Binding both borrowed and unborrowed field becomes impossible in the 2024 edition

The following code compiles on the 2021 edition:

enum MyCow<'a, T> {
    Owned(T),
    Borrowed(&'a T)
}

enum Inner<T> {
    Foo(T)
}

fn my_match<T>(val: MyCow<'_, Inner<T>>) {
    match val {
        MyCow::Owned(Inner::Foo(ref inner)) | MyCow::Borrowed(Inner::Foo(ref inner)) => {}
    }
}

Here, the inner pattern has type &T, allowing a single match arm to handle both the MyCow::Owned and MyCow::Borrowed cases.

In the 2024 edition, this produces an error:

error: binding modifiers may only be written when the default binding mode is `move`
  --> src/lib.rs:12:74
   |
12 |         MyCow::Owned(Inner::Foo(ref inner)) | MyCow::Borrowed(Inner::Foo(ref inner)) => {}
   |                                                                          ^^^ 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: matching on a reference type with a non-reference pattern changes the default binding mode
  --> src/lib.rs:12:63
   |
12 |         MyCow::Owned(Inner::Foo(ref inner)) | MyCow::Borrowed(Inner::Foo(ref inner)) => {}
   |                                                               ^^^^^^^^^^^^^^^^^^^^^ this matches on type `&_`
help: remove the unnecessary binding modifier
   |
12 -         MyCow::Owned(Inner::Foo(ref inner)) | MyCow::Borrowed(Inner::Foo(ref inner)) => {}
12 +         MyCow::Owned(Inner::Foo(ref inner)) | MyCow::Borrowed(Inner::Foo(inner)) => {}
   |

Unfortunately, the suggestion does not work:

error[E0409]: variable `inner` is bound inconsistently across alternatives separated by `|`
  --> src/lib.rs:12:74
   |
12 |         MyCow::Owned(Inner::Foo(ref inner)) | MyCow::Borrowed(Inner::Foo(inner)) => {}
   |                                     ----- first binding                  ^^^^^ bound in different ways

No combination of inner/ref inner compiles under the 2024 edition. This forces the original code to either be split into separate match arms, or factored out into a closure/method.

Meta

rustc --version --verbose:

rustc 1.91.0 (f8297e351 2025-10-28)
binary: rustc
commit-hash: f8297e351a40c1439a467bbbb6879088047f50b3
commit-date: 2025-10-28
host: x86_64-unknown-linux-gnu
release: 1.91.0
LLVM version: 21.1.2

Start with the src/lib.rs reproducer and compare its 2021 and 2024 results, including the suggested diagnostic change. Read the Rust 2024 match-ergonomics edition guide, then trace the compiler's pattern-binding handling for or-patterns. Done means the valid shared binding behavior is restored or the diagnostic clearly documents the required workaround.