remove prefix for default namespace

yaserde/tests/ser_namespace.rs

@@ -182,6 +182,29 @@ fn ser_struct_default_namespace_via_attribute() {
   convert_and_validate!(model, content);
 }
 
+#[test]
+fn ser_struct_default_namespace_via_attribute_with_prefix() {
+  #[derive(YaSerialize, PartialEq, Debug)]
+  #[yaserde(
+    root = "tt",
+    prefix = "TTML",
+    default_namespace = "TTML",
+    namespace = "TTML: http://www.w3.org/ns/ttml",
+    namespace = "ttm: http://www.w3.org/ns/ttml#metadata"
+  )]
+  pub struct XmlStruct {
+    #[yaserde(prefix="TTML")]
+    item: String,
+  }
+
+  let model = XmlStruct {
+    item: "something".to_string(),
+  };
+
+  let content = "<?xml version=\"1.0\" encoding=\"utf-8\"?><tt xmlns=\"http://www.w3.org/ns/ttml\" xmlns:ttm=\"http://www.w3.org/ns/ttml#metadata\"><item>something</item></tt>";
+  convert_and_validate!(model, content);
+}
+
 #[test]
 fn ser_struct_namespace_nested() {
   #[derive(YaSerialize, Default, PartialEq, Debug)]

yaserde_derive/src/ser/expand_struct.rs

@@ -27,7 +27,7 @@ pub fn serialize(
 
       let label = &field.ident;
 
-      let label_name = build_label_name(&field, &field_attrs);
+      let label_name = build_label_name(&field, &field_attrs, default_namespace);
 
       get_field_type(field).and_then(|f| match f {
         FieldType::FieldTypeString
@@ -240,7 +240,7 @@ pub fn serialize(
         ));
       }
 
-      let label_name = build_label_name(&field, &field_attrs);
+      let label_name = build_label_name(&field, &field_attrs, default_namespace);
       let conditions = condition_generator(label, &field_attrs);
 
       get_field_type(field).and_then(|f| match f {
@@ -411,16 +411,22 @@ pub fn serialize(
   }
 }
 
-fn build_label_name(field: &syn::Field, field_attrs: &YaSerdeAttribute) -> String {
-  format!(
-    "{}{}",
-    field_attrs
-      .prefix
-      .clone()
-      .map_or("".to_string(), |prefix| prefix + ":"),
+fn build_label_name(field: &syn::Field, field_attrs: &YaSerdeAttribute, default_namespace: &Option<String>) -> String {
+  let prefix =
+    if default_namespace == &field_attrs.prefix {
+      "".to_string()
+    } else {
+      field_attrs
+        .prefix
+        .clone()
+        .map_or("".to_string(), |prefix| prefix + ":")
+    };
+
+  let label =
     field_attrs
       .rename
       .clone()
-      .unwrap_or_else(|| field.ident.as_ref().unwrap().to_string())
-  )
+      .unwrap_or_else(|| field.ident.as_ref().unwrap().to_string());
+
+  format!("{}{}", prefix, label)
 }

yaserde_derive/src/ser/mod.rs

@@ -15,11 +15,14 @@ pub fn expand_derive_serialize(ast: &syn::DeriveInput) -> Result<TokenStream, St
   let root_attrs = attribute::YaSerdeAttribute::parse(attrs);
   let root = root_attrs.clone().root.unwrap_or_else(|| name.to_string());
 
-  let root = if let Some(prefix) = root_attrs.prefix {
-    prefix + ":" + &root
-  } else {
-    root
-  };
+  let prefix =
+    if root_attrs.default_namespace == root_attrs.prefix {
+      "".to_string()
+    } else {
+      root_attrs.prefix.map_or("".to_string(), |prefix| prefix + ":")
+    };
+
+  let root = format!("{}{}", prefix, root);
 
   let impl_block = match *data {
     syn::Data::Struct(ref data_struct) => expand_struct::serialize(