self::T {
+        match self {
+            mir::StatementKind::Assign(assign) => stable_mir::mir::StatementKind::Assign(
+                assign.0.stable(tables),
+                assign.1.stable(tables),
             ),
-            SetDiscriminant { place: plc, variant_index: idx } => {
-                stable_mir::mir::Statement::SetDiscriminant {
-                    place: plc.as_ref().stable(tables),
-                    variant_index: idx.stable(tables),
+            mir::StatementKind::FakeRead(fake_read_place) => {
+                stable_mir::mir::StatementKind::FakeRead(
+                    fake_read_place.0.stable(tables),
+                    fake_read_place.1.stable(tables),
+                )
+            }
+            mir::StatementKind::SetDiscriminant { place, variant_index } => {
+                stable_mir::mir::StatementKind::SetDiscriminant {
+                    place: place.as_ref().stable(tables),
+                    variant_index: variant_index.stable(tables),
                 }
             }
-            Deinit(place) => stable_mir::mir::Statement::Deinit(place.stable(tables)),
-            StorageLive(place) => stable_mir::mir::Statement::StorageLive(place.stable(tables)),
-            StorageDead(place) => stable_mir::mir::Statement::StorageDead(place.stable(tables)),
-            Retag(retag, place) => {
-                stable_mir::mir::Statement::Retag(retag.stable(tables), place.stable(tables))
+            mir::StatementKind::Deinit(place) => {
+                stable_mir::mir::StatementKind::Deinit(place.stable(tables))
+            }
+
+            mir::StatementKind::StorageLive(place) => {
+                stable_mir::mir::StatementKind::StorageLive(place.stable(tables))
+            }
+
+            mir::StatementKind::StorageDead(place) => {
+                stable_mir::mir::StatementKind::StorageDead(place.stable(tables))
+            }
+            mir::StatementKind::Retag(retag, place) => {
+                stable_mir::mir::StatementKind::Retag(retag.stable(tables), place.stable(tables))
+            }
+            mir::StatementKind::PlaceMention(place) => {
+                stable_mir::mir::StatementKind::PlaceMention(place.stable(tables))
             }
-            PlaceMention(place) => stable_mir::mir::Statement::PlaceMention(place.stable(tables)),
-            AscribeUserType(place_projection, variance) => {
-                stable_mir::mir::Statement::AscribeUserType {
+            mir::StatementKind::AscribeUserType(place_projection, variance) => {
+                stable_mir::mir::StatementKind::AscribeUserType {
                     place: place_projection.as_ref().0.stable(tables),
                     projections: place_projection.as_ref().1.stable(tables),
                     variance: variance.stable(tables),
                 }
             }
-            Coverage(coverage) => stable_mir::mir::Statement::Coverage(opaque(coverage)),
-            Intrinsic(intrinstic) => {
-                stable_mir::mir::Statement::Intrinsic(intrinstic.stable(tables))
+            mir::StatementKind::Coverage(coverage) => {
+                stable_mir::mir::StatementKind::Coverage(opaque(coverage))
+            }
+            mir::StatementKind::Intrinsic(intrinstic) => {
+                stable_mir::mir::StatementKind::Intrinsic(intrinstic.stable(tables))
+            }
+            mir::StatementKind::ConstEvalCounter => {
+                stable_mir::mir::StatementKind::ConstEvalCounter
             }
-            ConstEvalCounter => stable_mir::mir::Statement::ConstEvalCounter,
-            Nop => stable_mir::mir::Statement::Nop,
+            mir::StatementKind::Nop => stable_mir::mir::StatementKind::Nop,
         }
     }
 }
@@ -806,11 +836,20 @@ impl<'tcx> Stable<'tcx> for mir::InlineAsmOperand<'tcx> {
 impl<'tcx> Stable<'tcx> for mir::Terminator<'tcx> {
     type T = stable_mir::mir::Terminator;
     fn stable(&self, tables: &mut Tables<'tcx>) -> Self::T {
-        use rustc_middle::mir::TerminatorKind::*;
         use stable_mir::mir::Terminator;
-        match &self.kind {
-            Goto { target } => Terminator::Goto { target: target.as_usize() },
-            SwitchInt { discr, targets } => Terminator::SwitchInt {
+        Terminator { kind: self.kind.stable(tables), span: self.source_info.span.stable(tables) }
+    }
+}
+
+impl<'tcx> Stable<'tcx> for mir::TerminatorKind<'tcx> {
+    type T = stable_mir::mir::TerminatorKind;
+    fn stable(&self, tables: &mut Tables<'tcx>) -> Self::T {
+        use stable_mir::mir::TerminatorKind;
+        match self {
+            mir::TerminatorKind::Goto { target } => {
+                TerminatorKind::Goto { target: target.as_usize() }
+            }
+            mir::TerminatorKind::SwitchInt { discr, targets } => TerminatorKind::SwitchInt {
                 discr: discr.stable(tables),
                 targets: targets
                     .iter()
@@ -821,42 +860,60 @@ impl<'tcx> Stable<'tcx> for mir::Terminator<'tcx> {
                     .collect(),
                 otherwise: targets.otherwise().as_usize(),
             },
-            UnwindResume => Terminator::Resume,
-            UnwindTerminate(_) => Terminator::Abort,
-            Return => Terminator::Return,
-            Unreachable => Terminator::Unreachable,
-            Drop { place, target, unwind, replace: _ } => Terminator::Drop {
-                place: place.stable(tables),
-                target: target.as_usize(),
-                unwind: unwind.stable(tables),
-            },
-            Call { func, args, destination, target, unwind, call_source: _, fn_span: _ } => {
-                Terminator::Call {
-                    func: func.stable(tables),
-                    args: args.iter().map(|arg| arg.stable(tables)).collect(),
-                    destination: destination.stable(tables),
-                    target: target.map(|t| t.as_usize()),
+            mir::TerminatorKind::UnwindResume => TerminatorKind::Resume,
+            mir::TerminatorKind::UnwindTerminate(_) => TerminatorKind::Abort,
+            mir::TerminatorKind::Return => TerminatorKind::Return,
+            mir::TerminatorKind::Unreachable => TerminatorKind::Unreachable,
+            mir::TerminatorKind::Drop { place, target, unwind, replace: _ } => {
+                TerminatorKind::Drop {
+                    place: place.stable(tables),
+                    target: target.as_usize(),
                     unwind: unwind.stable(tables),
                 }
             }
-            Assert { cond, expected, msg, target, unwind } => Terminator::Assert {
-                cond: cond.stable(tables),
-                expected: *expected,
-                msg: msg.stable(tables),
-                target: target.as_usize(),
+            mir::TerminatorKind::Call {
+                func,
+                args,
+                destination,
+                target,
+                unwind,
+                call_source: _,
+                fn_span: _,
+            } => TerminatorKind::Call {
+                func: func.stable(tables),
+                args: args.iter().map(|arg| arg.stable(tables)).collect(),
+                destination: destination.stable(tables),
+                target: target.map(|t| t.as_usize()),
                 unwind: unwind.stable(tables),
             },
-            InlineAsm { template, operands, options, line_spans, destination, unwind } => {
-                Terminator::InlineAsm {
-                    template: format!("{template:?}"),
-                    operands: operands.iter().map(|operand| operand.stable(tables)).collect(),
-                    options: format!("{options:?}"),
-                    line_spans: format!("{line_spans:?}"),
-                    destination: destination.map(|d| d.as_usize()),
+            mir::TerminatorKind::Assert { cond, expected, msg, target, unwind } => {
+                TerminatorKind::Assert {
+                    cond: cond.stable(tables),
+                    expected: *expected,
+                    msg: msg.stable(tables),
+                    target: target.as_usize(),
                     unwind: unwind.stable(tables),
                 }
             }
-            Yield { .. } | GeneratorDrop | FalseEdge { .. } | FalseUnwind { .. } => unreachable!(),
+            mir::TerminatorKind::InlineAsm {
+                template,
+                operands,
+                options,
+                line_spans,
+                destination,
+                unwind,
+            } => TerminatorKind::InlineAsm {
+                template: format!("{template:?}"),
+                operands: operands.iter().map(|operand| operand.stable(tables)).collect(),
+                options: format!("{options:?}"),
+                line_spans: format!("{line_spans:?}"),
+                destination: destination.map(|d| d.as_usize()),
+                unwind: unwind.stable(tables),
+            },
+            mir::TerminatorKind::Yield { .. }
+            | mir::TerminatorKind::GeneratorDrop
+            | mir::TerminatorKind::FalseEdge { .. }
+            | mir::TerminatorKind::FalseUnwind { .. } => unreachable!(),
         }
     }
 }
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 9b8853b42ab..8871de194a6 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -3116,9 +3116,6 @@ fn bind_generator_hidden_types_above<'tcx>(
             bty.instantiate(tcx, args)
         })
         .collect();
-    if considering_regions {
-        debug_assert!(!hidden_types.has_erased_regions());
-    }
     let bound_vars =
         tcx.mk_bound_variable_kinds_from_iter(bound_vars.iter().chain(
             (num_bound_variables..counter).map(|_| ty::BoundVariableKind::Region(ty::BrAnon)),
diff --git a/compiler/stable_mir/src/mir/body.rs b/compiler/stable_mir/src/mir/body.rs
index 6f8f7b06fa3..72f026ee8de 100644
--- a/compiler/stable_mir/src/mir/body.rs
+++ b/compiler/stable_mir/src/mir/body.rs
@@ -5,7 +5,13 @@ use crate::{ty::Ty, Span};
 #[derive(Clone, Debug)]
 pub struct Body {
     pub blocks: Vec<BasicBlock>,
-    pub locals: Vec<Ty>,
+    pub locals: Vec<LocalDecl>,
+}
+
+#[derive(Clone, Debug)]
+pub struct LocalDecl {
+    pub ty: Ty,
+    pub span: Span,
 }
 
 #[derive(Clone, Debug)]
@@ -15,7 +21,13 @@ pub struct BasicBlock {
 }
 
 #[derive(Clone, Debug)]
-pub enum Terminator {
+pub struct Terminator {
+    pub kind: TerminatorKind,
+    pub span: Span,
+}
+
+#[derive(Clone, Debug)]
+pub enum TerminatorKind {
     Goto {
         target: usize,
     },
@@ -179,7 +191,13 @@ pub enum NonDivergingIntrinsic {
 }
 
 #[derive(Clone, Debug)]
-pub enum Statement {
+pub struct Statement {
+    pub kind: StatementKind,
+    pub span: Span,
+}
+
+#[derive(Clone, Debug)]
+pub enum StatementKind {
     Assign(Place, Rvalue),
     FakeRead(FakeReadCause, Place),
     SetDiscriminant { place: Place, variant_index: VariantIdx },
diff --git a/library/core/src/option.rs b/library/core/src/option.rs
index f2909a81d49..9899014e85a 100644
--- a/library/core/src/option.rs
+++ b/library/core/src/option.rs
@@ -743,8 +743,6 @@ impl<T> Option<T> {
     /// # Examples
     ///
     /// ```rust
-    /// #![feature(option_as_slice)]
-    ///
     /// assert_eq!(
     ///     [Some(1234).as_slice(), None.as_slice()],
     ///     [&[1234][..], &[][..]],
@@ -755,15 +753,13 @@ impl<T> Option<T> {
     /// borrowing) [`[_]::first`](slice::first):
     ///
     /// ```rust
-    /// #![feature(option_as_slice)]
-    ///
     /// for i in [Some(1234_u16), None] {
     ///     assert_eq!(i.as_ref(), i.as_slice().first());
     /// }
     /// ```
     #[inline]
     #[must_use]
-    #[unstable(feature = "option_as_slice", issue = "108545")]
+    #[stable(feature = "option_as_slice", since = "CURRENT_RUSTC_VERSION")]
     pub fn as_slice(&self) -> &[T] {
         // SAFETY: When the `Option` is `Some`, we're using the actual pointer
         // to the payload, with a length of 1, so this is equivalent to
@@ -794,8 +790,6 @@ impl<T> Option<T> {
     /// # Examples
     ///
     /// ```rust
-    /// #![feature(option_as_slice)]
-    ///
     /// assert_eq!(
     ///     [Some(1234).as_mut_slice(), None.as_mut_slice()],
     ///     [&mut [1234][..], &mut [][..]],
@@ -806,8 +800,6 @@ impl<T> Option<T> {
     /// our original `Option`:
     ///
     /// ```rust
-    /// #![feature(option_as_slice)]
-    ///
     /// let mut x = Some(1234);
     /// x.as_mut_slice()[0] += 1;
     /// assert_eq!(x, Some(1235));
@@ -817,13 +809,11 @@ impl<T> Option<T> {
     /// is [`[_]::first_mut`](slice::first_mut):
     ///
     /// ```rust
-    /// #![feature(option_as_slice)]
-    ///
     /// assert_eq!(Some(123).as_mut_slice().first_mut(), Some(&mut 123))
     /// ```
     #[inline]
     #[must_use]
-    #[unstable(feature = "option_as_slice", issue = "108545")]
+    #[stable(feature = "option_as_slice", since = "CURRENT_RUSTC_VERSION")]
     pub fn as_mut_slice(&mut self) -> &mut [T] {
         // SAFETY: When the `Option` is `Some`, we're using the actual pointer
         // to the payload, with a length of 1, so this is equivalent to
diff --git a/tests/mir-opt/inline/inline_generator.main.Inline.panic-abort.diff b/tests/mir-opt/inline/inline_generator.main.Inline.panic-abort.diff
index d592ddfd183..06ee8c464d5 100644
--- a/tests/mir-opt/inline/inline_generator.main.Inline.panic-abort.diff
+++ b/tests/mir-opt/inline/inline_generator.main.Inline.panic-abort.diff
@@ -7,12 +7,11 @@
       let mut _2: std::pin::Pin<&mut {generator@$DIR/inline_generator.rs:16:5: 16:8}>;
       let mut _3: &mut {generator@$DIR/inline_generator.rs:16:5: 16:8};
       let mut _4: {generator@$DIR/inline_generator.rs:16:5: 16:8};
-+     let mut _6: bool;
++     let mut _5: bool;
       scope 1 {
           debug _r => _1;
       }
 +     scope 2 (inlined g) {
-+         let mut _5: {generator@$DIR/inline_generator.rs:16:5: 16:8};
 +     }
 +     scope 3 (inlined Pin::<&mut {generator@$DIR/inline_generator.rs:16:5: 16:8}>::new) {
 +         debug pointer => _3;
@@ -23,10 +22,10 @@
 +         }
 +     }
 +     scope 6 (inlined g::{closure#0}) {
-+         debug a => _6;
-+         let mut _7: &mut {generator@$DIR/inline_generator.rs:16:5: 16:8};
-+         let mut _8: u32;
-+         let mut _9: i32;
++         debug a => _5;
++         let mut _6: &mut {generator@$DIR/inline_generator.rs:16:5: 16:8};
++         let mut _7: u32;
++         let mut _8: i32;
 +     }
   
       bb0: {
@@ -35,28 +34,25 @@
           StorageLive(_3);
           StorageLive(_4);
 -         _4 = g() -> [return: bb1, unwind unreachable];
-+         StorageLive(_5);
-+         _5 = {generator@$DIR/inline_generator.rs:16:5: 16:8 (#0)};
-+         _4 = move (_5 as subtype {generator@$DIR/inline_generator.rs:16:5: 16:8});
-+         StorageDead(_5);
++         _4 = {generator@$DIR/inline_generator.rs:16:5: 16:8 (#0)};
 +         _3 = &mut _4;
 +         _2 = Pin::<&mut {generator@$DIR/inline_generator.rs:16:5: 16:8}> { pointer: move _3 };
 +         StorageDead(_3);
++         StorageLive(_5);
++         _5 = const false;
 +         StorageLive(_6);
-+         _6 = const false;
 +         StorageLive(_7);
-+         StorageLive(_8);
-+         _7 = (_2.0: &mut {generator@$DIR/inline_generator.rs:16:5: 16:8});
-+         _8 = discriminant((*_7));
-+         switchInt(move _8) -> [0: bb3, 1: bb7, 3: bb8, otherwise: bb9];
++         _6 = (_2.0: &mut {generator@$DIR/inline_generator.rs:16:5: 16:8});
++         _7 = discriminant((*_6));
++         switchInt(move _7) -> [0: bb3, 1: bb7, 3: bb8, otherwise: bb9];
       }
   
       bb1: {
 -         _3 = &mut _4;
 -         _2 = Pin::<&mut {generator@$DIR/inline_generator.rs:16:5: 16:8}>::new(move _3) -> [return: bb2, unwind unreachable];
-+         StorageDead(_8);
 +         StorageDead(_7);
 +         StorageDead(_6);
++         StorageDead(_5);
 +         StorageDead(_2);
 +         drop(_4) -> [return: bb2, unwind unreachable];
       }
@@ -73,8 +69,8 @@
       bb3: {
 -         StorageDead(_2);
 -         drop(_4) -> [return: bb4, unwind unreachable];
-+         StorageLive(_9);
-+         switchInt(_6) -> [0: bb4, otherwise: bb5];
++         StorageLive(_8);
++         switchInt(_5) -> [0: bb4, otherwise: bb5];
       }
   
       bb4: {
@@ -82,18 +78,18 @@
 -         _0 = const ();
 -         StorageDead(_1);
 -         return;
-+         _9 = const 13_i32;
++         _8 = const 13_i32;
 +         goto -> bb6;
 +     }
 + 
 +     bb5: {
-+         _9 = const 7_i32;
++         _8 = const 7_i32;
 +         goto -> bb6;
 +     }
 + 
 +     bb6: {
-+         _1 = GeneratorState::<i32, bool>::Yielded(move _9);
-+         discriminant((*_7)) = 3;
++         _1 = GeneratorState::<i32, bool>::Yielded(move _8);
++         discriminant((*_6)) = 3;
 +         goto -> bb1;
 +     }
 + 
@@ -102,10 +98,10 @@
 +     }
 + 
 +     bb8: {
-+         StorageLive(_9);
-+         StorageDead(_9);
-+         _1 = GeneratorState::<i32, bool>::Complete(_6);
-+         discriminant((*_7)) = 1;
++         StorageLive(_8);
++         StorageDead(_8);
++         _1 = GeneratorState::<i32, bool>::Complete(_5);
++         discriminant((*_6)) = 1;
 +         goto -> bb1;
 +     }
 + 
diff --git a/tests/mir-opt/inline/inline_generator.main.Inline.panic-unwind.diff b/tests/mir-opt/inline/inline_generator.main.Inline.panic-unwind.diff
index 120aa52ac01..da29ba5f50d 100644
--- a/tests/mir-opt/inline/inline_generator.main.Inline.panic-unwind.diff
+++ b/tests/mir-opt/inline/inline_generator.main.Inline.panic-unwind.diff
@@ -7,12 +7,11 @@
       let mut _2: std::pin::Pin<&mut {generator@$DIR/inline_generator.rs:16:5: 16:8}>;
       let mut _3: &mut {generator@$DIR/inline_generator.rs:16:5: 16:8};
       let mut _4: {generator@$DIR/inline_generator.rs:16:5: 16:8};
-+     let mut _6: bool;
++     let mut _5: bool;
       scope 1 {
           debug _r => _1;
       }
 +     scope 2 (inlined g) {
-+         let mut _5: {generator@$DIR/inline_generator.rs:16:5: 16:8};
 +     }
 +     scope 3 (inlined Pin::<&mut {generator@$DIR/inline_generator.rs:16:5: 16:8}>::new) {
 +         debug pointer => _3;
@@ -23,10 +22,10 @@
 +         }
 +     }
 +     scope 6 (inlined g::{closure#0}) {
-+         debug a => _6;
-+         let mut _7: &mut {generator@$DIR/inline_generator.rs:16:5: 16:8};
-+         let mut _8: u32;
-+         let mut _9: i32;
++         debug a => _5;
++         let mut _6: &mut {generator@$DIR/inline_generator.rs:16:5: 16:8};
++         let mut _7: u32;
++         let mut _8: i32;
 +     }
   
       bb0: {
@@ -38,10 +37,7 @@
 -     }
 - 
 -     bb1: {
-+         StorageLive(_5);
-+         _5 = {generator@$DIR/inline_generator.rs:16:5: 16:8 (#0)};
-+         _4 = move (_5 as subtype {generator@$DIR/inline_generator.rs:16:5: 16:8});
-+         StorageDead(_5);
++         _4 = {generator@$DIR/inline_generator.rs:16:5: 16:8 (#0)};
           _3 = &mut _4;
 -         _2 = Pin::<&mut {generator@$DIR/inline_generator.rs:16:5: 16:8}>::new(move _3) -> [return: bb2, unwind: bb5];
 -     }
@@ -50,20 +46,20 @@
 +         _2 = Pin::<&mut {generator@$DIR/inline_generator.rs:16:5: 16:8}> { pointer: move _3 };
           StorageDead(_3);
 -         _1 = <{generator@$DIR/inline_generator.rs:16:5: 16:8} as Generator<bool>>::resume(move _2, const false) -> [return: bb3, unwind: bb5];
++         StorageLive(_5);
++         _5 = const false;
 +         StorageLive(_6);
-+         _6 = const false;
 +         StorageLive(_7);
-+         StorageLive(_8);
-+         _7 = (_2.0: &mut {generator@$DIR/inline_generator.rs:16:5: 16:8});
-+         _8 = discriminant((*_7));
-+         switchInt(move _8) -> [0: bb5, 1: bb9, 3: bb10, otherwise: bb11];
++         _6 = (_2.0: &mut {generator@$DIR/inline_generator.rs:16:5: 16:8});
++         _7 = discriminant((*_6));
++         switchInt(move _7) -> [0: bb5, 1: bb9, 3: bb10, otherwise: bb11];
       }
   
