Disallow to optimise out constants in OOB tests

Apparently our constant errors are only reported if there’s a use in MIR for that constant. This means that in these tests `let _ = B` is seen as a no-op use and thus is optimised out. Explicitly drop() the B to make sure it is not optimised (yet, until the inliner happens). NB: the `let _ = B` statement discussed here has no side effects (such as Drop implementation).
rust-lang · nagisa · Aug 2, 2016 · Aug 2, 2016 · Aug 2, 2016 · Aug 5, 2016
commit 3e2e8b9cd7dbe4779578d6b956f4762bc0ece913
diff --git a/src/test/compile-fail/array_const_index-0.rs b/src/test/compile-fail/array_const_index-0.rs
@@ -14,5 +14,5 @@ const B: i32 = (&A)[1];
 //~| index out of bounds: the len is 0 but the index is 1
 
 fn main() {
-    let _ = B;
+    drop(B);
 }
diff --git a/src/test/compile-fail/array_const_index-1.rs b/src/test/compile-fail/array_const_index-1.rs
@@ -14,5 +14,5 @@ const B: i32 = A[1];
 //~| index out of bounds: the len is 0 but the index is 1
 
 fn main() {
-    let _ = B;
+    drop(B);
 }
diff --git a/src/test/compile-fail/const-array-oob.rs b/src/test/compile-fail/const-array-oob.rs
@@ -20,5 +20,5 @@ const BLUB: [u32; FOO[4]] = [5, 6];
 //~| index out of bounds: the len is 3 but the index is 4
 
 fn main() {
-    let _ = BAR;
+    drop(BAR);
 }
diff --git a/src/test/compile-fail/const-slice-oob.rs b/src/test/compile-fail/const-slice-oob.rs
@@ -14,5 +14,5 @@ const BAR: u32 = FOO[5];
 //~| index out of bounds: the len is 3 but the index is 5
 
 fn main() {
-    let _ = BAR;
+    drop(BAR);
 }