avoid 'let _' in tests where we actually want the value to be computed

Author: RalfJung

src/tools/miri/tests/fail/both_borrows/aliasing_mut4.rs

@@ -8,7 +8,7 @@ use std::mem;
 pub fn safe(x: &i32, y: &mut Cell<i32>) {
     //~[stack]^ ERROR: protect
     y.set(1);
-    let _ = *x;
+    let _load = *x;
 }
 
 fn main() {

src/tools/miri/tests/fail/dangling_pointers/storage_dead_dangling.rs

@@ -10,7 +10,7 @@ fn fill(v: &mut i32) {
 }
 
 fn evil() {
-    let _ = unsafe { &mut *(LEAK as *mut i32) }; //~ ERROR: is a dangling pointer
+    let _ref = unsafe { &mut *(LEAK as *mut i32) }; //~ ERROR: is a dangling pointer
 }
 
 fn main() {

src/tools/miri/tests/fail/dangling_pointers/storage_dead_dangling.stderr

@@ -1,8 +1,8 @@
 error: Undefined Behavior: out-of-bounds pointer use: $HEX[noalloc] is a dangling pointer (it has no provenance)
   --> $DIR/storage_dead_dangling.rs:LL:CC
    |
-LL |     let _ = unsafe { &mut *(LEAK as *mut i32) };
-   |                      ^^^^^^^^^^^^^^^^^^^^^^^^ out-of-bounds pointer use: $HEX[noalloc] is a dangling pointer (it has no provenance)
+LL |     let _ref = unsafe { &mut *(LEAK as *mut i32) };
+   |                         ^^^^^^^^^^^^^^^^^^^^^^^^ out-of-bounds pointer use: $HEX[noalloc] is a dangling pointer (it has no provenance)
    |
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information

src/tools/miri/tests/pass/adjacent-allocs.rs

@@ -30,7 +30,7 @@ fn test1() {
         // See https://github.com/rust-lang/miri/issues/1866#issuecomment-985770125
         {
             let m = 0u64;
-            let _ = &m as *const u64;
+            let _ptr = &m as *const u64;
         }
 
         let iptr = ptr as usize;

src/tools/miri/tests/pass/dyn-upcast.rs

@@ -69,7 +69,7 @@ fn basic() {
     }
 
     let baz: &dyn Baz = &1;
-    let _: &dyn fmt::Debug = baz;
+    let _up: &dyn fmt::Debug = baz;
     assert_eq!(*baz, 1);
     assert_eq!(baz.a(), 100);
     assert_eq!(baz.b(), 200);
@@ -79,7 +79,7 @@ fn basic() {
     assert_eq!(baz.w(), 21);
 
     let bar: &dyn Bar = baz;
-    let _: &dyn fmt::Debug = bar;
+    let _up: &dyn fmt::Debug = bar;
     assert_eq!(*bar, 1);
     assert_eq!(bar.a(), 100);
     assert_eq!(bar.b(), 200);
@@ -88,14 +88,14 @@ fn basic() {
     assert_eq!(bar.w(), 21);
 
     let foo: &dyn Foo = baz;
-    let _: &dyn fmt::Debug = foo;
+    let _up: &dyn fmt::Debug = foo;
     assert_eq!(*foo, 1);
     assert_eq!(foo.a(), 100);
     assert_eq!(foo.z(), 11);
     assert_eq!(foo.y(), 12);
 
     let foo: &dyn Foo = bar;
-    let _: &dyn fmt::Debug = foo;
+    let _up: &dyn fmt::Debug = foo;
     assert_eq!(*foo, 1);
     assert_eq!(foo.a(), 100);
     assert_eq!(foo.z(), 11);
@@ -168,7 +168,7 @@ fn diamond() {
     }
 
     let baz: &dyn Baz = &1;
-    let _: &dyn fmt::Debug = baz;
+    let _up: &dyn fmt::Debug = baz;
     assert_eq!(*baz, 1);
     assert_eq!(baz.a(), 100);
     assert_eq!(baz.b(), 200);
@@ -180,7 +180,7 @@ fn diamond() {
     assert_eq!(baz.v(), 31);
 
     let bar1: &dyn Bar1 = baz;
-    let _: &dyn fmt::Debug = bar1;
+    let _up: &dyn fmt::Debug = bar1;
     assert_eq!(*bar1, 1);
     assert_eq!(bar1.a(), 100);
     assert_eq!(bar1.b(), 200);
@@ -189,7 +189,7 @@ fn diamond() {
     assert_eq!(bar1.w(), 21);
 
     let bar2: &dyn Bar2 = baz;
-    let _: &dyn fmt::Debug = bar2;
+    let _up: &dyn fmt::Debug = bar2;
     assert_eq!(*bar2, 1);
     assert_eq!(bar2.a(), 100);
     assert_eq!(bar2.c(), 300);
@@ -198,17 +198,17 @@ fn diamond() {
     assert_eq!(bar2.v(), 31);
 
     let foo: &dyn Foo = baz;
-    let _: &dyn fmt::Debug = foo;
+    let _up: &dyn fmt::Debug = foo;
     assert_eq!(*foo, 1);
     assert_eq!(foo.a(), 100);
 
     let foo: &dyn Foo = bar1;
-    let _: &dyn fmt::Debug = foo;
+    let _up: &dyn fmt::Debug = foo;
     assert_eq!(*foo, 1);
     assert_eq!(foo.a(), 100);
 
     let foo: &dyn Foo = bar2;
-    let _: &dyn fmt::Debug = foo;
+    let _up: &dyn fmt::Debug = foo;
     assert_eq!(*foo, 1);
     assert_eq!(foo.a(), 100);
 }