 -     bb3: {
 +     bb1: {
-+         StorageDead(_8);
 +         StorageDead(_7);
 +         StorageDead(_6);
++         StorageDead(_5);
           StorageDead(_2);
 -         drop(_4) -> [return: bb4, unwind: bb6];
 +         drop(_4) -> [return: bb2, unwind: bb4];
@@ -89,23 +85,23 @@
 +     }
 + 
 +     bb5: {
-+         StorageLive(_9);
-+         switchInt(_6) -> [0: bb6, otherwise: bb7];
++         StorageLive(_8);
++         switchInt(_5) -> [0: bb6, otherwise: bb7];
 +     }
 + 
 +     bb6: {
-+         _9 = const 13_i32;
++         _8 = const 13_i32;
 +         goto -> bb8;
 +     }
 + 
 +     bb7: {
-+         _9 = const 7_i32;
++         _8 = const 7_i32;
 +         goto -> bb8;
 +     }
 + 
 +     bb8: {
-+         _1 = GeneratorState::<i32, bool>::Yielded(move _9);
-+         discriminant((*_7)) = 3;
++         _1 = GeneratorState::<i32, bool>::Yielded(move _8);
++         discriminant((*_6)) = 3;
 +         goto -> bb1;
 +     }
 + 
@@ -114,10 +110,10 @@
 +     }
 + 
 +     bb10: {
-+         StorageLive(_9);
-+         StorageDead(_9);
-+         _1 = GeneratorState::<i32, bool>::Complete(_6);
-+         discriminant((*_7)) = 1;
++         StorageLive(_8);
++         StorageDead(_8);
++         _1 = GeneratorState::<i32, bool>::Complete(_5);
++         discriminant((*_6)) = 1;
 +         goto -> bb1;
 +     }
 + 
diff --git a/tests/rustdoc-ui/custom_code_classes_in_docs-warning3.stderr b/tests/rustdoc-ui/custom_code_classes_in_docs-warning3.stderr
index 4f2ded78c29..ad049804213 100644
--- a/tests/rustdoc-ui/custom_code_classes_in_docs-warning3.stderr
+++ b/tests/rustdoc-ui/custom_code_classes_in_docs-warning3.stderr
@@ -28,6 +28,8 @@ LL | |
 LL | | /// main;
 LL | | /// ```
    | |_______^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/rustdoc-ui/intra-doc/broken-link-in-unused-doc-string.stderr b/tests/rustdoc-ui/intra-doc/broken-link-in-unused-doc-string.stderr
index 83e0d3962ca..b25849f25b4 100644
--- a/tests/rustdoc-ui/intra-doc/broken-link-in-unused-doc-string.stderr
+++ b/tests/rustdoc-ui/intra-doc/broken-link-in-unused-doc-string.stderr
@@ -22,6 +22,7 @@ LL | /// [1]
    |      ^ no item named `1` in scope
    |
    = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: 3 warnings emitted
 
diff --git a/tests/rustdoc-ui/issues/issue-105742.stderr b/tests/rustdoc-ui/issues/issue-105742.stderr
index b63176c9149..4d3f9f5bced 100644
--- a/tests/rustdoc-ui/issues/issue-105742.stderr
+++ b/tests/rustdoc-ui/issues/issue-105742.stderr
@@ -169,6 +169,7 @@ note: associated type defined here, with 1 lifetime parameter: `'a`
    |
 LL |     type Item<'a, T>;
    |          ^^^^ --
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: add missing lifetime argument
    |
 LL |     <Self as SVec>::Item<'a>,
@@ -185,6 +186,7 @@ note: associated type defined here, with 1 generic parameter: `T`
    |
 LL |     type Item<'a, T>;
    |          ^^^^     -
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: add missing generic argument
    |
 LL |     <Self as SVec>::Item<T>,
@@ -201,6 +203,7 @@ note: associated type defined here, with 1 lifetime parameter: `'a`
    |
 LL |     type Item<'a, T>;
    |          ^^^^ --
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: add missing lifetime argument
    |
 LL |     Output = <Index<<Self as SVec>::Item<'a>,
@@ -217,6 +220,7 @@ note: associated type defined here, with 1 generic parameter: `T`
    |
 LL |     type Item<'a, T>;
    |          ^^^^     -
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: add missing generic argument
    |
 LL |     Output = <Index<<Self as SVec>::Item<T>,
@@ -233,6 +237,7 @@ note: associated type defined here, with 1 lifetime parameter: `'a`
    |
 LL |     type Item<'a, T>;
    |          ^^^^ --
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: add missing lifetime argument
    |
 LL |     Output = <Self as SVec>::Item<'a>> as SVec>::Item,
@@ -249,6 +254,7 @@ note: associated type defined here, with 1 generic parameter: `T`
    |
 LL |     type Item<'a, T>;
    |          ^^^^     -
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: add missing generic argument
    |
 LL |     Output = <Self as SVec>::Item<T>> as SVec>::Item,
@@ -265,6 +271,7 @@ note: associated type defined here, with 1 lifetime parameter: `'a`
    |
 LL |     type Item<'a, T>;
    |          ^^^^ --
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: add missing lifetime argument
    |
 LL |     Output = <Self as SVec>::Item> as SVec>::Item<'a>,
@@ -281,6 +288,7 @@ note: associated type defined here, with 1 generic parameter: `T`
    |
 LL |     type Item<'a, T>;
    |          ^^^^     -
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: add missing generic argument
    |
 LL |     Output = <Self as SVec>::Item> as SVec>::Item<T>,
@@ -327,6 +335,7 @@ note: associated type defined here, with 1 lifetime parameter: `'a`
    |
 LL |     type Item<'a, T>;
    |          ^^^^ --
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: add missing lifetime argument
    |
 LL |     <Self as SVec>::Item<'a>,
@@ -343,6 +352,7 @@ note: associated type defined here, with 1 generic parameter: `T`
    |
 LL |     type Item<'a, T>;
    |          ^^^^     -
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: add missing generic argument
    |
 LL |     <Self as SVec>::Item<T>,
@@ -359,6 +369,7 @@ note: associated type defined here, with 1 lifetime parameter: `'a`
    |
 LL |     type Item<'a, T>;
    |          ^^^^ --
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: add missing lifetime argument
    |
 LL |     Output = <Index<<Self as SVec>::Item<'a>,
@@ -375,6 +386,7 @@ note: associated type defined here, with 1 generic parameter: `T`
    |
 LL |     type Item<'a, T>;
    |          ^^^^     -
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: add missing generic argument
    |
 LL |     Output = <Index<<Self as SVec>::Item<T>,
@@ -391,6 +403,7 @@ note: associated type defined here, with 1 lifetime parameter: `'a`
    |
 LL |     type Item<'a, T>;
    |          ^^^^ --
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: add missing lifetime argument
    |
 LL |     Output = <Self as SVec>::Item<'a>> as SVec>::Item,
@@ -407,6 +420,7 @@ note: associated type defined here, with 1 generic parameter: `T`
    |
 LL |     type Item<'a, T>;
    |          ^^^^     -
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: add missing generic argument
    |
 LL |     Output = <Self as SVec>::Item<T>> as SVec>::Item,
@@ -423,6 +437,7 @@ note: associated type defined here, with 1 lifetime parameter: `'a`
    |
 LL |     type Item<'a, T>;
    |          ^^^^ --
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: add missing lifetime argument
    |
 LL |     Output = <Self as SVec>::Item> as SVec>::Item<'a>,
@@ -439,6 +454,7 @@ note: associated type defined here, with 1 generic parameter: `T`
    |
 LL |     type Item<'a, T>;
    |          ^^^^     -
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: add missing generic argument
    |
 LL |     Output = <Self as SVec>::Item> as SVec>::Item<T>,
diff --git a/tests/rustdoc-ui/lints/feature-gate-rustdoc_missing_doc_code_examples.rs b/tests/rustdoc-ui/lints/feature-gate-rustdoc_missing_doc_code_examples.rs
index c34ea0567a9..ce94a06c39e 100644
--- a/tests/rustdoc-ui/lints/feature-gate-rustdoc_missing_doc_code_examples.rs
+++ b/tests/rustdoc-ui/lints/feature-gate-rustdoc_missing_doc_code_examples.rs
@@ -1,12 +1,7 @@
+// compile-flags: -Zdeduplicate-diagnostics=yes
 #![deny(unknown_lints)]
 //~^ NOTE defined here
 #![allow(rustdoc::missing_doc_code_examples)]
 //~^ ERROR unknown lint
-//~| ERROR unknown lint
-//~| ERROR unknown lint
 //~| NOTE lint is unstable
-//~| NOTE lint is unstable
-//~| NOTE lint is unstable
-//~| NOTE see issue
-//~| NOTE see issue
 //~| NOTE see issue
diff --git a/tests/rustdoc-ui/lints/feature-gate-rustdoc_missing_doc_code_examples.stderr b/tests/rustdoc-ui/lints/feature-gate-rustdoc_missing_doc_code_examples.stderr
index 326dcfe3bde..b8a08e94312 100644
--- a/tests/rustdoc-ui/lints/feature-gate-rustdoc_missing_doc_code_examples.stderr
+++ b/tests/rustdoc-ui/lints/feature-gate-rustdoc_missing_doc_code_examples.stderr
@@ -1,5 +1,5 @@
 error: unknown lint: `rustdoc::missing_doc_code_examples`
-  --> $DIR/feature-gate-rustdoc_missing_doc_code_examples.rs:3:1
+  --> $DIR/feature-gate-rustdoc_missing_doc_code_examples.rs:4:1
    |
 LL | #![allow(rustdoc::missing_doc_code_examples)]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -8,30 +8,10 @@ LL | #![allow(rustdoc::missing_doc_code_examples)]
    = note: see issue #101730 <https://github.com/rust-lang/rust/issues/101730> for more information
    = help: add `#![feature(rustdoc_missing_doc_code_examples)]` to the crate attributes to enable
 note: the lint level is defined here
-  --> $DIR/feature-gate-rustdoc_missing_doc_code_examples.rs:1:9
+  --> $DIR/feature-gate-rustdoc_missing_doc_code_examples.rs:2:9
    |
 LL | #![deny(unknown_lints)]
    |         ^^^^^^^^^^^^^
 
-error: unknown lint: `rustdoc::missing_doc_code_examples`
-  --> $DIR/feature-gate-rustdoc_missing_doc_code_examples.rs:3:1
-   |
-LL | #![allow(rustdoc::missing_doc_code_examples)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: the `rustdoc::missing_doc_code_examples` lint is unstable
-   = note: see issue #101730 <https://github.com/rust-lang/rust/issues/101730> for more information
-   = help: add `#![feature(rustdoc_missing_doc_code_examples)]` to the crate attributes to enable
-
-error: unknown lint: `rustdoc::missing_doc_code_examples`
-  --> $DIR/feature-gate-rustdoc_missing_doc_code_examples.rs:3:1
-   |
-LL | #![allow(rustdoc::missing_doc_code_examples)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: the `rustdoc::missing_doc_code_examples` lint is unstable
-   = note: see issue #101730 <https://github.com/rust-lang/rust/issues/101730> for more information
-   = help: add `#![feature(rustdoc_missing_doc_code_examples)]` to the crate attributes to enable
-
-error: aborting due to 3 previous errors
+error: aborting due to previous error
 
diff --git a/tests/rustdoc-ui/unescaped_backticks.stderr b/tests/rustdoc-ui/unescaped_backticks.stderr
index 83822f778d0..2b4e491b1fe 100644
--- a/tests/rustdoc-ui/unescaped_backticks.stderr
+++ b/tests/rustdoc-ui/unescaped_backticks.stderr
@@ -302,6 +302,7 @@ LL | |     /// level changes.
    = help: if you meant to use a literal backtick, escape it
             change: or `None` if it isn't.
            to this: or `None\` if it isn't.
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: unescaped backtick
   --> $DIR/unescaped_backticks.rs:323:5
@@ -321,6 +322,7 @@ LL | |     /// level changes.
    = help: if you meant to use a literal backtick, escape it
             change: `on_event` should be called.
            to this: `on_event\` should be called.
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: unescaped backtick
   --> $DIR/unescaped_backticks.rs:323:5
@@ -340,6 +342,7 @@ LL | |     /// level changes.
    = help: if you meant to use a literal backtick, escape it
             change: [`rebuild_interest_cache`][rebuild] is called after the value of the max
            to this: [`rebuild_interest_cache\`][rebuild] is called after the value of the max
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: unescaped backtick
   --> $DIR/unescaped_backticks.rs:349:56
diff --git a/tests/ui-fulldeps/plugin/lint-plugin-forbid-attrs.stderr b/tests/ui-fulldeps/plugin/lint-plugin-forbid-attrs.stderr
index ae34b25cc2f..66ea2e88f0c 100644
--- a/tests/ui-fulldeps/plugin/lint-plugin-forbid-attrs.stderr
+++ b/tests/ui-fulldeps/plugin/lint-plugin-forbid-attrs.stderr
@@ -27,6 +27,8 @@ LL | #![forbid(test_lint)]
 ...
 LL | #[allow(test_lint)]
    |         ^^^^^^^^^ overruled by previous forbid
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/lint-plugin-forbid-attrs.rs:5:1
diff --git a/tests/ui-fulldeps/plugin/lint-plugin-forbid-cmdline.stderr b/tests/ui-fulldeps/plugin/lint-plugin-forbid-cmdline.stderr
index 491c4d20646..9dbad702545 100644
--- a/tests/ui-fulldeps/plugin/lint-plugin-forbid-cmdline.stderr
+++ b/tests/ui-fulldeps/plugin/lint-plugin-forbid-cmdline.stderr
@@ -21,6 +21,7 @@ LL | #[allow(test_lint)]
    |         ^^^^^^^^^ overruled by previous forbid
    |
    = note: `forbid` lint level was set on command line
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/lint-plugin-forbid-cmdline.rs:6:1
diff --git a/tests/ui-fulldeps/plugin/lint-tool-cmdline-allow.stderr b/tests/ui-fulldeps/plugin/lint-tool-cmdline-allow.stderr
index 0e661795999..4916b180a36 100644
--- a/tests/ui-fulldeps/plugin/lint-tool-cmdline-allow.stderr
+++ b/tests/ui-fulldeps/plugin/lint-tool-cmdline-allow.stderr
@@ -8,6 +8,7 @@ warning: lint name `test_lint` is deprecated and may not have an effect in the f
    |
    = help: change it to clippy::test_lint
    = note: requested on the command line with `-A test_lint`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: item is named 'lintme'
   --> $DIR/lint-tool-cmdline-allow.rs:9:1
@@ -29,6 +30,7 @@ warning: lint name `test_lint` is deprecated and may not have an effect in the f
    |
    = help: change it to clippy::test_lint
    = note: requested on the command line with `-A test_lint`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: 5 warnings emitted
 
diff --git a/tests/ui-fulldeps/plugin/lint-tool-test.stderr b/tests/ui-fulldeps/plugin/lint-tool-test.stderr
index 027cf8f80cf..d1f0714f042 100644
--- a/tests/ui-fulldeps/plugin/lint-tool-test.stderr
+++ b/tests/ui-fulldeps/plugin/lint-tool-test.stderr
@@ -23,12 +23,16 @@ warning: lint name `test_lint` is deprecated and may not have an effect in the f
    |
 LL | #![cfg_attr(foo, warn(test_lint))]
    |                       ^^^^^^^^^ help: change it to: `clippy::test_lint`
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: lint name `clippy_group` is deprecated and may not have an effect in the future.
   --> $DIR/lint-tool-test.rs:13:9
    |
 LL | #![deny(clippy_group)]
    |         ^^^^^^^^^^^^ help: change it to: `clippy::group`
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: item is named 'lintme'
   --> $DIR/lint-tool-test.rs:18:1
@@ -56,6 +60,8 @@ warning: lint name `test_group` is deprecated and may not have an effect in the
    |
 LL | #[allow(test_group)]
    |         ^^^^^^^^^^ help: change it to: `clippy::test_group`
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: unknown lint: `this_lint_does_not_exist`
   --> $DIR/lint-tool-test.rs:33:8
@@ -78,18 +84,24 @@ warning: lint name `test_lint` is deprecated and may not have an effect in the f
    |
 LL | #![cfg_attr(foo, warn(test_lint))]
    |                       ^^^^^^^^^ help: change it to: `clippy::test_lint`
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: lint name `clippy_group` is deprecated and may not have an effect in the future.
   --> $DIR/lint-tool-test.rs:13:9
    |
 LL | #![deny(clippy_group)]
    |         ^^^^^^^^^^^^ help: change it to: `clippy::group`
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: lint name `test_group` is deprecated and may not have an effect in the future.
   --> $DIR/lint-tool-test.rs:29:9
    |
 LL | #[allow(test_group)]
    |         ^^^^^^^^^^ help: change it to: `clippy::test_group`
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors; 11 warnings emitted
 
diff --git a/tests/ui-fulldeps/session-diagnostic/diagnostic-derive.stderr b/tests/ui-fulldeps/session-diagnostic/diagnostic-derive.stderr
index ca09f1f0153..014cd5a73bd 100644
--- a/tests/ui-fulldeps/session-diagnostic/diagnostic-derive.stderr
+++ b/tests/ui-fulldeps/session-diagnostic/diagnostic-derive.stderr
@@ -414,6 +414,8 @@ error: `#[lint(...)]` is not a valid attribute
    |
 LL | #[lint(no_crate_example, code = "E0123")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: diagnostic slug not specified
   --> $DIR/diagnostic-derive.rs:601:1
diff --git a/tests/ui-fulldeps/stable-mir/crate-info.rs b/tests/ui-fulldeps/stable-mir/crate-info.rs
index ce4ee3c2463..d482f62ff06 100644
--- a/tests/ui-fulldeps/stable-mir/crate-info.rs
+++ b/tests/ui-fulldeps/stable-mir/crate-info.rs
@@ -47,12 +47,12 @@ fn test_stable_mir(_tcx: TyCtxt<'_>) -> ControlFlow<()> {
     assert_eq!(body.blocks.len(), 1);
     let block = &body.blocks[0];
     assert_eq!(block.statements.len(), 1);
-    match &block.statements[0] {
-        stable_mir::mir::Statement::Assign(..) => {}
+    match &block.statements[0].kind {
+        stable_mir::mir::StatementKind::Assign(..) => {}
         other => panic!("{other:?}"),
     }
-    match &block.terminator {
-        stable_mir::mir::Terminator::Return => {}
+    match &block.terminator.kind {
+        stable_mir::mir::TerminatorKind::Return => {}
         other => panic!("{other:?}"),
     }
 
@@ -61,8 +61,8 @@ fn test_stable_mir(_tcx: TyCtxt<'_>) -> ControlFlow<()> {
     assert_eq!(body.locals.len(), 7);
     assert_eq!(body.blocks.len(), 4);
     let block = &body.blocks[0];
-    match &block.terminator {
-        stable_mir::mir::Terminator::Call { .. } => {}
+    match &block.terminator.kind {
+        stable_mir::mir::TerminatorKind::Call { .. } => {}
         other => panic!("{other:?}"),
     }
 
@@ -70,27 +70,27 @@ fn test_stable_mir(_tcx: TyCtxt<'_>) -> ControlFlow<()> {
     let body = types.body();
     assert_eq!(body.locals.len(), 6);
     assert_matches!(
-        body.locals[0].kind(),
+        body.locals[0].ty.kind(),
         stable_mir::ty::TyKind::RigidTy(stable_mir::ty::RigidTy::Bool)
     );
     assert_matches!(
-        body.locals[1].kind(),
+        body.locals[1].ty.kind(),
         stable_mir::ty::TyKind::RigidTy(stable_mir::ty::RigidTy::Bool)
     );
     assert_matches!(
-        body.locals[2].kind(),
+        body.locals[2].ty.kind(),
         stable_mir::ty::TyKind::RigidTy(stable_mir::ty::RigidTy::Char)
     );
     assert_matches!(
-        body.locals[3].kind(),
+        body.locals[3].ty.kind(),
         stable_mir::ty::TyKind::RigidTy(stable_mir::ty::RigidTy::Int(stable_mir::ty::IntTy::I32))
     );
     assert_matches!(
-        body.locals[4].kind(),
+        body.locals[4].ty.kind(),
         stable_mir::ty::TyKind::RigidTy(stable_mir::ty::RigidTy::Uint(stable_mir::ty::UintTy::U64))
     );
     assert_matches!(
-        body.locals[5].kind(),
+        body.locals[5].ty.kind(),
         stable_mir::ty::TyKind::RigidTy(stable_mir::ty::RigidTy::Float(
             stable_mir::ty::FloatTy::F64
         ))
@@ -100,8 +100,8 @@ fn test_stable_mir(_tcx: TyCtxt<'_>) -> ControlFlow<()> {
     let body = drop.body();
     assert_eq!(body.blocks.len(), 2);
     let block = &body.blocks[0];
-    match &block.terminator {
-        stable_mir::mir::Terminator::Drop { .. } => {}
+    match &block.terminator.kind {
+        stable_mir::mir::TerminatorKind::Drop { .. } => {}
         other => panic!("{other:?}"),
     }
 
@@ -109,15 +109,15 @@ fn test_stable_mir(_tcx: TyCtxt<'_>) -> ControlFlow<()> {
     let body = assert.body();
     assert_eq!(body.blocks.len(), 2);
     let block = &body.blocks[0];
-    match &block.terminator {
-        stable_mir::mir::Terminator::Assert { .. } => {}
+    match &block.terminator.kind {
+        stable_mir::mir::TerminatorKind::Assert { .. } => {}
         other => panic!("{other:?}"),
     }
 
     let monomorphic = get_item(&items, (DefKind::Fn, "monomorphic")).unwrap();
     for block in monomorphic.body().blocks {
-        match &block.terminator {
-            stable_mir::mir::Terminator::Call { func, .. } => match func {
+        match &block.terminator.kind {
+            stable_mir::mir::TerminatorKind::Call { func, .. } => match func {
                 stable_mir::mir::Operand::Constant(c) => match &c.literal.literal {
                     stable_mir::ty::ConstantKind::Allocated(alloc) => {
                         assert!(alloc.bytes.is_empty());
@@ -127,7 +127,7 @@ fn test_stable_mir(_tcx: TyCtxt<'_>) -> ControlFlow<()> {
                                 mut args,
                             )) => {
                                 let func = def.body();
-                                match func.locals[1]
+                                match func.locals[1].ty
                                     .fold(&mut args)
                                     .continue_value()
                                     .unwrap()
@@ -149,7 +149,7 @@ fn test_stable_mir(_tcx: TyCtxt<'_>) -> ControlFlow<()> {
                 },
                 other => panic!("{other:?}"),
             },
-            stable_mir::mir::Terminator::Return => {}
+            stable_mir::mir::TerminatorKind::Return => {}
             other => panic!("{other:?}"),
         }
     }
diff --git a/tests/ui/allocator/not-an-allocator.stderr b/tests/ui/allocator/not-an-allocator.stderr
index 62bb0679f81..e1967b70013 100644
--- a/tests/ui/allocator/not-an-allocator.stderr
+++ b/tests/ui/allocator/not-an-allocator.stderr
@@ -18,6 +18,7 @@ LL | static A: usize = 0;
    |           ^^^^^ the trait `GlobalAlloc` is not implemented for `usize`
    |
    = help: the trait `GlobalAlloc` is implemented for `System`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
    = note: this error originates in the attribute macro `global_allocator` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0277]: the trait bound `usize: GlobalAlloc` is not satisfied
@@ -29,6 +30,7 @@ LL | static A: usize = 0;
    |           ^^^^^ the trait `GlobalAlloc` is not implemented for `usize`
    |
    = help: the trait `GlobalAlloc` is implemented for `System`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
    = note: this error originates in the attribute macro `global_allocator` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0277]: the trait bound `usize: GlobalAlloc` is not satisfied
@@ -40,6 +42,7 @@ LL | static A: usize = 0;
    |           ^^^^^ the trait `GlobalAlloc` is not implemented for `usize`
    |
    = help: the trait `GlobalAlloc` is implemented for `System`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
    = note: this error originates in the attribute macro `global_allocator` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 4 previous errors
diff --git a/tests/ui/associated-consts/defaults-not-assumed-fail.stderr b/tests/ui/associated-consts/defaults-not-assumed-fail.stderr
index d659912341a..ac5ec8e05ea 100644
--- a/tests/ui/associated-consts/defaults-not-assumed-fail.stderr
+++ b/tests/ui/associated-consts/defaults-not-assumed-fail.stderr
@@ -24,6 +24,7 @@ note: erroneous constant encountered
 LL |     assert_eq!(<() as Tr>::B, 0);    // causes the error above
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
    = note: this note originates in the macro `assert_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to previous error
diff --git a/tests/ui/associated-inherent-types/issue-109789.stderr b/tests/ui/associated-inherent-types/issue-109789.stderr
index 84fc85cd09e..e844f6795e6 100644
--- a/tests/ui/associated-inherent-types/issue-109789.stderr
+++ b/tests/ui/associated-inherent-types/issue-109789.stderr
@@ -15,6 +15,7 @@ LL | fn bar(_: Foo<for<'a> fn(&'a ())>::Assoc) {}
    |
    = note: expected struct `Foo<fn(&'static ())>`
               found struct `Foo<for<'a> fn(&'a ())>`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/associated-type-bounds/duplicate.stderr b/tests/ui/associated-type-bounds/duplicate.stderr
index 08721eff7b0..3629aa4fcea 100644
--- a/tests/ui/associated-type-bounds/duplicate.stderr
+++ b/tests/ui/associated-type-bounds/duplicate.stderr
@@ -373,6 +373,8 @@ LL | trait TRS1: Iterator<Item: Copy, Item: Send> {}
    |                      ----------  ^^^^^^^^^^ re-bound here
    |                      |
    |                      `Item` bound here first
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0719]: the value of the associated type `Item` (from trait `Iterator`) is already specified
   --> $DIR/duplicate.rs:197:34
@@ -389,6 +391,8 @@ LL | trait TRS2: Iterator<Item: Copy, Item: Copy> {}
    |                      ----------  ^^^^^^^^^^ re-bound here
    |                      |
    |                      `Item` bound here first
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0719]: the value of the associated type `Item` (from trait `Iterator`) is already specified
   --> $DIR/duplicate.rs:200:37
@@ -405,6 +409,8 @@ LL | trait TRS3: Iterator<Item: 'static, Item: 'static> {}
    |                      -------------  ^^^^^^^^^^^^^ re-bound here
    |                      |
    |                      `Item` bound here first
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0719]: the value of the associated type `Item` (from trait `Iterator`) is already specified
   --> $DIR/duplicate.rs:205:29
@@ -445,6 +451,8 @@ LL |     Self: Iterator<Item: Copy, Item: Send>,
    |                    ----------  ^^^^^^^^^^ re-bound here
    |                    |
    |                    `Item` bound here first
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0719]: the value of the associated type `Item` (from trait `Iterator`) is already specified
   --> $DIR/duplicate.rs:230:32
@@ -461,6 +469,8 @@ LL |     Self: Iterator<Item: Copy, Item: Copy>,
    |                    ----------  ^^^^^^^^^^ re-bound here
    |                    |
    |                    `Item` bound here first
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0719]: the value of the associated type `Item` (from trait `Iterator`) is already specified
   --> $DIR/duplicate.rs:237:35
@@ -477,6 +487,8 @@ LL |     Self: Iterator<Item: 'static, Item: 'static>,
    |                    -------------  ^^^^^^^^^^^^^ re-bound here
    |                    |
    |                    `Item` bound here first
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0719]: the value of the associated type `Item` (from trait `Iterator`) is already specified
   --> $DIR/duplicate.rs:255:40
diff --git a/tests/ui/associated-types/hr-associated-type-bound-param-2.stderr b/tests/ui/associated-types/hr-associated-type-bound-param-2.stderr
index 366670269d7..1a749007ab6 100644
--- a/tests/ui/associated-types/hr-associated-type-bound-param-2.stderr
+++ b/tests/ui/associated-types/hr-associated-type-bound-param-2.stderr
@@ -45,6 +45,7 @@ LL | trait Z<'a, T: ?Sized>
 ...
 LL |     for<'b> <T as Z<'b, u16>>::W: Clone,
    |                                   ^^^^^ required by this bound in `Z`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 3 previous errors
 
