Skip serializing empty libs

src/designspace.rs

@@ -29,7 +29,7 @@ pub struct DesignSpaceDocument {
     #[serde(default, with = "serde_impls::instances", skip_serializing_if = "Vec::is_empty")]
     pub instances: Vec<Instance>,
     /// Additional arbitrary user data
-    #[serde(default, with = "serde_plist")]
+    #[serde(default, with = "serde_plist", skip_serializing_if = "Dictionary::is_empty")]
     pub lib: Dictionary,
 }
 
@@ -140,7 +140,7 @@ pub struct Instance {
     #[serde(with = "serde_impls::location")]
     pub location: Vec<Dimension>,
     /// Arbitrary data about this instance
-    #[serde(default, with = "serde_plist")]
+    #[serde(default, with = "serde_plist", skip_serializing_if = "Dictionary::is_empty")]
     pub lib: Dictionary,
 }
 
@@ -389,6 +389,15 @@ mod tests {
         );
     }
 
+    #[test]
+    fn do_not_serialize_empty_lib() {
+        let ds_initial = DesignSpaceDocument::load("testdata/single_wght.designspace").unwrap();
+        let serialized = quick_xml::se::to_string(&ds_initial).expect("should serialize");
+
+        assert!(!serialized.contains("<lib>"));
+        assert!(!serialized.contains("<lib/>"));
+    }
+
     #[test]
     fn load_save_round_trip() {
         // Given