separate labels for default binding mode spans into their own notes

(cherry picked from commit 767f82039c221fa609f752d2a2ea4ffd664f8138)

5 files changed, 202 insertions, 124 deletions

diff --git a/compiler/rustc_hir_typeck/src/pat.rs b/compiler/rustc_hir_typeck/src/pat.rs
index 91deaa72604..3e4b50ff528 100644
--- a/compiler/rustc_hir_typeck/src/pat.rs
+++ b/compiler/rustc_hir_typeck/src/pat.rs
@@ -699,7 +699,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         // Determine the binding mode...
         let bm = match user_bind_annot {
-            BindingMode(ByRef::No, Mutability::Mut) if matches!(def_br, ByRef::Yes(_)) => {
+            BindingMode(ByRef::No, Mutability::Mut) if let ByRef::Yes(def_br_mutbl) = def_br => {
                 if pat.span.at_least_rust_2024()
                     && (self.tcx.features().ref_pat_eat_one_layer_2024()
                         || self.tcx.features().ref_pat_eat_one_layer_2024_structural())
@@ -721,18 +721,20 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         pat_info.top_info.hir_id,
                         pat,
                         ident.span,
+                        def_br_mutbl,
                     );
                     BindingMode(ByRef::No, Mutability::Mut)
                 }
             }
             BindingMode(ByRef::No, mutbl) => BindingMode(def_br, mutbl),
             BindingMode(ByRef::Yes(_), _) => {
-                if matches!(def_br, ByRef::Yes(_)) {
+                if let ByRef::Yes(def_br_mutbl) = def_br {
                     // `ref`/`ref mut` overrides the binding mode on edition <= 2021
                     self.add_rust_2024_migration_desugared_pat(
                         pat_info.top_info.hir_id,
                         pat,
                         ident.span,
+                        def_br_mutbl,
                     );
                 }
                 user_bind_annot
@@ -2261,12 +2263,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             }
         } else {
             // Reset binding mode on old editions
-            if pat_info.binding_mode != ByRef::No {
+            if let ByRef::Yes(inh_mut) = pat_info.binding_mode {
                 pat_info.binding_mode = ByRef::No;
                 self.add_rust_2024_migration_desugared_pat(
                     pat_info.top_info.hir_id,
                     pat,
                     inner.span,
+                    inh_mut,
                 )
             }
         }
@@ -2634,6 +2637,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         pat_id: HirId,
         subpat: &'tcx Pat<'tcx>,
         cutoff_span: Span,
+        def_br_mutbl: Mutability,
     ) {
         // Try to trim the span we're labeling to just the `&` or binding mode that's an issue.
         // If the subpattern's span is is from an expansion, the emitted label will not be trimmed.
@@ -2656,16 +2660,21 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             // NB: This wording assumes the only expansions that can produce problematic reference
             // patterns and bindings are macros. If a desugaring or AST pass is added that can do
             // so, we may want to inspect the span's source callee or macro backtrace.
-            "occurs within macro expansion"
+            "occurs within macro expansion".to_owned()
         } else {
-            if matches!(subpat.kind, PatKind::Binding(_, _, _, _)) {
+            let pat_kind = if matches!(subpat.kind, PatKind::Binding(_, _, _, _)) {
                 info.bad_modifiers |= true;
-                "this binding modifier"
+                "binding modifier"
             } else {
                 info.bad_ref_pats |= true;
-                "this reference pattern"
-            }
+                "reference pattern"
+            };
+            let dbm_str = match def_br_mutbl {
+                Mutability::Not => "ref",
+                Mutability::Mut => "ref mut",
+            };
+            format!("{pat_kind} not allowed under `{dbm_str}` default binding mode")
         };
-        info.primary_labels.push((trimmed_span, primary_label.to_owned()));
+        info.primary_labels.push((trimmed_span, primary_label));
     }
 }
diff --git a/compiler/rustc_mir_build/src/errors.rs b/compiler/rustc_mir_build/src/errors.rs
index da34419997e..f62869de815 100644
--- a/compiler/rustc_mir_build/src/errors.rs
+++ b/compiler/rustc_mir_build/src/errors.rs
@@ -1114,6 +1114,27 @@ impl Subdiagnostic for Rust2024IncompatiblePatSugg {
         diag: &mut Diag<'_, G>,
         _f: &F,
     ) {
+        // Format and emit explanatory notes about default binding modes. Reversing the spans' order
+        // means if we have nested spans, the innermost ones will be visited first.
