Auto merge of #106004 - fee1-dead-contrib:const-closures, r=oli-obk

Const closures

cc rust-lang/rust#106003

Author: bors

core/src/cmp.rs

@@ -1234,17 +1234,23 @@ where
     F: ~const Destruct,
     K: ~const Destruct,
 {
-    const fn imp<T, F: ~const FnMut(&T) -> K, K: ~const Ord>(
-        f: &mut F,
-        (v1, v2): (&T, &T),
-    ) -> Ordering
-    where
-        T: ~const Destruct,
-        K: ~const Destruct,
-    {
-        f(v1).cmp(&f(v2))
+    cfg_if! {
+        if #[cfg(bootstrap)] {
+            const fn imp<T, F: ~const FnMut(&T) -> K, K: ~const Ord>(
+                f: &mut F,
+                (v1, v2): (&T, &T),
+            ) -> Ordering
+            where
+                T: ~const Destruct,
+                K: ~const Destruct,
+            {
+                f(v1).cmp(&f(v2))
+            }
+            min_by(v1, v2, ConstFnMutClosure::new(&mut f, imp))
+        } else {
+            min_by(v1, v2, const |v1, v2| f(v1).cmp(&f(v2)))
+        }
     }
-    min_by(v1, v2, ConstFnMutClosure::new(&mut f, imp))
 }
 
 /// Compares and returns the maximum of two values.

core/src/lib.rs

@@ -191,6 +191,7 @@
 #![feature(cfg_sanitize)]
 #![feature(cfg_target_has_atomic)]
 #![feature(cfg_target_has_atomic_equal_alignment)]
+#![cfg_attr(not(bootstrap), feature(const_closures))]
 #![feature(const_fn_floating_point_arithmetic)]
 #![feature(const_mut_refs)]
 #![feature(const_precise_live_drops)]