reword pattern migration diagnostic to make sense in all editions

This aligns the main error message a bit more with the phrasing in the
Edition Guide and provides a bit more information on the labels to
(hopefully!) aid in understanding.

compiler/rustc_hir_typeck/src/pat.rs

@@ -804,7 +804,7 @@ 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 => {
                 // Only mention the experimental `mut_ref` feature if if we're in edition 2024 and
                 // using other experimental matching features compatible with it.
                 if pat.span.at_least_rust_2024()
@@ -826,22 +826,22 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     // `mut` resets the binding mode on edition <= 2021
                     self.add_rust_2024_migration_desugared_pat(
                         pat_info.top_info.hir_id,
-                        pat.span,
+                        pat,
                         ident.span,
-                        "requires binding by-value, but the implicit default is by-reference",
+                        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.span,
+                        pat,
                         ident.span,
-                        "cannot override to bind by-reference when that is the implicit default",
+                        def_br_mutbl,
                     );
                 }
                 user_bind_annot
@@ -2378,9 +2378,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     pat_info.binding_mode = ByRef::No;
                     self.add_rust_2024_migration_desugared_pat(
                         pat_info.top_info.hir_id,
-                        pat.span,
+                        pat,
                         inner.span,
-                        "cannot implicitly match against multiple layers of reference",
+                        inh_mut,
                     )
                 }
             }
@@ -2770,9 +2770,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     fn add_rust_2024_migration_desugared_pat(
         &self,
         pat_id: HirId,
-        subpat_span: Span,
+        subpat: &'tcx Pat<'tcx>,
         cutoff_span: Span,
-        detailed_label: &str,
+        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.
@@ -2780,23 +2780,30 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let cutoff_span = source_map
             .span_extend_prev_while(cutoff_span, char::is_whitespace)
             .unwrap_or(cutoff_span);
-        // Ensure we use the syntax context and thus edition of `subpat_span`; this will be a hard
+        // Ensure we use the syntax context and thus edition of `subpat.span`; this will be a hard
         // error if the subpattern is of edition >= 2024.
-        let trimmed_span = subpat_span.until(cutoff_span).with_ctxt(subpat_span.ctxt());
+        let trimmed_span = subpat.span.until(cutoff_span).with_ctxt(subpat.span.ctxt());
 
         // Only provide a detailed label if the problematic subpattern isn't from an expansion.
         // In the case that it's from a macro, we'll add a more detailed note in the emitter.
-        let desc = if subpat_span.from_expansion() {
+        let desc = if subpat.span.from_expansion() {
-            "default binding mode is reset within expansion"
+            "occurs within expansion"
         } else {
-            detailed_label
+            match def_br_mutbl {
+                Mutability::Not => "default binding mode is `ref`",
+                Mutability::Mut => "default binding mode is `ref mut`",
+            }
         };
 
-        self.typeck_results
+        let mut typeck_results = self.typeck_results.borrow_mut();
-            .borrow_mut()
+        let mut table = typeck_results.rust_2024_migration_desugared_pats_mut();
-            .rust_2024_migration_desugared_pats_mut()
+        let info = table.entry(pat_id).or_default();
-            .entry(pat_id)
+
-            .or_default()
+        info.labels.push((trimmed_span, desc.to_owned()));
-            .push((trimmed_span, desc.to_owned()));
+        if matches!(subpat.kind, PatKind::Binding(_, _, _, _)) {
+            info.bad_modifiers |= true;
+        } else {
+            info.bad_ref_pats |= true;
+        }
     }
 }

compiler/rustc_middle/src/ty/mod.rs

@@ -94,7 +94,7 @@ pub use self::sty::{
 pub use self::trait_def::TraitDef;
 pub use self::typeck_results::{
     CanonicalUserType, CanonicalUserTypeAnnotation, CanonicalUserTypeAnnotations, IsIdentity,
-    TypeckResults, UserType, UserTypeAnnotationIndex, UserTypeKind,
+    Rust2024IncompatiblePatInfo, TypeckResults, UserType, UserTypeAnnotationIndex, UserTypeKind,
 };
 pub use self::visit::{TypeSuperVisitable, TypeVisitable, TypeVisitableExt, TypeVisitor};
 use crate::error::{OpaqueHiddenTypeMismatch, TypeMismatchReason};

compiler/rustc_middle/src/ty/typeck_results.rs

@@ -73,9 +73,9 @@ pub struct TypeckResults<'tcx> {
     /// Stores the actual binding mode for all instances of [`BindingMode`].
     pat_binding_modes: ItemLocalMap<BindingMode>,
 
-    /// Top-level patterns whose match ergonomics need to be desugared by the Rust 2021 -> 2024
+    /// Top-level patterns incompatible with Rust 2024's match ergonomics. These will be translated
-    /// migration lint. Problematic subpatterns are stored in the `Vec` for the lint to highlight.
+    /// to a form valid in all Editions, either as a lint diagnostic or hard error.
-    rust_2024_migration_desugared_pats: ItemLocalMap<Vec<(Span, String)>>,
+    rust_2024_migration_desugared_pats: ItemLocalMap<Rust2024IncompatiblePatInfo>,
 
     /// Stores the types which were implicitly dereferenced in pattern binding modes
     /// for later usage in THIR lowering. For example,
@@ -420,7 +420,7 @@ impl<'tcx> TypeckResults<'tcx> {
 
     pub fn rust_2024_migration_desugared_pats(
         &self,
-    ) -> LocalTableInContext<'_, Vec<(Span, String)>> {
+    ) -> LocalTableInContext<'_, Rust2024IncompatiblePatInfo> {
         LocalTableInContext {
             hir_owner: self.hir_owner,
             data: &self.rust_2024_migration_desugared_pats,
@@ -429,7 +429,7 @@ impl<'tcx> TypeckResults<'tcx> {
 
     pub fn rust_2024_migration_desugared_pats_mut(
         &mut self,
-    ) -> LocalTableInContextMut<'_, Vec<(Span, String)>> {
+    ) -> LocalTableInContextMut<'_, Rust2024IncompatiblePatInfo> {
         LocalTableInContextMut {
             hir_owner: self.hir_owner,
             data: &mut self.rust_2024_migration_desugared_pats,
@@ -811,3 +811,15 @@ impl<'tcx> std::fmt::Display for UserTypeKind<'tcx> {
         }
     }
 }
+
+/// Information on a pattern incompatible with Rust 2024, for use by the error/migration diagnostic
+/// emitted during THIR construction.
+#[derive(TyEncodable, TyDecodable, Debug, HashStable, Default)]
+pub struct Rust2024IncompatiblePatInfo {
+    /// Labels for subpatterns incompatible with Rust 2024.
+    pub labels: Vec<(Span, String)>,
+    /// Whether any binding modifiers occur under a non-`move` default binding mode.
+    pub bad_modifiers: bool,
+    /// Whether any `&` or `&mut` patterns occur under a non-`move` default binding mode.
+    pub bad_ref_pats: bool,
+}

compiler/rustc_mir_build/messages.ftl

@@ -285,7 +285,16 @@ mir_build_pointer_pattern = function pointers and raw pointers not derived from
 
 mir_build_privately_uninhabited = pattern `{$witness_1}` is currently uninhabited, but this variant contains private fields which may become inhabited in the future
 
