Auto merge of #63118 - Centril:stabilize-bind-by-move, r=matthewjasper

Stabilize `bind_by_move_pattern_guards` in Rust 1.39.0

Closes https://github.com/rust-lang/rust/issues/15287.

After stabilizing `#![feature(bind_by_move_pattern_guards)]`, you can now use bind-by-move bindings in patterns and take references to those bindings in `if` guards of `match` expressions. For example, the following now becomes legal:

```rust
fn main() {
    let array: Box<[u8; 4]> = Box::new([1, 2, 3, 4]);

    match array {
        nums
//      ---- `nums` is bound by move.
            if nums.iter().sum::<u8>() == 10
//                 ^------ `.iter()` implicitly takes a reference to `nums`.
        => {
            drop(nums);
//          --------- Legal as `nums` was bound by move and so we have ownership.
        }
        _ => unreachable!(),
    }
}
```

r? @matthewjasper

3 files changed, 3 insertions, 4 deletions

diff --git a/src/libsyntax/feature_gate/accepted.rs b/src/libsyntax/feature_gate/accepted.rs
index 6c0b271c6c5..eff9f90a861 100644
--- a/src/libsyntax/feature_gate/accepted.rs
+++ b/src/libsyntax/feature_gate/accepted.rs
@@ -241,6 +241,8 @@ declare_features! (
     (accepted, underscore_const_names, "1.37.0", Some(54912), None),
     /// Allows free and inherent `async fn`s, `async` blocks, and `<expr>.await` expressions.
     (accepted, async_await, "1.39.0", Some(50547), None),
+    /// Allows mixing bind-by-move in patterns and references to those identifiers in guards.
+    (accepted, bind_by_move_pattern_guards, "1.39.0", Some(15287), None),
 
     // -------------------------------------------------------------------------
     // feature-group-end: accepted features
diff --git a/src/libsyntax/feature_gate/active.rs b/src/libsyntax/feature_gate/active.rs
index 5a248df6af2..dd78777b569 100644
--- a/src/libsyntax/feature_gate/active.rs
+++ b/src/libsyntax/feature_gate/active.rs
@@ -461,9 +461,6 @@ declare_features! (
     /// Allows non-builtin attributes in inner attribute position.
     (active, custom_inner_attributes, "1.30.0", Some(54726), None),
 
-    /// Allows mixing bind-by-move in patterns and references to those identifiers in guards.
-    (active, bind_by_move_pattern_guards, "1.30.0", Some(15287), None),
-
     /// Allows `impl Trait` in bindings (`let`, `const`, `static`).
     (active, impl_trait_in_bindings, "1.30.0", Some(63065), None),
 
diff --git a/src/libsyntax/lib.rs b/src/libsyntax/lib.rs
index 49efbce482f..aaf6f3e537e 100644
--- a/src/libsyntax/lib.rs
+++ b/src/libsyntax/lib.rs
@@ -7,7 +7,7 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/",
        test(attr(deny(warnings))))]
 
-#![feature(bind_by_move_pattern_guards)]
+#![cfg_attr(bootstrap, feature(bind_by_move_pattern_guards))]
 #![feature(box_syntax)]
 #![feature(const_fn)]
 #![feature(const_transmute)]