+        for (span, def_br_mutbl) in self.default_mode_labels.into_iter().rev() {
+            // Don't point to a macro call site.
+            if !span.from_expansion() {
+                let dbm_str = match def_br_mutbl {
+                    ty::Mutability::Not => "ref",
+                    ty::Mutability::Mut => "ref mut",
+                };
+                let note_msg = format!(
+                    "the default binding mode changed to `{dbm_str}` because this has type `{}_`",
+                    def_br_mutbl.ref_prefix_str()
+                );
+                let label_msg = format!("the default binding mode is `{dbm_str}`, introduced here");
+                let mut label = MultiSpan::from(span);
+                label.push_span_label(span, label_msg);
+                diag.span_note(label, note_msg);
+            }
+        }
+
+        // Format and emit the suggestion.
         let applicability =
             if self.suggestion.iter().all(|(span, _)| span.can_be_used_for_suggestions()) {
                 Applicability::MachineApplicable
diff --git a/compiler/rustc_mir_build/src/thir/pattern/mod.rs b/compiler/rustc_mir_build/src/thir/pattern/mod.rs
index 9e1451f4caa..b9501667fc3 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/mod.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/mod.rs
@@ -66,16 +66,6 @@ pub(super) fn pat_from_hir<'a, 'tcx>(
         for (span, label) in &info.primary_labels {
             spans.push_span_label(*span, label.clone());
         }
-        for (span, label_mutbl) in &sugg.default_mode_labels {
-            // Don't point to a macro call site.
-            if !span.from_expansion() {
-                let label = match label_mutbl {
-                    Mutability::Not => "default binding mode is `ref`",
-                    Mutability::Mut => "default binding mode is `ref mut`",
-                };
-                spans.push_span_label(*span, label.to_owned())
-            }
-        }
         // If a relevant span is from at least edition 2024, this is a hard error.
         let is_hard_error = spans.primary_spans().iter().any(|span| span.at_least_rust_2024());
         if is_hard_error {
diff --git a/tests/ui/pattern/rfc-3627-match-ergonomics-2024/migration_lint.stderr b/tests/ui/pattern/rfc-3627-match-ergonomics-2024/migration_lint.stderr
index eaba337f06b..cfbd260e0e9 100644
--- a/tests/ui/pattern/rfc-3627-match-ergonomics-2024/migration_lint.stderr
+++ b/tests/ui/pattern/rfc-3627-match-ergonomics-2024/migration_lint.stderr
@@ -2,13 +2,15 @@ error: binding modifiers may only be written when the default binding mode is `m
   --> $DIR/migration_lint.rs:25:13
    |
 LL |     let Foo(mut x) = &Foo(0);
-   |         ----^^^---
-   |         |   |
-   |         |   this binding modifier
-   |         default binding mode is `ref`
+   |             ^^^ binding modifier not allowed under `ref` default binding mode
    |
    = warning: this changes meaning in Rust 2024
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
+note: the default binding mode changed to `ref` because this has type `&_`
+  --> $DIR/migration_lint.rs:25:9
+   |
+LL |     let Foo(mut x) = &Foo(0);
+   |         ^^^^^^^^^^ the default binding mode is `ref`, introduced here
 note: the lint level is defined here
   --> $DIR/migration_lint.rs:7:9
    |
@@ -23,13 +25,15 @@ error: binding modifiers may only be written when the default binding mode is `m
   --> $DIR/migration_lint.rs:30:13
    |
 LL |     let Foo(mut x) = &mut Foo(0);
-   |         ----^^^---
-   |         |   |
-   |         |   this binding modifier
-   |         default binding mode is `ref mut`
+   |             ^^^ binding modifier not allowed under `ref mut` default binding mode
    |
    = warning: this changes meaning in Rust 2024
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
+note: the default binding mode changed to `ref mut` because this has type `&mut _`
+  --> $DIR/migration_lint.rs:30:9
+   |
+LL |     let Foo(mut x) = &mut Foo(0);
+   |         ^^^^^^^^^^ the default binding mode is `ref mut`, introduced here
 help: make the implied reference pattern explicit
    |
 LL |     let &mut Foo(mut x) = &mut Foo(0);
@@ -39,13 +43,15 @@ error: binding modifiers may only be written when the default binding mode is `m
   --> $DIR/migration_lint.rs:35:13
    |
 LL |     let Foo(ref x) = &Foo(0);
-   |         ----^^^---