-mir_build_rust_2024_incompatible_pat = this pattern relies on behavior which may change in edition 2024
+mir_build_rust_2024_incompatible_pat = {$bad_modifiers ->
+        *[true] binding modifiers{$bad_ref_pats ->
+            *[true] {" "}and reference patterns
+            [false] {""}
+        }
+        [false] reference patterns
+    } may only be written when the default binding mode is `move`{$is_hard_error ->
+        *[true] {""}
+        [false] {" "}in Rust 2024
+    }
 
 mir_build_static_in_pattern = statics cannot be referenced in patterns
     .label = can't be used in patterns

compiler/rustc_mir_build/src/errors.rs

@@ -1100,6 +1100,9 @@ pub(crate) enum MiscPatternSuggestion {
 pub(crate) struct Rust2024IncompatiblePat {
     #[subdiagnostic]
     pub(crate) sugg: Rust2024IncompatiblePatSugg,
+    pub(crate) bad_modifiers: bool,
+    pub(crate) bad_ref_pats: bool,
+    pub(crate) is_hard_error: bool,
 }
 
 pub(crate) struct Rust2024IncompatiblePatSugg {

compiler/rustc_mir_build/src/thir/pattern/mod.rs

@@ -44,12 +44,12 @@ pub(super) fn pat_from_hir<'a, 'tcx>(
     typeck_results: &'a ty::TypeckResults<'tcx>,
     pat: &'tcx hir::Pat<'tcx>,
 ) -> Box<Pat<'tcx>> {
-    let migration_labels = typeck_results.rust_2024_migration_desugared_pats().get(pat.hir_id);
+    let migration_info = typeck_results.rust_2024_migration_desugared_pats().get(pat.hir_id);
     let mut pcx = PatCtxt {
         tcx,
         typing_env,
         typeck_results,
-        rust_2024_migration_suggestion: migration_labels.and(Some(Rust2024IncompatiblePatSugg {
+        rust_2024_migration_suggestion: migration_info.and(Some(Rust2024IncompatiblePatSugg {
             suggestion: Vec::new(),
             ref_pattern_count: 0,
             binding_mode_count: 0,
@@ -57,10 +57,10 @@ pub(super) fn pat_from_hir<'a, 'tcx>(
     };
     let result = pcx.lower_pattern(pat);
     debug!("pat_from_hir({:?}) = {:?}", pat, result);
-    if let Some(labels) = migration_labels {
+    if let Some(info) = migration_info {
         let sugg = pcx.rust_2024_migration_suggestion.expect("suggestion should be present");
-        let mut spans = MultiSpan::from_spans(labels.iter().map(|(span, _)| *span).collect());
+        let mut spans = MultiSpan::from_spans(info.labels.iter().map(|(span, _)| *span).collect());
-        for (span, label) in labels {
+        for (span, label) in &info.labels {
             spans.push_span_label(*span, label.clone());
         }
         // If a relevant span is from at least edition 2024, this is a hard error.
@@ -68,10 +68,13 @@ pub(super) fn pat_from_hir<'a, 'tcx>(
         if is_hard_error {
             let mut err =
                 tcx.dcx().struct_span_err(spans, fluent::mir_build_rust_2024_incompatible_pat);
-            if let Some(info) = lint::builtin::RUST_2024_INCOMPATIBLE_PAT.future_incompatible {
+            if let Some(lint_info) = lint::builtin::RUST_2024_INCOMPATIBLE_PAT.future_incompatible {
                 // provide the same reference link as the lint
-                err.note(format!("for more information, see {}", info.reference));
+                err.note(format!("for more information, see {}", lint_info.reference));
             }
+            err.arg("bad_modifiers", info.bad_modifiers);
+            err.arg("bad_ref_pats", info.bad_ref_pats);
+            err.arg("is_hard_error", true);
             err.subdiagnostic(sugg);
             err.emit();
         } else {
@@ -79,7 +82,12 @@ pub(super) fn pat_from_hir<'a, 'tcx>(
                 lint::builtin::RUST_2024_INCOMPATIBLE_PAT,
                 pat.hir_id,
                 spans,
-                Rust2024IncompatiblePat { sugg },
+                Rust2024IncompatiblePat {
+                    sugg,
+                    bad_modifiers: info.bad_modifiers,
+                    bad_ref_pats: info.bad_ref_pats,
+                    is_hard_error,
+                },
             );
         }
     }

tests/ui/pattern/rfc-3627-match-ergonomics-2024/experimental/ref-binding-on-inh-ref-errors.classic2024.stderr

@@ -1,5 +1,5 @@
 error[E0308]: mismatched types
-  --> $DIR/ref-binding-on-inh-ref-errors.rs:60:10
+  --> $DIR/ref-binding-on-inh-ref-errors.rs:54:10
    |
 LL |     let [&mut ref x] = &[&mut 0];
    |          ^^^^^
@@ -10,11 +10,11 @@ help: replace this `&mut` pattern with `&`
 LL |     let [&ref x] = &[&mut 0];
    |          ~
 
-error: this pattern relies on behavior which may change in edition 2024
+error: binding modifiers may only be written when the default binding mode is `move`
-  --> $DIR/ref-binding-on-inh-ref-errors.rs:74:10
+  --> $DIR/ref-binding-on-inh-ref-errors.rs:67:10
    |
 LL |     let [ref mut x] = &[0];
-   |          ^^^^^^^ cannot override to bind by-reference when that is the implicit default
+   |          ^^^^^^^ default binding mode is `ref`
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
 help: make the implied reference pattern explicit
@@ -23,16 +23,16 @@ LL |     let &[ref mut x] = &[0];
    |         +
 
 error[E0596]: cannot borrow data in a `&` reference as mutable
-  --> $DIR/ref-binding-on-inh-ref-errors.rs:74:10
+  --> $DIR/ref-binding-on-inh-ref-errors.rs:67:10
    |
 LL |     let [ref mut x] = &[0];
    |          ^^^^^^^^^ cannot borrow as mutable
 
-error: this pattern relies on behavior which may change in edition 2024
+error: binding modifiers may only be written when the default binding mode is `move`
-  --> $DIR/ref-binding-on-inh-ref-errors.rs:83:10
+  --> $DIR/ref-binding-on-inh-ref-errors.rs:75:10
    |
 LL |     let [ref x] = &[0];
-   |          ^^^ cannot override to bind by-reference when that is the implicit default
+   |          ^^^ default binding mode is `ref`
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
 help: make the implied reference pattern explicit
@@ -40,11 +40,11 @@ help: make the implied reference pattern explicit
 LL |     let &[ref x] = &[0];
    |         +
 
