Add and use OnDrop::disable

src/librustc_data_structures/lib.rs

@@ -80,6 +80,14 @@ pub mod sorted_map;
 
 pub struct OnDrop<F: Fn()>(pub F);
 
+impl<F: Fn()> OnDrop<F> {
+      /// Forgets the function which prevents it from running.
+      /// Ensure that the function owns no memory, otherwise it will be leaked.
+      pub fn disable(self) {
+            std::mem::forget(self);
+      }
+}
+
 impl<F: Fn()> Drop for OnDrop<F> {
       fn drop(&mut self) {
             (self.0)();