-   |         |   |
-   |         |   this binding modifier
-   |         default binding mode is `ref`
+   |             ^^^ binding modifier not allowed under `ref` default binding mode
    |
    = warning: this changes meaning in Rust 2024
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
+note: the default binding mode changed to `ref` because this has type `&_`
+  --> $DIR/migration_lint.rs:35:9
+   |
+LL |     let Foo(ref x) = &Foo(0);
+   |         ^^^^^^^^^^ the default binding mode is `ref`, introduced here
 help: make the implied reference pattern explicit
    |
 LL |     let &Foo(ref x) = &Foo(0);
@@ -55,13 +61,15 @@ error: binding modifiers may only be written when the default binding mode is `m
   --> $DIR/migration_lint.rs:40:13
    |
 LL |     let Foo(ref x) = &mut Foo(0);
-   |         ----^^^---
-   |         |   |
-   |         |   this binding modifier
-   |         default binding mode is `ref mut`
+   |             ^^^ binding modifier not allowed under `ref mut` default binding mode
    |
    = warning: this changes meaning in Rust 2024
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
+note: the default binding mode changed to `ref mut` because this has type `&mut _`
+  --> $DIR/migration_lint.rs:40:9
+   |
+LL |     let Foo(ref x) = &mut Foo(0);
+   |         ^^^^^^^^^^ the default binding mode is `ref mut`, introduced here
 help: make the implied reference pattern explicit
    |
 LL |     let &mut Foo(ref x) = &mut Foo(0);
@@ -71,13 +79,15 @@ error: reference patterns may only be written when the default binding mode is `
   --> $DIR/migration_lint.rs:57:13
    |
 LL |     let Foo(&x) = &Foo(&0);
-   |         ----^--
-   |         |   |
-   |         |   this reference pattern
-   |         default binding mode is `ref`
+   |             ^ reference pattern not allowed under `ref` default binding mode
    |
    = warning: this changes meaning in Rust 2024
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
+note: the default binding mode changed to `ref` because this has type `&_`
+  --> $DIR/migration_lint.rs:57:9
+   |
+LL |     let Foo(&x) = &Foo(&0);
+   |         ^^^^^^^ the default binding mode is `ref`, introduced here
 help: make the implied reference pattern explicit
    |
 LL |     let &Foo(&x) = &Foo(&0);
@@ -87,13 +97,15 @@ error: reference patterns may only be written when the default binding mode is `
   --> $DIR/migration_lint.rs:62:13
    |
 LL |     let Foo(&mut x) = &Foo(&mut 0);
-   |         ----^^^^---
-   |         |   |
-   |         |   this reference pattern
-   |         default binding mode is `ref`
+   |             ^^^^ reference pattern not allowed under `ref` default binding mode
    |
    = warning: this changes meaning in Rust 2024
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
+note: the default binding mode changed to `ref` because this has type `&_`
+  --> $DIR/migration_lint.rs:62:9
+   |
+LL |     let Foo(&mut x) = &Foo(&mut 0);
+   |         ^^^^^^^^^^^ the default binding mode is `ref`, introduced here
 help: make the implied reference pattern explicit
    |
 LL |     let &Foo(&mut x) = &Foo(&mut 0);
@@ -103,13 +115,15 @@ error: reference patterns may only be written when the default binding mode is `
   --> $DIR/migration_lint.rs:67:13
    |
 LL |     let Foo(&x) = &mut Foo(&0);
-   |         ----^--
-   |         |   |
-   |         |   this reference pattern
-   |         default binding mode is `ref mut`
+   |             ^ reference pattern not allowed under `ref mut` default binding mode
    |
    = warning: this changes meaning in Rust 2024
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
+note: the default binding mode changed to `ref mut` because this has type `&mut _`
+  --> $DIR/migration_lint.rs:67:9
+   |
+LL |     let Foo(&x) = &mut Foo(&0);
+   |         ^^^^^^^ the default binding mode is `ref mut`, introduced here
 help: make the implied reference pattern explicit
    |
 LL |     let &mut Foo(&x) = &mut Foo(&0);
@@ -119,13 +133,15 @@ error: reference patterns may only be written when the default binding mode is `
   --> $DIR/migration_lint.rs:72:13
    |
 LL |     let Foo(&mut x) = &mut Foo(&mut 0);
-   |         ----^^^^---
-   |         |   |
-   |         |   this reference pattern
-   |         default binding mode is `ref mut`
+   |             ^^^^ reference pattern not allowed under `ref mut` default binding mode