-error: this pattern relies on behavior which may change in edition 2024
+error: binding modifiers may only be written when the default binding mode is `move`
-  --> $DIR/ref-binding-on-inh-ref-errors.rs:88:10
+  --> $DIR/ref-binding-on-inh-ref-errors.rs:79:10
    |
 LL |     let [ref x] = &mut [0];
-   |          ^^^ cannot override to bind by-reference when that is the implicit default
+   |          ^^^ default binding mode is `ref mut`
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
 help: make the implied reference pattern explicit
@@ -52,11 +52,11 @@ help: make the implied reference pattern explicit
 LL |     let &mut [ref x] = &mut [0];
    |         ++++
 
-error: this pattern relies on behavior which may change in edition 2024
+error: binding modifiers may only be written when the default binding mode is `move`
-  --> $DIR/ref-binding-on-inh-ref-errors.rs:93:10
+  --> $DIR/ref-binding-on-inh-ref-errors.rs:83:10
    |
 LL |     let [ref mut x] = &mut [0];
-   |          ^^^^^^^ cannot override to bind by-reference when that is the implicit default
+   |          ^^^^^^^ default binding mode is `ref mut`
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
 help: make the implied reference pattern explicit

tests/ui/pattern/rfc-3627-match-ergonomics-2024/experimental/ref-binding-on-inh-ref-errors.rs

@@ -13,26 +13,22 @@
 /// The eat-outer variant eats the inherited reference, so binding with `ref` isn't a problem.
 fn errors_from_eating_the_real_reference() {
     let [&ref x] = &[&0];
-    //[structural2024]~^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //[structural2024]~^ ERROR: binding modifiers may only be written when the default binding mode is `move`
-    //[structural2024]~| cannot override to bind by-reference when that is the implicit default
     #[cfg(stable2021)] let _: &u32 = x;
     #[cfg(classic2024)] let _: &&u32 = x;
 
     let [&ref x] = &mut [&0];
-    //[structural2024]~^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //[structural2024]~^ ERROR: binding modifiers may only be written when the default binding mode is `move`
-    //[structural2024]~| cannot override to bind by-reference when that is the implicit default
     #[cfg(stable2021)] let _: &u32 = x;
     #[cfg(classic2024)] let _: &&u32 = x;
 
     let [&mut ref x] = &mut [&mut 0];
-    //[structural2024]~^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //[structural2024]~^ ERROR: binding modifiers may only be written when the default binding mode is `move`
-    //[structural2024]~| cannot override to bind by-reference when that is the implicit default
     #[cfg(stable2021)] let _: &u32 = x;
     #[cfg(classic2024)] let _: &&mut u32 = x;
 
     let [&mut ref mut x] = &mut [&mut 0];
-    //[structural2024]~^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //[structural2024]~^ ERROR: binding modifiers may only be written when the default binding mode is `move`
-    //[structural2024]~| cannot override to bind by-reference when that is the implicit default
     #[cfg(stable2021)] let _: &mut u32 = x;
     #[cfg(classic2024)] let _: &mut &mut u32 = x;
 }
@@ -43,15 +39,13 @@ fn errors_from_eating_the_real_reference_caught_in_hir_typeck_on_stable() {
     let [&ref x] = &[&mut 0];
     //[stable2021]~^ ERROR: mismatched types
     //[stable2021]~| types differ in mutability
-    //[structural2024]~^^^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //[structural2024]~^^^ ERROR: binding modifiers may only be written when the default binding mode is `move`
-    //[structural2024]~| cannot override to bind by-reference when that is the implicit default
     #[cfg(classic2024)] let _: &&mut u32 = x;
 
     let [&ref x] = &mut [&mut 0];
     //[stable2021]~^ ERROR: mismatched types
     //[stable2021]~| types differ in mutability
-    //[structural2024]~^^^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //[structural2024]~^^^ ERROR: binding modifiers may only be written when the default binding mode is `move`
-    //[structural2024]~| cannot override to bind by-reference when that is the implicit default
     #[cfg(classic2024)] let _: &&mut u32 = x;
 }
 
@@ -60,8 +54,7 @@ fn errors_dependent_on_eating_order_caught_in_hir_typeck_when_eating_outer() {
     let [&mut ref x] = &[&mut 0];
     //[classic2024]~^ ERROR: mismatched types
     //[classic2024]~| cannot match inherited `&` with `&mut` pattern
-    //[structural2024]~^^^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //[structural2024]~^^^ ERROR: binding modifiers may only be written when the default binding mode is `move`
-    //[structural2024]~| cannot override to bind by-reference when that is the implicit default
     #[cfg(stable2021)] let _: &u32 = x;
 }
 
@@ -73,25 +66,21 @@ fn errors_dependent_on_eating_order_caught_in_hir_typeck_when_eating_outer() {
 fn borrowck_errors_in_old_editions() {
     let [ref mut x] = &[0];
     //~^ ERROR: cannot borrow data in a `&` reference as mutable
-    //[classic2024,structural2024]~| ERROR: this pattern relies on behavior which may change in edition 2024
+    //[classic2024,structural2024]~| ERROR: binding modifiers may only be written when the default binding mode is `move`
-    //[classic2024,structural2024]~| cannot override to bind by-reference when that is the implicit default
 }
 
 /// The remaining tests are purely for testing `ref` bindings in the presence of an inherited
 /// reference. These should always fail on edition 2024 and succeed on edition 2021.
 pub fn main() {
     let [ref x] = &[0];
-    //[classic2024,structural2024]~^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //[classic2024,structural2024]~^ ERROR: binding modifiers may only be written when the default binding mode is `move`
-    //[classic2024,structural2024]~| cannot override to bind by-reference when that is the implicit default
     #[cfg(stable2021)] let _: &u32 = x;
 
     let [ref x] = &mut [0];
-    //[classic2024,structural2024]~^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //[classic2024,structural2024]~^ ERROR: binding modifiers may only be written when the default binding mode is `move`
-    //[classic2024,structural2024]~| cannot override to bind by-reference when that is the implicit default
     #[cfg(stable2021)] let _: &u32 = x;
 
     let [ref mut x] = &mut [0];
-    //[classic2024,structural2024]~^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //[classic2024,structural2024]~^ ERROR: binding modifiers may only be written when the default binding mode is `move`
-    //[classic2024,structural2024]~| cannot override to bind by-reference when that is the implicit default
     #[cfg(stable2021)] let _: &mut u32 = x;
 }

tests/ui/pattern/rfc-3627-match-ergonomics-2024/experimental/ref-binding-on-inh-ref-errors.stable2021.stderr

@@ -1,5 +1,5 @@
 error[E0308]: mismatched types
-  --> $DIR/ref-binding-on-inh-ref-errors.rs:43:10
+  --> $DIR/ref-binding-on-inh-ref-errors.rs:39:10
    |
 LL |     let [&ref x] = &[&mut 0];
    |          ^^^^^^    --------- this expression has type `&[&mut {integer}; 1]`
@@ -15,7 +15,7 @@ LL +     let [ref x] = &[&mut 0];
    |
 
 error[E0308]: mismatched types
-  --> $DIR/ref-binding-on-inh-ref-errors.rs:50:10
+  --> $DIR/ref-binding-on-inh-ref-errors.rs:45:10
    |
 LL |     let [&ref x] = &mut [&mut 0];
    |          ^^^^^^    ------------- this expression has type `&mut [&mut {integer}; 1]`
@@ -31,7 +31,7 @@ LL +     let [ref x] = &mut [&mut 0];
    |
 
 error[E0596]: cannot borrow data in a `&` reference as mutable
-  --> $DIR/ref-binding-on-inh-ref-errors.rs:74:10
+  --> $DIR/ref-binding-on-inh-ref-errors.rs:67:10
    |
 LL |     let [ref mut x] = &[0];
    |          ^^^^^^^^^ cannot borrow as mutable

tests/ui/pattern/rfc-3627-match-ergonomics-2024/experimental/ref-binding-on-inh-ref-errors.structural2024.stderr

