Rollup merge of #125082 - kpreid:const-uninit, r=dtolnay

Remove `MaybeUninit::uninit_array()` and replace it with inline const blocks.

\[This PR originally contained the changes in #125995 too. See edit history for the original PR description.]

The documentation of `MaybeUninit::uninit_array()` says:

> Note: in a future Rust version this method may become unnecessary when Rust allows [inline const expressions](https://github.com/rust-lang/rust/issues/76001). The example below could then use `let mut buf = [const { MaybeUninit::<u8>::uninit() }; 32];`.

The PR adding it also said: <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];`

That time has come to pass — inline const expressions are stable — so `MaybeUninit::uninit_array()` is now unnecessary. The only remaining question is whether it is an important enough *convenience* to keep it around.

I believe it is net good to remove this function, on the principle that it is better to compose two orthogonal features (`MaybeUninit` and array construction) than to have a specific function for the specific combination, now that that is possible.

5 files changed, 4 insertions, 6 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()));
diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs
index caa8c7375ec..27ed2e4137c 100644
--- a/library/std/src/lib.rs
+++ b/library/std/src/lib.rs
@@ -337,7 +337,6 @@
 #![feature(hint_assert_unchecked)]
 #![feature(ip)]
 #![feature(maybe_uninit_slice)]
-#![feature(maybe_uninit_uninit_array)]
 #![feature(maybe_uninit_write_slice)]
 #![feature(panic_can_unwind)]
 #![feature(panic_info_message)]
@@ -407,7 +406,6 @@
 #![feature(const_ip)]
 #![feature(const_ipv4)]
 #![feature(const_ipv6)]
-#![feature(const_maybe_uninit_uninit_array)]
 #![feature(const_waker)]
 #![feature(thread_local_internals)]
 // tidy-alphabetical-end
diff --git a/library/std/src/net/tcp/tests.rs b/library/std/src/net/tcp/tests.rs
index ec8b62f9687..3ad046733a6 100644
--- a/library/std/src/net/tcp/tests.rs
+++ b/library/std/src/net/tcp/tests.rs
@@ -301,7 +301,7 @@ fn read_buf() {
         });
 
         let mut s = t!(srv.accept()).0;
-        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());
         t!(s.read_buf(buf.unfilled()));
         assert_eq!(buf.filled(), &[1, 2, 3, 4]);
diff --git a/library/std/src/process/tests.rs b/library/std/src/process/tests.rs
index 07d4de5c1a2..63455a274fa 100644
--- a/library/std/src/process/tests.rs
+++ b/library/std/src/process/tests.rs
@@ -137,7 +137,7 @@ fn child_stdout_read_buf() {
     let child = cmd.spawn().unwrap();
 
     let mut stdout = child.stdout.unwrap();
-    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());
     stdout.read_buf(buf.unfilled()).unwrap();
 
diff --git a/library/std/src/sys/pal/windows/mod.rs b/library/std/src/sys/pal/windows/mod.rs
index a1bc2965e2e..6406cec9c27 100644
--- a/library/std/src/sys/pal/windows/mod.rs
+++ b/library/std/src/sys/pal/windows/mod.rs
@@ -225,7 +225,7 @@ where
     // This initial size also works around `GetFullPathNameW` returning
     // incorrect size hints for some short paths:
     // https://github.com/dylni/normpath/issues/5
-    let mut stack_buf: [MaybeUninit<u16>; 512] = MaybeUninit::uninit_array();
+    let mut stack_buf: [MaybeUninit<u16>; 512] = [MaybeUninit::uninit(); 512];
     let mut heap_buf: Vec<MaybeUninit<u16>> = Vec::new();
     unsafe {
         let mut n = stack_buf.len();