    |
    = warning: this changes meaning in Rust 2024
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
+note: the default binding mode changed to `ref mut` because this has type `&mut _`
+  --> $DIR/migration_lint.rs:72:9
+   |
+LL |     let Foo(&mut x) = &mut Foo(&mut 0);
+   |         ^^^^^^^^^^^ the default binding mode is `ref mut`, introduced here
 help: make the implied reference pattern explicit
    |
 LL |     let &mut Foo(&mut x) = &mut Foo(&mut 0);
@@ -135,13 +151,15 @@ error: reference patterns may only be written when the default binding mode is `
   --> $DIR/migration_lint.rs:81:17
    |
 LL |     if let Some(&x) = &&&&&Some(&0u8) {
-   |            -----^--
-   |            |    |
-   |            |    this reference pattern
-   |            default binding mode is `ref`
+   |                 ^ reference pattern not allowed under `ref` default binding mode
    |
    = warning: this changes meaning in Rust 2024
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
+note: the default binding mode changed to `ref` because this has type `&_`
+  --> $DIR/migration_lint.rs:81:12
+   |
+LL |     if let Some(&x) = &&&&&Some(&0u8) {
+   |            ^^^^^^^^ the default binding mode is `ref`, introduced here
 help: make the implied reference patterns explicit
    |
 LL |     if let &&&&&Some(&x) = &&&&&Some(&0u8) {
@@ -151,13 +169,15 @@ error: reference patterns may only be written when the default binding mode is `
   --> $DIR/migration_lint.rs:87:17
    |
 LL |     if let Some(&mut x) = &&&&&Some(&mut 0u8) {
-   |            -----^^^^---
-   |            |    |
-   |            |    this reference pattern
-   |            default binding mode is `ref`
+   |                 ^^^^ reference pattern not allowed under `ref` default binding mode
    |
    = warning: this changes meaning in Rust 2024
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
+note: the default binding mode changed to `ref` because this has type `&_`
+  --> $DIR/migration_lint.rs:87:12
+   |
+LL |     if let Some(&mut x) = &&&&&Some(&mut 0u8) {
+   |            ^^^^^^^^^^^^ the default binding mode is `ref`, introduced here
 help: make the implied reference patterns explicit
    |
 LL |     if let &&&&&Some(&mut x) = &&&&&Some(&mut 0u8) {
@@ -167,13 +187,15 @@ error: reference patterns may only be written when the default binding mode is `
   --> $DIR/migration_lint.rs:93:17
    |
 LL |     if let Some(&x) = &&&&&mut Some(&0u8) {
-   |            -----^--
-   |            |    |
-   |            |    this reference pattern
-   |            default binding mode is `ref`
+   |                 ^ reference pattern not allowed under `ref` default binding mode
    |
    = warning: this changes meaning in Rust 2024
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
+note: the default binding mode changed to `ref` because this has type `&_`
+  --> $DIR/migration_lint.rs:93:12
+   |
+LL |     if let Some(&x) = &&&&&mut Some(&0u8) {
+   |            ^^^^^^^^ the default binding mode is `ref`, introduced here
 help: make the implied reference patterns explicit
    |
 LL |     if let &&&&&mut Some(&x) = &&&&&mut Some(&0u8) {
@@ -183,13 +205,15 @@ error: reference patterns may only be written when the default binding mode is `
   --> $DIR/migration_lint.rs:99:17
    |
 LL |     if let Some(&mut Some(Some(x))) = &mut Some(&mut Some(&mut Some(0u8))) {
-   |            -----^^^^---------------
-   |            |    |
-   |            |    this reference pattern
-   |            default binding mode is `ref mut`
+   |                 ^^^^ reference pattern not allowed under `ref mut` default binding mode
    |
    = warning: this changes meaning in Rust 2024
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
+note: the default binding mode changed to `ref mut` because this has type `&mut _`
+  --> $DIR/migration_lint.rs:99:12
+   |
+LL |     if let Some(&mut Some(Some(x))) = &mut Some(&mut Some(&mut Some(0u8))) {
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^ the default binding mode is `ref mut`, introduced here
 help: make the implied reference patterns and variable binding mode explicit
    |
 LL |     if let &mut Some(&mut Some(&mut Some(ref mut x))) = &mut Some(&mut Some(&mut Some(0u8))) {
@@ -199,13 +223,15 @@ error: binding modifiers may only be written when the default binding mode is `m
   --> $DIR/migration_lint.rs:111:21