@@ -1,8 +1,8 @@
-error: this pattern relies on behavior which may change in edition 2024
+error: binding modifiers may only be written when the default binding mode is `move`
   --> $DIR/ref-binding-on-inh-ref-errors.rs:15:11
    |
 LL |     let [&ref x] = &[&0];
-   |           ^^^ cannot override to bind by-reference when that is the implicit default
+   |           ^^^ default binding mode is `ref`
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
 help: make the implied reference pattern explicit
@@ -10,11 +10,11 @@ help: make the implied reference pattern explicit
 LL |     let &[&ref x] = &[&0];
    |         +
 
-error: this pattern relies on behavior which may change in edition 2024
+error: binding modifiers may only be written when the default binding mode is `move`
-  --> $DIR/ref-binding-on-inh-ref-errors.rs:21:11
+  --> $DIR/ref-binding-on-inh-ref-errors.rs:20:11
    |
 LL |     let [&ref x] = &mut [&0];
-   |           ^^^ cannot override to bind by-reference when that is the implicit default
+   |           ^^^ default binding mode is `ref`
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
 help: make the implied reference pattern explicit
@@ -22,11 +22,11 @@ help: make the implied reference pattern explicit
 LL |     let &mut [&ref x] = &mut [&0];
    |         ++++
 
-error: this pattern relies on behavior which may change in edition 2024
+error: binding modifiers may only be written when the default binding mode is `move`
-  --> $DIR/ref-binding-on-inh-ref-errors.rs:27:15
+  --> $DIR/ref-binding-on-inh-ref-errors.rs:25:15
    |
 LL |     let [&mut ref x] = &mut [&mut 0];
-   |               ^^^ cannot override to bind by-reference when that is the implicit default
+   |               ^^^ default binding mode is `ref mut`
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
 help: make the implied reference pattern explicit
@@ -34,11 +34,11 @@ help: make the implied reference pattern explicit
 LL |     let &mut [&mut ref x] = &mut [&mut 0];
    |         ++++
 
-error: this pattern relies on behavior which may change in edition 2024
+error: binding modifiers may only be written when the default binding mode is `move`
-  --> $DIR/ref-binding-on-inh-ref-errors.rs:33:15
+  --> $DIR/ref-binding-on-inh-ref-errors.rs:30:15
    |
 LL |     let [&mut ref mut x] = &mut [&mut 0];
-   |               ^^^^^^^ cannot override to bind by-reference when that is the implicit default
+   |               ^^^^^^^ default binding mode is `ref mut`
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
 help: make the implied reference pattern explicit
@@ -46,11 +46,11 @@ help: make the implied reference pattern explicit
 LL |     let &mut [&mut ref mut x] = &mut [&mut 0];
    |         ++++
 
-error: this pattern relies on behavior which may change in edition 2024
+error: binding modifiers may only be written when the default binding mode is `move`
-  --> $DIR/ref-binding-on-inh-ref-errors.rs:43:11
+  --> $DIR/ref-binding-on-inh-ref-errors.rs:39:11
    |
 LL |     let [&ref x] = &[&mut 0];
-   |           ^^^ cannot override to bind by-reference when that is the implicit default
+   |           ^^^ default binding mode is `ref`
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
 help: make the implied reference pattern explicit
@@ -58,11 +58,11 @@ help: make the implied reference pattern explicit
 LL |     let &[&ref x] = &[&mut 0];
    |         +
 
-error: this pattern relies on behavior which may change in edition 2024
+error: binding modifiers may only be written when the default binding mode is `move`
-  --> $DIR/ref-binding-on-inh-ref-errors.rs:50:11
+  --> $DIR/ref-binding-on-inh-ref-errors.rs:45:11
    |
 LL |     let [&ref x] = &mut [&mut 0];
-   |           ^^^ cannot override to bind by-reference when that is the implicit default
+   |           ^^^ default binding mode is `ref`
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
 help: make the implied reference pattern explicit
@@ -70,11 +70,11 @@ help: make the implied reference pattern explicit
 LL |     let &mut [&ref x] = &mut [&mut 0];
    |         ++++
 
-error: this pattern relies on behavior which may change in edition 2024
+error: binding modifiers may only be written when the default binding mode is `move`
-  --> $DIR/ref-binding-on-inh-ref-errors.rs:60:15
+  --> $DIR/ref-binding-on-inh-ref-errors.rs:54:15
    |
 LL |     let [&mut ref x] = &[&mut 0];
-   |               ^^^ cannot override to bind by-reference when that is the implicit default
+   |               ^^^ default binding mode is `ref`
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
 help: make the implied reference pattern explicit
@@ -82,11 +82,11 @@ help: make the implied reference pattern explicit
 LL |     let &[&mut ref x] = &[&mut 0];
    |         +
 
-error: this pattern relies on behavior which may change in edition 2024
+error: binding modifiers may only be written when the default binding mode is `move`
-  --> $DIR/ref-binding-on-inh-ref-errors.rs:74:10
+  --> $DIR/ref-binding-on-inh-ref-errors.rs:67:10
    |
 LL |     let [ref mut x] = &[0];
-   |          ^^^^^^^ cannot override to bind by-reference when that is the implicit default
+   |          ^^^^^^^ default binding mode is `ref`
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
 help: make the implied reference pattern explicit
@@ -95,16 +95,16 @@ LL |     let &[ref mut x] = &[0];
    |         +
 
 error[E0596]: cannot borrow data in a `&` reference as mutable
-  --> $DIR/ref-binding-on-inh-ref-errors.rs:74:10
+  --> $DIR/ref-binding-on-inh-ref-errors.rs:67:10
    |
 LL |     let [ref mut x] = &[0];
    |          ^^^^^^^^^ cannot borrow as mutable
 
-error: this pattern relies on behavior which may change in edition 2024
+error: binding modifiers may only be written when the default binding mode is `move`
-  --> $DIR/ref-binding-on-inh-ref-errors.rs:83:10
+  --> $DIR/ref-binding-on-inh-ref-errors.rs:75:10
    |
 LL |     let [ref x] = &[0];
-   |          ^^^ cannot override to bind by-reference when that is the implicit default
+   |          ^^^ default binding mode is `ref`
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
 help: make the implied reference pattern explicit
@@ -112,11 +112,11 @@ help: make the implied reference pattern explicit
 LL |     let &[ref x] = &[0];
    |         +
 