diff --git a/tests/ui/async-await/drop-tracking-unresolved-typeck-results.stderr b/tests/ui/async-await/drop-tracking-unresolved-typeck-results.stderr
index cfb0ebe38b6..0d3ee8a9377 100644
--- a/tests/ui/async-await/drop-tracking-unresolved-typeck-results.stderr
+++ b/tests/ui/async-await/drop-tracking-unresolved-typeck-results.stderr
@@ -23,6 +23,7 @@ LL | |     });
    |
    = note: `fn(&'0 ()) -> std::future::Ready<&'0 ()> {std::future::ready::<&'0 ()>}` must implement `FnOnce<(&'1 (),)>`, for any two lifetimes `'0` and `'1`...
    = note: ...but it actually implements `FnOnce<(&(),)>`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/async-await/return-type-notation/issue-110963-early.stderr b/tests/ui/async-await/return-type-notation/issue-110963-early.stderr
index 969094a2c58..98e3cbd0d7f 100644
--- a/tests/ui/async-await/return-type-notation/issue-110963-early.stderr
+++ b/tests/ui/async-await/return-type-notation/issue-110963-early.stderr
@@ -44,6 +44,7 @@ note: the lifetime requirement is introduced here
    |
 LL |     F: Future + Send + 'static,
    |                 ^^^^
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors; 1 warning emitted
 
diff --git a/tests/ui/borrowck/regions-bound-missing-bound-in-impl.stderr b/tests/ui/borrowck/regions-bound-missing-bound-in-impl.stderr
index 930fea9158d..7ebea3c03d3 100644
--- a/tests/ui/borrowck/regions-bound-missing-bound-in-impl.stderr
+++ b/tests/ui/borrowck/regions-bound-missing-bound-in-impl.stderr
@@ -53,6 +53,7 @@ note: ...does not necessarily outlive the lifetime `'c` as defined here
    |
 LL |     fn wrong_bound1<'b,'c,'d:'a+'c>(self, b: Inv<'b>, c: Inv<'c>, d: Inv<'d>) {
    |                        ^^
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0195]: lifetime parameters or bounds on method `wrong_bound2` do not match the trait declaration
   --> $DIR/regions-bound-missing-bound-in-impl.rs:42:20
diff --git a/tests/ui/cfg/future-compat-crate-attributes-using-cfg_attr.stderr b/tests/ui/cfg/future-compat-crate-attributes-using-cfg_attr.stderr
index 9ce4710d69b..75df314e0ba 100644
--- a/tests/ui/cfg/future-compat-crate-attributes-using-cfg_attr.stderr
+++ b/tests/ui/cfg/future-compat-crate-attributes-using-cfg_attr.stderr
@@ -25,6 +25,7 @@ LL | #![cfg_attr(foo, crate_type="bin")]
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #91632 <https://github.com/rust-lang/rust/issues/91632>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: `crate_name` within an `#![cfg_attr] attribute is deprecated`
   --> $DIR/future-compat-crate-attributes-using-cfg_attr.rs:9:18
@@ -34,6 +35,7 @@ LL | #![cfg_attr(foo, crate_name="bar")]
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #91632 <https://github.com/rust-lang/rust/issues/91632>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 4 previous errors
 
diff --git a/tests/ui/conditional-compilation/cfg-attr-syntax-validation.stderr b/tests/ui/conditional-compilation/cfg-attr-syntax-validation.stderr
index d5b4349c00f..12557ff6360 100644
--- a/tests/ui/conditional-compilation/cfg-attr-syntax-validation.stderr
+++ b/tests/ui/conditional-compilation/cfg-attr-syntax-validation.stderr
@@ -74,6 +74,7 @@ LL |         #[cfg(feature = $expr)]
 LL | generate_s10!(concat!("nonexistent"));
    | ------------------------------------- in this macro invocation
    |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
    = note: this error originates in the macro `generate_s10` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 11 previous errors
diff --git a/tests/ui/const-generics/assoc_const_eq_diagnostic.stderr b/tests/ui/const-generics/assoc_const_eq_diagnostic.stderr
index d7e5e50cba8..6d5cd45479e 100644
--- a/tests/ui/const-generics/assoc_const_eq_diagnostic.stderr
+++ b/tests/ui/const-generics/assoc_const_eq_diagnostic.stderr
@@ -39,6 +39,7 @@ note: associated constant defined here
    |
 LL |     const MODE: Mode;
    |     ^^^^^^^^^^^^^^^^
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 4 previous errors
 
diff --git a/tests/ui/const-generics/issues/issue-74950.min.stderr b/tests/ui/const-generics/issues/issue-74950.min.stderr
index a5dbe10b78a..54ef1ea1e94 100644
--- a/tests/ui/const-generics/issues/issue-74950.min.stderr
+++ b/tests/ui/const-generics/issues/issue-74950.min.stderr
@@ -15,6 +15,7 @@ LL | struct Outer<const I: Inner>;
    |
    = note: the only supported types are integers, `bool` and `char`
    = help: add `#![feature(adt_const_params)]` to the crate attributes to enable more complex and user defined types
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: `Inner` is forbidden as the type of a const generic parameter
   --> $DIR/issue-74950.rs:20:23
@@ -24,6 +25,7 @@ LL | struct Outer<const I: Inner>;
    |
    = note: the only supported types are integers, `bool` and `char`
    = help: add `#![feature(adt_const_params)]` to the crate attributes to enable more complex and user defined types
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: `Inner` is forbidden as the type of a const generic parameter
   --> $DIR/issue-74950.rs:20:23
@@ -33,6 +35,7 @@ LL | struct Outer<const I: Inner>;
    |
    = note: the only supported types are integers, `bool` and `char`
    = help: add `#![feature(adt_const_params)]` to the crate attributes to enable more complex and user defined types
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: `Inner` is forbidden as the type of a const generic parameter
   --> $DIR/issue-74950.rs:20:23
@@ -42,6 +45,7 @@ LL | struct Outer<const I: Inner>;
    |
    = note: the only supported types are integers, `bool` and `char`
    = help: add `#![feature(adt_const_params)]` to the crate attributes to enable more complex and user defined types
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 5 previous errors
 
diff --git a/tests/ui/consts/const-err-late.stderr b/tests/ui/consts/const-err-late.stderr
index 85bc56baed8..35c3d000117 100644
--- a/tests/ui/consts/const-err-late.stderr
+++ b/tests/ui/consts/const-err-late.stderr
@@ -27,6 +27,8 @@ note: erroneous constant encountered
    |
 LL |     black_box((S::<i32>::FOO, S::<u32>::FOO));
    |                ^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/consts/const-eval/issue-44578.stderr b/tests/ui/consts/const-eval/issue-44578.stderr
index c7aaee94271..eea42c8ce45 100644
--- a/tests/ui/consts/const-eval/issue-44578.stderr
+++ b/tests/ui/consts/const-eval/issue-44578.stderr
@@ -24,6 +24,7 @@ note: erroneous constant encountered
 LL |     println!("{}", <Bar<u16, u8> as Foo>::AMT);
    |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
    = note: this note originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to previous error
diff --git a/tests/ui/consts/const-eval/panic-assoc-never-type.stderr b/tests/ui/consts/const-eval/panic-assoc-never-type.stderr
index 4706497dbc4..50660664f87 100644
--- a/tests/ui/consts/const-eval/panic-assoc-never-type.stderr
+++ b/tests/ui/consts/const-eval/panic-assoc-never-type.stderr
@@ -17,6 +17,8 @@ note: erroneous constant encountered
    |
 LL |     let _ = PrintName::VOID;
    |             ^^^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to previous error
 
diff --git a/tests/ui/consts/const-eval/stable-metric/ctfe-simple-loop.warn.stderr b/tests/ui/consts/const-eval/stable-metric/ctfe-simple-loop.warn.stderr
index 40fc4a876e9..8eee392d15c 100644
--- a/tests/ui/consts/const-eval/stable-metric/ctfe-simple-loop.warn.stderr
+++ b/tests/ui/consts/const-eval/stable-metric/ctfe-simple-loop.warn.stderr
@@ -40,6 +40,7 @@ help: the constant being evaluated
    |
 LL | const Y: u32 = simple_loop(35);
    | ^^^^^^^^^^^^
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: constant evaluation is taking a long time
   --> $DIR/ctfe-simple-loop.rs:9:5
diff --git a/tests/ui/consts/const-eval/union-const-eval-field.rs b/tests/ui/consts/const-eval/union-const-eval-field.rs
index a94fcbbfa56..c9799989ea8 100644
--- a/tests/ui/consts/const-eval/union-const-eval-field.rs
+++ b/tests/ui/consts/const-eval/union-const-eval-field.rs
@@ -1,5 +1,3 @@
-// only-x86_64
-
 type Field1 = i32;
 type Field2 = f32;
 type Field3 = i64;
diff --git a/tests/ui/consts/const-eval/union-const-eval-field.stderr b/tests/ui/consts/const-eval/union-const-eval-field.stderr
index ce260300fc8..b299208ae81 100644
--- a/tests/ui/consts/const-eval/union-const-eval-field.stderr
+++ b/tests/ui/consts/const-eval/union-const-eval-field.stderr
@@ -1,20 +1,22 @@
 error[E0080]: evaluation of constant value failed
-  --> $DIR/union-const-eval-field.rs:28:37
+  --> $DIR/union-const-eval-field.rs:26:37
    |
 LL |     const FIELD3: Field3 = unsafe { UNION.field3 };
    |                                     ^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory
 
 note: erroneous constant encountered
-  --> $DIR/union-const-eval-field.rs:31:5
+  --> $DIR/union-const-eval-field.rs:29:5
    |
 LL |     FIELD3
    |     ^^^^^^
 
 note: erroneous constant encountered
-  --> $DIR/union-const-eval-field.rs:31:5
+  --> $DIR/union-const-eval-field.rs:29:5
    |
 LL |     FIELD3
    |     ^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to previous error
 
diff --git a/tests/ui/consts/const_in_pattern/reject_non_structural.rs b/tests/ui/consts/const_in_pattern/reject_non_structural.rs
index dc6b9a33197..df772740ab1 100644
--- a/tests/ui/consts/const_in_pattern/reject_non_structural.rs
+++ b/tests/ui/consts/const_in_pattern/reject_non_structural.rs
@@ -1,3 +1,5 @@
+// compile-flags: -Zdeduplicate-diagnostics=yes
+
 // This test of structural match checking enumerates the different kinds of
 // const definitions, collecting cases where the const pattern is rejected.
 //
@@ -78,9 +80,6 @@ fn main() {
     //~^ ERROR must be annotated with `#[derive(PartialEq, Eq)]`
     //~| NOTE the traits must be derived
     //~| NOTE StructuralEq.html for details
-    //~| ERROR must be annotated with `#[derive(PartialEq, Eq)]`
-    //~| NOTE the traits must be derived
-    //~| NOTE StructuralEq.html for details
 
     trait Trait: Sized { const ASSOC: Option<Self>; }
     impl Trait for NoDerive { const ASSOC: Option<NoDerive> = Some(NoDerive); }
diff --git a/tests/ui/consts/const_in_pattern/reject_non_structural.stderr b/tests/ui/consts/const_in_pattern/reject_non_structural.stderr
index b6e439f2139..72bb0aeafa4 100644
--- a/tests/ui/consts/const_in_pattern/reject_non_structural.stderr
+++ b/tests/ui/consts/const_in_pattern/reject_non_structural.stderr
@@ -1,5 +1,5 @@
 error: to use a constant of type `NoDerive` in a pattern, `NoDerive` must be annotated with `#[derive(PartialEq, Eq)]`
-  --> $DIR/reject_non_structural.rs:40:36
+  --> $DIR/reject_non_structural.rs:42:36
    |
 LL |     match Derive::Some(NoDerive) { ENUM => dbg!(ENUM), _ => panic!("whoops"), };
    |                                    ^^^^
@@ -8,7 +8,7 @@ LL |     match Derive::Some(NoDerive) { ENUM => dbg!(ENUM), _ => panic!("whoops"
    = note: see https://doc.rust-lang.org/stable/std/marker/trait.StructuralEq.html for details
 
 error: to use a constant of type `NoDerive` in a pattern, `NoDerive` must be annotated with `#[derive(PartialEq, Eq)]`
-  --> $DIR/reject_non_structural.rs:46:28
+  --> $DIR/reject_non_structural.rs:48:28
    |
 LL |     match Some(NoDerive) { FIELD => dbg!(FIELD), _ => panic!("whoops"), };
    |                            ^^^^^
@@ -17,7 +17,7 @@ LL |     match Some(NoDerive) { FIELD => dbg!(FIELD), _ => panic!("whoops"), };
    = note: see https://doc.rust-lang.org/stable/std/marker/trait.StructuralEq.html for details
 
 error: to use a constant of type `NoDerive` in a pattern, `NoDerive` must be annotated with `#[derive(PartialEq, Eq)]`
-  --> $DIR/reject_non_structural.rs:53:27
+  --> $DIR/reject_non_structural.rs:55:27
    |
 LL |     match Some(NoDerive) {INDIRECT => dbg!(INDIRECT), _ => panic!("whoops"), };
    |                           ^^^^^^^^
@@ -26,7 +26,7 @@ LL |     match Some(NoDerive) {INDIRECT => dbg!(INDIRECT), _ => panic!("whoops")
    = note: see https://doc.rust-lang.org/stable/std/marker/trait.StructuralEq.html for details
 
 error: to use a constant of type `NoDerive` in a pattern, `NoDerive` must be annotated with `#[derive(PartialEq, Eq)]`
-  --> $DIR/reject_non_structural.rs:59:36
+  --> $DIR/reject_non_structural.rs:61:36
    |
 LL |     match (None, Some(NoDerive)) { TUPLE => dbg!(TUPLE), _ => panic!("whoops"), };
    |                                    ^^^^^
@@ -35,7 +35,7 @@ LL |     match (None, Some(NoDerive)) { TUPLE => dbg!(TUPLE), _ => panic!("whoop
    = note: see https://doc.rust-lang.org/stable/std/marker/trait.StructuralEq.html for details
 
 error: to use a constant of type `NoDerive` in a pattern, `NoDerive` must be annotated with `#[derive(PartialEq, Eq)]`
-  --> $DIR/reject_non_structural.rs:65:28
+  --> $DIR/reject_non_structural.rs:67:28
    |
 LL |     match Some(NoDerive) { TYPE_ASCRIPTION => dbg!(TYPE_ASCRIPTION), _ => panic!("whoops"), };
    |                            ^^^^^^^^^^^^^^^
@@ -44,7 +44,7 @@ LL |     match Some(NoDerive) { TYPE_ASCRIPTION => dbg!(TYPE_ASCRIPTION), _ => p
    = note: see https://doc.rust-lang.org/stable/std/marker/trait.StructuralEq.html for details
 
 error: to use a constant of type `NoDerive` in a pattern, `NoDerive` must be annotated with `#[derive(PartialEq, Eq)]`
-  --> $DIR/reject_non_structural.rs:71:36
+  --> $DIR/reject_non_structural.rs:73:36
    |
 LL |     match [None, Some(NoDerive)] { ARRAY => dbg!(ARRAY), _ => panic!("whoops"), };
    |                                    ^^^^^
@@ -53,7 +53,7 @@ LL |     match [None, Some(NoDerive)] { ARRAY => dbg!(ARRAY), _ => panic!("whoop
    = note: see https://doc.rust-lang.org/stable/std/marker/trait.StructuralEq.html for details
 
 error: to use a constant of type `NoDerive` in a pattern, `NoDerive` must be annotated with `#[derive(PartialEq, Eq)]`
-  --> $DIR/reject_non_structural.rs:77:33
+  --> $DIR/reject_non_structural.rs:79:33
    |
 LL |     match [Some(NoDerive); 2] { REPEAT => dbg!(REPEAT), _ => panic!("whoops"), };
    |                                 ^^^^^^
@@ -62,16 +62,7 @@ LL |     match [Some(NoDerive); 2] { REPEAT => dbg!(REPEAT), _ => panic!("whoops
    = note: see https://doc.rust-lang.org/stable/std/marker/trait.StructuralEq.html for details
 
 error: to use a constant of type `NoDerive` in a pattern, `NoDerive` must be annotated with `#[derive(PartialEq, Eq)]`
-  --> $DIR/reject_non_structural.rs:77:33
-   |
-LL |     match [Some(NoDerive); 2] { REPEAT => dbg!(REPEAT), _ => panic!("whoops"), };
-   |                                 ^^^^^^
-   |
-   = note: the traits must be derived, manual `impl`s are not sufficient
-   = note: see https://doc.rust-lang.org/stable/std/marker/trait.StructuralEq.html for details
-
-error: to use a constant of type `NoDerive` in a pattern, `NoDerive` must be annotated with `#[derive(PartialEq, Eq)]`
-  --> $DIR/reject_non_structural.rs:87:28
+  --> $DIR/reject_non_structural.rs:86:28
    |
 LL |     match Some(NoDerive) { NoDerive::ASSOC => dbg!(NoDerive::ASSOC), _ => panic!("whoops"), };
    |                            ^^^^^^^^^^^^^^^
@@ -80,7 +71,7 @@ LL |     match Some(NoDerive) { NoDerive::ASSOC => dbg!(NoDerive::ASSOC), _ => p
    = note: see https://doc.rust-lang.org/stable/std/marker/trait.StructuralEq.html for details
 
 error: to use a constant of type `NoDerive` in a pattern, `NoDerive` must be annotated with `#[derive(PartialEq, Eq)]`
-  --> $DIR/reject_non_structural.rs:93:28
+  --> $DIR/reject_non_structural.rs:92:28
    |
 LL |     match Some(NoDerive) { BLOCK => dbg!(BLOCK), _ => panic!("whoops"), };
    |                            ^^^^^
@@ -89,7 +80,7 @@ LL |     match Some(NoDerive) { BLOCK => dbg!(BLOCK), _ => panic!("whoops"), };
    = note: see https://doc.rust-lang.org/stable/std/marker/trait.StructuralEq.html for details
 
 warning: to use a constant of type `NoDerive` in a pattern, `NoDerive` must be annotated with `#[derive(PartialEq, Eq)]`
-  --> $DIR/reject_non_structural.rs:99:29
+  --> $DIR/reject_non_structural.rs:98:29
    |
 LL |     match &Some(NoDerive) { ADDR_OF => dbg!(ADDR_OF), _ => panic!("whoops"), };
    |                             ^^^^^^^
@@ -99,10 +90,10 @@ LL |     match &Some(NoDerive) { ADDR_OF => dbg!(ADDR_OF), _ => panic!("whoops")
    = note: the traits must be derived, manual `impl`s are not sufficient
    = note: see https://doc.rust-lang.org/stable/std/marker/trait.StructuralEq.html for details
 note: the lint level is defined here
-  --> $DIR/reject_non_structural.rs:12:9
+  --> $DIR/reject_non_structural.rs:14:9
    |
 LL | #![warn(indirect_structural_match)]
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 10 previous errors; 1 warning emitted
+error: aborting due to 9 previous errors; 1 warning emitted
 
diff --git a/tests/ui/consts/enum-discr-type-err.stderr b/tests/ui/consts/enum-discr-type-err.stderr
index 2f97582bea8..9a09d6a96f1 100644
--- a/tests/ui/consts/enum-discr-type-err.stderr
+++ b/tests/ui/consts/enum-discr-type-err.stderr
@@ -24,6 +24,7 @@ LL | |     B = T,
 LL | | }
    | |_- in this macro invocation
    |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
    = note: this error originates in the macro `mac` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 2 previous errors
diff --git a/tests/ui/consts/fn_trait_refs.stderr b/tests/ui/consts/fn_trait_refs.stderr
index 658a0b7b2a0..3d82837d530 100644
--- a/tests/ui/consts/fn_trait_refs.stderr
+++ b/tests/ui/consts/fn_trait_refs.stderr
@@ -21,6 +21,8 @@ error: ~const can only be applied to `#[const_trait]` traits
    |
 LL |     T: ~const Fn<()> + ~const Destruct,
    |               ^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: ~const can only be applied to `#[const_trait]` traits
   --> $DIR/fn_trait_refs.rs:22:15
@@ -33,6 +35,8 @@ error: ~const can only be applied to `#[const_trait]` traits
    |
 LL |     T: ~const FnMut<()> + ~const Destruct,
    |               ^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: ~const can only be applied to `#[const_trait]` traits
   --> $DIR/fn_trait_refs.rs:29:15
@@ -45,6 +49,8 @@ error: ~const can only be applied to `#[const_trait]` traits
    |
 LL |     T: ~const FnOnce<()>,
    |               ^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: ~const can only be applied to `#[const_trait]` traits
   --> $DIR/fn_trait_refs.rs:36:15
@@ -57,6 +63,8 @@ error: ~const can only be applied to `#[const_trait]` traits
    |
 LL |     T: ~const Fn<()> + ~const Destruct,
    |               ^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: ~const can only be applied to `#[const_trait]` traits
   --> $DIR/fn_trait_refs.rs:50:15
@@ -69,6 +77,8 @@ error: ~const can only be applied to `#[const_trait]` traits
    |
 LL |     T: ~const FnMut<()> + ~const Destruct,
    |               ^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 12 previous errors
 
diff --git a/tests/ui/consts/invalid-union.32bit.stderr b/tests/ui/consts/invalid-union.32bit.stderr
index b6cf060e5ae..0c57751cbfa 100644
--- a/tests/ui/consts/invalid-union.32bit.stderr
+++ b/tests/ui/consts/invalid-union.32bit.stderr
@@ -20,6 +20,8 @@ note: erroneous constant encountered
    |
 LL |     let _: &'static _ = &C;
    |                         ^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to previous error
 
diff --git a/tests/ui/consts/invalid-union.64bit.stderr b/tests/ui/consts/invalid-union.64bit.stderr
index e3a3ef62c4a..6c4d5882158 100644
--- a/tests/ui/consts/invalid-union.64bit.stderr
+++ b/tests/ui/consts/invalid-union.64bit.stderr
@@ -20,6 +20,8 @@ note: erroneous constant encountered
    |
 LL |     let _: &'static _ = &C;
    |                         ^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to previous error
 
diff --git a/tests/ui/consts/issue-102117.stderr b/tests/ui/consts/issue-102117.stderr
index f42bcf90fb7..a297916b30f 100644
--- a/tests/ui/consts/issue-102117.stderr
+++ b/tests/ui/consts/issue-102117.stderr
@@ -15,6 +15,7 @@ error[E0310]: the parameter type `T` may not live long enough
 LL |                 type_id: TypeId::of::<T>(),
    |                          ^^^^^^^^^^^^^^^^^ ...so that the type `T` will meet its required lifetime bounds
    |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: consider adding an explicit lifetime bound...
    |
 LL |     pub fn new<T: 'static>() -> &'static Self {
diff --git a/tests/ui/consts/issue-17718-const-bad-values.stderr b/tests/ui/consts/issue-17718-const-bad-values.stderr
index ce60aaa0797..405c2195dec 100644
--- a/tests/ui/consts/issue-17718-const-bad-values.stderr
+++ b/tests/ui/consts/issue-17718-const-bad-values.stderr
@@ -19,6 +19,7 @@ LL | const C2: &'static mut usize = unsafe { &mut S };
    |                                              ^
    |
    = help: consider extracting the value of the `static` to a `const`, and referring to that
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 3 previous errors
 
diff --git a/tests/ui/consts/miri_unleashed/assoc_const.stderr b/tests/ui/consts/miri_unleashed/assoc_const.stderr
index 274b1de7e7d..b129aef3452 100644
--- a/tests/ui/consts/miri_unleashed/assoc_const.stderr
+++ b/tests/ui/consts/miri_unleashed/assoc_const.stderr
@@ -24,6 +24,8 @@ note: erroneous constant encountered
    |
 LL |     let y = <String as Bar<Vec<u32>, String>>::F;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: skipping const checks
    |
diff --git a/tests/ui/consts/miri_unleashed/assoc_const_2.stderr b/tests/ui/consts/miri_unleashed/assoc_const_2.stderr
index c8e4cab4e71..46408f6748d 100644
--- a/tests/ui/consts/miri_unleashed/assoc_const_2.stderr
+++ b/tests/ui/consts/miri_unleashed/assoc_const_2.stderr
@@ -15,6 +15,8 @@ note: erroneous constant encountered
    |
 LL |     let y = <String as Bar<String>>::F;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to previous error
 