    |
 LL |     let Struct { a, mut b, c } = &Struct { a: 0, b: 0, c: 0 };
-   |         ------------^^^-------
-   |         |           |
-   |         |           this binding modifier
-   |         default binding mode is `ref`
+   |                     ^^^ binding modifier not allowed under `ref` default binding mode
    |
    = warning: this changes meaning in Rust 2024
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
+note: the default binding mode changed to `ref` because this has type `&_`
+  --> $DIR/migration_lint.rs:111:9
+   |
+LL |     let Struct { a, mut b, c } = &Struct { a: 0, b: 0, c: 0 };
+   |         ^^^^^^^^^^^^^^^^^^^^^^ the default binding mode is `ref`, introduced here
 help: make the implied reference pattern and variable binding modes explicit
    |
 LL |     let &Struct { ref a, mut b, ref c } = &Struct { a: 0, b: 0, c: 0 };
@@ -215,14 +241,17 @@ error: binding modifiers and reference patterns may only be written when the def
   --> $DIR/migration_lint.rs:117:21
    |
 LL |     let Struct { a: &a, b, ref c } = &Struct { a: &0, b: &0, c: &0 };
-   |         ------------^------^^^----
-   |         |           |      |
-   |         |           |      this binding modifier
-   |         |           this reference pattern
-   |         default binding mode is `ref`
+   |                     ^      ^^^ binding modifier not allowed under `ref` default binding mode
+   |                     |
+   |                     reference pattern not allowed under `ref` default binding mode
    |
    = warning: this changes meaning in Rust 2024
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
+note: the default binding mode changed to `ref` because this has type `&_`
+  --> $DIR/migration_lint.rs:117:9
+   |
+LL |     let Struct { a: &a, b, ref c } = &Struct { a: &0, b: &0, c: &0 };
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^ the default binding mode is `ref`, introduced here
 help: make the implied reference pattern and variable binding mode explicit
    |
 LL |     let &Struct { a: &a, ref b, ref c } = &Struct { a: &0, b: &0, c: &0 };
@@ -232,14 +261,17 @@ error: reference patterns may only be written when the default binding mode is `
   --> $DIR/migration_lint.rs:124:24
    |
 LL |     if let Struct { a: &Some(a), b: Some(&b), c: Some(c) } =
-   |            ------------^-----------------^----------------
-   |            |           |                 |
-   |            |           |                 this reference pattern
-   |            |           this reference pattern
-   |            default binding mode is `ref`
+   |                        ^                 ^ reference pattern not allowed under `ref` default binding mode
+   |                        |
+   |                        reference pattern not allowed under `ref` default binding mode
    |
    = warning: this changes meaning in Rust 2024
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
+note: the default binding mode changed to `ref` because this has type `&_`
+  --> $DIR/migration_lint.rs:124:12
+   |
+LL |     if let Struct { a: &Some(a), b: Some(&b), c: Some(c) } =
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the default binding mode is `ref`, introduced here
 help: make the implied reference patterns and variable binding mode explicit
    |
 LL |     if let &Struct { a: &Some(a), b: &Some(&b), c: &Some(ref c) } =
@@ -249,13 +281,16 @@ error: binding modifiers may only be written when the default binding mode is `m
   --> $DIR/migration_lint.rs:137:15
    |
 LL |         (Some(mut x), migration_lint_macros::mixed_edition_pat!(y)) => {
-   |         ------^^^-----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
-   |         |     |       |
-   |         |     |       occurs within macro expansion
-   |         |     this binding modifier
-   |         default binding mode is `ref`
+   |               ^^^     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ occurs within macro expansion
+   |               |
+   |               binding modifier not allowed under `ref` default binding mode
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
+note: the default binding mode changed to `ref` because this has type `&_`
+  --> $DIR/migration_lint.rs:137:9
+   |
+LL |         (Some(mut x), migration_lint_macros::mixed_edition_pat!(y)) => {