-error: this pattern relies on behavior which may change in edition 2024
+error: binding modifiers may only be written when the default binding mode is `move`
-  --> $DIR/ref-binding-on-inh-ref-errors.rs:88:10
+  --> $DIR/ref-binding-on-inh-ref-errors.rs:79:10
    |
 LL |     let [ref x] = &mut [0];
-   |          ^^^ cannot override to bind by-reference when that is the implicit default
+   |          ^^^ default binding mode is `ref mut`
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
 help: make the implied reference pattern explicit
@@ -124,11 +124,11 @@ help: make the implied reference pattern explicit
 LL |     let &mut [ref x] = &mut [0];
    |         ++++
 
-error: this pattern relies on behavior which may change in edition 2024
+error: binding modifiers may only be written when the default binding mode is `move`
-  --> $DIR/ref-binding-on-inh-ref-errors.rs:93:10
+  --> $DIR/ref-binding-on-inh-ref-errors.rs:83:10
    |
 LL |     let [ref mut x] = &mut [0];
-   |          ^^^^^^^ cannot override to bind by-reference when that is the implicit default
+   |          ^^^^^^^ default binding mode is `ref mut`
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
 help: make the implied reference pattern explicit

tests/ui/pattern/rfc-3627-match-ergonomics-2024/migration_lint.fixed

@@ -23,22 +23,22 @@ fn main() {
     assert_type_eq(x, &mut 0u8);
 
     let &Foo(mut x) = &Foo(0);
-    //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //~^ ERROR: binding modifiers may only be written when the default binding mode is `move` in Rust 2024
     //~| WARN: this changes meaning in Rust 2024
     assert_type_eq(x, 0u8);
 
     let &mut Foo(mut x) = &mut Foo(0);
-    //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //~^ ERROR: binding modifiers may only be written when the default binding mode is `move` in Rust 2024
     //~| WARN: this changes meaning in Rust 2024
     assert_type_eq(x, 0u8);
 
     let &Foo(ref x) = &Foo(0);
-    //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //~^ ERROR: binding modifiers may only be written when the default binding mode is `move` in Rust 2024
     //~| WARN: this changes meaning in Rust 2024
     assert_type_eq(x, &0u8);
 
     let &mut Foo(ref x) = &mut Foo(0);
-    //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //~^ ERROR: binding modifiers may only be written when the default binding mode is `move` in Rust 2024
     //~| WARN: this changes meaning in Rust 2024
     assert_type_eq(x, &0u8);
 
@@ -55,22 +55,22 @@ fn main() {
     assert_type_eq(x, &0u8);
 
     let &Foo(&x) = &Foo(&0);
-    //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //~^ ERROR: reference patterns may only be written when the default binding mode is `move` in Rust 2024
     //~| WARN: this changes meaning in Rust 2024
     assert_type_eq(x, 0u8);
 
     let &Foo(&mut x) = &Foo(&mut 0);
-    //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //~^ ERROR: reference patterns may only be written when the default binding mode is `move` in Rust 2024
     //~| WARN: this changes meaning in Rust 2024
     assert_type_eq(x, 0u8);
 
     let &mut Foo(&x) = &mut Foo(&0);
-    //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //~^ ERROR: reference patterns may only be written when the default binding mode is `move` in Rust 2024
     //~| WARN: this changes meaning in Rust 2024
     assert_type_eq(x, 0u8);
 
     let &mut Foo(&mut x) = &mut Foo(&mut 0);
-    //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //~^ ERROR: reference patterns may only be written when the default binding mode is `move` in Rust 2024
     //~| WARN: this changes meaning in Rust 2024
     assert_type_eq(x, 0u8);
 
@@ -79,25 +79,25 @@ fn main() {
     }
 
     if let &&&&&Some(&x) = &&&&&Some(&0u8) {
-        //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+        //~^ ERROR: reference patterns may only be written when the default binding mode is `move` in Rust 2024
         //~| WARN: this changes meaning in Rust 2024
         assert_type_eq(x, 0u8);
     }
 
     if let &&&&&Some(&mut x) = &&&&&Some(&mut 0u8) {
-        //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+        //~^ ERROR: reference patterns may only be written when the default binding mode is `move` in Rust 2024
         //~| WARN: this changes meaning in Rust 2024
         assert_type_eq(x, 0u8);
     }
 
     if let &&&&&mut Some(&x) = &&&&&mut Some(&0u8) {
-        //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+        //~^ ERROR: reference patterns may only be written when the default binding mode is `move` in Rust 2024
         //~| WARN: this changes meaning in Rust 2024
         assert_type_eq(x, 0u8);
     }
 
     if let &mut Some(&mut Some(&mut Some(ref mut x))) = &mut Some(&mut Some(&mut Some(0u8))) {
-        //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+        //~^ ERROR: reference patterns may only be written when the default binding mode is `move` in Rust 2024
         //~| WARN: this changes meaning in Rust 2024
         assert_type_eq(x, &mut 0u8);
     }
@@ -109,20 +109,20 @@ fn main() {
     }
 
     let &Struct { ref a, mut b, ref c } = &Struct { a: 0, b: 0, c: 0 };
-    //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //~^ ERROR: binding modifiers may only be written when the default binding mode is `move` in Rust 2024
     //~| WARN: this changes meaning in Rust 2024
     assert_type_eq(a, &0u32);
     assert_type_eq(b, 0u32);
 
     let &Struct { a: &a, ref b, ref c } = &Struct { a: &0, b: &0, c: &0 };
-    //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //~^ ERROR: binding modifiers and reference patterns may only be written when the default binding mode is `move` in Rust 2024
     //~| WARN: this changes meaning in Rust 2024
     assert_type_eq(a, 0u32);
     assert_type_eq(b, &&0u32);
     assert_type_eq(c, &&0u32);
 
     if let &Struct { a: &Some(a), b: &Some(&b), c: &Some(ref c) } =
-        //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+        //~^ ERROR: reference patterns may only be written when the default binding mode is `move` in Rust 2024
         //~| WARN: this changes meaning in Rust 2024
         &(Struct { a: &Some(&0), b: &Some(&0), c: &Some(&0) })
     {
@@ -135,7 +135,7 @@ fn main() {
         // The two patterns are the same syntactically, but because they're defined in different
         // editions they don't mean the same thing.
         &(Some(mut x), migration_lint_macros::mixed_edition_pat!(y)) => {
-            //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+            //~^ ERROR: binding modifiers may only be written when the default binding mode is `move`
             assert_type_eq(x, 0u32);
             assert_type_eq(y, 0u32);
         }

tests/ui/pattern/rfc-3627-match-ergonomics-2024/migration_lint.rs

@@ -23,22 +23,22 @@ fn main() {
     assert_type_eq(x, &mut 0u8);
 
     let Foo(mut x) = &Foo(0);
-    //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //~^ ERROR: binding modifiers may only be written when the default binding mode is `move` in Rust 2024
     //~| WARN: this changes meaning in Rust 2024
     assert_type_eq(x, 0u8);
 
     let Foo(mut x) = &mut Foo(0);
-    //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //~^ ERROR: binding modifiers may only be written when the default binding mode is `move` in Rust 2024
     //~| WARN: this changes meaning in Rust 2024
     assert_type_eq(x, 0u8);
 
     let Foo(ref x) = &Foo(0);
-    //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //~^ ERROR: binding modifiers may only be written when the default binding mode is `move` in Rust 2024
     //~| WARN: this changes meaning in Rust 2024
     assert_type_eq(x, &0u8);
 
     let Foo(ref x) = &mut Foo(0);
-    //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //~^ ERROR: binding modifiers may only be written when the default binding mode is `move` in Rust 2024
     //~| WARN: this changes meaning in Rust 2024
     assert_type_eq(x, &0u8);
 