diff --git a/tests/ui/consts/uninhabited-const-issue-61744.stderr b/tests/ui/consts/uninhabited-const-issue-61744.stderr
index f48e6c4ce51..c92824a0d1a 100644
--- a/tests/ui/consts/uninhabited-const-issue-61744.stderr
+++ b/tests/ui/consts/uninhabited-const-issue-61744.stderr
@@ -656,6 +656,8 @@ note: erroneous constant encountered
    |
 LL |     dbg!(i32::CONSTANT);
    |          ^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to previous error
 
diff --git a/tests/ui/crate-loading/invalid-rlib.rs b/tests/ui/crate-loading/invalid-rlib.rs
index aea861e3261..0997bee19bb 100644
--- a/tests/ui/crate-loading/invalid-rlib.rs
+++ b/tests/ui/crate-loading/invalid-rlib.rs
@@ -8,3 +8,4 @@ use ::foo; //~ ERROR invalid metadata files for crate `foo`
 //~| NOTE failed to mmap file
 //~^^ ERROR invalid metadata files for crate `foo`
 //~| NOTE failed to mmap file
+//~| NOTE duplicate diagnostic
diff --git a/tests/ui/crate-loading/invalid-rlib.stderr b/tests/ui/crate-loading/invalid-rlib.stderr
index 3c0d23bf7b4..63bb1b95cbb 100644
--- a/tests/ui/crate-loading/invalid-rlib.stderr
+++ b/tests/ui/crate-loading/invalid-rlib.stderr
@@ -13,6 +13,7 @@ LL | use ::foo;
    |       ^^^
    |
    = note: failed to mmap file 'auxiliary/libfoo.rlib'
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/deduplicate-diagnostics.duplicate.stderr b/tests/ui/deduplicate-diagnostics.duplicate.stderr
index cd4700c7a7c..0544b993278 100644
--- a/tests/ui/deduplicate-diagnostics.duplicate.stderr
+++ b/tests/ui/deduplicate-diagnostics.duplicate.stderr
@@ -15,12 +15,16 @@ error: cannot find derive macro `Unresolved` in this scope
    |
 LL | #[derive(Unresolved)]
    |          ^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0452]: malformed lint attribute input
   --> $DIR/deduplicate-diagnostics.rs:8:8
    |
 LL | #[deny("literal")]
    |        ^^^^^^^^^ bad attribute argument
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 4 previous errors
 
diff --git a/tests/ui/derives/deriving-bounds.stderr b/tests/ui/derives/deriving-bounds.stderr
index 74ca37287d2..4461652eb02 100644
--- a/tests/ui/derives/deriving-bounds.stderr
+++ b/tests/ui/derives/deriving-bounds.stderr
@@ -21,6 +21,7 @@ note: unsafe traits like `Sync` should be implemented explicitly
    |
 LL | #[derive(Sync)]
    |          ^^^^
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: cannot find derive macro `Send` in this scope
   --> $DIR/deriving-bounds.rs:1:10
@@ -45,6 +46,7 @@ note: unsafe traits like `Send` should be implemented explicitly
    |
 LL | #[derive(Send)]
    |          ^^^^
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 4 previous errors
 
diff --git a/tests/ui/derives/deriving-meta-unknown-trait.stderr b/tests/ui/derives/deriving-meta-unknown-trait.stderr
index 053d34f6825..28753b8f9f2 100644
--- a/tests/ui/derives/deriving-meta-unknown-trait.stderr
+++ b/tests/ui/derives/deriving-meta-unknown-trait.stderr
@@ -15,6 +15,8 @@ LL | #[derive(Eqr)]
   --> $SRC_DIR/core/src/cmp.rs:LL:COL
    |
    = note: similarly named derive macro `Eq` defined here
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/derives/deriving-primitive.stderr b/tests/ui/derives/deriving-primitive.stderr
index ca64c9ee732..b39637825e5 100644
--- a/tests/ui/derives/deriving-primitive.stderr
+++ b/tests/ui/derives/deriving-primitive.stderr
@@ -9,6 +9,8 @@ error: cannot find derive macro `FromPrimitive` in this scope
    |
 LL | #[derive(FromPrimitive)]
    |          ^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/diagnostic_namespace/on_unimplemented/do_not_fail_parsing_on_invalid_options_1.stderr b/tests/ui/diagnostic_namespace/on_unimplemented/do_not_fail_parsing_on_invalid_options_1.stderr
index bb1b29ef248..bd39c91ffe8 100644
--- a/tests/ui/diagnostic_namespace/on_unimplemented/do_not_fail_parsing_on_invalid_options_1.stderr
+++ b/tests/ui/diagnostic_namespace/on_unimplemented/do_not_fail_parsing_on_invalid_options_1.stderr
@@ -35,6 +35,8 @@ warning: malformed `on_unimplemented` attribute
    |
 LL | #[diagnostic::on_unimplemented(unsupported = "foo")]
    |                                ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0277]: the trait bound `i32: Foo` is not satisfied
   --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:31:14
@@ -60,6 +62,8 @@ warning: malformed `on_unimplemented` attribute
    |
 LL | #[diagnostic::on_unimplemented(message = "Boom", unsupported = "Bar")]
    |                                                  ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0277]: Boom
   --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:33:14
@@ -85,6 +89,8 @@ warning: malformed `on_unimplemented` attribute
    |
 LL | #[diagnostic::on_unimplemented(message = "Boom", on(_Self = "i32", message = "whatever"))]
    |                                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0277]: Boom
   --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:35:15
diff --git a/tests/ui/dyn-keyword/dyn-2018-edition-lint.stderr b/tests/ui/dyn-keyword/dyn-2018-edition-lint.stderr
index 6bafff9192a..93178667214 100644
--- a/tests/ui/dyn-keyword/dyn-2018-edition-lint.stderr
+++ b/tests/ui/dyn-keyword/dyn-2018-edition-lint.stderr
@@ -50,6 +50,7 @@ LL | fn function(x: &SomeTrait, y: Box<SomeTrait>) {
    |
    = warning: this is accepted in the current edition (Rust 2018) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: use `dyn`
    |
 LL | fn function(x: &dyn SomeTrait, y: Box<SomeTrait>) {
@@ -63,6 +64,7 @@ LL | fn function(x: &SomeTrait, y: Box<SomeTrait>) {
    |
    = warning: this is accepted in the current edition (Rust 2018) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: use `dyn`
    |
 LL | fn function(x: &dyn SomeTrait, y: Box<SomeTrait>) {
@@ -76,6 +78,7 @@ LL | fn function(x: &SomeTrait, y: Box<SomeTrait>) {
    |
    = warning: this is accepted in the current edition (Rust 2018) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: use `dyn`
    |
 LL | fn function(x: &SomeTrait, y: Box<dyn SomeTrait>) {
@@ -89,6 +92,7 @@ LL | fn function(x: &SomeTrait, y: Box<SomeTrait>) {
    |
    = warning: this is accepted in the current edition (Rust 2018) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: use `dyn`
    |
 LL | fn function(x: &SomeTrait, y: Box<dyn SomeTrait>) {
diff --git a/tests/ui/error-codes/E0452.stderr b/tests/ui/error-codes/E0452.stderr
index f67b740ffe2..986c135ed89 100644
--- a/tests/ui/error-codes/E0452.stderr
+++ b/tests/ui/error-codes/E0452.stderr
@@ -9,18 +9,24 @@ error[E0452]: malformed lint attribute input
    |
 LL | #![allow(foo = "")]
    |          ^^^^^^^^ bad attribute argument
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0452]: malformed lint attribute input
   --> $DIR/E0452.rs:1:10
    |
 LL | #![allow(foo = "")]
    |          ^^^^^^^^ bad attribute argument
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0452]: malformed lint attribute input
   --> $DIR/E0452.rs:1:10
    |
 LL | #![allow(foo = "")]
    |          ^^^^^^^^ bad attribute argument
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 4 previous errors
 
diff --git a/tests/ui/error-codes/E0453.stderr b/tests/ui/error-codes/E0453.stderr
index f982ed26f5c..bb2c39298c0 100644
--- a/tests/ui/error-codes/E0453.stderr
+++ b/tests/ui/error-codes/E0453.stderr
@@ -15,6 +15,8 @@ LL | #![forbid(non_snake_case)]
 LL |
 LL | #[allow(non_snake_case)]
    |         ^^^^^^^^^^^^^^ overruled by previous forbid
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/error-codes/E0602.stderr b/tests/ui/error-codes/E0602.stderr
index 60ecec7cdd7..b6b5cd5c3d3 100644
--- a/tests/ui/error-codes/E0602.stderr
+++ b/tests/ui/error-codes/E0602.stderr
@@ -6,10 +6,12 @@ warning[E0602]: unknown lint: `bogus`
 warning[E0602]: unknown lint: `bogus`
    |
    = note: requested on the command line with `-D bogus`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning[E0602]: unknown lint: `bogus`
    |
    = note: requested on the command line with `-D bogus`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: 3 warnings emitted
 
diff --git a/tests/ui/error-codes/E0719.stderr b/tests/ui/error-codes/E0719.stderr
index e302f406d02..685bd7175e3 100644
--- a/tests/ui/error-codes/E0719.stderr
+++ b/tests/ui/error-codes/E0719.stderr
@@ -13,6 +13,8 @@ LL | trait Foo: Iterator<Item = i32, Item = i32> {}
    |                     ----------  ^^^^^^^^^^ re-bound here
    |                     |
    |                     `Item` bound here first
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0719]: the value of the associated type `Item` (from trait `Iterator`) is already specified
   --> $DIR/E0719.rs:7:42
diff --git a/tests/ui/error-codes/E0789.stderr b/tests/ui/error-codes/E0789.stderr
index faab92bae03..6df9daafec7 100644
--- a/tests/ui/error-codes/E0789.stderr
+++ b/tests/ui/error-codes/E0789.stderr
@@ -9,6 +9,8 @@ error[E0789]: `rustc_allowed_through_unstable_modules` attribute must be paired
    |
 LL | struct Foo;
    | ^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/feature-gates/feature-gate-lint-reasons.stderr b/tests/ui/feature-gates/feature-gate-lint-reasons.stderr
index 12793c7a28f..6d49b7ed2cd 100644
--- a/tests/ui/feature-gates/feature-gate-lint-reasons.stderr
+++ b/tests/ui/feature-gates/feature-gate-lint-reasons.stderr
@@ -15,6 +15,7 @@ LL | #![warn(nonstandard_style, reason = "the standard should be respected")]
    |
    = note: see issue #54503 <https://github.com/rust-lang/rust/issues/54503> for more information
    = help: add `#![feature(lint_reasons)]` to the crate attributes to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/feature-gates/feature-gate-multiple_supertrait_upcastable.stderr b/tests/ui/feature-gates/feature-gate-multiple_supertrait_upcastable.stderr
index 1f725f35417..5e14bf6397f 100644
--- a/tests/ui/feature-gates/feature-gate-multiple_supertrait_upcastable.stderr
+++ b/tests/ui/feature-gates/feature-gate-multiple_supertrait_upcastable.stderr
@@ -25,6 +25,7 @@ LL | #![deny(multiple_supertrait_upcastable)]
    |
    = note: the `multiple_supertrait_upcastable` lint is unstable
    = help: add `#![feature(multiple_supertrait_upcastable)]` to the crate attributes to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: unknown lint: `multiple_supertrait_upcastable`
   --> $DIR/feature-gate-multiple_supertrait_upcastable.rs:7:1
@@ -34,6 +35,7 @@ LL | #![warn(multiple_supertrait_upcastable)]
    |
    = note: the `multiple_supertrait_upcastable` lint is unstable
    = help: add `#![feature(multiple_supertrait_upcastable)]` to the crate attributes to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: unknown lint: `multiple_supertrait_upcastable`
   --> $DIR/feature-gate-multiple_supertrait_upcastable.rs:3:1
@@ -43,6 +45,7 @@ LL | #![deny(multiple_supertrait_upcastable)]
    |
    = note: the `multiple_supertrait_upcastable` lint is unstable
    = help: add `#![feature(multiple_supertrait_upcastable)]` to the crate attributes to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: unknown lint: `multiple_supertrait_upcastable`
   --> $DIR/feature-gate-multiple_supertrait_upcastable.rs:7:1
@@ -52,6 +55,7 @@ LL | #![warn(multiple_supertrait_upcastable)]
    |
    = note: the `multiple_supertrait_upcastable` lint is unstable
    = help: add `#![feature(multiple_supertrait_upcastable)]` to the crate attributes to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: 6 warnings emitted
 
diff --git a/tests/ui/feature-gates/feature-gate-non_exhaustive_omitted_patterns_lint.stderr b/tests/ui/feature-gates/feature-gate-non_exhaustive_omitted_patterns_lint.stderr
index fb39c404c20..1c14622d637 100644
--- a/tests/ui/feature-gates/feature-gate-non_exhaustive_omitted_patterns_lint.stderr
+++ b/tests/ui/feature-gates/feature-gate-non_exhaustive_omitted_patterns_lint.stderr
@@ -38,6 +38,7 @@ LL |     #[allow(non_exhaustive_omitted_patterns)]
    = note: the `non_exhaustive_omitted_patterns` lint is unstable
    = note: see issue #89554 <https://github.com/rust-lang/rust/issues/89554> for more information
    = help: add `#![feature(non_exhaustive_omitted_patterns_lint)]` to the crate attributes to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: unknown lint: `non_exhaustive_omitted_patterns`
   --> $DIR/feature-gate-non_exhaustive_omitted_patterns_lint.rs:29:9
@@ -58,6 +59,7 @@ LL | #![deny(non_exhaustive_omitted_patterns)]
    = note: the `non_exhaustive_omitted_patterns` lint is unstable
    = note: see issue #89554 <https://github.com/rust-lang/rust/issues/89554> for more information
    = help: add `#![feature(non_exhaustive_omitted_patterns_lint)]` to the crate attributes to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: unknown lint: `non_exhaustive_omitted_patterns`
   --> $DIR/feature-gate-non_exhaustive_omitted_patterns_lint.rs:6:1
@@ -68,6 +70,7 @@ LL | #![allow(non_exhaustive_omitted_patterns)]
    = note: the `non_exhaustive_omitted_patterns` lint is unstable
    = note: see issue #89554 <https://github.com/rust-lang/rust/issues/89554> for more information
    = help: add `#![feature(non_exhaustive_omitted_patterns_lint)]` to the crate attributes to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: unknown lint: `non_exhaustive_omitted_patterns`
   --> $DIR/feature-gate-non_exhaustive_omitted_patterns_lint.rs:15:5
@@ -78,6 +81,7 @@ LL |     #[allow(non_exhaustive_omitted_patterns)]
    = note: the `non_exhaustive_omitted_patterns` lint is unstable
    = note: see issue #89554 <https://github.com/rust-lang/rust/issues/89554> for more information
    = help: add `#![feature(non_exhaustive_omitted_patterns_lint)]` to the crate attributes to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: unknown lint: `non_exhaustive_omitted_patterns`
   --> $DIR/feature-gate-non_exhaustive_omitted_patterns_lint.rs:15:5
@@ -88,6 +92,7 @@ LL |     #[allow(non_exhaustive_omitted_patterns)]
    = note: the `non_exhaustive_omitted_patterns` lint is unstable
    = note: see issue #89554 <https://github.com/rust-lang/rust/issues/89554> for more information
    = help: add `#![feature(non_exhaustive_omitted_patterns_lint)]` to the crate attributes to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: unknown lint: `non_exhaustive_omitted_patterns`
   --> $DIR/feature-gate-non_exhaustive_omitted_patterns_lint.rs:29:9
@@ -98,6 +103,7 @@ LL |         #[warn(non_exhaustive_omitted_patterns)]
    = note: the `non_exhaustive_omitted_patterns` lint is unstable
    = note: see issue #89554 <https://github.com/rust-lang/rust/issues/89554> for more information
    = help: add `#![feature(non_exhaustive_omitted_patterns_lint)]` to the crate attributes to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0004]: non-exhaustive patterns: `Foo::C` not covered
   --> $DIR/feature-gate-non_exhaustive_omitted_patterns_lint.rs:20:11
diff --git a/tests/ui/feature-gates/feature-gate-strict_provenance.stderr b/tests/ui/feature-gates/feature-gate-strict_provenance.stderr
index 751da87cc0d..1e6d762a540 100644
--- a/tests/ui/feature-gates/feature-gate-strict_provenance.stderr
+++ b/tests/ui/feature-gates/feature-gate-strict_provenance.stderr
@@ -28,6 +28,7 @@ LL | #![deny(fuzzy_provenance_casts)]
    = note: the `fuzzy_provenance_casts` lint is unstable
    = note: see issue #95228 <https://github.com/rust-lang/rust/issues/95228> for more information
    = help: add `#![feature(strict_provenance)]` to the crate attributes to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: unknown lint: `lossy_provenance_casts`
   --> $DIR/feature-gate-strict_provenance.rs:7:1
@@ -38,6 +39,7 @@ LL | #![deny(lossy_provenance_casts)]
    = note: the `lossy_provenance_casts` lint is unstable
    = note: see issue #95228 <https://github.com/rust-lang/rust/issues/95228> for more information
    = help: add `#![feature(strict_provenance)]` to the crate attributes to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: unknown lint: `fuzzy_provenance_casts`
   --> $DIR/feature-gate-strict_provenance.rs:3:1
@@ -48,6 +50,7 @@ LL | #![deny(fuzzy_provenance_casts)]
    = note: the `fuzzy_provenance_casts` lint is unstable
    = note: see issue #95228 <https://github.com/rust-lang/rust/issues/95228> for more information
    = help: add `#![feature(strict_provenance)]` to the crate attributes to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: unknown lint: `lossy_provenance_casts`
   --> $DIR/feature-gate-strict_provenance.rs:7:1
@@ -58,6 +61,7 @@ LL | #![deny(lossy_provenance_casts)]
    = note: the `lossy_provenance_casts` lint is unstable
    = note: see issue #95228 <https://github.com/rust-lang/rust/issues/95228> for more information
    = help: add `#![feature(strict_provenance)]` to the crate attributes to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: 6 warnings emitted
 
diff --git a/tests/ui/feature-gates/feature-gate-test_unstable_lint.stderr b/tests/ui/feature-gates/feature-gate-test_unstable_lint.stderr
index b4d6aa658e1..562aa478a93 100644
--- a/tests/ui/feature-gates/feature-gate-test_unstable_lint.stderr
+++ b/tests/ui/feature-gates/feature-gate-test_unstable_lint.stderr
@@ -16,6 +16,7 @@ LL | #![allow(test_unstable_lint)]
    |
    = note: the `test_unstable_lint` lint is unstable
    = help: add `#![feature(test_unstable_lint)]` to the crate attributes to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: unknown lint: `test_unstable_lint`
   --> $DIR/feature-gate-test_unstable_lint.rs:4:1
@@ -25,6 +26,7 @@ LL | #![allow(test_unstable_lint)]
    |
    = note: the `test_unstable_lint` lint is unstable
    = help: add `#![feature(test_unstable_lint)]` to the crate attributes to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: 3 warnings emitted
 
diff --git a/tests/ui/feature-gates/feature-gate-type_privacy_lints.stderr b/tests/ui/feature-gates/feature-gate-type_privacy_lints.stderr
index 4349fea6f89..2614f2b3c35 100644
--- a/tests/ui/feature-gates/feature-gate-type_privacy_lints.stderr
+++ b/tests/ui/feature-gates/feature-gate-type_privacy_lints.stderr
@@ -18,6 +18,7 @@ LL | #![warn(unnameable_types)]
    = note: the `unnameable_types` lint is unstable
    = note: see issue #48054 <https://github.com/rust-lang/rust/issues/48054> for more information
    = help: add `#![feature(type_privacy_lints)]` to the crate attributes to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: unknown lint: `unnameable_types`
   --> $DIR/feature-gate-type_privacy_lints.rs:3:1
@@ -28,6 +29,7 @@ LL | #![warn(unnameable_types)]
    = note: the `unnameable_types` lint is unstable
    = note: see issue #48054 <https://github.com/rust-lang/rust/issues/48054> for more information
    = help: add `#![feature(type_privacy_lints)]` to the crate attributes to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: 3 warnings emitted
 
diff --git a/tests/ui/feature-gates/issue-43106-gating-of-derive-2.stderr b/tests/ui/feature-gates/issue-43106-gating-of-derive-2.stderr
index ab165917344..1e47259cb7e 100644
--- a/tests/ui/feature-gates/issue-43106-gating-of-derive-2.stderr
+++ b/tests/ui/feature-gates/issue-43106-gating-of-derive-2.stderr
@@ -9,6 +9,8 @@ error: cannot find derive macro `x3300` in this scope
    |
 LL |     #[derive(x3300)]
    |              ^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: cannot find derive macro `x3300` in this scope
   --> $DIR/issue-43106-gating-of-derive-2.rs:9:14
@@ -21,6 +23,8 @@ error: cannot find derive macro `x3300` in this scope
    |
 LL |     #[derive(x3300)]
    |              ^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: cannot find derive macro `x3300` in this scope
   --> $DIR/issue-43106-gating-of-derive-2.rs:4:14
@@ -33,6 +37,8 @@ error: cannot find derive macro `x3300` in this scope
    |
 LL |     #[derive(x3300)]
    |              ^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 6 previous errors
 
diff --git a/tests/ui/generic-associated-types/gat-trait-path-missing-lifetime.stderr b/tests/ui/generic-associated-types/gat-trait-path-missing-lifetime.stderr
index 499221637ba..7f535ec432c 100644
--- a/tests/ui/generic-associated-types/gat-trait-path-missing-lifetime.stderr
+++ b/tests/ui/generic-associated-types/gat-trait-path-missing-lifetime.stderr
@@ -25,6 +25,7 @@ note: associated type defined here, with 1 lifetime parameter: `'a`
    |
 LL |   type Y<'a>;
    |        ^ --
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: add missing lifetime argument
    |
 LL |   fn foo<'a, T1: X<Y<'a> = T1>>(t : T1) -> T1::Y<'a> {
diff --git a/tests/ui/generic-associated-types/issue-91139.stderr b/tests/ui/generic-associated-types/issue-91139.stderr
index d9d76adfbb5..89a4ba77e4e 100644
--- a/tests/ui/generic-associated-types/issue-91139.stderr
+++ b/tests/ui/generic-associated-types/issue-91139.stderr
@@ -9,6 +9,8 @@ error: `T` does not live long enough
    |
 LL |     let _: for<'a> fn(<() as Foo<T>>::Type<'a>, &'a T) = |_, _| ();
    |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/higher-ranked/subtype/hr-subtype.bound_inv_a_b_vs_bound_inv_a.stderr b/tests/ui/higher-ranked/subtype/hr-subtype.bound_inv_a_b_vs_bound_inv_a.stderr
index a73c03feb87..48703186cc6 100644
--- a/tests/ui/higher-ranked/subtype/hr-subtype.bound_inv_a_b_vs_bound_inv_a.stderr
+++ b/tests/ui/higher-ranked/subtype/hr-subtype.bound_inv_a_b_vs_bound_inv_a.stderr
@@ -24,6 +24,7 @@ LL | | for<'a>    fn(Inv<'a>, Inv<'a>)) }
    |
    = note: expected enum `Option<for<'a, 'b> fn(Inv<'a>, Inv<'b>)>`
               found enum `Option<for<'a> fn(Inv<'a>, Inv<'a>)>`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
    = note: this error originates in the macro `check` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 2 previous errors
diff --git a/tests/ui/higher-ranked/trait-bounds/hrtb-conflate-regions.stderr b/tests/ui/higher-ranked/trait-bounds/hrtb-conflate-regions.stderr
index 46f5308dd87..69c58c5919e 100644
--- a/tests/ui/higher-ranked/trait-bounds/hrtb-conflate-regions.stderr
+++ b/tests/ui/higher-ranked/trait-bounds/hrtb-conflate-regions.stderr
@@ -15,6 +15,7 @@ LL | fn b() { want_foo2::<SomeStruct>(); }
    |
    = note: `SomeStruct` must implement `Foo<(&'0 isize, &'1 isize)>`, for any two lifetimes `'0` and `'1`...
    = note: ...but it actually implements `Foo<(&'2 isize, &'2 isize)>`, for some specific lifetime `'2`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/impl-trait/fresh-lifetime-from-bare-trait-obj-114664.stderr b/tests/ui/impl-trait/fresh-lifetime-from-bare-trait-obj-114664.stderr
index fad0b812d43..d3c2d5d5b9f 100644
--- a/tests/ui/impl-trait/fresh-lifetime-from-bare-trait-obj-114664.stderr
+++ b/tests/ui/impl-trait/fresh-lifetime-from-bare-trait-obj-114664.stderr
@@ -20,6 +20,7 @@ LL | fn ice() -> impl AsRef<Fn(&())> {
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: use `dyn`
    |
 LL | fn ice() -> impl AsRef<dyn Fn(&())> {
@@ -33,6 +34,7 @@ LL | fn ice() -> impl AsRef<Fn(&())> {
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: use `dyn`
    |
 LL | fn ice() -> impl AsRef<dyn Fn(&())> {
diff --git a/tests/ui/impl-trait/impl-subtyper.rs b/tests/ui/impl-trait/impl-subtyper.rs
new file mode 100644
index 00000000000..2d99cdd4f50
--- /dev/null
+++ b/tests/ui/impl-trait/impl-subtyper.rs
@@ -0,0 +1,18 @@
+// check-pass
+
+#![crate_type = "lib"]
+fn checkpoints() -> impl Iterator {
+    Some(()).iter().flat_map(|_| std::iter::once(()))
+}
+
+fn block_checkpoints() -> impl Iterator {
+    checkpoints()
+}
+
+fn iter_raw() -> impl Iterator {
+    let mut iter = block_checkpoints();
+
+    (0..9).map(move |_| {
+        iter.next();
+    })
+}
diff --git a/tests/ui/impl-trait/impl-subtyper2.rs b/tests/ui/impl-trait/impl-subtyper2.rs
new file mode 100644
index 00000000000..2e0acbae68b
--- /dev/null
+++ b/tests/ui/impl-trait/impl-subtyper2.rs
@@ -0,0 +1,7 @@
+// check-pass
+
+fn ages() -> Option<impl Iterator> {
+    None::<std::slice::Iter<()>>
+}
+
+fn main(){}
diff --git a/tests/ui/impl-trait/issue-55872-2.stderr b/tests/ui/impl-trait/issue-55872-2.stderr
index 3e70f1cf800..b5b7f293a40 100644
--- a/tests/ui/impl-trait/issue-55872-2.stderr
+++ b/tests/ui/impl-trait/issue-55872-2.stderr
@@ -9,6 +9,8 @@ error: type parameter `T` is part of concrete type but not used in parameter lis
    |
 LL |         async {}
    |         ^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/imports/ambiguous-9.stderr b/tests/ui/imports/ambiguous-9.stderr
index 6c7d79174da..2731ed2ba86 100644
--- a/tests/ui/imports/ambiguous-9.stderr
+++ b/tests/ui/imports/ambiguous-9.stderr
@@ -60,6 +60,7 @@ note: `date_range` could also refer to the function imported here
 LL | use prelude::*;
    |     ^^^^^^^^^^
    = help: consider adding an explicit import of `date_range` to disambiguate
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: 4 warnings emitted
 
