Set up test cases which demonstrate the issue.

Author: jumbatm

src/test/ui/associated-const/lints-used-unused.rs

@@ -0,0 +1,27 @@
+// Tests that associated constants are checked whether they are used or not.
+//
+// revisions: used unused
+// compile-flags: -Copt-level=2 --emit link
+
+#![cfg_attr(unused, allow(dead_code))]
+#![deny(arithmetic_overflow)]
+
+pub trait Foo {
+    const N: i32;
+}
+
+struct S;
+
+impl Foo for S {
+    const N: i32 = 1 << 42;
+    //~^ ERROR this arithmetic operation will overflow
+}
+
+impl<T: Foo> Foo for Vec<T> {
+    const N: i32 = --T::N + (-i32::MIN); //~ ERROR this arithmetic operation will overflow
+}
+
+fn main() {
+    #[cfg(used)]
+    let _ = S::N; //[used]~ ERROR erroneous constant used
+}

src/test/ui/lint/lint-exceeding-bitshifts.rs

@@ -15,7 +15,7 @@ pub trait Foo {
 }
 
 impl<T: Foo> Foo for Vec<T> {
-    const N: i32 = T::N << 42; // FIXME this should warn
+    const N: i32 = T::N << 42; // ERROR: arithmetic operation will overflow
 }
 
 pub fn foo(x: i32) {