@@ -55,22 +55,22 @@ fn main() {
     assert_type_eq(x, &0u8);
 
     let Foo(&x) = &Foo(&0);
-    //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //~^ ERROR: reference patterns may only be written when the default binding mode is `move` in Rust 2024
     //~| WARN: this changes meaning in Rust 2024
     assert_type_eq(x, 0u8);
 
     let Foo(&mut x) = &Foo(&mut 0);
-    //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //~^ ERROR: reference patterns may only be written when the default binding mode is `move` in Rust 2024
     //~| WARN: this changes meaning in Rust 2024
     assert_type_eq(x, 0u8);
 
     let Foo(&x) = &mut Foo(&0);
-    //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //~^ ERROR: reference patterns may only be written when the default binding mode is `move` in Rust 2024
     //~| WARN: this changes meaning in Rust 2024
     assert_type_eq(x, 0u8);
 
     let Foo(&mut x) = &mut Foo(&mut 0);
-    //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //~^ ERROR: reference patterns may only be written when the default binding mode is `move` in Rust 2024
     //~| WARN: this changes meaning in Rust 2024
     assert_type_eq(x, 0u8);
 
@@ -79,25 +79,25 @@ fn main() {
     }
 
     if let Some(&x) = &&&&&Some(&0u8) {
-        //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+        //~^ ERROR: reference patterns may only be written when the default binding mode is `move` in Rust 2024
         //~| WARN: this changes meaning in Rust 2024
         assert_type_eq(x, 0u8);
     }
 
     if let Some(&mut x) = &&&&&Some(&mut 0u8) {
-        //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+        //~^ ERROR: reference patterns may only be written when the default binding mode is `move` in Rust 2024
         //~| WARN: this changes meaning in Rust 2024
         assert_type_eq(x, 0u8);
     }
 
     if let Some(&x) = &&&&&mut Some(&0u8) {
-        //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+        //~^ ERROR: reference patterns may only be written when the default binding mode is `move` in Rust 2024
         //~| WARN: this changes meaning in Rust 2024
         assert_type_eq(x, 0u8);
     }
 
     if let Some(&mut Some(Some(x))) = &mut Some(&mut Some(&mut Some(0u8))) {
-        //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+        //~^ ERROR: reference patterns may only be written when the default binding mode is `move` in Rust 2024
         //~| WARN: this changes meaning in Rust 2024
         assert_type_eq(x, &mut 0u8);
     }
@@ -109,20 +109,20 @@ fn main() {
     }
 
     let Struct { a, mut b, c } = &Struct { a: 0, b: 0, c: 0 };
-    //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //~^ ERROR: binding modifiers may only be written when the default binding mode is `move` in Rust 2024
     //~| WARN: this changes meaning in Rust 2024
     assert_type_eq(a, &0u32);
     assert_type_eq(b, 0u32);
 
     let Struct { a: &a, b, ref c } = &Struct { a: &0, b: &0, c: &0 };
-    //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+    //~^ ERROR: binding modifiers and reference patterns may only be written when the default binding mode is `move` in Rust 2024
     //~| WARN: this changes meaning in Rust 2024
     assert_type_eq(a, 0u32);
     assert_type_eq(b, &&0u32);
     assert_type_eq(c, &&0u32);
 
     if let Struct { a: &Some(a), b: Some(&b), c: Some(c) } =
-        //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+        //~^ ERROR: reference patterns may only be written when the default binding mode is `move` in Rust 2024
         //~| WARN: this changes meaning in Rust 2024
         &(Struct { a: &Some(&0), b: &Some(&0), c: &Some(&0) })
     {
@@ -135,7 +135,7 @@ fn main() {
         // The two patterns are the same syntactically, but because they're defined in different
         // editions they don't mean the same thing.
         (Some(mut x), migration_lint_macros::mixed_edition_pat!(y)) => {
-            //~^ ERROR: this pattern relies on behavior which may change in edition 2024
+            //~^ ERROR: binding modifiers may only be written when the default binding mode is `move`
             assert_type_eq(x, 0u32);
             assert_type_eq(y, 0u32);
         }

tests/ui/pattern/rfc-3627-match-ergonomics-2024/migration_lint.stderr

@@ -1,8 +1,8 @@
-error: this pattern relies on behavior which may change in edition 2024
+error: binding modifiers may only be written when the default binding mode is `move` in Rust 2024
   --> $DIR/migration_lint.rs:25:13
    |
 LL |     let Foo(mut x) = &Foo(0);
-   |             ^^^ requires binding by-value, but the implicit default is by-reference
+   |             ^^^ default binding mode is `ref`
    |
    = 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>
@@ -16,11 +16,11 @@ help: make the implied reference pattern explicit
 LL |     let &Foo(mut x) = &Foo(0);
    |         +
 
-error: this pattern relies on behavior which may change in edition 2024
+error: binding modifiers may only be written when the default binding mode is `move` in Rust 2024
   --> $DIR/migration_lint.rs:30:13
    |
 LL |     let Foo(mut x) = &mut Foo(0);
-   |             ^^^ requires binding by-value, but the implicit default is by-reference
+   |             ^^^ default binding mode is `ref mut`
    |
    = 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>
@@ -29,11 +29,11 @@ help: make the implied reference pattern explicit
 LL |     let &mut Foo(mut x) = &mut Foo(0);
    |         ++++
 
-error: this pattern relies on behavior which may change in edition 2024
+error: binding modifiers may only be written when the default binding mode is `move` in Rust 2024
   --> $DIR/migration_lint.rs:35:13
    |
 LL |     let Foo(ref x) = &Foo(0);
-   |             ^^^ cannot override to bind by-reference when that is the implicit default
+   |             ^^^ default binding mode is `ref`
    |
    = 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>
@@ -42,11 +42,11 @@ help: make the implied reference pattern explicit
 LL |     let &Foo(ref x) = &Foo(0);
    |         +
 
-error: this pattern relies on behavior which may change in edition 2024
+error: binding modifiers may only be written when the default binding mode is `move` in Rust 2024
   --> $DIR/migration_lint.rs:40:13
    |
 LL |     let Foo(ref x) = &mut Foo(0);
-   |             ^^^ cannot override to bind by-reference when that is the implicit default
+   |             ^^^ default binding mode is `ref mut`
    |
    = 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>
@@ -55,11 +55,11 @@ help: make the implied reference pattern explicit
 LL |     let &mut Foo(ref x) = &mut Foo(0);
    |         ++++
 