diff --git a/tests/ui/imports/issue-55457.stderr b/tests/ui/imports/issue-55457.stderr
index 788fcc830ae..30d2373652b 100644
--- a/tests/ui/imports/issue-55457.stderr
+++ b/tests/ui/imports/issue-55457.stderr
@@ -38,6 +38,7 @@ LL | #[derive(NonExistent)]
    |          ^^^^^^^^^^^
    |
    = note: import resolution is stuck, try simplifying macro imports
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: cannot determine resolution for the derive macro `NonExistent`
   --> $DIR/issue-55457.rs:5:10
@@ -46,6 +47,7 @@ LL | #[derive(NonExistent)]
    |          ^^^^^^^^^^^
    |
    = note: import resolution is stuck, try simplifying macro imports
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 6 previous errors
 
diff --git a/tests/ui/issues/issue-33571.stderr b/tests/ui/issues/issue-33571.stderr
index 2a9ba5ba71b..819a533ddbe 100644
--- a/tests/ui/issues/issue-33571.stderr
+++ b/tests/ui/issues/issue-33571.stderr
@@ -21,6 +21,7 @@ note: unsafe traits like `Sync` should be implemented explicitly
    |
 LL |          Sync,
    |          ^^^^
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/issues/issue-40000.stderr b/tests/ui/issues/issue-40000.stderr
index c41fbb9d2ec..0737a9610e2 100644
--- a/tests/ui/issues/issue-40000.stderr
+++ b/tests/ui/issues/issue-40000.stderr
@@ -15,6 +15,7 @@ LL |     foo(bar);
    |
    = note: expected trait object `dyn for<'a> Fn(&'a i32)`
               found trait object `dyn Fn(&i32)`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/issues/issue-46101.stderr b/tests/ui/issues/issue-46101.stderr
index 40295b8a115..a0cdd5d5f05 100644
--- a/tests/ui/issues/issue-46101.stderr
+++ b/tests/ui/issues/issue-46101.stderr
@@ -9,6 +9,8 @@ error[E0433]: failed to resolve: partially resolved path in a derive macro
    |
 LL | #[derive(Foo::Anything)]
    |          ^^^^^^^^^^^^^ partially resolved path in a derive macro
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/issues/issue-53251.stderr b/tests/ui/issues/issue-53251.stderr
index d5f14e8deb9..05ea6311589 100644
--- a/tests/ui/issues/issue-53251.stderr
+++ b/tests/ui/issues/issue-53251.stderr
@@ -32,6 +32,7 @@ note: associated function defined here, with 0 generic parameters
    |
 LL |     fn f() {}
    |        ^
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
    = note: this error originates in the macro `impl_add` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 2 previous errors
diff --git a/tests/ui/lifetimes/issue-105675.stderr b/tests/ui/lifetimes/issue-105675.stderr
index 66415f72bcb..54ecd35ed6a 100644
--- a/tests/ui/lifetimes/issue-105675.stderr
+++ b/tests/ui/lifetimes/issue-105675.stderr
@@ -81,6 +81,7 @@ note: the lifetime requirement is introduced here
    |
 LL | fn thing(x: impl FnOnce(&u32, &u32, u32)) {}
    |                  ^^^^^^^^^^^^^^^^^^^^^^^
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: consider specifying the type of the closure parameters
    |
 LL |     let f = |x: &_, y: &_, z: u32| ();
diff --git a/tests/ui/limits/issue-55878.stderr b/tests/ui/limits/issue-55878.stderr
index 93716c0b347..6b463930b00 100644
--- a/tests/ui/limits/issue-55878.stderr
+++ b/tests/ui/limits/issue-55878.stderr
@@ -25,6 +25,7 @@ note: erroneous constant encountered
 LL |     println!("Size: {}", std::mem::size_of::<[u8; u64::MAX as usize]>());
    |                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
    = note: this note originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to previous error
diff --git a/tests/ui/lint/cli-unknown-force-warn.stderr b/tests/ui/lint/cli-unknown-force-warn.stderr
index 2ee718a8c8e..5084b4a4001 100644
--- a/tests/ui/lint/cli-unknown-force-warn.stderr
+++ b/tests/ui/lint/cli-unknown-force-warn.stderr
@@ -6,10 +6,12 @@ warning[E0602]: unknown lint: `foo_qux`
 warning[E0602]: unknown lint: `foo_qux`
    |
    = note: requested on the command line with `--force-warn foo_qux`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning[E0602]: unknown lint: `foo_qux`
    |
    = note: requested on the command line with `--force-warn foo_qux`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: 3 warnings emitted
 
diff --git a/tests/ui/lint/command-line-register-unknown-lint-tool.stderr b/tests/ui/lint/command-line-register-unknown-lint-tool.stderr
index c9a2aff2137..65aa1962830 100644
--- a/tests/ui/lint/command-line-register-unknown-lint-tool.stderr
+++ b/tests/ui/lint/command-line-register-unknown-lint-tool.stderr
@@ -5,6 +5,7 @@ error[E0602]: unknown lint tool: `unknown_tool`
 error[E0602]: unknown lint tool: `unknown_tool`
    |
    = note: requested on the command line with `-A unknown_tool::foo`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/lint/crate_level_only_lint.stderr b/tests/ui/lint/crate_level_only_lint.stderr
index 8fb06df2a48..fbb1ec381c8 100644
--- a/tests/ui/lint/crate_level_only_lint.stderr
+++ b/tests/ui/lint/crate_level_only_lint.stderr
@@ -27,36 +27,48 @@ error: allow(uncommon_codepoints) is ignored unless specified at crate level
    |
 LL | #![allow(uncommon_codepoints)]
    |          ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: allow(uncommon_codepoints) is ignored unless specified at crate level
   --> $DIR/crate_level_only_lint.rs:9:9
    |
 LL | #[allow(uncommon_codepoints)]
    |         ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: allow(uncommon_codepoints) is ignored unless specified at crate level
   --> $DIR/crate_level_only_lint.rs:17:9
    |
 LL | #[allow(uncommon_codepoints)]
    |         ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: allow(uncommon_codepoints) is ignored unless specified at crate level
   --> $DIR/crate_level_only_lint.rs:4:10
    |
 LL | #![allow(uncommon_codepoints)]
    |          ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: allow(uncommon_codepoints) is ignored unless specified at crate level
   --> $DIR/crate_level_only_lint.rs:9:9
    |
 LL | #[allow(uncommon_codepoints)]
    |         ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: allow(uncommon_codepoints) is ignored unless specified at crate level
   --> $DIR/crate_level_only_lint.rs:17:9
    |
 LL | #[allow(uncommon_codepoints)]
    |         ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 9 previous errors
 
diff --git a/tests/ui/lint/forbid-group-group-2.stderr b/tests/ui/lint/forbid-group-group-2.stderr
index b2e2bcea1b4..4a2c8fbd68a 100644
--- a/tests/ui/lint/forbid-group-group-2.stderr
+++ b/tests/ui/lint/forbid-group-group-2.stderr
@@ -26,6 +26,7 @@ LL | #[allow(nonstandard_style)]
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: allow(nonstandard_style) incompatible with previous forbid
   --> $DIR/forbid-group-group-2.rs:7:9
@@ -38,6 +39,7 @@ LL | #[allow(nonstandard_style)]
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: allow(nonstandard_style) incompatible with previous forbid
   --> $DIR/forbid-group-group-2.rs:7:9
@@ -50,6 +52,7 @@ LL | #[allow(nonstandard_style)]
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: allow(nonstandard_style) incompatible with previous forbid
   --> $DIR/forbid-group-group-2.rs:7:9
@@ -62,6 +65,7 @@ LL | #[allow(nonstandard_style)]
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: allow(nonstandard_style) incompatible with previous forbid
   --> $DIR/forbid-group-group-2.rs:7:9
@@ -74,6 +78,7 @@ LL | #[allow(nonstandard_style)]
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: allow(nonstandard_style) incompatible with previous forbid
   --> $DIR/forbid-group-group-2.rs:7:9
@@ -86,6 +91,7 @@ LL | #[allow(nonstandard_style)]
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: allow(nonstandard_style) incompatible with previous forbid
   --> $DIR/forbid-group-group-2.rs:7:9
@@ -98,6 +104,7 @@ LL | #[allow(nonstandard_style)]
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: allow(nonstandard_style) incompatible with previous forbid
   --> $DIR/forbid-group-group-2.rs:7:9
@@ -110,6 +117,7 @@ LL | #[allow(nonstandard_style)]
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 9 previous errors
 
diff --git a/tests/ui/lint/forbid-group-member.stderr b/tests/ui/lint/forbid-group-member.stderr
index 47336d4d890..ddaaafa12ec 100644
--- a/tests/ui/lint/forbid-group-member.stderr
+++ b/tests/ui/lint/forbid-group-member.stderr
@@ -22,6 +22,7 @@ LL | #[allow(unused_variables)]
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: allow(unused_variables) incompatible with previous forbid
   --> $DIR/forbid-group-member.rs:8:9
@@ -34,6 +35,7 @@ LL | #[allow(unused_variables)]
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: 3 warnings emitted
 
diff --git a/tests/ui/lint/forbid-member-group.stderr b/tests/ui/lint/forbid-member-group.stderr
index e6530177833..612dccd8d6c 100644
--- a/tests/ui/lint/forbid-member-group.stderr
+++ b/tests/ui/lint/forbid-member-group.stderr
@@ -15,6 +15,8 @@ LL | #![forbid(unused_variables)]
 LL |
 LL | #[allow(unused)]
    |         ^^^^^^ overruled by previous forbid
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/lint/force-warn/allowed-group-warn-by-default-lint.stderr b/tests/ui/lint/force-warn/allowed-group-warn-by-default-lint.stderr
index 0f58953a54b..ecdc625015e 100644
--- a/tests/ui/lint/force-warn/allowed-group-warn-by-default-lint.stderr
+++ b/tests/ui/lint/force-warn/allowed-group-warn-by-default-lint.stderr
@@ -20,6 +20,7 @@ LL | pub fn function(_x: Box<SomeTrait>) {}
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: use `dyn`
    |
 LL | pub fn function(_x: Box<dyn SomeTrait>) {}
@@ -33,6 +34,7 @@ LL | pub fn function(_x: Box<SomeTrait>) {}
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: use `dyn`
    |
 LL | pub fn function(_x: Box<dyn SomeTrait>) {}
diff --git a/tests/ui/lint/force-warn/cap-lints-allow.stderr b/tests/ui/lint/force-warn/cap-lints-allow.stderr
index 03a32fa6f08..5f5f2ff52b6 100644
--- a/tests/ui/lint/force-warn/cap-lints-allow.stderr
+++ b/tests/ui/lint/force-warn/cap-lints-allow.stderr
@@ -20,6 +20,7 @@ LL | pub fn function(_x: Box<SomeTrait>) {}
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: use `dyn`
    |
 LL | pub fn function(_x: Box<dyn SomeTrait>) {}
@@ -33,6 +34,7 @@ LL | pub fn function(_x: Box<SomeTrait>) {}
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: use `dyn`
    |
 LL | pub fn function(_x: Box<dyn SomeTrait>) {}
diff --git a/tests/ui/lint/force-warn/lint-group-allowed-cli-warn-by-default-lint.stderr b/tests/ui/lint/force-warn/lint-group-allowed-cli-warn-by-default-lint.stderr
index b0cd3ddd26f..3a0b1201b0c 100644
--- a/tests/ui/lint/force-warn/lint-group-allowed-cli-warn-by-default-lint.stderr
+++ b/tests/ui/lint/force-warn/lint-group-allowed-cli-warn-by-default-lint.stderr
@@ -21,6 +21,7 @@ LL | pub fn function(_x: Box<SomeTrait>) {}
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: use `dyn`
    |
 LL | pub fn function(_x: Box<dyn SomeTrait>) {}
@@ -34,6 +35,7 @@ LL | pub fn function(_x: Box<SomeTrait>) {}
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: use `dyn`
    |
 LL | pub fn function(_x: Box<dyn SomeTrait>) {}
diff --git a/tests/ui/lint/force-warn/lint-group-allowed-lint-group.stderr b/tests/ui/lint/force-warn/lint-group-allowed-lint-group.stderr
index 8c841916c93..92555eda2a7 100644
--- a/tests/ui/lint/force-warn/lint-group-allowed-lint-group.stderr
+++ b/tests/ui/lint/force-warn/lint-group-allowed-lint-group.stderr
@@ -21,6 +21,7 @@ LL | pub fn function(_x: Box<SomeTrait>) {}
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: use `dyn`
    |
 LL | pub fn function(_x: Box<dyn SomeTrait>) {}
@@ -34,6 +35,7 @@ LL | pub fn function(_x: Box<SomeTrait>) {}
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: use `dyn`
    |
 LL | pub fn function(_x: Box<dyn SomeTrait>) {}
diff --git a/tests/ui/lint/force-warn/lint-group-allowed-warn-by-default-lint.stderr b/tests/ui/lint/force-warn/lint-group-allowed-warn-by-default-lint.stderr
index c0144205d6a..c14c7957a25 100644
--- a/tests/ui/lint/force-warn/lint-group-allowed-warn-by-default-lint.stderr
+++ b/tests/ui/lint/force-warn/lint-group-allowed-warn-by-default-lint.stderr
@@ -21,6 +21,7 @@ LL | pub fn function(_x: Box<SomeTrait>) {}
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: use `dyn`
    |
 LL | pub fn function(_x: Box<dyn SomeTrait>) {}
@@ -34,6 +35,7 @@ LL | pub fn function(_x: Box<SomeTrait>) {}
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: use `dyn`
    |
 LL | pub fn function(_x: Box<dyn SomeTrait>) {}
diff --git a/tests/ui/lint/force-warn/warnings-lint-group.stderr b/tests/ui/lint/force-warn/warnings-lint-group.stderr
index 1faeed33704..3e73269a233 100644
--- a/tests/ui/lint/force-warn/warnings-lint-group.stderr
+++ b/tests/ui/lint/force-warn/warnings-lint-group.stderr
@@ -1,6 +1,8 @@
 error[E0602]: `warnings` lint group is not supported with ´--force-warn´
 
 error[E0602]: `warnings` lint group is not supported with ´--force-warn´
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/lint/issue-80988.stderr b/tests/ui/lint/issue-80988.stderr
index 73e27ffda7f..7a65881b5ed 100644
--- a/tests/ui/lint/issue-80988.stderr
+++ b/tests/ui/lint/issue-80988.stderr
@@ -22,6 +22,7 @@ LL | #[deny(warnings)]
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: deny(warnings) incompatible with previous forbid
   --> $DIR/issue-80988.rs:7:8
@@ -34,6 +35,7 @@ LL | #[deny(warnings)]
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: 3 warnings emitted
 
diff --git a/tests/ui/lint/lint-forbid-attr.stderr b/tests/ui/lint/lint-forbid-attr.stderr
index 5977b9c949d..bd476a0e362 100644
--- a/tests/ui/lint/lint-forbid-attr.stderr
+++ b/tests/ui/lint/lint-forbid-attr.stderr
@@ -15,6 +15,8 @@ LL | #![forbid(deprecated)]
 LL |
 LL | #[allow(deprecated)]
    |         ^^^^^^^^^^ overruled by previous forbid
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/lint/lint-forbid-cmdline.stderr b/tests/ui/lint/lint-forbid-cmdline.stderr
index 0a92e58c04a..ed49a2cb427 100644
--- a/tests/ui/lint/lint-forbid-cmdline.stderr
+++ b/tests/ui/lint/lint-forbid-cmdline.stderr
@@ -13,6 +13,7 @@ LL | #[allow(deprecated)]
    |         ^^^^^^^^^^ overruled by previous forbid
    |
    = note: `forbid` lint level was set on command line
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/lint/lint-malformed.stderr b/tests/ui/lint/lint-malformed.stderr
index 91b4e509b26..2c9f045de71 100644
--- a/tests/ui/lint/lint-malformed.stderr
+++ b/tests/ui/lint/lint-malformed.stderr
@@ -9,6 +9,8 @@ error[E0452]: malformed lint attribute input
    |
 LL | #![allow(bar = "baz")]
    |          ^^^^^^^^^^^ bad attribute argument
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: malformed `deny` attribute input
   --> $DIR/lint-malformed.rs:1:1
@@ -21,12 +23,16 @@ error[E0452]: malformed lint attribute input
    |
 LL | #![allow(bar = "baz")]
    |          ^^^^^^^^^^^ bad attribute argument
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0452]: malformed lint attribute input
   --> $DIR/lint-malformed.rs:2:10
    |
 LL | #![allow(bar = "baz")]
    |          ^^^^^^^^^^^ bad attribute argument
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 5 previous errors
 
diff --git a/tests/ui/lint/lint-removed-cmdline-deny.stderr b/tests/ui/lint/lint-removed-cmdline-deny.stderr
index 80c85d01e53..3321afa7fcd 100644
--- a/tests/ui/lint/lint-removed-cmdline-deny.stderr
+++ b/tests/ui/lint/lint-removed-cmdline-deny.stderr
@@ -6,10 +6,12 @@ error: lint `raw_pointer_derive` has been removed: using derive with raw pointer
 error: lint `raw_pointer_derive` has been removed: using derive with raw pointers is ok
    |
    = note: requested on the command line with `-D raw_pointer_derive`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: lint `raw_pointer_derive` has been removed: using derive with raw pointers is ok
    |
    = note: requested on the command line with `-D raw_pointer_derive`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: unused variable: `unused`
   --> $DIR/lint-removed-cmdline-deny.rs:13:17
diff --git a/tests/ui/lint/lint-removed-cmdline.stderr b/tests/ui/lint/lint-removed-cmdline.stderr
index ebfae34ade9..6b76ad3b578 100644
--- a/tests/ui/lint/lint-removed-cmdline.stderr
+++ b/tests/ui/lint/lint-removed-cmdline.stderr
@@ -6,10 +6,12 @@ warning: lint `raw_pointer_derive` has been removed: using derive with raw point
 warning: lint `raw_pointer_derive` has been removed: using derive with raw pointers is ok
    |
    = note: requested on the command line with `-D raw_pointer_derive`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: lint `raw_pointer_derive` has been removed: using derive with raw pointers is ok
    |
    = note: requested on the command line with `-D raw_pointer_derive`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: unused variable: `unused`
   --> $DIR/lint-removed-cmdline.rs:13:17
diff --git a/tests/ui/lint/lint-renamed-cmdline-deny.stderr b/tests/ui/lint/lint-renamed-cmdline-deny.stderr
index df22ef60daf..0e182a4e5de 100644
--- a/tests/ui/lint/lint-renamed-cmdline-deny.stderr
+++ b/tests/ui/lint/lint-renamed-cmdline-deny.stderr
@@ -8,11 +8,13 @@ error: lint `bare_trait_object` has been renamed to `bare_trait_objects`
    |
    = help: use the new name `bare_trait_objects`
    = note: requested on the command line with `-D bare_trait_object`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: lint `bare_trait_object` has been renamed to `bare_trait_objects`
    |
    = help: use the new name `bare_trait_objects`
    = note: requested on the command line with `-D bare_trait_object`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: unused variable: `unused`
   --> $DIR/lint-renamed-cmdline-deny.rs:10:17
diff --git a/tests/ui/lint/lint-renamed-cmdline.stderr b/tests/ui/lint/lint-renamed-cmdline.stderr
index a41284003ed..675443ddedf 100644
--- a/tests/ui/lint/lint-renamed-cmdline.stderr
+++ b/tests/ui/lint/lint-renamed-cmdline.stderr
@@ -8,11 +8,13 @@ warning: lint `bare_trait_object` has been renamed to `bare_trait_objects`
    |
    = help: use the new name `bare_trait_objects`
    = note: requested on the command line with `-D bare_trait_object`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: lint `bare_trait_object` has been renamed to `bare_trait_objects`
    |
    = help: use the new name `bare_trait_objects`
    = note: requested on the command line with `-D bare_trait_object`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: unused variable: `unused`
   --> $DIR/lint-renamed-cmdline.rs:9:17
diff --git a/tests/ui/lint/lint-stability-deprecated.stderr b/tests/ui/lint/lint-stability-deprecated.stderr
index 19a4649e168..609fc56a8ae 100644
--- a/tests/ui/lint/lint-stability-deprecated.stderr
+++ b/tests/ui/lint/lint-stability-deprecated.stderr
@@ -639,18 +639,24 @@ warning: use of deprecated associated type `lint_stability::TraitWithAssociatedT
    |
 LL |         struct S2<T: TraitWithAssociatedTypes>(T::TypeDeprecated);
    |                                                ^^^^^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: use of deprecated associated type `lint_stability::TraitWithAssociatedTypes::TypeDeprecated`: text
   --> $DIR/lint-stability-deprecated.rs:102:13
    |
 LL |             TypeDeprecated = u16,
    |             ^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: use of deprecated associated type `lint_stability::TraitWithAssociatedTypes::TypeDeprecated`: text
   --> $DIR/lint-stability-deprecated.rs:102:13
    |
 LL |             TypeDeprecated = u16,
    |             ^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: 108 warnings emitted
 
