Add test for const MaybeUninit

library/core/tests/lib.rs

@@ -10,6 +10,7 @@
 #![feature(const_assume)]
 #![feature(const_cell_into_inner)]
 #![feature(const_convert)]
+#![feature(const_maybe_uninit_as_mut_ptr)]
 #![feature(const_maybe_uninit_assume_init)]
 #![feature(const_ptr_read)]
 #![feature(const_ptr_write)]

library/core/tests/mem.rs

@@ -269,3 +269,35 @@ fn uninit_const_assume_init_read() {
  const FOO: u32 = unsafe { MaybeUninit::new(42).assume_init_read() };
  assert_eq!(FOO, 42);
 }
+
+#[test]
+fn const_maybe_uninit() {
+ use std::ptr;
+
+ #[derive(Debug, PartialEq)]
+ struct Foo {
+ x: u8,
+ y: u8,
+ }
+
+ const FIELD_BY_FIELD: Foo = unsafe {
+ let mut val = MaybeUninit::uninit();
+ init_y(&mut val); // order shouldn't matter
+ init_x(&mut val);
+ val.assume_init()
+ };
+
+ const fn init_x(foo: &mut MaybeUninit<Foo>) {
+ unsafe {
+ *ptr::addr_of_mut!((*foo.as_mut_ptr()).x) = 1;
+ }
+ }
+
+ const fn init_y(foo: &mut MaybeUninit<Foo>) {
+ unsafe {
+ *ptr::addr_of_mut!((*foo.as_mut_ptr()).y) = 2;
+ }
+ }
+
+ assert_eq!(FIELD_BY_FIELD, Foo { x: 1, y: 2 });
+}