-error: this pattern relies on behavior which may change in edition 2024
+error: reference patterns may only be written when the default binding mode is `move` in Rust 2024
   --> $DIR/migration_lint.rs:57:13
    |
 LL |     let Foo(&x) = &Foo(&0);
-   |             ^ cannot implicitly match against multiple layers of reference
+   |             ^ default binding mode is `ref`
    |
    = 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>
@@ -68,11 +68,11 @@ help: make the implied reference pattern explicit
 LL |     let &Foo(&x) = &Foo(&0);
    |         +
 
-error: this pattern relies on behavior which may change in edition 2024
+error: reference patterns may only be written when the default binding mode is `move` in Rust 2024
   --> $DIR/migration_lint.rs:62:13
    |
 LL |     let Foo(&mut x) = &Foo(&mut 0);
-   |             ^^^^ cannot implicitly match against multiple layers of reference
+   |             ^^^^ default binding mode is `ref`
    |
    = 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>
@@ -81,11 +81,11 @@ help: make the implied reference pattern explicit
 LL |     let &Foo(&mut x) = &Foo(&mut 0);
    |         +
 
-error: this pattern relies on behavior which may change in edition 2024
+error: reference patterns may only be written when the default binding mode is `move` in Rust 2024
   --> $DIR/migration_lint.rs:67:13
    |
 LL |     let Foo(&x) = &mut Foo(&0);
-   |             ^ cannot implicitly match against multiple layers of reference
+   |             ^ default binding mode is `ref mut`
    |
    = 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>
@@ -94,11 +94,11 @@ help: make the implied reference pattern explicit
 LL |     let &mut Foo(&x) = &mut Foo(&0);
    |         ++++
 
-error: this pattern relies on behavior which may change in edition 2024
+error: reference patterns may only be written when the default binding mode is `move` in Rust 2024
   --> $DIR/migration_lint.rs:72:13
    |
 LL |     let Foo(&mut x) = &mut Foo(&mut 0);
-   |             ^^^^ cannot implicitly match against multiple layers of reference
+   |             ^^^^ default binding mode is `ref mut`
    |
    = 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>
@@ -107,11 +107,11 @@ help: make the implied reference pattern explicit
 LL |     let &mut Foo(&mut x) = &mut Foo(&mut 0);
    |         ++++
 
-error: this pattern relies on behavior which may change in edition 2024
+error: reference patterns may only be written when the default binding mode is `move` in Rust 2024
   --> $DIR/migration_lint.rs:81:17
    |
 LL |     if let Some(&x) = &&&&&Some(&0u8) {
-   |                 ^ cannot implicitly match against multiple layers of reference
+   |                 ^ default binding mode is `ref`
    |
    = 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>
@@ -120,11 +120,11 @@ help: make the implied reference patterns explicit
 LL |     if let &&&&&Some(&x) = &&&&&Some(&0u8) {
    |            +++++
 
-error: this pattern relies on behavior which may change in edition 2024
+error: reference patterns may only be written when the default binding mode is `move` in Rust 2024
   --> $DIR/migration_lint.rs:87:17
    |
 LL |     if let Some(&mut x) = &&&&&Some(&mut 0u8) {
-   |                 ^^^^ cannot implicitly match against multiple layers of reference
+   |                 ^^^^ default binding mode is `ref`
    |
    = 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>
@@ -133,11 +133,11 @@ help: make the implied reference patterns explicit
 LL |     if let &&&&&Some(&mut x) = &&&&&Some(&mut 0u8) {
    |            +++++
 
-error: this pattern relies on behavior which may change in edition 2024
+error: reference patterns may only be written when the default binding mode is `move` in Rust 2024
   --> $DIR/migration_lint.rs:93:17
    |
 LL |     if let Some(&x) = &&&&&mut Some(&0u8) {
-   |                 ^ cannot implicitly match against multiple layers of reference
+   |                 ^ default binding mode is `ref`
    |
    = 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>
@@ -146,11 +146,11 @@ help: make the implied reference patterns explicit
 LL |     if let &&&&&mut Some(&x) = &&&&&mut Some(&0u8) {
    |            ++++++++
 
-error: this pattern relies on behavior which may change in edition 2024
+error: reference patterns may only be written when the default binding mode is `move` in Rust 2024
   --> $DIR/migration_lint.rs:99:17
    |
 LL |     if let Some(&mut Some(Some(x))) = &mut Some(&mut Some(&mut Some(0u8))) {
-   |                 ^^^^ cannot implicitly match against multiple layers of reference
+   |                 ^^^^ default binding mode is `ref mut`
    |
    = 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>
@@ -159,11 +159,11 @@ 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))) {
    |            ++++                ++++      +++++++
 
-error: this pattern relies on behavior which may change in edition 2024
+error: binding modifiers may only be written when the default binding mode is `move` in Rust 2024
   --> $DIR/migration_lint.rs:111:21
    |
 LL |     let Struct { a, mut b, c } = &Struct { a: 0, b: 0, c: 0 };
-   |                     ^^^ requires binding by-value, but the implicit default is by-reference
+   |                     ^^^ default binding mode is `ref`
    |
    = 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>
@@ -172,13 +172,13 @@ 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 };
    |         +         +++           +++
 
-error: this pattern relies on behavior which may change in edition 2024
+error: binding modifiers and reference patterns may only be written when the default binding mode is `move` in Rust 2024
   --> $DIR/migration_lint.rs:117:21
    |
 LL |     let Struct { a: &a, b, ref c } = &Struct { a: &0, b: &0, c: &0 };
-   |                     ^      ^^^ cannot override to bind by-reference when that is the implicit default
+   |                     ^      ^^^ default binding mode is `ref`
    |                     |
-   |                     cannot implicitly match against multiple layers of reference
+   |                     default binding mode is `ref`
    |
    = 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>
@@ -187,13 +187,13 @@ 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 };
    |         +                +++
 
-error: this pattern relies on behavior which may change in edition 2024
+error: reference patterns may only be written when the default binding mode is `move` in Rust 2024
   --> $DIR/migration_lint.rs:124:24
    |
 LL |     if let Struct { a: &Some(a), b: Some(&b), c: Some(c) } =
-   |                        ^                 ^ cannot implicitly match against multiple layers of reference
+   |                        ^                 ^ default binding mode is `ref`
    |                        |
-   |                        cannot implicitly match against multiple layers of reference
+   |                        default binding mode is `ref`
    |
    = 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>
@@ -202,13 +202,13 @@ 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) } =
    |            +                         +             +     +++
 