diff --git a/tests/ui/lint/lint-unexported-no-mangle.stderr b/tests/ui/lint/lint-unexported-no-mangle.stderr
index 85852782222..0efec51abaf 100644
--- a/tests/ui/lint/lint-unexported-no-mangle.stderr
+++ b/tests/ui/lint/lint-unexported-no-mangle.stderr
@@ -10,18 +10,22 @@ warning: lint `private_no_mangle_statics` has been removed: no longer a warning,
 warning: lint `private_no_mangle_fns` has been removed: no longer a warning, `#[no_mangle]` functions always exported
    |
    = note: requested on the command line with `-F private_no_mangle_fns`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: lint `private_no_mangle_statics` has been removed: no longer a warning, `#[no_mangle]` statics always exported
    |
    = note: requested on the command line with `-F private_no_mangle_statics`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: lint `private_no_mangle_fns` has been removed: no longer a warning, `#[no_mangle]` functions always exported
    |
    = note: requested on the command line with `-F private_no_mangle_fns`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: lint `private_no_mangle_statics` has been removed: no longer a warning, `#[no_mangle]` statics always exported
    |
    = note: requested on the command line with `-F private_no_mangle_statics`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: const items should never be `#[no_mangle]`
   --> $DIR/lint-unexported-no-mangle.rs:9:1
diff --git a/tests/ui/lint/lint-unknown-lint-cmdline-deny.stderr b/tests/ui/lint/lint-unknown-lint-cmdline-deny.stderr
index 677b5edc894..f12ce03ddfc 100644
--- a/tests/ui/lint/lint-unknown-lint-cmdline-deny.stderr
+++ b/tests/ui/lint/lint-unknown-lint-cmdline-deny.stderr
@@ -11,20 +11,24 @@ error[E0602]: unknown lint: `dead_cod`
 error[E0602]: unknown lint: `bogus`
    |
    = note: requested on the command line with `-D bogus`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0602]: unknown lint: `dead_cod`
    |
    = help: did you mean: `dead_code`
    = note: requested on the command line with `-D dead_cod`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0602]: unknown lint: `bogus`
    |
    = note: requested on the command line with `-D bogus`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0602]: unknown lint: `dead_cod`
    |
    = help: did you mean: `dead_code`
    = note: requested on the command line with `-D dead_cod`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 6 previous errors
 
diff --git a/tests/ui/lint/lint-unknown-lint-cmdline.stderr b/tests/ui/lint/lint-unknown-lint-cmdline.stderr
index 10db76ac4f1..f452fc9eb94 100644
--- a/tests/ui/lint/lint-unknown-lint-cmdline.stderr
+++ b/tests/ui/lint/lint-unknown-lint-cmdline.stderr
@@ -11,20 +11,24 @@ warning[E0602]: unknown lint: `dead_cod`
 warning[E0602]: unknown lint: `bogus`
    |
    = note: requested on the command line with `-D bogus`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning[E0602]: unknown lint: `dead_cod`
    |
    = help: did you mean: `dead_code`
    = note: requested on the command line with `-D dead_cod`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning[E0602]: unknown lint: `bogus`
    |
    = note: requested on the command line with `-D bogus`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning[E0602]: unknown lint: `dead_cod`
    |
    = help: did you mean: `dead_code`
    = note: requested on the command line with `-D dead_cod`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: 6 warnings emitted
 
diff --git a/tests/ui/lint/must_not_suspend/gated.stderr b/tests/ui/lint/must_not_suspend/gated.stderr
index 64de1ebeaab..f0d2117d42b 100644
--- a/tests/ui/lint/must_not_suspend/gated.stderr
+++ b/tests/ui/lint/must_not_suspend/gated.stderr
@@ -18,6 +18,7 @@ LL | #![deny(must_not_suspend)]
    = note: the `must_not_suspend` lint is unstable
    = note: see issue #83310 <https://github.com/rust-lang/rust/issues/83310> for more information
    = help: add `#![feature(must_not_suspend)]` to the crate attributes to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: unknown lint: `must_not_suspend`
   --> $DIR/gated.rs:4:1
@@ -28,6 +29,7 @@ LL | #![deny(must_not_suspend)]
    = note: the `must_not_suspend` lint is unstable
    = note: see issue #83310 <https://github.com/rust-lang/rust/issues/83310> for more information
    = help: add `#![feature(must_not_suspend)]` to the crate attributes to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: 3 warnings emitted
 
diff --git a/tests/ui/lint/reasons-erroneous.rs b/tests/ui/lint/reasons-erroneous.rs
index cd693ae166c..7b286eb1d18 100644
--- a/tests/ui/lint/reasons-erroneous.rs
+++ b/tests/ui/lint/reasons-erroneous.rs
@@ -1,51 +1,27 @@
+// compile-flags: -Zdeduplicate-diagnostics=yes
+
 #![feature(lint_reasons)]
 
 #![warn(absolute_paths_not_starting_with_crate, reason = 0)]
 //~^ ERROR malformed lint attribute
-//~| ERROR malformed lint attribute
-//~| NOTE reason must be a string literal
 //~| NOTE reason must be a string literal
 #![warn(anonymous_parameters, reason = b"consider these, for we have condemned them")]
 //~^ ERROR malformed lint attribute
-//~| ERROR malformed lint attribute
-//~| NOTE reason must be a string literal
 //~| NOTE reason must be a string literal
 #![warn(bare_trait_objects, reasons = "leaders to no sure land, guides their bearings lost")]
 //~^ ERROR malformed lint attribute
-//~| ERROR malformed lint attribute
-//~| ERROR malformed lint attribute
-//~| ERROR malformed lint attribute
-//~| NOTE bad attribute argument
-//~| NOTE bad attribute argument
-//~| NOTE bad attribute argument
 //~| NOTE bad attribute argument
 #![warn(box_pointers, blerp = "or in league with robbers have reversed the signposts")]
 //~^ ERROR malformed lint attribute
-//~| ERROR malformed lint attribute
-//~| ERROR malformed lint attribute
-//~| ERROR malformed lint attribute
-//~| NOTE bad attribute argument
-//~| NOTE bad attribute argument
-//~| NOTE bad attribute argument
 //~| NOTE bad attribute argument
 #![warn(elided_lifetimes_in_paths, reason("disrespectful to ancestors", "irresponsible to heirs"))]
 //~^ ERROR malformed lint attribute
-//~| ERROR malformed lint attribute
-//~| ERROR malformed lint attribute
-//~| ERROR malformed lint attribute
-//~| NOTE bad attribute argument
-//~| NOTE bad attribute argument
-//~| NOTE bad attribute argument
 //~| NOTE bad attribute argument
 #![warn(ellipsis_inclusive_range_patterns, reason = "born barren", reason = "a freak growth")]
 //~^ ERROR malformed lint attribute
-//~| ERROR malformed lint attribute
-//~| NOTE reason in lint attribute must come last
 //~| NOTE reason in lint attribute must come last
 #![warn(keyword_idents, reason = "root in rubble", macro_use_extern_crate)]
 //~^ ERROR malformed lint attribute
-//~| ERROR malformed lint attribute
-//~| NOTE reason in lint attribute must come last
 //~| NOTE reason in lint attribute must come last
 #![warn(missing_copy_implementations, reason)]
 //~^ WARN unknown lint
diff --git a/tests/ui/lint/reasons-erroneous.stderr b/tests/ui/lint/reasons-erroneous.stderr
index 5521af17c84..003da567370 100644
--- a/tests/ui/lint/reasons-erroneous.stderr
+++ b/tests/ui/lint/reasons-erroneous.stderr
@@ -1,5 +1,5 @@
 error[E0452]: malformed lint attribute input
-  --> $DIR/reasons-erroneous.rs:3:58
+  --> $DIR/reasons-erroneous.rs:5:58
    |
 LL | #![warn(absolute_paths_not_starting_with_crate, reason = 0)]
    |                                                          ^ reason must be a string literal
@@ -11,121 +11,43 @@ LL | #![warn(anonymous_parameters, reason = b"consider these, for we have condem
    |                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ reason must be a string literal
 
 error[E0452]: malformed lint attribute input
-  --> $DIR/reasons-erroneous.rs:13:29
+  --> $DIR/reasons-erroneous.rs:11:29
    |
 LL | #![warn(bare_trait_objects, reasons = "leaders to no sure land, guides their bearings lost")]
    |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ bad attribute argument
 
 error[E0452]: malformed lint attribute input
-  --> $DIR/reasons-erroneous.rs:13:29
-   |
-LL | #![warn(bare_trait_objects, reasons = "leaders to no sure land, guides their bearings lost")]
-   |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ bad attribute argument
-
-error[E0452]: malformed lint attribute input
-  --> $DIR/reasons-erroneous.rs:22:23
-   |
-LL | #![warn(box_pointers, blerp = "or in league with robbers have reversed the signposts")]
-   |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ bad attribute argument
-
-error[E0452]: malformed lint attribute input
-  --> $DIR/reasons-erroneous.rs:22:23
-   |
-LL | #![warn(box_pointers, blerp = "or in league with robbers have reversed the signposts")]
-   |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ bad attribute argument
-
-error[E0452]: malformed lint attribute input
-  --> $DIR/reasons-erroneous.rs:31:36
-   |
-LL | #![warn(elided_lifetimes_in_paths, reason("disrespectful to ancestors", "irresponsible to heirs"))]
-   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ bad attribute argument
-
-error[E0452]: malformed lint attribute input
-  --> $DIR/reasons-erroneous.rs:31:36
-   |
-LL | #![warn(elided_lifetimes_in_paths, reason("disrespectful to ancestors", "irresponsible to heirs"))]
-   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ bad attribute argument
-
-error[E0452]: malformed lint attribute input
-  --> $DIR/reasons-erroneous.rs:40:44
-   |
-LL | #![warn(ellipsis_inclusive_range_patterns, reason = "born barren", reason = "a freak growth")]
-   |                                            ^^^^^^^^^^^^^^^^^^^^^^ reason in lint attribute must come last
-
-error[E0452]: malformed lint attribute input
-  --> $DIR/reasons-erroneous.rs:45:25
-   |
-LL | #![warn(keyword_idents, reason = "root in rubble", macro_use_extern_crate)]
-   |                         ^^^^^^^^^^^^^^^^^^^^^^^^^ reason in lint attribute must come last
-
-error[E0452]: malformed lint attribute input
-  --> $DIR/reasons-erroneous.rs:3:58
-   |
-LL | #![warn(absolute_paths_not_starting_with_crate, reason = 0)]
-   |                                                          ^ reason must be a string literal
-
-error[E0452]: malformed lint attribute input
-  --> $DIR/reasons-erroneous.rs:8:40
-   |
-LL | #![warn(anonymous_parameters, reason = b"consider these, for we have condemned them")]
-   |                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ reason must be a string literal
-
-error[E0452]: malformed lint attribute input
-  --> $DIR/reasons-erroneous.rs:13:29
-   |
-LL | #![warn(bare_trait_objects, reasons = "leaders to no sure land, guides their bearings lost")]
-   |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ bad attribute argument
-
-error[E0452]: malformed lint attribute input
-  --> $DIR/reasons-erroneous.rs:13:29
-   |
-LL | #![warn(bare_trait_objects, reasons = "leaders to no sure land, guides their bearings lost")]
-   |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ bad attribute argument
-
-error[E0452]: malformed lint attribute input
-  --> $DIR/reasons-erroneous.rs:22:23
-   |
-LL | #![warn(box_pointers, blerp = "or in league with robbers have reversed the signposts")]
-   |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ bad attribute argument
-
-error[E0452]: malformed lint attribute input
-  --> $DIR/reasons-erroneous.rs:22:23
+  --> $DIR/reasons-erroneous.rs:14:23
    |
 LL | #![warn(box_pointers, blerp = "or in league with robbers have reversed the signposts")]
    |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ bad attribute argument
 
 error[E0452]: malformed lint attribute input
-  --> $DIR/reasons-erroneous.rs:31:36
-   |
-LL | #![warn(elided_lifetimes_in_paths, reason("disrespectful to ancestors", "irresponsible to heirs"))]
-   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ bad attribute argument
-
-error[E0452]: malformed lint attribute input
-  --> $DIR/reasons-erroneous.rs:31:36
+  --> $DIR/reasons-erroneous.rs:17:36
    |
 LL | #![warn(elided_lifetimes_in_paths, reason("disrespectful to ancestors", "irresponsible to heirs"))]
    |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ bad attribute argument
 
 error[E0452]: malformed lint attribute input
-  --> $DIR/reasons-erroneous.rs:40:44
+  --> $DIR/reasons-erroneous.rs:20:44
    |
 LL | #![warn(ellipsis_inclusive_range_patterns, reason = "born barren", reason = "a freak growth")]
    |                                            ^^^^^^^^^^^^^^^^^^^^^^ reason in lint attribute must come last
 
 error[E0452]: malformed lint attribute input
-  --> $DIR/reasons-erroneous.rs:45:25
+  --> $DIR/reasons-erroneous.rs:23:25
    |
 LL | #![warn(keyword_idents, reason = "root in rubble", macro_use_extern_crate)]
    |                         ^^^^^^^^^^^^^^^^^^^^^^^^^ reason in lint attribute must come last
 
 warning: unknown lint: `reason`
-  --> $DIR/reasons-erroneous.rs:50:39
+  --> $DIR/reasons-erroneous.rs:26:39
    |
 LL | #![warn(missing_copy_implementations, reason)]
    |                                       ^^^^^^
    |
    = note: `#[warn(unknown_lints)]` on by default
 
-error: aborting due to 20 previous errors; 1 warning emitted
+error: aborting due to 7 previous errors; 1 warning emitted
 
 For more information about this error, try `rustc --explain E0452`.
diff --git a/tests/ui/lint/register-tool-lint.stderr b/tests/ui/lint/register-tool-lint.stderr
index 842d845ff7c..7ebdbdec929 100644
--- a/tests/ui/lint/register-tool-lint.stderr
+++ b/tests/ui/lint/register-tool-lint.stderr
@@ -13,6 +13,7 @@ LL | #![warn(abc::my_lint)]
    |         ^^^
    |
    = help: add `#![register_tool(abc)]` to the crate root
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/lint/rfc-2383-lint-reason/expect_with_forbid.rs b/tests/ui/lint/rfc-2383-lint-reason/expect_with_forbid.rs
index 479ee198e17..77cb5e88bf7 100644
--- a/tests/ui/lint/rfc-2383-lint-reason/expect_with_forbid.rs
+++ b/tests/ui/lint/rfc-2383-lint-reason/expect_with_forbid.rs
@@ -1,24 +1,20 @@
+// compile-flags: -Zdeduplicate-diagnostics=yes
+
 #![feature(lint_reasons)]
 
 #[forbid(unused_variables)]
 //~^ NOTE `forbid` level set here
-//~| NOTE `forbid` level set here
 #[expect(unused_variables)]
 //~^ ERROR incompatible with previous forbid [E0453]
 //~| NOTE overruled by previous forbid
-//~| ERROR incompatible with previous forbid [E0453]
-//~| NOTE overruled by previous forbid
 fn expect_forbidden_lint_1() {}
 
 #[forbid(while_true)]
 //~^ NOTE `forbid` level set here
-//~| NOTE `forbid` level set here
 //~| NOTE the lint level is defined here
 #[expect(while_true)]
 //~^ ERROR incompatible with previous forbid [E0453]
 //~| NOTE overruled by previous forbid
-//~| ERROR incompatible with previous forbid [E0453]
-//~| NOTE overruled by previous forbid
 fn expect_forbidden_lint_2() {
     // This while loop will produce a `while_true` lint as the lint level
     // at this node is still `forbid` and the `while_true` check happens
diff --git a/tests/ui/lint/rfc-2383-lint-reason/expect_with_forbid.stderr b/tests/ui/lint/rfc-2383-lint-reason/expect_with_forbid.stderr
index a8116e93404..0f42ffbdea3 100644
--- a/tests/ui/lint/rfc-2383-lint-reason/expect_with_forbid.stderr
+++ b/tests/ui/lint/rfc-2383-lint-reason/expect_with_forbid.stderr
@@ -1,32 +1,14 @@
 error[E0453]: expect(unused_variables) incompatible with previous forbid
-  --> $DIR/expect_with_forbid.rs:6:10
+  --> $DIR/expect_with_forbid.rs:7:10
    |
 LL | #[forbid(unused_variables)]
    |          ---------------- `forbid` level set here
-...
-LL | #[expect(unused_variables)]
-   |          ^^^^^^^^^^^^^^^^ overruled by previous forbid
-
-error[E0453]: expect(while_true) incompatible with previous forbid
-  --> $DIR/expect_with_forbid.rs:17:10
-   |
-LL | #[forbid(while_true)]
-   |          ---------- `forbid` level set here
-...
-LL | #[expect(while_true)]
-   |          ^^^^^^^^^^ overruled by previous forbid
-
-error[E0453]: expect(unused_variables) incompatible with previous forbid
-  --> $DIR/expect_with_forbid.rs:6:10
-   |
-LL | #[forbid(unused_variables)]
-   |          ---------------- `forbid` level set here
-...
+LL |
 LL | #[expect(unused_variables)]
    |          ^^^^^^^^^^^^^^^^ overruled by previous forbid
 
 error[E0453]: expect(while_true) incompatible with previous forbid
-  --> $DIR/expect_with_forbid.rs:17:10
+  --> $DIR/expect_with_forbid.rs:15:10
    |
 LL | #[forbid(while_true)]
    |          ---------- `forbid` level set here
@@ -35,17 +17,17 @@ LL | #[expect(while_true)]
    |          ^^^^^^^^^^ overruled by previous forbid
 
 error: denote infinite loops with `loop { ... }`
-  --> $DIR/expect_with_forbid.rs:26:5
+  --> $DIR/expect_with_forbid.rs:22:5
    |
 LL |     while true {}
    |     ^^^^^^^^^^ help: use `loop`
    |
 note: the lint level is defined here
-  --> $DIR/expect_with_forbid.rs:13:10
+  --> $DIR/expect_with_forbid.rs:12:10
    |
 LL | #[forbid(while_true)]
    |          ^^^^^^^^^^
 
-error: aborting due to 5 previous errors
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0453`.
diff --git a/tests/ui/lub-glb/old-lub-glb-object.stderr b/tests/ui/lub-glb/old-lub-glb-object.stderr
index 3d0c171e013..c476d6f692b 100644
--- a/tests/ui/lub-glb/old-lub-glb-object.stderr
+++ b/tests/ui/lub-glb/old-lub-glb-object.stderr
@@ -15,6 +15,7 @@ LL |         _ => y,
    |
    = note: expected trait object `dyn for<'a, 'b> Foo<&'a u8, &'b u8>`
               found trait object `dyn for<'a> Foo<&'a u8, &'a u8>`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/macros/builtin-std-paths-fail.stderr b/tests/ui/macros/builtin-std-paths-fail.stderr
index 004a39043b7..331943843c0 100644
--- a/tests/ui/macros/builtin-std-paths-fail.stderr
+++ b/tests/ui/macros/builtin-std-paths-fail.stderr
@@ -15,12 +15,16 @@ error[E0433]: failed to resolve: could not find `RustcDecodable` in `core`
    |
 LL |     core::RustcDecodable,
    |           ^^^^^^^^^^^^^^ could not find `RustcDecodable` in `core`
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0433]: failed to resolve: could not find `RustcDecodable` in `core`
   --> $DIR/builtin-std-paths-fail.rs:4:11
    |
 LL |     core::RustcDecodable,
    |           ^^^^^^^^^^^^^^ could not find `RustcDecodable` in `core`
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0433]: failed to resolve: could not find `bench` in `core`
   --> $DIR/builtin-std-paths-fail.rs:7:9
@@ -63,12 +67,16 @@ error[E0433]: failed to resolve: could not find `RustcDecodable` in `std`
    |
 LL |     std::RustcDecodable,
    |          ^^^^^^^^^^^^^^ could not find `RustcDecodable` in `std`
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0433]: failed to resolve: could not find `RustcDecodable` in `std`
   --> $DIR/builtin-std-paths-fail.rs:16:10
    |
 LL |     std::RustcDecodable,
    |          ^^^^^^^^^^^^^^ could not find `RustcDecodable` in `std`
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0433]: failed to resolve: could not find `bench` in `std`
   --> $DIR/builtin-std-paths-fail.rs:19:8
diff --git a/tests/ui/macros/meta-item-absolute-path.stderr b/tests/ui/macros/meta-item-absolute-path.stderr
index c53971e245f..f0d763d7abb 100644
--- a/tests/ui/macros/meta-item-absolute-path.stderr
+++ b/tests/ui/macros/meta-item-absolute-path.stderr
@@ -9,6 +9,8 @@ error[E0433]: failed to resolve: maybe a missing crate `Absolute`?
    |
 LL | #[derive(::Absolute)]
    |            ^^^^^^^^ maybe a missing crate `Absolute`?
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/native-library-link-flags/modifiers-override.stderr b/tests/ui/native-library-link-flags/modifiers-override.stderr
index eb3ab55c310..64427651e9f 100644
--- a/tests/ui/native-library-link-flags/modifiers-override.stderr
+++ b/tests/ui/native-library-link-flags/modifiers-override.stderr
@@ -21,6 +21,8 @@ error: overriding linking modifiers from command line is not supported
    |
 LL | extern "C" {}
    | ^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 4 previous errors
 
diff --git a/tests/ui/nll/closure-malformed-projection-input-issue-102800.stderr b/tests/ui/nll/closure-malformed-projection-input-issue-102800.stderr
index 46dba006433..aeb0a1394cc 100644
--- a/tests/ui/nll/closure-malformed-projection-input-issue-102800.stderr
+++ b/tests/ui/nll/closure-malformed-projection-input-issue-102800.stderr
@@ -15,6 +15,7 @@ LL |     let _: for<'a> fn(<&'a () as Trait>::Ty) = |_| {};
    |
    = note: `&'0 ()` must implement `Trait`, for any lifetime `'0`...
    = note: ...but `Trait` is actually implemented for the type `&'static ()`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/nll/issue-97997.stderr b/tests/ui/nll/issue-97997.stderr
index 46440c021f5..89eaf77adf0 100644
--- a/tests/ui/nll/issue-97997.stderr
+++ b/tests/ui/nll/issue-97997.stderr
@@ -15,6 +15,7 @@ LL |     <fn(&u8) as Foo>::ASSOC;
    |
    = note: `Foo` would have to be implemented for the type `for<'a> fn(&'a u8)`
    = note: ...but `Foo` is actually implemented for the type `fn(&'0 u8)`, for some specific lifetime `'0`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/nll/missing-universe-cause-issue-114907.stderr b/tests/ui/nll/missing-universe-cause-issue-114907.stderr
index c3dd4257a73..988eee61027 100644
--- a/tests/ui/nll/missing-universe-cause-issue-114907.stderr
+++ b/tests/ui/nll/missing-universe-cause-issue-114907.stderr
@@ -38,6 +38,7 @@ LL |     accept(callback);
    |
    = note: closure with signature `fn(&'2 ())` must implement `FnOnce<(&'1 (),)>`, for any lifetime `'1`...
    = note: ...but it actually implements `FnOnce<(&'2 (),)>`, for some specific lifetime `'2`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0308]: mismatched types
   --> $DIR/missing-universe-cause-issue-114907.rs:33:5
@@ -73,6 +74,8 @@ error: higher-ranked subtype error
    |
 LL |     accept(callback);
    |                     ^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 6 previous errors
 
diff --git a/tests/ui/nll/relate_tys/impl-fn-ignore-binder-via-bottom.stderr b/tests/ui/nll/relate_tys/impl-fn-ignore-binder-via-bottom.stderr
index b945ffedda5..804071a3e6f 100644
--- a/tests/ui/nll/relate_tys/impl-fn-ignore-binder-via-bottom.stderr
+++ b/tests/ui/nll/relate_tys/impl-fn-ignore-binder-via-bottom.stderr
@@ -15,6 +15,7 @@ LL |     let _x = <fn(&())>::make_f();
    |
    = note: `Y` would have to be implemented for the type `for<'a> fn(&'a ())`
    = note: ...but `Y` is actually implemented for the type `fn(&'0 ())`, for some specific lifetime `'0`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: implementation of `Y` is not general enough
   --> $DIR/impl-fn-ignore-binder-via-bottom.rs:30:14
@@ -24,6 +25,7 @@ LL |     let _x = <fn(&())>::make_f();
    |
    = note: `Y` would have to be implemented for the type `for<'a> fn(&'a ())`
    = note: ...but `Y` is actually implemented for the type `fn(&'0 ())`, for some specific lifetime `'0`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 3 previous errors
 
diff --git a/tests/ui/nll/type-check-pointer-comparisons.stderr b/tests/ui/nll/type-check-pointer-comparisons.stderr
index 0d8480a42c1..37098b585df 100644
--- a/tests/ui/nll/type-check-pointer-comparisons.stderr
+++ b/tests/ui/nll/type-check-pointer-comparisons.stderr
@@ -61,6 +61,8 @@ LL |     x == y;
    = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
 
 help: `'a` and `'b` must be the same: replace one with the other
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: lifetime may not live long enough
   --> $DIR/type-check-pointer-comparisons.rs:16:5
@@ -93,6 +95,8 @@ LL |     f == g;
    = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
 
 help: `'a` and `'b` must be the same: replace one with the other
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 6 previous errors
 
