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::process::Command;
 use std::thread;
 use std::env;
@@ -50,8 +50,7 @@ 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() };
+    let local: [u64; 1024] = [0; 1024];
     recurse(&local);
 }
 

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

@@ -7,8 +7,8 @@ use std::mem;
 
 fn foo<const SIZE: usize>() {
     let arr: [u8; SIZE] = unsafe {
-        #[allow(deprecated)]
-        let array: [u8; SIZE] = mem::uninitialized();
+
+        let array: [u8; SIZE] = mem::zeroed();
         array
     };
 }

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

@@ -2,8 +2,7 @@
 fn main() {
     // Check that the tail statement in the body unifies with something
     for _ in 0..3 {
-        #[allow(deprecated)]
-        unsafe { std::mem::uninitialized() }
+        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() {
@@ -21,7 +21,7 @@ pub fn b() {
                                          //~^ NOTE
         }
 
-        let () = ::std::mem::uninitialized();
+        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();
 }
 
 impl FromUnchecked for [u8; 1] {
     unsafe fn from_unchecked() {
-        #[allow(deprecated)]
-        let mut array: Self = std::mem::uninitialized();
+        let mut array: Self = std::mem::zeroed();
         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 +69,7 @@ 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();
+        let mut dest: MyEnum = mem::zeroed();
         while buf.len() > 0 {
             match parse_my_enum(&mut dest, &mut buf) {
                 Ok(()) => output.push(Ok(dest)),

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

@@ -69,8 +69,7 @@ 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();
+        let mut dest: MyEnum = mem::zeroed();
         while buf.len() > 0 {
             match parse_my_enum(&mut dest, &mut buf) {
                 Ok(()) => output.push(Ok(dest)),

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

@@ -65,8 +65,7 @@ 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();
+        let mut dest: MyEnum = mem::zeroed();
         while buf.len() > 0 {
             match parse_my_enum(&mut dest, &mut buf) {
                 Ok(()) => output.push(Ok(dest)),

src/test/ui/uninhabited/uninhabited-matches-feature-gated.rs

@@ -1,4 +1,4 @@
-#![allow(deprecated)]
+use std::mem::zeroed;
 
 enum Void {}
 
@@ -8,21 +8,25 @@ fn main() {
         Ok(n) => n,
     };
 
-    let x: &Void = unsafe { std::mem::uninitialized() };
+    // This is pretty much instant UB. However, we have no choice -- we need to
+    // test matching on a reference to `&Void`; we cannot do anything other than
+    // just accept the fact that this is UB if `main` did run, but it doesn't;
+    // this test only checks that these are feature-gated.
+    let x: &Void = unsafe { zeroed() };
     let _ = match x {}; //~ ERROR non-exhaustive
 
-    let x: (Void,) = unsafe { std::mem::uninitialized() };
+    let x: (Void,) = unsafe { zeroed() };
     let _ = match x {}; //~ ERROR non-exhaustive
 
-    let x: [Void; 1] = unsafe { std::mem::uninitialized() };
+    let x: [Void; 1] = unsafe { zeroed() };
     let _ = match x {}; //~ ERROR non-exhaustive
 
-    let x: &[Void] = unsafe { std::mem::uninitialized() };
+    let x: &[Void] = unsafe { zeroed() };
     let _ = match x {   //~ ERROR non-exhaustive
         &[] => (),
     };
 
-    let x: Void = unsafe { std::mem::uninitialized() };
+    let x: Void = unsafe { zeroed() };
     let _ = match x {}; // okay
 
     let x: Result<u32, Void> = Ok(23);

src/test/ui/uninhabited/uninhabited-matches-feature-gated.stderr

@@ -7,7 +7,7 @@ LL |     let _ = match x {
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
 
 error[E0004]: non-exhaustive patterns: type `&Void` is non-empty
-  --> $DIR/uninhabited-matches-feature-gated.rs:12:19
+  --> $DIR/uninhabited-matches-feature-gated.rs:15:19
    |
 LL | enum Void {}
    | ------------ `Void` defined here
@@ -18,39 +18,39 @@ LL |     let _ = match x {};
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
 
 error[E0004]: non-exhaustive patterns: type `(Void,)` is non-empty
-  --> $DIR/uninhabited-matches-feature-gated.rs:15:19
+  --> $DIR/uninhabited-matches-feature-gated.rs:18:19
    |
 LL |     let _ = match x {};
    |                   ^
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
 
 error[E0004]: non-exhaustive patterns: type `[Void; 1]` is non-empty
-  --> $DIR/uninhabited-matches-feature-gated.rs:18:19
+  --> $DIR/uninhabited-matches-feature-gated.rs:21:19
    |
 LL |     let _ = match x {};
    |                   ^
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
 
 error[E0004]: non-exhaustive patterns: `&[_, ..]` not covered
-  --> $DIR/uninhabited-matches-feature-gated.rs:21:19
+  --> $DIR/uninhabited-matches-feature-gated.rs:24:19
    |
 LL |     let _ = match x {
    |                   ^ pattern `&[_, ..]` not covered
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
 
 error[E0004]: non-exhaustive patterns: `Err(_)` not covered
-  --> $DIR/uninhabited-matches-feature-gated.rs:29:19
+  --> $DIR/uninhabited-matches-feature-gated.rs:32:19
    |
 LL |     let _ = match x {
    |                   ^ pattern `Err(_)` not covered
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
 
 error[E0005]: refutable pattern in local binding: `Err(_)` not covered
-  --> $DIR/uninhabited-matches-feature-gated.rs:34:9
+  --> $DIR/uninhabited-matches-feature-gated.rs:37:9
    |
 LL |     let Ok(x) = x;
    |         ^^^^^ pattern `Err(_)` not covered

src/test/ui/uninit-empty-types.rs

@@ -3,15 +3,18 @@
 
 // pretty-expanded FIXME #23616
 
-use std::mem;
+use std::mem::MaybeUninit;
 
 #[derive(Clone)]
 struct Foo;
 
 #[allow(deprecated)]
 pub fn main() {
     unsafe {
-        let _x: Foo = mem::uninitialized();
-        let _x: [Foo; 2] = mem::uninitialized();
+        // `Foo` and `[Foo; 2]` are both zero sized so this is safe.
+        let _x: Foo = MaybeUninit::uninit().assume_init();
+        let _x: [Foo; 2] = MaybeUninit::uninit().assume_init();
+        let _x: Foo = std::mem::uninitialized();
+        let _x: [Foo; 2] = std::mem::uninitialized();
     }
 }