Remove mem::uninitalized from tests

This purges uses of uninitialized where possible from test cases. Some
are merely moved over to the equally bad pattern of
MaybeUninit::uninit().assume_init() but with an annotation that this is
"the best we can do".

Author: Mark-Simulacrum

src/test/run-make-fulldeps/sanitizer-memory/Makefile

@@ -7,3 +7,5 @@
 all:
 	$(RUSTC) -g -Z sanitizer=memory -Z print-link-args uninit.rs | $(CGREP) librustc_msan
 	$(TMPDIR)/uninit 2>&1 | $(CGREP) use-of-uninitialized-value
+	$(RUSTC) -g -Z sanitizer=memory -Z print-link-args maybeuninit.rs | $(CGREP) librustc_msan
+	$(TMPDIR)/maybeuninit 2>&1 | $(CGREP) use-of-uninitialized-value

src/test/run-make-fulldeps/sanitizer-memory/maybeuninit.rs

@@ -0,0 +1,8 @@
+use std::mem::MaybeUninit;
+
+fn main() {
+    // This is technically not sound -- but we're literally trying to test
+    // that the sanitizer catches this, so I guess "intentionally unsound"?
+    let xs: [u8; 4] = unsafe { MaybeUninit::uninit().assume_init() };
+    let y = xs[0] + xs[1];
+}

src/test/run-make-fulldeps/sanitizer-memory/uninit.rs

@@ -1,7 +1,7 @@
-use std::mem;
-
 fn main() {
+    // This is technically not sound -- but we're literally trying to test
+    // that the sanitizer catches this, so I guess "intentionally unsound"?
     #[allow(deprecated)]
-    let xs: [u8; 4] = unsafe { mem::uninitialized() };
+    let xs: [u8; 4] = unsafe { std::mem::uninitialized() };
     let y = xs[0] + xs[1];
 }

src/test/rustdoc/issue-52873.rs

@@ -105,8 +105,7 @@ impl<U: Unsigned, B: Bit> Add<B0> for UInt<U, B> {
 impl<U: Unsigned> Add<U> for UTerm {
     type Output = U;
     fn add(self, _: U) -> Self::Output {
-        #[allow(deprecated)]
-        unsafe { ::std::mem::uninitialized() }
+        unimplemented!()
     }
 }
 
@@ -137,7 +136,7 @@ where
 {
     type Output = UInt<Prod<Ul, UInt<Ur, B>>, B0>;
     fn mul(self, _: UInt<Ur, B>) -> Self::Output {
-        unsafe { ::std::mem::uninitialized() }
+        unimplemented!()
     }
 }
 

src/test/ui/abi/stack-probes.rs

@@ -13,7 +13,7 @@
 // ignore-sgx no processes
 // ignore-musl FIXME #31506
 
-use std::mem;
+use std::mem::MaybeUninit;
 use std::process::Command;
 use std::thread;
 use std::env;
@@ -28,8 +28,8 @@ fn main() {
     let args = env::args().skip(1).collect::<Vec<_>>();
     if args.len() > 0 {
         match &args[0][..] {
-            "main-thread" => recurse(&[]),
-            "child-thread" => thread::spawn(|| recurse(&[])).join().unwrap(),
+            "main-thread" => recurse(&MaybeUninit::uninit()),
+            "child-thread" => thread::spawn(|| recurse(&MaybeUninit::uninit())).join().unwrap(),
             _ => panic!(),
         }
         return
@@ -48,10 +48,11 @@ fn main() {
 }
 
 #[allow(unconditional_recursion)]
-fn recurse(array: &[u64]) {
-    unsafe { black_box(array.as_ptr() as u64); }
-    #[allow(deprecated)]
-    let local: [_; 1024] = unsafe { mem::uninitialized() };
+fn recurse(array: &MaybeUninit<[u64; 1024]>) {
+    unsafe {
+        black_box(array.as_ptr() as u64);
+    }
+    let local: MaybeUninit<[u64; 1024]> = MaybeUninit::uninit();
     recurse(&local);
 }
 

src/test/ui/const-generics/issues/issue-61422.rs

@@ -5,6 +5,10 @@
 
 use std::mem;
 
+// Neither of the uninits below are currently accepted as not UB, however,
+// this code does not run and is merely checking that we do not ICE on this pattern,
+// so this is fine.
+
 fn foo<const SIZE: usize>() {
     let arr: [u8; SIZE] = unsafe {
         #[allow(deprecated)]
@@ -13,4 +17,12 @@ fn foo<const SIZE: usize>() {
     };
 }
 
+fn bar<const SIZE: usize>() {
+    let arr: [u8; SIZE] = unsafe {
+        let array: [u8; SIZE] = mem::MaybeUninit::uninit().assume_init();
+        array
+    };
+}
+
+
 fn main() {}

src/test/ui/for-loop-while/for-loop-has-unit-body.rs

@@ -2,8 +2,8 @@
 fn main() {
     // Check that the tail statement in the body unifies with something
     for _ in 0..3 {
-        #[allow(deprecated)]
-        unsafe { std::mem::uninitialized() }
+        // `()` is fine to zero-initialize as it is zero sized and inhabited.
+        unsafe { std::mem::zeroed() }
     }
 
     // Check that the tail statement in the body can be unit

src/test/ui/issues/issue-48131.rs

@@ -1,7 +1,7 @@
 // This note is annotated because the purpose of the test
 // is to ensure that certain other notes are not generated.
 #![deny(unused_unsafe)] //~ NOTE
-#![allow(deprecated)]
+
 
 // (test that no note is generated on this unsafe fn)
 pub unsafe fn a() {
@@ -20,8 +20,8 @@ pub fn b() {
             unsafe { /* unnecessary */ } //~ ERROR unnecessary `unsafe`
                                          //~^ NOTE
         }
-
-        let () = ::std::mem::uninitialized();
+        // `()` is fine to zero-initialize as it is zero sized and inhabited.
+        let () = ::std::mem::zeroed();
 
         inner()
     }

src/test/ui/issues/issue-58212.rs

@@ -1,13 +1,12 @@
-// run-pass
+// check-pass
 
 trait FromUnchecked {
-    unsafe fn from_unchecked();
+    fn from_unchecked();
 }
 
 impl FromUnchecked for [u8; 1] {
-    unsafe fn from_unchecked() {
-        #[allow(deprecated)]
-        let mut array: Self = std::mem::uninitialized();
+    fn from_unchecked() {
+        let mut array: Self = [0; 1];
         let _ptr = &mut array as *mut [u8] as *mut u8;
     }
 }

src/test/ui/structs-enums/enum-non-c-like-repr-c-and-int.rs

@@ -69,8 +69,10 @@ fn main() {
     unsafe {
         // This should be safe, because we don't match on it unless it's fully formed,
         // and it doesn't have a destructor.
-        #[allow(deprecated)]
-        let mut dest: MyEnum = mem::uninitialized();
+        //
+        // MyEnum is repr(C, u8) so it is guaranteed to have a separate discriminant and each
+        // variant can be zero initialized.
+        let mut dest: MyEnum = mem::zeroed();
         while buf.len() > 0 {
             match parse_my_enum(&mut dest, &mut buf) {
                 Ok(()) => output.push(Ok(dest)),