-error: this pattern relies on behavior which may change in edition 2024
+error: binding modifiers may only be written when the default binding mode is `move`
   --> $DIR/migration_lint.rs:137:15
    |
 LL |         (Some(mut x), migration_lint_macros::mixed_edition_pat!(y)) => {
-   |               ^^^     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ default binding mode is reset within expansion
+   |               ^^^     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ occurs within expansion
    |               |
-   |               requires binding by-value, but the implicit default is by-reference
+   |               default binding mode is `ref`
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
    = note: this error originates in the macro `migration_lint_macros::mixed_edition_pat` (in Nightly builds, run with -Z macro-backtrace for more info)

tests/ui/pattern/rfc-3627-match-ergonomics-2024/min_match_ergonomics_fail.rs

@@ -21,17 +21,17 @@ macro_rules! test_pat_on_type {
 }
 
 test_pat_on_type![(&x,): &(T,)]; //~ ERROR mismatched types
-test_pat_on_type![(&x,): &(&T,)]; //~ ERROR this pattern relies on behavior which may change in edition 2024
+test_pat_on_type![(&x,): &(&T,)]; //~ ERROR reference patterns may only be written when the default binding mode is `move`
 test_pat_on_type![(&x,): &(&mut T,)]; //~ ERROR mismatched types
 test_pat_on_type![(&mut x,): &(&T,)]; //~ ERROR mismatched types
-test_pat_on_type![(&mut x,): &(&mut T,)]; //~ ERROR this pattern relies on behavior which may change in edition 2024
+test_pat_on_type![(&mut x,): &(&mut T,)]; //~ ERROR reference patterns may only be written when the default binding mode is `move`
 test_pat_on_type![(&x,): &&mut &(T,)]; //~ ERROR mismatched types
 test_pat_on_type![Foo { f: (&x,) }: Foo]; //~ ERROR mismatched types
 test_pat_on_type![Foo { f: (&x,) }: &mut Foo]; //~ ERROR mismatched types
-test_pat_on_type![Foo { f: &(x,) }: &Foo]; //~ ERROR this pattern relies on behavior which may change in edition 2024
+test_pat_on_type![Foo { f: &(x,) }: &Foo]; //~ ERROR reference patterns may only be written when the default binding mode is `move`
-test_pat_on_type![(mut x,): &(T,)]; //~ ERROR this pattern relies on behavior which may change in edition 2024
+test_pat_on_type![(mut x,): &(T,)]; //~ ERROR binding modifiers may only be written when the default binding mode is `move`
-test_pat_on_type![(ref x,): &(T,)]; //~ ERROR this pattern relies on behavior which may change in edition 2024
+test_pat_on_type![(ref x,): &(T,)]; //~ ERROR binding modifiers may only be written when the default binding mode is `move`
-test_pat_on_type![(ref mut x,): &mut (T,)]; //~ ERROR this pattern relies on behavior which may change in edition 2024
+test_pat_on_type![(ref mut x,): &mut (T,)]; //~ ERROR binding modifiers may only be written when the default binding mode is `move`
 
 fn get<X>() -> X {
     unimplemented!()
@@ -40,6 +40,6 @@ fn get<X>() -> X {
 // Make sure this works even when the underlying type is inferred. This test passes on rust stable.
 fn infer<X: Copy>() -> X {
     match &get() {
-        (&x,) => x, //~ ERROR this pattern relies on behavior which may change in edition 2024
+        (&x,) => x, //~ ERROR reference patterns may only be written when the default binding mode is `move`
     }
 }

tests/ui/pattern/rfc-3627-match-ergonomics-2024/min_match_ergonomics_fail.stderr

@@ -99,11 +99,11 @@ LL - test_pat_on_type![Foo { f: (&x,) }: &mut Foo];
 LL + test_pat_on_type![Foo { f: (x,) }: &mut Foo];
    |
 
-error: this pattern relies on behavior which may change in edition 2024
+error: reference patterns may only be written when the default binding mode is `move`
   --> $DIR/min_match_ergonomics_fail.rs:24:20
    |
 LL | test_pat_on_type![(&x,): &(&T,)];
-   |                    ^ cannot implicitly match against multiple layers of reference
+   |                    ^ default binding mode is `ref`
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
 help: make the implied reference pattern explicit
@@ -111,11 +111,11 @@ help: make the implied reference pattern explicit
 LL | test_pat_on_type![&(&x,): &(&T,)];
    |                   +
 
-error: this pattern relies on behavior which may change in edition 2024
+error: reference patterns may only be written when the default binding mode is `move`
   --> $DIR/min_match_ergonomics_fail.rs:27:20
    |
 LL | test_pat_on_type![(&mut x,): &(&mut T,)];
-   |                    ^^^^ cannot implicitly match against multiple layers of reference
+   |                    ^^^^ default binding mode is `ref`
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
 help: make the implied reference pattern explicit
@@ -123,11 +123,11 @@ help: make the implied reference pattern explicit
 LL | test_pat_on_type![&(&mut x,): &(&mut T,)];
    |                   +
 
-error: this pattern relies on behavior which may change in edition 2024
+error: reference patterns may only be written when the default binding mode is `move`
   --> $DIR/min_match_ergonomics_fail.rs:31:28
    |
 LL | test_pat_on_type![Foo { f: &(x,) }: &Foo];
-   |                            ^ cannot implicitly match against multiple layers of reference
+   |                            ^ default binding mode is `ref`
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
 help: make the implied reference pattern explicit
@@ -135,11 +135,11 @@ help: make the implied reference pattern explicit
 LL | test_pat_on_type![&Foo { f: &(x,) }: &Foo];
    |                   +
 
-error: this pattern relies on behavior which may change in edition 2024
+error: binding modifiers may only be written when the default binding mode is `move`
   --> $DIR/min_match_ergonomics_fail.rs:32:20
    |
 LL | test_pat_on_type![(mut x,): &(T,)];
-   |                    ^^^ requires binding by-value, but the implicit default is by-reference
+   |                    ^^^ default binding mode is `ref`
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
 help: make the implied reference pattern explicit
@@ -147,11 +147,11 @@ help: make the implied reference pattern explicit
 LL | test_pat_on_type![&(mut x,): &(T,)];
    |                   +
 
-error: this pattern relies on behavior which may change in edition 2024
+error: binding modifiers may only be written when the default binding mode is `move`
   --> $DIR/min_match_ergonomics_fail.rs:33:20
    |
 LL | test_pat_on_type![(ref x,): &(T,)];
-   |                    ^^^ cannot override to bind by-reference when that is the implicit default
+   |                    ^^^ default binding mode is `ref`
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
 help: make the implied reference pattern explicit
@@ -159,11 +159,11 @@ help: make the implied reference pattern explicit
 LL | test_pat_on_type![&(ref x,): &(T,)];
    |                   +
 
-error: this pattern relies on behavior which may change in edition 2024
+error: binding modifiers may only be written when the default binding mode is `move`
   --> $DIR/min_match_ergonomics_fail.rs:34:20
    |
 LL | test_pat_on_type![(ref mut x,): &mut (T,)];
-   |                    ^^^^^^^ cannot override to bind by-reference when that is the implicit default
+   |                    ^^^^^^^ default binding mode is `ref mut`
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
 help: make the implied reference pattern explicit
@@ -171,11 +171,11 @@ help: make the implied reference pattern explicit
 LL | test_pat_on_type![&mut (ref mut x,): &mut (T,)];
    |                   ++++
 
-error: this pattern relies on behavior which may change in edition 2024
+error: reference patterns may only be written when the default binding mode is `move`
   --> $DIR/min_match_ergonomics_fail.rs:43:10
    |
 LL |         (&x,) => x,
-   |          ^ cannot implicitly match against multiple layers of reference
+   |          ^ default binding mode is `ref`
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
 help: make the implied reference pattern explicit