disable get_disjoint_mut for rust versions below 1.51

Author: cmrschwarz

build.rs

@@ -1,6 +1,8 @@
 fn main() {
     println!("cargo:rerun-if-changed=build.rs");
-    println!("cargo:rustc-check-cfg=cfg(slab_no_const_vec_new,slab_no_track_caller)");
+    println!(
+        "cargo:rustc-check-cfg=cfg(slab_no_const_vec_new,slab_no_track_caller,slab_no_const_generics)"
+    );
 
     let cfg = match autocfg::AutoCfg::new() {
         Ok(cfg) => cfg,
@@ -24,4 +26,7 @@ fn main() {
     if !cfg.probe_rustc_version(1, 46) {
         println!("cargo:rustc-cfg=slab_no_track_caller");
     }
+    if !cfg.probe_rustc_version(1, 51) {
+        println!("cargo:rustc-cfg=slab_no_const_generics");
+    }
 }

src/lib.rs

@@ -810,6 +810,7 @@ impl<T> Slab<T> {
     /// Returns mutable references to many indices at once.
     /// Returns [`GetDisjointMutError`] if the indices are out of bounds,
     /// overlapping, or vacant.
+    #[cfg(not(slab_no_const_generics))]
     pub fn get_disjoint_mut<const N: usize>(
         &mut self,
         keys: [usize; N],

tests/slab.rs

@@ -735,6 +735,7 @@ fn clone_from() {
     assert!(slab2.capacity() >= 10);
 }
 
+#[rustversion::since(1.51)]
 #[test]
 fn get_disjoint_mut() {
     let mut slab = Slab::from_iter((0..5).enumerate());