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the default binding mode is `ref`, introduced here
    = note: this error originates in the macro `migration_lint_macros::mixed_edition_pat` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: make the implied reference pattern explicit
    |
@@ -266,15 +301,22 @@ error: binding modifiers and reference patterns may only be written when the def
   --> $DIR/migration_lint.rs:145:10
    |
 LL |     let [&mut [ref a]] = &mut [&mut &[0]];
-   |         -^^^^--^^^----
-   |         ||    ||
-   |         ||    |this binding modifier
-   |         ||    default binding mode is `ref`
-   |         |this reference pattern
-   |         default binding mode is `ref mut`
+   |          ^^^^  ^^^ binding modifier not allowed under `ref` default binding mode
+   |          |
+   |          reference pattern not allowed under `ref mut` default binding mode
    |
    = warning: this changes meaning in Rust 2024
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
+note: the default binding mode changed to `ref` because this has type `&_`
+  --> $DIR/migration_lint.rs:145:15
+   |
+LL |     let [&mut [ref a]] = &mut [&mut &[0]];
+   |               ^^^^^^^ the default binding mode is `ref`, introduced here
+note: the default binding mode changed to `ref mut` because this has type `&mut _`
+  --> $DIR/migration_lint.rs:145:9
+   |
+LL |     let [&mut [ref a]] = &mut [&mut &[0]];
+   |         ^^^^^^^^^^^^^^ the default binding mode is `ref mut`, introduced here
 help: make the implied reference patterns explicit
    |
 LL |     let &mut [&mut &[ref a]] = &mut [&mut &[0]];
@@ -284,13 +326,15 @@ error: reference patterns may only be written when the default binding mode is `
   --> $DIR/migration_lint.rs:150:10
    |
 LL |     let [&(_)] = &[&0];
-   |         -^----
-   |         ||
-   |         |this reference pattern
-   |         default binding mode is `ref`
+   |          ^ reference pattern not allowed under `ref` default binding mode
    |
    = warning: this changes meaning in Rust 2024
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
+note: the default binding mode changed to `ref` because this has type `&_`
+  --> $DIR/migration_lint.rs:150:9
+   |
+LL |     let [&(_)] = &[&0];
+   |         ^^^^^^ the default binding mode is `ref`, introduced here
 help: make the implied reference pattern explicit
    |
 LL |     let &[&(_)] = &[&0];
diff --git a/tests/ui/pattern/rfc-3627-match-ergonomics-2024/min_match_ergonomics_fail.stderr b/tests/ui/pattern/rfc-3627-match-ergonomics-2024/min_match_ergonomics_fail.stderr
index ca1749074c1..1d13723370e 100644
--- a/tests/ui/pattern/rfc-3627-match-ergonomics-2024/min_match_ergonomics_fail.stderr
+++ b/tests/ui/pattern/rfc-3627-match-ergonomics-2024/min_match_ergonomics_fail.stderr
@@ -103,12 +103,14 @@ error: reference patterns may only be written when the default binding mode is `
   --> $DIR/min_match_ergonomics_fail.rs:24:20
    |
 LL | test_pat_on_type![(&x,): &(&T,)];
-   |                   -^---
-   |                   ||
-   |                   |this reference pattern
-   |                   default binding mode is `ref`
+   |                    ^ reference pattern not allowed under `ref` default binding mode
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
+note: the default binding mode changed to `ref` because this has type `&_`
+  --> $DIR/min_match_ergonomics_fail.rs:24:19
+   |
+LL | test_pat_on_type![(&x,): &(&T,)];
+   |                   ^^^^^ the default binding mode is `ref`, introduced here
 help: make the implied reference pattern explicit
    |
 LL | test_pat_on_type![&(&x,): &(&T,)];
@@ -118,12 +120,14 @@ error: reference patterns may only be written when the default binding mode is `
   --> $DIR/min_match_ergonomics_fail.rs:27:20
    |
 LL | test_pat_on_type![(&mut x,): &(&mut T,)];
-   |                   -^^^^----
-   |                   ||
-   |                   |this reference pattern
-   |                   default binding mode is `ref`
+   |                    ^^^^ reference pattern not allowed under `ref` default binding mode
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
+note: the default binding mode changed to `ref` because this has type `&_`
+  --> $DIR/min_match_ergonomics_fail.rs:27:19
+   |
+LL | test_pat_on_type![(&mut x,): &(&mut T,)];
+   |                   ^^^^^^^^^ the default binding mode is `ref`, introduced here
