nouns: function to assert a noun doesn't contain any forwarding pointers

rust/ares/src/noun.rs

@@ -895,6 +895,20 @@ impl Noun {
         Noun { raw }
     }
 
+    pub unsafe fn assert_no_forwarding_pointers(self) {
+        let mut dbg_stack = Vec::new();
+        dbg_stack.push(self);
+        while !dbg_stack.is_empty() {
+            let noun = dbg_stack.pop().unwrap();
+            if noun.raw & FORWARDING_MASK == FORWARDING_TAG {
+                panic!("Noun {:#x} has a forwarding pointer as a child", self.raw);
+            } else if let Ok(cell) = noun.as_cell() {
+                dbg_stack.push(cell.tail());
+                dbg_stack.push(cell.head());
+            }
+        }
+    }
+
     /** Produce the total size of a noun, in words
      *
      * This counts the total size, see mass_frame() to count the size in the current frame.