Add false negative test for uninit_assumed_init

Author: Jarcho

tests/ui/repl_uninit.rs

@@ -1,5 +1,5 @@
-#![allow(deprecated, invalid_value)]
-#![warn(clippy::all)]
+#![allow(deprecated, invalid_value, clippy::uninit_assumed_init)]
+#![warn(clippy::mem_replace_with_uninit)]
 
 use std::mem;
 

tests/ui/repl_uninit.stderr

@@ -12,14 +12,6 @@ error: replacing with `mem::MaybeUninit::uninit().assume_init()`
 LL |         let taken_v = mem::replace(&mut v, mem::MaybeUninit::uninit().assume_init());
    |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `std::ptr::read(&mut v)`
 
-error: this call for this type may be undefined behavior
-  --> $DIR/repl_uninit.rs:21:44
-   |
-LL |         let taken_v = mem::replace(&mut v, mem::MaybeUninit::uninit().assume_init());
-   |                                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: `-D clippy::uninit-assumed-init` implied by `-D warnings`
-
 error: replacing with `mem::zeroed()`
   --> $DIR/repl_uninit.rs:27:23
    |
@@ -34,5 +26,5 @@ error: replacing with `mem::uninitialized()`
 LL |     let taken_u = unsafe { mem::replace(uref, mem::uninitialized()) };
    |                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `std::ptr::read(uref)`
 
-error: aborting due to 5 previous errors
+error: aborting due to 4 previous errors
 

tests/ui/uninit.rs

@@ -1,6 +1,6 @@
 #![feature(stmt_expr_attributes)]
 
-use std::mem::MaybeUninit;
+use std::mem::{self, MaybeUninit};
 
 fn main() {
     let _: usize = unsafe { MaybeUninit::uninit().assume_init() };
@@ -19,4 +19,7 @@ fn main() {
 
     // This is OK, because all constitutent types are uninit-compatible.
     let _: (MaybeUninit<usize>, [MaybeUninit<bool>; 2]) = unsafe { MaybeUninit::uninit().assume_init() };
+
+    // Was a false negative.
+    let _: usize = unsafe { mem::MaybeUninit::uninit().assume_init() };
 }

tests/ui/uninit.stderr

@@ -12,5 +12,11 @@ error: this call for this type may be undefined behavior
 LL |     let _: [u8; 0] = unsafe { MaybeUninit::uninit().assume_init() };
    |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 2 previous errors
+error: this call for this type may be undefined behavior
+  --> $DIR/uninit.rs:24:29
+   |
+LL |     let _: usize = unsafe { mem::MaybeUninit::uninit().assume_init() };
+   |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 3 previous errors