 help: make the implied reference pattern explicit
    |
 LL | test_pat_on_type![&(&mut x,): &(&mut T,)];
@@ -133,12 +137,14 @@ error: reference patterns may only be written when the default binding mode is `
   --> $DIR/min_match_ergonomics_fail.rs:31:28
    |
 LL | test_pat_on_type![Foo { f: &(x,) }: &Foo];
-   |                   ---------^------
-   |                   |        |
-   |                   |        this reference pattern
-   |                   default binding mode is `ref`
+   |                            ^ reference pattern not allowed under `ref` default binding mode
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
+note: the default binding mode changed to `ref` because this has type `&_`
+  --> $DIR/min_match_ergonomics_fail.rs:31:19
+   |
+LL | test_pat_on_type![Foo { f: &(x,) }: &Foo];
+   |                   ^^^^^^^^^^^^^^^^ the default binding mode is `ref`, introduced here
 help: make the implied reference pattern explicit
    |
 LL | test_pat_on_type![&Foo { f: &(x,) }: &Foo];
@@ -148,12 +154,14 @@ error: binding modifiers may only be written when the default binding mode is `m
   --> $DIR/min_match_ergonomics_fail.rs:32:20
    |
 LL | test_pat_on_type![(mut x,): &(T,)];
-   |                   -^^^----
-   |                   ||
-   |                   |this binding modifier
-   |                   default binding mode is `ref`
+   |                    ^^^ binding modifier not allowed under `ref` default binding mode
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
+note: the default binding mode changed to `ref` because this has type `&_`
+  --> $DIR/min_match_ergonomics_fail.rs:32:19
+   |
+LL | test_pat_on_type![(mut x,): &(T,)];
+   |                   ^^^^^^^^ the default binding mode is `ref`, introduced here
 help: make the implied reference pattern explicit
    |
 LL | test_pat_on_type![&(mut x,): &(T,)];
@@ -163,12 +171,14 @@ error: binding modifiers may only be written when the default binding mode is `m
   --> $DIR/min_match_ergonomics_fail.rs:33:20
    |
 LL | test_pat_on_type![(ref x,): &(T,)];
-   |                   -^^^----
-   |                   ||
-   |                   |this binding modifier
-   |                   default binding mode is `ref`
+   |                    ^^^ binding modifier not allowed under `ref` default binding mode
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
+note: the default binding mode changed to `ref` because this has type `&_`
+  --> $DIR/min_match_ergonomics_fail.rs:33:19
+   |
+LL | test_pat_on_type![(ref x,): &(T,)];
+   |                   ^^^^^^^^ the default binding mode is `ref`, introduced here
 help: make the implied reference pattern explicit
    |
 LL | test_pat_on_type![&(ref x,): &(T,)];
@@ -178,12 +188,14 @@ error: binding modifiers may only be written when the default binding mode is `m
   --> $DIR/min_match_ergonomics_fail.rs:34:20
    |
 LL | test_pat_on_type![(ref mut x,): &mut (T,)];
-   |                   -^^^^^^^----
-   |                   ||
-   |                   |this binding modifier
-   |                   default binding mode is `ref mut`
+   |                    ^^^^^^^ binding modifier not allowed under `ref mut` default binding mode
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
+note: the default binding mode changed to `ref mut` because this has type `&mut _`
+  --> $DIR/min_match_ergonomics_fail.rs:34:19
+   |
+LL | test_pat_on_type![(ref mut x,): &mut (T,)];
+   |                   ^^^^^^^^^^^^ the default binding mode is `ref mut`, introduced here
 help: make the implied reference pattern explicit
    |
 LL | test_pat_on_type![&mut (ref mut x,): &mut (T,)];
@@ -193,12 +205,14 @@ error: reference patterns may only be written when the default binding mode is `
   --> $DIR/min_match_ergonomics_fail.rs:43:10
    |
 LL |         (&x,) => x,
-   |         -^---
-   |         ||
-   |         |this reference pattern
-   |         default binding mode is `ref`
+   |          ^ reference pattern not allowed under `ref` default binding mode
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
+note: the default binding mode changed to `ref` because this has type `&_`
+  --> $DIR/min_match_ergonomics_fail.rs:43:9
+   |
+LL |         (&x,) => x,
+   |         ^^^^^ the default binding mode is `ref`, introduced here
 help: make the implied reference pattern explicit
    |
 LL |         &(&x,) => x,