Serialize empty elements more efficiently

instant-xml-macros/src/ser.rs

@@ -177,26 +177,31 @@ fn serialize_struct(
     data: &syn::DataStruct,
     meta: ContainerMeta,
 ) -> proc_macro2::TokenStream {
+    let tag = meta.tag();
     let mut body = TokenStream::new();
     let mut attributes = TokenStream::new();
 
     match &data.fields {
         syn::Fields::Named(fields) => {
+            body.extend(quote!(serializer.end_start()?;));
             for field in &fields.named {
                 if let Err(err) = named_field(field, &mut body, &mut attributes, &meta) {
                     return err.to_compile_error();
                 }
             }
+            body.extend(quote!(serializer.write_close(prefix, #tag)?;));
         }
         syn::Fields::Unnamed(fields) => {
+            body.extend(quote!(serializer.end_start()?;));
             for (index, field) in fields.unnamed.iter().enumerate() {
                 if let Err(err) = unnamed_field(field, index, &mut body) {
                     return err.to_compile_error();
                 }
             }
+            body.extend(quote!(serializer.write_close(prefix, #tag)?;));
         }
-        syn::Fields::Unit => {}
-    };
+        syn::Fields::Unit => body.extend(quote!(serializer.end_empty()?;)),
+    }
 
     let default_namespace = meta.default_namespace();
     let cx_len = meta.ns.prefixes.len();
@@ -221,7 +226,6 @@ fn serialize_struct(
     let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
     let tag = meta.tag();
     let ident = &input.ident;
-
     quote!(
         impl #impl_generics ToXml for #ident #ty_generics #where_clause {
             fn serialize<W: ::core::fmt::Write + ?::core::marker::Sized>(
@@ -239,14 +243,9 @@ fn serialize_struct(
 
                 // Finalize start element
                 #attributes
-                serializer.end_start()?;
-
                 #body
 
-                // Close tag
-                serializer.write_close(prefix, #tag)?;
                 serializer.pop(old);
-
                 Ok(())
             }
 

instant-xml/src/ser.rs

@@ -111,6 +111,16 @@ impl<'xml, W: fmt::Write + ?Sized> Serializer<'xml, W> {
         Ok(())
     }
 
+    pub fn end_empty(&mut self) -> Result<(), Error> {
+        if self.state != State::Attribute {
+            return Err(Error::UnexpectedState("invalid state for element end"));
+        }
+
+        self.output.write_str(" />")?;
+        self.state = State::Element;
+        Ok(())
+    }
+
     pub fn write_close(&mut self, prefix: Option<&str>, name: &str) -> Result<(), Error> {
         if self.state != State::Element {
             return Err(Error::UnexpectedState("invalid state for close element"));

instant-xml/tests/ser-unit.rs

@@ -7,6 +7,5 @@ struct Unit;
 
 #[test]
 fn unit() {
-    assert_eq!(to_string(&Unit).unwrap(), "<Unit></Unit>");
-    //assert_eq!(Unit::from_xml("<Unit/>").unwrap(), Unit);
+    assert_eq!(to_string(&Unit).unwrap(), "<Unit />");
 }

instant-xml/tests/unnamed.rs

@@ -33,7 +33,7 @@ struct Foo;
 #[test]
 fn string_element() {
     let v = StringElement("f42".to_owned(), Foo);
-    let xml = r#"<StringElement>f42<Foo></Foo></StringElement>"#;
+    let xml = r#"<StringElement>f42<Foo /></StringElement>"#;
     assert_eq!(xml, to_string(&v).unwrap());
     assert_eq!(v, from_str(xml).unwrap());
 }