Implement Display for Id newtypes.

src/_macros.rs

@@ -266,6 +266,15 @@ macro_rules! impl_id_traits {
             }
         }
 
+        impl std::fmt::Display for $idtype {
+            fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+                match *self == Self::NULL {
+                    false => write!(f, "{}({})", stringify!($idtype), self.0),
+                    true => write!(f, "{}(NULL)", stringify!($idtype)),
+                }
+            }
+        }
+
         impl From<$crate::tsk_id_t> for $idtype {
             fn from(value: $crate::tsk_id_t) -> Self {
                 Self(value)

src/lib.rs

@@ -149,6 +149,17 @@ pub use bindings::tsk_size_t;
 /// assert_eq!(interesting(x), x);
 /// ```
 ///
+/// The types also implement `Display`:
+///
+/// ```
+/// use tskit::NodeId;
+///
+/// let n = NodeId::from(11);
+/// assert_eq!(format!("{}", n), "NodeId(11)".to_string());
+/// let n = NodeId::from(NodeId::NULL);
+/// assert_eq!(format!("{}", n), "NodeId(NULL)".to_string());
+/// ```
+///
 #[repr(transparent)]
 #[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd, std::hash::Hash)]
 pub struct NodeId(tsk_id_t);

src/provenance.rs

@@ -127,12 +127,6 @@ impl PartialEq for ProvenanceTableRow {
     }
 }
 
-impl std::fmt::Display for ProvenanceId {
-    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
-        write!(f, "ProvenanceId({})", self.0)
-    }
-}
-
 impl std::fmt::Display for ProvenanceTableRow {
     fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
         write!(