1 files changed, 57 insertions, 0 deletions
diff --git a/third_party/rust/generic-array/src/arr.rs b/third_party/rust/generic-array/src/arr.rs
new file mode 100644
index 0000000000..a07d129ad3
--- /dev/null
+++ b/third_party/rust/generic-array/src/arr.rs
@@ -0,0 +1,57 @@
+//! Implementation for `arr!` macro.
+
+use super::ArrayLength;
+use core::ops::Add;
+use typenum::U1;
+
+/// Helper trait for `arr!` macro
+pub trait AddLength<T, N: ArrayLength<T>>: ArrayLength<T> {
+    /// Resulting length
+    type Output: ArrayLength<T>;
+}
+
+impl<T, N1, N2> AddLength<T, N2> for N1
+where
+    N1: ArrayLength<T> + Add<N2>,
+    N2: ArrayLength<T>,
+    <N1 as Add<N2>>::Output: ArrayLength<T>,
+{
+    type Output = <N1 as Add<N2>>::Output;
+}
+
+/// Helper type for `arr!` macro
+pub type Inc<T, U> = <U as AddLength<T, U1>>::Output;
+
+#[doc(hidden)]
+#[macro_export]
+macro_rules! arr_impl {
+    ($T:ty; $N:ty, [$($x:expr),*], []) => ({
+        unsafe { $crate::transmute::<_, $crate::GenericArray<$T, $N>>([$($x),*]) }
+    });
+    ($T:ty; $N:ty, [], [$x1:expr]) => (
+        arr_impl!($T; $crate::arr::Inc<$T, $N>, [$x1 as $T], [])
+    );
+    ($T:ty; $N:ty, [], [$x1:expr, $($x:expr),+]) => (
+        arr_impl!($T; $crate::arr::Inc<$T, $N>, [$x1 as $T], [$($x),+])
+    );
+    ($T:ty; $N:ty, [$($y:expr),+], [$x1:expr]) => (
+        arr_impl!($T; $crate::arr::Inc<$T, $N>, [$($y),+, $x1 as $T], [])
+    );
+    ($T:ty; $N:ty, [$($y:expr),+], [$x1:expr, $($x:expr),+]) => (
+        arr_impl!($T; $crate::arr::Inc<$T, $N>, [$($y),+, $x1 as $T], [$($x),+])
+    );
+}
+
+/// Macro allowing for easy generation of Generic Arrays.
+/// Example: `let test = arr![u32; 1, 2, 3];`
+#[macro_export]
+macro_rules! arr {
+    ($T:ty; $(,)*) => ({
+        unsafe { $crate::transmute::<[$T; 0], $crate::GenericArray<$T, $crate::typenum::U0>>([]) }
+    });
+    ($T:ty; $($x:expr),* $(,)*) => (
+        arr_impl!($T; $crate::typenum::U0, [], [$($x),*])
+    );
+    ($($x:expr,)+) => (arr![$($x),*]);
+    () => ("""Macro requires a type, e.g. `let array = arr![u32; 1, 2, 3];`")
+}