the private doctest now failes to compile for the right reason

Author: molpopgen

Cargo.toml

@@ -34,6 +34,7 @@ anyhow = {version = "1.0.66"}
 clap = {version = "~3.2.8", features = ["derive"]}
 serde = {version = "1.0.118", features = ["derive"]}
 serde-pickle = "1.1.0"
+serde_json = {version = "1.0.67"}
 bincode = "1.3.1"
 rand = "0.8.3"
 rand_distr = "0.4.0"

src/node_table.rs

@@ -282,7 +282,7 @@ pub struct NodeDefaults {
 ///
 /// See [the book](https://tskit-dev.github.io/tskit-rust/)
 /// for details.
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, Default)]
 pub struct NodeDefaultsWithMetadata<M>
 where
     M: crate::metadata::NodeMetadata,
@@ -362,6 +362,12 @@ where
 ///     value: i32,
 /// }
 ///
+/// impl Default for NodeMetadata {
+///     fn default() -> Self {
+///         Self{value: 0}
+///     }
+/// }
+///
 /// impl tskit::metadata::MetadataRoundtrip for NodeMetadata {
 ///     fn encode(&self) -> Result<Vec<u8>, tskit::metadata::MetadataError> {
 ///         match serde_json::to_string(self) {
@@ -398,6 +404,12 @@ where
 ///     value: i32,
 /// }
 ///
+/// impl Default for NodeMetadata {
+///     fn default() -> Self {
+///         Self{value: 0}
+///     }
+/// }
+///
 /// impl tskit::metadata::MetadataRoundtrip for NodeMetadata {
 ///     fn encode(&self) -> Result<Vec<u8>, tskit::metadata::MetadataError> {
 ///         match serde_json::to_string(self) {