diff --git a/tests/ui/nll/user-annotations/normalization-2.stderr b/tests/ui/nll/user-annotations/normalization-2.stderr
index 6b0dcb414ae..dcf049a7a61 100644
--- a/tests/ui/nll/user-annotations/normalization-2.stderr
+++ b/tests/ui/nll/user-annotations/normalization-2.stderr
@@ -131,6 +131,7 @@ help: the following changes may resolve your lifetime errors
    |
    = help: replace `'a` with `'static`
    = help: replace `'b` with `'static`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: lifetime may not live long enough
   --> $DIR/normalization-2.rs:89:5
@@ -185,6 +186,7 @@ help: the following changes may resolve your lifetime errors
    |
    = help: replace `'a` with `'static`
    = help: replace `'b` with `'static`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: lifetime may not live long enough
   --> $DIR/normalization-2.rs:117:5
diff --git a/tests/ui/object-safety/assoc_type_bounds_sized_unnecessary.stderr b/tests/ui/object-safety/assoc_type_bounds_sized_unnecessary.stderr
index d0a4179fe3e..659679e4440 100644
--- a/tests/ui/object-safety/assoc_type_bounds_sized_unnecessary.stderr
+++ b/tests/ui/object-safety/assoc_type_bounds_sized_unnecessary.stderr
@@ -14,6 +14,7 @@ LL | fn foo(_: &dyn Foo<Bar = ()>) {}
    |                    ^^^^^^^^ help: remove this bound
    |
    = note: this associated type has a `where Self: Sized` bound. Thus, while the associated type can be specified, it cannot be used in any way, because trait objects are not `Sized`.
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: unnecessary associated type bound for not object safe associated type
   --> $DIR/assoc_type_bounds_sized_unnecessary.rs:9:20
@@ -22,6 +23,7 @@ LL | fn foo(_: &dyn Foo<Bar = ()>) {}
    |                    ^^^^^^^^ help: remove this bound
    |
    = note: this associated type has a `where Self: Sized` bound. Thus, while the associated type can be specified, it cannot be used in any way, because trait objects are not `Sized`.
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: 3 warnings emitted
 
diff --git a/tests/ui/parser/attr-stmt-expr-attr-bad.stderr b/tests/ui/parser/attr-stmt-expr-attr-bad.stderr
index 96899fd3fc5..e46c591080d 100644
--- a/tests/ui/parser/attr-stmt-expr-attr-bad.stderr
+++ b/tests/ui/parser/attr-stmt-expr-attr-bad.stderr
@@ -27,6 +27,7 @@ LL | #[cfg(FALSE)] fn e() { let _ = foo(#![attr]); }
    |
    = note: inner attributes, like `#![no_std]`, annotate the item enclosing them, and are usually found at the beginning of source files
    = note: outer attributes, like `#[test]`, annotate the item following them
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: expected expression, found `)`
   --> $DIR/attr-stmt-expr-attr-bad.rs:7:44
diff --git a/tests/ui/parser/issues/issue-84117.stderr b/tests/ui/parser/issues/issue-84117.stderr
index 237bc11bd06..958f3b40bb0 100644
--- a/tests/ui/parser/issues/issue-84117.stderr
+++ b/tests/ui/parser/issues/issue-84117.stderr
@@ -47,6 +47,7 @@ LL |     let outer_local:e_outer<&str, { let inner_local:e_inner<&str, }
    |                                         |
    |                                         while parsing the type for `inner_local`
    |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: you might have meant to end the type parameters here
    |
 LL |     let outer_local:e_outer<&str, { let inner_local:e_inner<&str>, }
@@ -61,6 +62,8 @@ error: expected one of `!`, `.`, `::`, `;`, `?`, `else`, `{`, or an operator, fo
    |
 LL |     let outer_local:e_outer<&str, { let inner_local:e_inner<&str, }
    |                                                                 ^ expected one of 8 possible tokens
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: expected one of `!`, `.`, `::`, `;`, `?`, `else`, `{`, or an operator, found `,`
   --> $DIR/issue-84117.rs:2:33
diff --git a/tests/ui/parser/macro/macro-repeat.stderr b/tests/ui/parser/macro/macro-repeat.stderr
index 63554b197b9..ade2bbf9b0b 100644
--- a/tests/ui/parser/macro/macro-repeat.stderr
+++ b/tests/ui/parser/macro/macro-repeat.stderr
@@ -9,6 +9,8 @@ error: variable 'v' is still repeating at this depth
    |
 LL |         $v
    |         ^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/pattern/bindings-after-at/borrowck-pat-ref-mut-and-ref.stderr b/tests/ui/pattern/bindings-after-at/borrowck-pat-ref-mut-and-ref.stderr
index c0a6558a1bf..0b432487615 100644
--- a/tests/ui/pattern/bindings-after-at/borrowck-pat-ref-mut-and-ref.stderr
+++ b/tests/ui/pattern/bindings-after-at/borrowck-pat-ref-mut-and-ref.stderr
@@ -307,6 +307,7 @@ LL |         ref a @ Ok(ref mut b) | ref a @ Err(ref mut b) if { drop(b); false
    |                                                                  ^ move occurs because `b` has type `&mut U`, which does not implement the `Copy` trait
    |
    = note: variables bound in patterns cannot be moved from until after the end of the pattern guard
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0507]: cannot move out of `a` in pattern guard
   --> $DIR/borrowck-pat-ref-mut-and-ref.rs:109:66
@@ -323,6 +324,7 @@ LL |         ref mut a @ Ok(ref b) | ref mut a @ Err(ref b) if { drop(a); false
    |                                                                  ^ move occurs because `a` has type `&mut Result<U, U>`, which does not implement the `Copy` trait
    |
    = note: variables bound in patterns cannot be moved from until after the end of the pattern guard
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0502]: cannot borrow value as immutable because it is also borrowed as mutable
   --> $DIR/borrowck-pat-ref-mut-and-ref.rs:117:9
diff --git a/tests/ui/pattern/patkind-litrange-no-expr.stderr b/tests/ui/pattern/patkind-litrange-no-expr.stderr
index eb1ee7e4567..45a26148940 100644
--- a/tests/ui/pattern/patkind-litrange-no-expr.stderr
+++ b/tests/ui/pattern/patkind-litrange-no-expr.stderr
@@ -9,6 +9,8 @@ error: arbitrary expressions aren't allowed in patterns
    |
 LL |     Arith = 1 + 1,
    |             ^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/privacy/effective_visibilities.stderr b/tests/ui/privacy/effective_visibilities.stderr
index f74f812e1a0..41d63532dea 100644
--- a/tests/ui/privacy/effective_visibilities.stderr
+++ b/tests/ui/privacy/effective_visibilities.stderr
@@ -45,6 +45,8 @@ error: not in the table
    |
 LL |         struct PrivStruct;
    |         ^^^^^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: Direct: pub(crate), Reexported: pub, Reachable: pub, ReachableThroughImplTrait: pub
   --> $DIR/effective_visibilities.rs:25:9
@@ -81,6 +83,8 @@ error: Direct: pub(crate), Reexported: pub, Reachable: pub, ReachableThroughImpl
    |
 LL |             A(
    |             ^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: Direct: pub(crate), Reexported: pub, Reachable: pub, ReachableThroughImplTrait: pub
   --> $DIR/effective_visibilities.rs:38:17
diff --git a/tests/ui/privacy/effective_visibilities_full_priv.stderr b/tests/ui/privacy/effective_visibilities_full_priv.stderr
index 29d82e2ee01..0577be1475f 100644
--- a/tests/ui/privacy/effective_visibilities_full_priv.stderr
+++ b/tests/ui/privacy/effective_visibilities_full_priv.stderr
@@ -9,6 +9,8 @@ error: not in the table
    |
 LL |     struct Priv;
    |     ^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: Direct: pub(crate), Reexported: pub(crate), Reachable: pub(crate), ReachableThroughImplTrait: pub(crate)
   --> $DIR/effective_visibilities_full_priv.rs:13:5
diff --git a/tests/ui/privacy/privacy1.stderr b/tests/ui/privacy/privacy1.stderr
index ca8f242e0be..a3552e146a6 100644
--- a/tests/ui/privacy/privacy1.stderr
+++ b/tests/ui/privacy/privacy1.stderr
@@ -21,6 +21,7 @@ note: the module `baz` is defined here
    |
 LL |     mod baz {
    |     ^^^^^^^
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0603]: module `baz` is private
   --> $DIR/privacy1.rs:141:18
diff --git a/tests/ui/proc-macro/issue-75930-derive-cfg.stderr b/tests/ui/proc-macro/issue-75930-derive-cfg.stderr
index 6d1efb0dc28..f3f470676e4 100644
--- a/tests/ui/proc-macro/issue-75930-derive-cfg.stderr
+++ b/tests/ui/proc-macro/issue-75930-derive-cfg.stderr
@@ -22,6 +22,7 @@ LL | #[derive(Print)]
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #79202 <https://github.com/rust-lang/rust/issues/79202>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: 2 warnings emitted
 
diff --git a/tests/ui/proc-macro/macro-namespace-reserved-2.stderr b/tests/ui/proc-macro/macro-namespace-reserved-2.stderr
index b9effe7cf21..0471124061e 100644
--- a/tests/ui/proc-macro/macro-namespace-reserved-2.stderr
+++ b/tests/ui/proc-macro/macro-namespace-reserved-2.stderr
@@ -143,6 +143,7 @@ LL | #[derive(my_macro)]
    |          ^^^^^^^^
    |
    = note: `my_macro` is in scope, but it is a function-like macro
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 20 previous errors
 
diff --git a/tests/ui/proc-macro/pretty-print-hack-show.local.stderr b/tests/ui/proc-macro/pretty-print-hack-show.local.stderr
index 873054927c9..118882f73a3 100644
--- a/tests/ui/proc-macro/pretty-print-hack-show.local.stderr
+++ b/tests/ui/proc-macro/pretty-print-hack-show.local.stderr
@@ -18,6 +18,7 @@ LL | enum ProceduralMasqueradeDummyType {
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #83125 <https://github.com/rust-lang/rust/issues/83125>
    = note: older versions of the `rental` crate will stop compiling in future versions of Rust; please update to `rental` v0.5.6, or switch to one of the `rental` alternatives
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: using an old version of `rental`
   --> $DIR/pretty-print-hack/allsorts-rental-0.5.6/src/lib.rs:4:6
@@ -28,6 +29,7 @@ LL | enum ProceduralMasqueradeDummyType {
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #83125 <https://github.com/rust-lang/rust/issues/83125>
    = note: older versions of the `rental` crate will stop compiling in future versions of Rust; please update to `rental` v0.5.6, or switch to one of the `rental` alternatives
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: using an old version of `rental`
   --> $DIR/pretty-print-hack/allsorts-rental-0.5.6/src/lib.rs:4:6
@@ -38,6 +40,7 @@ LL | enum ProceduralMasqueradeDummyType {
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #83125 <https://github.com/rust-lang/rust/issues/83125>
    = note: older versions of the `rental` crate will stop compiling in future versions of Rust; please update to `rental` v0.5.6, or switch to one of the `rental` alternatives
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: using an old version of `rental`
   --> $DIR/pretty-print-hack/rental-0.5.5/src/lib.rs:4:6
@@ -58,6 +61,7 @@ LL | enum ProceduralMasqueradeDummyType {
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #83125 <https://github.com/rust-lang/rust/issues/83125>
    = note: older versions of the `rental` crate will stop compiling in future versions of Rust; please update to `rental` v0.5.6, or switch to one of the `rental` alternatives
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: using an old version of `rental`
   --> $DIR/pretty-print-hack/rental-0.5.5/src/lib.rs:4:6
@@ -68,6 +72,7 @@ LL | enum ProceduralMasqueradeDummyType {
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #83125 <https://github.com/rust-lang/rust/issues/83125>
    = note: older versions of the `rental` crate will stop compiling in future versions of Rust; please update to `rental` v0.5.6, or switch to one of the `rental` alternatives
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: using an old version of `rental`
   --> $DIR/pretty-print-hack/rental-0.5.5/src/lib.rs:4:6
@@ -78,6 +83,7 @@ LL | enum ProceduralMasqueradeDummyType {
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #83125 <https://github.com/rust-lang/rust/issues/83125>
    = note: older versions of the `rental` crate will stop compiling in future versions of Rust; please update to `rental` v0.5.6, or switch to one of the `rental` alternatives
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 8 previous errors
 
diff --git a/tests/ui/proc-macro/pretty-print-hack-show.remapped.stderr b/tests/ui/proc-macro/pretty-print-hack-show.remapped.stderr
index 873054927c9..118882f73a3 100644
--- a/tests/ui/proc-macro/pretty-print-hack-show.remapped.stderr
+++ b/tests/ui/proc-macro/pretty-print-hack-show.remapped.stderr
@@ -18,6 +18,7 @@ LL | enum ProceduralMasqueradeDummyType {
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #83125 <https://github.com/rust-lang/rust/issues/83125>
    = note: older versions of the `rental` crate will stop compiling in future versions of Rust; please update to `rental` v0.5.6, or switch to one of the `rental` alternatives
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: using an old version of `rental`
   --> $DIR/pretty-print-hack/allsorts-rental-0.5.6/src/lib.rs:4:6
@@ -28,6 +29,7 @@ LL | enum ProceduralMasqueradeDummyType {
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #83125 <https://github.com/rust-lang/rust/issues/83125>
    = note: older versions of the `rental` crate will stop compiling in future versions of Rust; please update to `rental` v0.5.6, or switch to one of the `rental` alternatives
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: using an old version of `rental`
   --> $DIR/pretty-print-hack/allsorts-rental-0.5.6/src/lib.rs:4:6
@@ -38,6 +40,7 @@ LL | enum ProceduralMasqueradeDummyType {
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #83125 <https://github.com/rust-lang/rust/issues/83125>
    = note: older versions of the `rental` crate will stop compiling in future versions of Rust; please update to `rental` v0.5.6, or switch to one of the `rental` alternatives
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: using an old version of `rental`
   --> $DIR/pretty-print-hack/rental-0.5.5/src/lib.rs:4:6
@@ -58,6 +61,7 @@ LL | enum ProceduralMasqueradeDummyType {
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #83125 <https://github.com/rust-lang/rust/issues/83125>
    = note: older versions of the `rental` crate will stop compiling in future versions of Rust; please update to `rental` v0.5.6, or switch to one of the `rental` alternatives
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: using an old version of `rental`
   --> $DIR/pretty-print-hack/rental-0.5.5/src/lib.rs:4:6
@@ -68,6 +72,7 @@ LL | enum ProceduralMasqueradeDummyType {
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #83125 <https://github.com/rust-lang/rust/issues/83125>
    = note: older versions of the `rental` crate will stop compiling in future versions of Rust; please update to `rental` v0.5.6, or switch to one of the `rental` alternatives
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: using an old version of `rental`
   --> $DIR/pretty-print-hack/rental-0.5.5/src/lib.rs:4:6
@@ -78,6 +83,7 @@ LL | enum ProceduralMasqueradeDummyType {
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #83125 <https://github.com/rust-lang/rust/issues/83125>
    = note: older versions of the `rental` crate will stop compiling in future versions of Rust; please update to `rental` v0.5.6, or switch to one of the `rental` alternatives
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 8 previous errors
 
diff --git a/tests/ui/proc-macro/resolve-error.stderr b/tests/ui/proc-macro/resolve-error.stderr
index 3c3f24d0ff2..e7639f474c7 100644
--- a/tests/ui/proc-macro/resolve-error.stderr
+++ b/tests/ui/proc-macro/resolve-error.stderr
@@ -44,6 +44,8 @@ error: cannot find derive macro `attr_proc_macra` in this scope
    |
 LL | #[derive(attr_proc_macra)]
    |          ^^^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: cannot find derive macro `Dlona` in this scope
   --> $DIR/resolve-error.rs:40:10
@@ -66,6 +68,8 @@ LL | #[derive(Dlona)]
    |
 LL | pub fn derive_clonea(input: TokenStream) -> TokenStream {
    | ------------------------------------------------------- similarly named derive macro `Clona` defined here
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: cannot find derive macro `Dlone` in this scope
   --> $DIR/resolve-error.rs:35:10
@@ -84,6 +88,8 @@ LL | #[derive(Dlone)]
   --> $SRC_DIR/core/src/clone.rs:LL:COL
    |
    = note: similarly named derive macro `Clone` defined here
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: cannot find attribute `FooWithLongNan` in this scope
   --> $DIR/resolve-error.rs:32:3
@@ -123,6 +129,8 @@ LL | #[derive(FooWithLongNan)]
    |
 LL | pub fn derive_foo(input: TokenStream) -> TokenStream {
    | ---------------------------------------------------- similarly named derive macro `FooWithLongName` defined here
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 14 previous errors
 
diff --git a/tests/ui/recursion_limit/empty.stderr b/tests/ui/recursion_limit/empty.stderr
index cb5c0c35a5e..2f730677507 100644
--- a/tests/ui/recursion_limit/empty.stderr
+++ b/tests/ui/recursion_limit/empty.stderr
@@ -13,6 +13,8 @@ LL | #![recursion_limit = ""]
    | ^^^^^^^^^^^^^^^^^^^^^--^
    |                      |
    |                      `limit` must be a non-negative integer
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/recursion_limit/invalid_digit.stderr b/tests/ui/recursion_limit/invalid_digit.stderr
index 4dc93ad5f67..4fda3039032 100644
--- a/tests/ui/recursion_limit/invalid_digit.stderr
+++ b/tests/ui/recursion_limit/invalid_digit.stderr
@@ -13,6 +13,8 @@ LL | #![recursion_limit = "-100"]
    | ^^^^^^^^^^^^^^^^^^^^^------^
    |                      |
    |                      not a valid integer
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/recursion_limit/overflow.stderr b/tests/ui/recursion_limit/overflow.stderr
index 2f622d28b45..6057177deb2 100644
--- a/tests/ui/recursion_limit/overflow.stderr
+++ b/tests/ui/recursion_limit/overflow.stderr
@@ -13,6 +13,8 @@ LL | #![recursion_limit = "999999999999999999999999"]
    | ^^^^^^^^^^^^^^^^^^^^^--------------------------^
    |                      |
    |                      `limit` is too large
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/regions/regions-close-object-into-object-4.stderr b/tests/ui/regions/regions-close-object-into-object-4.stderr
index 7a9f1ab0001..3ff7f891c66 100644
--- a/tests/ui/regions/regions-close-object-into-object-4.stderr
+++ b/tests/ui/regions/regions-close-object-into-object-4.stderr
@@ -26,6 +26,7 @@ error[E0310]: the parameter type `U` may not live long enough
 LL |     Box::new(B(&*v)) as Box<dyn X>
    |     ^^^^^^^^^^^^^^^^ ...so that the type `U` will meet its required lifetime bounds
    |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: consider adding an explicit lifetime bound...
    |
 LL | fn i<'a, T, U: 'static>(v: Box<dyn A<U>+'a>) -> Box<dyn X + 'static> {
diff --git a/tests/ui/regions/regions-close-object-into-object-5.stderr b/tests/ui/regions/regions-close-object-into-object-5.stderr
index 311e8868c09..88c13483263 100644
--- a/tests/ui/regions/regions-close-object-into-object-5.stderr
+++ b/tests/ui/regions/regions-close-object-into-object-5.stderr
@@ -26,6 +26,7 @@ error[E0310]: the parameter type `T` may not live long enough
 LL |     Box::new(B(&*v)) as Box<dyn X>
    |     ^^^^^^^^^^^^^^^^ ...so that the type `T` will meet its required lifetime bounds
    |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: consider adding an explicit lifetime bound...
    |
 LL | fn f<'a, T: 'static, U>(v: Box<A<T> + 'static>) -> Box<X + 'static> {
diff --git a/tests/ui/repr/repr-align-assign.stderr b/tests/ui/repr/repr-align-assign.stderr
index b878ae0d173..3606d02210b 100644
--- a/tests/ui/repr/repr-align-assign.stderr
+++ b/tests/ui/repr/repr-align-assign.stderr
@@ -15,12 +15,16 @@ error[E0693]: incorrect `repr(align)` attribute format
    |
 LL | #[repr(align=8)]
    |        ^^^^^^^ help: use parentheses instead: `align(8)`
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0693]: incorrect `repr(align)` attribute format
   --> $DIR/repr-align-assign.rs:9:8
    |
 LL | #[repr(align="8")]
    |        ^^^^^^^^^ help: use parentheses instead: `align(8)`
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 4 previous errors
 
diff --git a/tests/ui/repr/repr-align.stderr b/tests/ui/repr/repr-align.stderr
index 900a811bb8a..84d33a08a6f 100644
--- a/tests/ui/repr/repr-align.stderr
+++ b/tests/ui/repr/repr-align.stderr
@@ -39,36 +39,48 @@ error[E0589]: invalid `repr(align)` attribute: not an unsuffixed integer
    |
 LL | #[repr(align(16.0))]
    |        ^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0589]: invalid `repr(align)` attribute: not a power of two
   --> $DIR/repr-align.rs:7:8
    |
 LL | #[repr(align(15))]
    |        ^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0589]: invalid `repr(align)` attribute: larger than 2^29
   --> $DIR/repr-align.rs:11:8
    |
 LL | #[repr(align(4294967296))]
    |        ^^^^^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0589]: invalid `repr(align)` attribute: not an unsuffixed integer
   --> $DIR/repr-align.rs:18:8
    |
 LL | #[repr(align(16.0))]
    |        ^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0589]: invalid `repr(align)` attribute: not a power of two
   --> $DIR/repr-align.rs:22:8
    |
 LL | #[repr(align(15))]
    |        ^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0589]: invalid `repr(align)` attribute: larger than 2^29
   --> $DIR/repr-align.rs:26:8
    |
 LL | #[repr(align(4294967296))]
    |        ^^^^^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 12 previous errors
 
diff --git a/tests/ui/rfcs/rfc-1623-static/rfc1623-2.stderr b/tests/ui/rfcs/rfc-1623-static/rfc1623-2.stderr
index d183eaaa623..5f8c5dbe619 100644
--- a/tests/ui/rfcs/rfc-1623-static/rfc1623-2.stderr
+++ b/tests/ui/rfcs/rfc-1623-static/rfc1623-2.stderr
@@ -15,6 +15,7 @@ LL |     f: &id,
    |
    = note: expected trait `for<'a, 'b> Fn<(&'a Foo<'b>,)>`
               found trait `Fn<(&Foo<'_>,)>`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: implementation of `FnOnce` is not general enough
   --> $DIR/rfc1623-2.rs:28:8
diff --git a/tests/ui/rfcs/rfc-2632-const-trait-impl/issue-102156.stderr b/tests/ui/rfcs/rfc-2632-const-trait-impl/issue-102156.stderr
index 8bf00eaff1f..e8ae7e4e36c 100644
--- a/tests/ui/rfcs/rfc-2632-const-trait-impl/issue-102156.stderr
+++ b/tests/ui/rfcs/rfc-2632-const-trait-impl/issue-102156.stderr
@@ -13,6 +13,7 @@ LL | use core::convert::{From, TryFrom};
    |     ^^^^ maybe a missing crate `core`?
    |
    = help: consider adding `extern crate core` to use the `core` crate
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/rfcs/rfc-2632-const-trait-impl/super-traits-fail-2.nn.stderr b/tests/ui/rfcs/rfc-2632-const-trait-impl/super-traits-fail-2.nn.stderr
index 97f346e8c1d..b60399c57dc 100644
--- a/tests/ui/rfcs/rfc-2632-const-trait-impl/super-traits-fail-2.nn.stderr
+++ b/tests/ui/rfcs/rfc-2632-const-trait-impl/super-traits-fail-2.nn.stderr
@@ -9,6 +9,8 @@ error: ~const can only be applied to `#[const_trait]` traits
    |
 LL | trait Bar: ~const Foo {}
    |                   ^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/rfcs/rfc-2632-const-trait-impl/super-traits-fail-2.ny.stderr b/tests/ui/rfcs/rfc-2632-const-trait-impl/super-traits-fail-2.ny.stderr
index 97f346e8c1d..b60399c57dc 100644
--- a/tests/ui/rfcs/rfc-2632-const-trait-impl/super-traits-fail-2.ny.stderr
+++ b/tests/ui/rfcs/rfc-2632-const-trait-impl/super-traits-fail-2.ny.stderr
@@ -9,6 +9,8 @@ error: ~const can only be applied to `#[const_trait]` traits
    |
 LL | trait Bar: ~const Foo {}
    |                   ^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/rfcs/rfc-2632-const-trait-impl/super-traits-fail-3.nn.stderr b/tests/ui/rfcs/rfc-2632-const-trait-impl/super-traits-fail-3.nn.stderr
index 2897eabb081..eb12a236d8c 100644
--- a/tests/ui/rfcs/rfc-2632-const-trait-impl/super-traits-fail-3.nn.stderr
+++ b/tests/ui/rfcs/rfc-2632-const-trait-impl/super-traits-fail-3.nn.stderr
@@ -9,6 +9,8 @@ error: ~const can only be applied to `#[const_trait]` traits
    |
 LL | trait Bar: ~const Foo {}
    |                   ^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: ~const can only be applied to `#[const_trait]` traits
   --> $DIR/super-traits-fail-3.rs:17:24
diff --git a/tests/ui/rfcs/rfc-2632-const-trait-impl/super-traits-fail-3.ny.stderr b/tests/ui/rfcs/rfc-2632-const-trait-impl/super-traits-fail-3.ny.stderr
index 9839a4f2480..cd0ee73277d 100644
--- a/tests/ui/rfcs/rfc-2632-const-trait-impl/super-traits-fail-3.ny.stderr
+++ b/tests/ui/rfcs/rfc-2632-const-trait-impl/super-traits-fail-3.ny.stderr
@@ -9,6 +9,8 @@ error: ~const can only be applied to `#[const_trait]` traits
    |
 LL | trait Bar: ~const Foo {}
    |                   ^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/rust-2018/edition-lint-fully-qualified-paths.stderr b/tests/ui/rust-2018/edition-lint-fully-qualified-paths.stderr
index 497ee440dfd..c0a322edcd6 100644
--- a/tests/ui/rust-2018/edition-lint-fully-qualified-paths.stderr
+++ b/tests/ui/rust-2018/edition-lint-fully-qualified-paths.stderr
@@ -20,6 +20,7 @@ LL |     let _: <foo::Baz as ::foo::Foo>::Bar = ();
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2018!
    = note: for more information, see issue #53130 <https://github.com/rust-lang/rust/issues/53130>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: absolute paths must start with `self`, `super`, `crate`, or an external crate name in the 2018 edition
   --> $DIR/edition-lint-fully-qualified-paths.rs:25:13
diff --git a/tests/ui/rust-2018/edition-lint-nested-empty-paths.stderr b/tests/ui/rust-2018/edition-lint-nested-empty-paths.stderr
index 8769cbb35b0..041572be844 100644
--- a/tests/ui/rust-2018/edition-lint-nested-empty-paths.stderr
+++ b/tests/ui/rust-2018/edition-lint-nested-empty-paths.stderr
@@ -29,6 +29,7 @@ LL | use foo::{bar::{XX, baz::{}}};
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2018!
    = note: for more information, see issue #53130 <https://github.com/rust-lang/rust/issues/53130>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: absolute paths must start with `self`, `super`, `crate`, or an external crate name in the 2018 edition
   --> $DIR/edition-lint-nested-empty-paths.rs:27:5
@@ -47,6 +48,7 @@ LL | use foo::{bar::{baz::{}, baz1::{}}};
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2018!
    = note: for more information, see issue #53130 <https://github.com/rust-lang/rust/issues/53130>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 5 previous errors
 
