add another compile-fail test for validation

tests/compile-fail/validation_buggy_as_mut_slice.rs

@@ -0,0 +1,20 @@
+#![allow(unused_variables)]
+
+// For some reason, the error location is different when using fullmir
+// error-pattern: in conflict with lock WriteLock
+
+mod safe {
+    use std::slice::from_raw_parts_mut;
+
+    pub fn as_mut_slice<T>(self_: &Vec<T>) -> &mut [T] {
+        unsafe {
+            from_raw_parts_mut(self_.as_ptr() as *mut T, self_.len())
+        }
+    }
+}
+
+fn main() {
+    let v = vec![0,1,2];
+    let v1_ = safe::as_mut_slice(&v);
+    let v2_ = safe::as_mut_slice(&v);
+}