Replace `MaybeUninit::uninit_array()` with array repeat expression.

This is possible now that inline const blocks are stable; the idea was
even mentioned as an alternative when `uninit_array()` was added:
<https://github.com/rust-lang/rust/pull/65580#issuecomment-544200681>

> if it’s stabilized soon enough maybe it’s not worth having a
> standard library method that will be replaceable with
> `let buffer = [MaybeUninit::<T>::uninit(); $N];`

Const array repetition and inline const blocks are now stable (in the
next release), so that circumstance has come to pass, and we no longer
have reason to want `uninit_array()` other than convenience. Therefore,
let’s evaluate the inconvenience by not using `uninit_array()` in
the standard library, before potentially deleting it entirely.

1 files changed, 1 insertions, 1 deletions

diff --git a/library/std/src/fs/tests.rs b/library/std/src/fs/tests.rs
index 62a268facb6..b75579d6d5e 100644
--- a/library/std/src/fs/tests.rs
+++ b/library/std/src/fs/tests.rs
@@ -406,7 +406,7 @@ fn file_test_read_buf() {
     let filename = &tmpdir.join("test");
     check!(fs::write(filename, &[1, 2, 3, 4]));
 
-    let mut buf: [MaybeUninit<u8>; 128] = MaybeUninit::uninit_array();
+    let mut buf: [MaybeUninit<u8>; 128] = [MaybeUninit::uninit(); 128];
     let mut buf = BorrowedBuf::from(buf.as_mut_slice());
     let mut file = check!(File::open(filename));
     check!(file.read_buf(buf.unfilled()));