diff --git a/tests/ui/rust-2018/edition-lint-nested-paths.stderr b/tests/ui/rust-2018/edition-lint-nested-paths.stderr
index 354a6fe3252..4a70bb7e5c8 100644
--- a/tests/ui/rust-2018/edition-lint-nested-paths.stderr
+++ b/tests/ui/rust-2018/edition-lint-nested-paths.stderr
@@ -20,6 +20,7 @@ LL | use foo::{a, b};
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2018!
    = note: for more information, see issue #53130 <https://github.com/rust-lang/rust/issues/53130>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: absolute paths must start with `self`, `super`, `crate`, or an external crate name in the 2018 edition
   --> $DIR/edition-lint-nested-paths.rs:23:13
@@ -38,6 +39,7 @@ LL |         use foo::{self as x, c};
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2018!
    = note: for more information, see issue #53130 <https://github.com/rust-lang/rust/issues/53130>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 4 previous errors
 
diff --git a/tests/ui/rust-2018/edition-lint-paths.stderr b/tests/ui/rust-2018/edition-lint-paths.stderr
index 42652be9401..fde17338d98 100644
--- a/tests/ui/rust-2018/edition-lint-paths.stderr
+++ b/tests/ui/rust-2018/edition-lint-paths.stderr
@@ -38,6 +38,7 @@ LL |     use {main, Bar as SomethingElse};
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2018!
    = note: for more information, see issue #53130 <https://github.com/rust-lang/rust/issues/53130>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: absolute paths must start with `self`, `super`, `crate`, or an external crate name in the 2018 edition
   --> $DIR/edition-lint-paths.rs:25:9
@@ -47,6 +48,7 @@ LL |     use {main, Bar as SomethingElse};
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2018!
    = note: for more information, see issue #53130 <https://github.com/rust-lang/rust/issues/53130>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: absolute paths must start with `self`, `super`, `crate`, or an external crate name in the 2018 edition
   --> $DIR/edition-lint-paths.rs:40:5
diff --git a/tests/ui/rust-2018/uniform-paths/cross-crate.stderr b/tests/ui/rust-2018/uniform-paths/cross-crate.stderr
index 45f77a0c9fe..8682c56d2a5 100644
--- a/tests/ui/rust-2018/uniform-paths/cross-crate.stderr
+++ b/tests/ui/rust-2018/uniform-paths/cross-crate.stderr
@@ -33,6 +33,7 @@ note: the tool module imported here
    |
 LL | use cross_crate::*;
    |     ^^^^^^^^^^^^^^
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 3 previous errors
 
diff --git a/tests/ui/rust-2018/uniform-paths/prelude-fail-2.stderr b/tests/ui/rust-2018/uniform-paths/prelude-fail-2.stderr
index 908bb498586..3dacb796911 100644
--- a/tests/ui/rust-2018/uniform-paths/prelude-fail-2.stderr
+++ b/tests/ui/rust-2018/uniform-paths/prelude-fail-2.stderr
@@ -51,6 +51,7 @@ note: the tool module imported here
    |
 LL | use rustfmt as imported_rustfmt;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: cannot use a tool module through an import
   --> $DIR/prelude-fail-2.rs:19:13
@@ -63,6 +64,7 @@ note: the tool module imported here
    |
 LL |     pub use rustfmt as imported_rustfmt;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 6 previous errors
 
diff --git a/tests/ui/sanitize/sanitizer-cfi-is-incompatible-with-saniziter-kcfi.aarch64.stderr b/tests/ui/sanitize/sanitizer-cfi-is-incompatible-with-saniziter-kcfi.aarch64.stderr
index 8328178e8d0..1006c3bc17e 100644
--- a/tests/ui/sanitize/sanitizer-cfi-is-incompatible-with-saniziter-kcfi.aarch64.stderr
+++ b/tests/ui/sanitize/sanitizer-cfi-is-incompatible-with-saniziter-kcfi.aarch64.stderr
@@ -3,6 +3,8 @@ error: cfi sanitizer is not supported for this target
 error: `-Zsanitizer=cfi` is incompatible with `-Zsanitizer=kcfi`
 
 error: `-Zsanitizer=cfi` is incompatible with `-Zsanitizer=kcfi`
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 3 previous errors
 
diff --git a/tests/ui/sanitize/sanitizer-cfi-is-incompatible-with-saniziter-kcfi.x86_64.stderr b/tests/ui/sanitize/sanitizer-cfi-is-incompatible-with-saniziter-kcfi.x86_64.stderr
index 8328178e8d0..1006c3bc17e 100644
--- a/tests/ui/sanitize/sanitizer-cfi-is-incompatible-with-saniziter-kcfi.x86_64.stderr
+++ b/tests/ui/sanitize/sanitizer-cfi-is-incompatible-with-saniziter-kcfi.x86_64.stderr
@@ -3,6 +3,8 @@ error: cfi sanitizer is not supported for this target
 error: `-Zsanitizer=cfi` is incompatible with `-Zsanitizer=kcfi`
 
 error: `-Zsanitizer=cfi` is incompatible with `-Zsanitizer=kcfi`
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 3 previous errors
 
diff --git a/tests/ui/suggestions/issue-61963.stderr b/tests/ui/suggestions/issue-61963.stderr
index b99b1b0b9b3..ec62153b0a7 100644
--- a/tests/ui/suggestions/issue-61963.stderr
+++ b/tests/ui/suggestions/issue-61963.stderr
@@ -37,6 +37,7 @@ LL |     bar: Box<Bar>,
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: use `dyn`
    |
 LL |     bar: Box<dyn Bar>,
@@ -50,6 +51,7 @@ LL |     bar: Box<Bar>,
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: use `dyn`
    |
 LL |     bar: Box<dyn Bar>,
@@ -63,6 +65,7 @@ LL | pub struct Foo {
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: use `dyn`
    |
 LL | dyn pub struct Foo {
@@ -76,6 +79,7 @@ LL | pub struct Foo {
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: use `dyn`
    |
 LL | dyn pub struct Foo {
@@ -89,6 +93,7 @@ LL | pub struct Foo {
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: use `dyn`
    |
 LL | dyn pub struct Foo {
diff --git a/tests/ui/suggestions/missing-lifetime-specifier.stderr b/tests/ui/suggestions/missing-lifetime-specifier.stderr
index 21d2378382c..fa4bc2fa79d 100644
--- a/tests/ui/suggestions/missing-lifetime-specifier.stderr
+++ b/tests/ui/suggestions/missing-lifetime-specifier.stderr
@@ -164,6 +164,7 @@ note: union defined here, with 2 lifetime parameters: `'t`, `'k`
    |
 LL | pub union Qux<'t, 'k, I> {
    |           ^^^ --  --
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: add missing lifetime argument
    |
 LL |     static e: RefCell<HashMap<i32, Vec<Vec<Qux<'static, 'static, i32>>>>> = RefCell::new(HashMap::new());
@@ -182,6 +183,7 @@ note: union defined here, with 2 lifetime parameters: `'t`, `'k`
    |
 LL | pub union Qux<'t, 'k, I> {
    |           ^^^ --  --
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: add missing lifetime argument
    |
 LL |     static e: RefCell<HashMap<i32, Vec<Vec<Qux<'static, 'static, i32>>>>> = RefCell::new(HashMap::new());
@@ -200,6 +202,7 @@ note: union defined here, with 2 lifetime parameters: `'t`, `'k`
    |
 LL | pub union Qux<'t, 'k, I> {
    |           ^^^ --  --
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: add missing lifetime argument
    |
 LL |     static e: RefCell<HashMap<i32, Vec<Vec<Qux<'static, 'static, i32>>>>> = RefCell::new(HashMap::new());
@@ -218,6 +221,7 @@ note: union defined here, with 2 lifetime parameters: `'t`, `'k`
    |
 LL | pub union Qux<'t, 'k, I> {
    |           ^^^ --  --
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: add missing lifetime argument
    |
 LL |     static e: RefCell<HashMap<i32, Vec<Vec<Qux<'static, 'static, i32>>>>> = RefCell::new(HashMap::new());
@@ -254,6 +258,7 @@ note: trait defined here, with 2 lifetime parameters: `'t`, `'k`
    |
 LL | trait Tar<'t, 'k, I> {}
    |       ^^^ --  --
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: add missing lifetime argument
    |
 LL |     static f: RefCell<HashMap<i32, Vec<Vec<&Tar<'static, 'static, i32>>>>> = RefCell::new(HashMap::new());
@@ -272,6 +277,7 @@ note: trait defined here, with 2 lifetime parameters: `'t`, `'k`
    |
 LL | trait Tar<'t, 'k, I> {}
    |       ^^^ --  --
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: add missing lifetime argument
    |
 LL |     static f: RefCell<HashMap<i32, Vec<Vec<&Tar<'static, 'static, i32>>>>> = RefCell::new(HashMap::new());
@@ -290,6 +296,7 @@ note: trait defined here, with 2 lifetime parameters: `'t`, `'k`
    |
 LL | trait Tar<'t, 'k, I> {}
    |       ^^^ --  --
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: add missing lifetime argument
    |
 LL |     static f: RefCell<HashMap<i32, Vec<Vec<&Tar<'static, 'static, i32>>>>> = RefCell::new(HashMap::new());
@@ -308,6 +315,7 @@ note: trait defined here, with 2 lifetime parameters: `'t`, `'k`
    |
 LL | trait Tar<'t, 'k, I> {}
    |       ^^^ --  --
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: add missing lifetime argument
    |
 LL |     static f: RefCell<HashMap<i32, Vec<Vec<&Tar<'static, 'static, i32>>>>> = RefCell::new(HashMap::new());
diff --git a/tests/ui/tool-attributes/tool-attributes-misplaced-1.stderr b/tests/ui/tool-attributes/tool-attributes-misplaced-1.stderr
index 71fd5f1d44a..2045dc6a36e 100644
--- a/tests/ui/tool-attributes/tool-attributes-misplaced-1.stderr
+++ b/tests/ui/tool-attributes/tool-attributes-misplaced-1.stderr
@@ -9,6 +9,8 @@ error: cannot find derive macro `rustfmt` in this scope
    |
 LL | #[derive(rustfmt)]
    |          ^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: cannot find attribute `rustfmt` in this scope
   --> $DIR/tool-attributes-misplaced-1.rs:9:3
diff --git a/tests/ui/tool_lints.stderr b/tests/ui/tool_lints.stderr
index d36cd193b15..f1d825caba1 100644
--- a/tests/ui/tool_lints.stderr
+++ b/tests/ui/tool_lints.stderr
@@ -13,6 +13,7 @@ LL | #[warn(foo::bar)]
    |        ^^^
    |
    = help: add `#![register_tool(foo)]` to the crate root
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/traits/issue-38404.stderr b/tests/ui/traits/issue-38404.stderr
index f8625f53b78..a5c258eb36e 100644
--- a/tests/ui/traits/issue-38404.stderr
+++ b/tests/ui/traits/issue-38404.stderr
@@ -25,6 +25,7 @@ LL | trait A<T>: std::ops::Add<Self> + Sized {}
    |             ^^^^^^^^^^^^^^^^^^^ ...because it uses `Self` as a type parameter
 LL | trait B<T>: A<T> {}
    |       - this trait cannot be made into an object...
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/traits/issue-59029-1.stderr b/tests/ui/traits/issue-59029-1.stderr
index 203a8928530..51354bcc545 100644
--- a/tests/ui/traits/issue-59029-1.stderr
+++ b/tests/ui/traits/issue-59029-1.stderr
@@ -9,6 +9,8 @@ error[E0220]: associated type `Res` not found for `Self`
    |
 LL | trait MkSvc<Target, Req> = Svc<Target> where Self::Res: Svc<Req>;
    |                                                    ^^^ there is a similarly named associated type `Res` in the trait `Svc`
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/tuple/tuple-struct-fields/test2.stderr b/tests/ui/tuple/tuple-struct-fields/test2.stderr
index 64a9ac13566..784411aba8f 100644
--- a/tests/ui/tuple/tuple-struct-fields/test2.stderr
+++ b/tests/ui/tuple/tuple-struct-fields/test2.stderr
@@ -22,6 +22,8 @@ error[E0412]: cannot find type `foo` in this scope
    |
 LL |     define_struct! { (foo) }
    |                       ^^^ not found in this scope
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 3 previous errors
 
diff --git a/tests/ui/tuple/tuple-struct-fields/test3.stderr b/tests/ui/tuple/tuple-struct-fields/test3.stderr
index 75262ed5780..00b07c03152 100644
--- a/tests/ui/tuple/tuple-struct-fields/test3.stderr
+++ b/tests/ui/tuple/tuple-struct-fields/test3.stderr
@@ -22,6 +22,8 @@ error[E0412]: cannot find type `foo` in this scope
    |
 LL |     define_struct! { foo }
    |                      ^^^ not found in this scope
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 3 previous errors
 
diff --git a/tests/ui/type-alias-enum-variants/enum-variant-priority-lint-ambiguous_associated_items.stderr b/tests/ui/type-alias-enum-variants/enum-variant-priority-lint-ambiguous_associated_items.stderr
index 0202a2fea49..359bd09ecd0 100644
--- a/tests/ui/type-alias-enum-variants/enum-variant-priority-lint-ambiguous_associated_items.stderr
+++ b/tests/ui/type-alias-enum-variants/enum-variant-priority-lint-ambiguous_associated_items.stderr
@@ -36,6 +36,7 @@ note: `V` could also refer to the associated type defined here
    |
 LL |     type V;
    |     ^^^^^^
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/type-alias-impl-trait/normalize-alias-type.rs b/tests/ui/type-alias-impl-trait/normalize-alias-type.rs
new file mode 100644
index 00000000000..7c62002b931
--- /dev/null
+++ b/tests/ui/type-alias-impl-trait/normalize-alias-type.rs
@@ -0,0 +1,32 @@
+// check-pass
+// compile-flags: -Z mir-opt-level=3
+#![feature(type_alias_impl_trait)]
+#![crate_type = "lib"]
+pub trait Tr {
+    fn get(&self) -> u32;
+}
+
+impl Tr for (u32,) {
+    #[inline]
+    fn get(&self) -> u32 { self.0 }
+}
+
+pub fn tr1() -> impl Tr {
+    (32,)
+}
+
+pub fn tr2() -> impl Tr {
+    struct Inner {
+        x: X,
+    }
+    type X = impl Tr;
+    impl Tr for Inner {
+        fn get(&self) -> u32 {
+            self.x.get()
+        }
+    }
+
+    Inner {
+        x: tr1(),
+    }
+}
diff --git a/tests/ui/type-alias-impl-trait/tait-normalize.rs b/tests/ui/type-alias-impl-trait/tait-normalize.rs
new file mode 100644
index 00000000000..26d94dbb42a
--- /dev/null
+++ b/tests/ui/type-alias-impl-trait/tait-normalize.rs
@@ -0,0 +1,14 @@
+// check-pass
+
+#![feature(type_alias_impl_trait)]
+
+fn enum_upvar() {
+    type T = impl Copy;
+    let foo: T = Some((1u32, 2u32));
+    let x = move || match foo {
+        None => (),
+        Some((a, b)) => (),
+    };
+}
+
+fn main(){}
diff --git a/tests/ui/type/subtyping-opaque-type.rs b/tests/ui/type/subtyping-opaque-type.rs
new file mode 100644
index 00000000000..beda232ea8b
--- /dev/null
+++ b/tests/ui/type/subtyping-opaque-type.rs
@@ -0,0 +1,19 @@
+// check-pass
+// compile-flags: -Zvalidate-mir
+trait Duh {}
+
+impl Duh for i32 {}
+
+trait Trait {
+    type Assoc: Duh;
+}
+
+impl<R: Duh, F: FnMut() -> R> Trait for F {
+    type Assoc = R;
+}
+
+fn foo() -> impl Trait<Assoc = impl Send> {
+    || 42
+}
+
+fn main() {}
diff --git a/tests/ui/typeck/typeck-builtin-bound-type-parameters.stderr b/tests/ui/typeck/typeck-builtin-bound-type-parameters.stderr
index a3517af877c..67ca2b061f9 100644
--- a/tests/ui/typeck/typeck-builtin-bound-type-parameters.stderr
+++ b/tests/ui/typeck/typeck-builtin-bound-type-parameters.stderr
@@ -21,6 +21,8 @@ LL | trait Trait: Copy<dyn Send> {}
    |              ^^^^---------- help: remove these generics
    |              |
    |              expected 0 generic arguments
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0107]: trait takes 0 generic arguments but 1 generic argument was supplied
   --> $DIR/typeck-builtin-bound-type-parameters.rs:8:21
diff --git a/tests/ui/unknown-lint-tool-name.stderr b/tests/ui/unknown-lint-tool-name.stderr
index 5f8349ce6c3..72731ab1e3d 100644
--- a/tests/ui/unknown-lint-tool-name.stderr
+++ b/tests/ui/unknown-lint-tool-name.stderr
@@ -21,6 +21,7 @@ LL | #![deny(foo::bar)]
    |         ^^^
    |
    = help: add `#![register_tool(foo)]` to the crate root
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0710]: unknown tool name `foo` found in scoped lint: `foo::bar`
   --> $DIR/unknown-lint-tool-name.rs:4:9
@@ -29,6 +30,7 @@ LL | #[allow(foo::bar)]
    |         ^^^
    |
    = help: add `#![register_tool(foo)]` to the crate root
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 4 previous errors
 
diff --git a/tests/ui/unknown-unstable-lints/deny-unstable-lint-command-line.stderr b/tests/ui/unknown-unstable-lints/deny-unstable-lint-command-line.stderr
index 32f8d2f45dc..f0450aea49a 100644
--- a/tests/ui/unknown-unstable-lints/deny-unstable-lint-command-line.stderr
+++ b/tests/ui/unknown-unstable-lints/deny-unstable-lint-command-line.stderr
@@ -8,11 +8,13 @@ error: unknown lint: `test_unstable_lint`
    |
    = note: the `test_unstable_lint` lint is unstable
    = help: add `-Zcrate-attr="feature(test_unstable_lint)"` to the command-line options to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: unknown lint: `test_unstable_lint`
    |
    = note: the `test_unstable_lint` lint is unstable
    = help: add `-Zcrate-attr="feature(test_unstable_lint)"` to the command-line options to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 3 previous errors
 
diff --git a/tests/ui/unknown-unstable-lints/deny-unstable-lint-inline.stderr b/tests/ui/unknown-unstable-lints/deny-unstable-lint-inline.stderr
index 2a2a9811bfb..20a36b28dc6 100644
--- a/tests/ui/unknown-unstable-lints/deny-unstable-lint-inline.stderr
+++ b/tests/ui/unknown-unstable-lints/deny-unstable-lint-inline.stderr
@@ -20,6 +20,7 @@ LL | #![allow(test_unstable_lint)]
    |
    = note: the `test_unstable_lint` lint is unstable
    = help: add `#![feature(test_unstable_lint)]` to the crate attributes to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: unknown lint: `test_unstable_lint`
   --> $DIR/deny-unstable-lint-inline.rs:4:1
@@ -29,6 +30,7 @@ LL | #![allow(test_unstable_lint)]
    |
    = note: the `test_unstable_lint` lint is unstable
    = help: add `#![feature(test_unstable_lint)]` to the crate attributes to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 3 previous errors
 
diff --git a/tests/ui/unknown-unstable-lints/warn-unknown-unstable-lint-command-line.stderr b/tests/ui/unknown-unstable-lints/warn-unknown-unstable-lint-command-line.stderr
index dd9ecf02fa6..a2deecf1caf 100644
--- a/tests/ui/unknown-unstable-lints/warn-unknown-unstable-lint-command-line.stderr
+++ b/tests/ui/unknown-unstable-lints/warn-unknown-unstable-lint-command-line.stderr
@@ -8,11 +8,13 @@ warning: unknown lint: `test_unstable_lint`
    |
    = note: the `test_unstable_lint` lint is unstable
    = help: add `-Zcrate-attr="feature(test_unstable_lint)"` to the command-line options to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: unknown lint: `test_unstable_lint`
    |
    = note: the `test_unstable_lint` lint is unstable
    = help: add `-Zcrate-attr="feature(test_unstable_lint)"` to the command-line options to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: 3 warnings emitted
 
diff --git a/tests/ui/unknown-unstable-lints/warn-unknown-unstable-lint-inline.stderr b/tests/ui/unknown-unstable-lints/warn-unknown-unstable-lint-inline.stderr
index 0548cd226d8..12afb2e294a 100644
--- a/tests/ui/unknown-unstable-lints/warn-unknown-unstable-lint-inline.stderr
+++ b/tests/ui/unknown-unstable-lints/warn-unknown-unstable-lint-inline.stderr
@@ -20,6 +20,7 @@ LL | #![allow(test_unstable_lint)]
    |
    = note: the `test_unstable_lint` lint is unstable
    = help: add `#![feature(test_unstable_lint)]` to the crate attributes to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: unknown lint: `test_unstable_lint`
   --> $DIR/warn-unknown-unstable-lint-inline.rs:4:1
@@ -29,6 +30,7 @@ LL | #![allow(test_unstable_lint)]
    |
    = note: the `test_unstable_lint` lint is unstable
    = help: add `#![feature(test_unstable_lint)]` to the crate attributes to enable
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: 3 warnings emitted
 
diff --git a/tests/ui/use/use-super-global-path.stderr b/tests/ui/use/use-super-global-path.stderr
index 7014a12e9dd..00d172f4799 100644
--- a/tests/ui/use/use-super-global-path.stderr
+++ b/tests/ui/use/use-super-global-path.stderr
@@ -9,6 +9,8 @@ error[E0433]: failed to resolve: global paths cannot start with `super`
    |
 LL |     use ::super::{S, Z};
    |           ^^^^^ global paths cannot start with `super`
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0433]: failed to resolve: global paths cannot start with `super`
   --> $DIR/use-super-global-path.rs:11:15