From 5bd58698d7f60937b3728e0937cdde66930ee373 Mon Sep 17 00:00:00 2001
From: Dirkjan Ochtman <dirkjan@ochtman.nl>
Date: Tue, 29 Nov 2022 12:14:24 +0100
Subject: [PATCH] Simplify logic for serializing prefixes

---
 instant-xml-macros/src/ser.rs |  6 +++---
 instant-xml/src/impls.rs      |  4 ++--
 instant-xml/src/ser.rs        | 34 ++++++++++++----------------------
 3 files changed, 17 insertions(+), 27 deletions(-)

diff --git a/instant-xml-macros/src/ser.rs b/instant-xml-macros/src/ser.rs
index 87f1a61..d5f93ed 100644
--- a/instant-xml-macros/src/ser.rs
+++ b/instant-xml-macros/src/ser.rs
@@ -54,7 +54,7 @@ fn serialize_scalar_enum(
             ) -> Result<(), instant_xml::Error> {
                 let prefix = match field {
                     Some(id) => {
-                        let prefix = serializer.write_start(id.name, id.ns, true)?;
+                        let prefix = serializer.write_start(id.name, id.ns)?;
                         serializer.end_start()?;
                         Some((prefix, id.name))
                     }
@@ -143,7 +143,7 @@ fn serialize_wrapped_enum(
                 serializer: &mut instant_xml::Serializer<W>,
             ) -> Result<(), instant_xml::Error> {
                 // Start tag
-                let prefix = serializer.write_start(#tag, #default_namespace, false)?;
+                let prefix = serializer.write_start(#tag, #default_namespace)?;
                 debug_assert_eq!(prefix, None);
 
                 // Set up element context, this will also emit namespace declarations
@@ -234,7 +234,7 @@ fn serialize_struct(
                 serializer: &mut instant_xml::Serializer<W>,
             ) -> Result<(), instant_xml::Error> {
                 // Start tag
-                let prefix = serializer.write_start(#tag, #default_namespace, false)?;
+                let prefix = serializer.write_start(#tag, #default_namespace)?;
                 debug_assert_eq!(prefix, None);
 
                 // Set up element context, this will also emit namespace declarations
diff --git a/instant-xml/src/impls.rs b/instant-xml/src/impls.rs
index ab2392f..ced4cc3 100644
--- a/instant-xml/src/impls.rs
+++ b/instant-xml/src/impls.rs
@@ -69,7 +69,7 @@ where
     ) -> Result<(), Error> {
         let prefix = match field {
             Some(id) => {
-                let prefix = serializer.write_start(id.name, id.ns, true)?;
+                let prefix = serializer.write_start(id.name, id.ns)?;
                 serializer.end_start()?;
                 Some((prefix, id.name))
             }
@@ -489,7 +489,7 @@ impl ToXml for DateTime<Utc> {
     ) -> Result<(), Error> {
         let prefix = match field {
             Some(id) => {
-                let prefix = serializer.write_start(id.name, id.ns, true)?;
+                let prefix = serializer.write_start(id.name, id.ns)?;
                 serializer.end_start()?;
                 Some((prefix, id.name))
             }
diff --git a/instant-xml/src/ser.rs b/instant-xml/src/ser.rs
index 18d1e74..773c8ca 100644
--- a/instant-xml/src/ser.rs
+++ b/instant-xml/src/ser.rs
@@ -28,35 +28,25 @@ impl<'xml, W: fmt::Write + ?Sized> Serializer<'xml, W> {
         }
     }
 
-    pub fn write_start(
-        &mut self,
-        name: &str,
-        ns: &str,
-        scalar: bool,
-    ) -> Result<Option<&'static str>, Error> {
+    pub fn write_start(&mut self, name: &str, ns: &str) -> Result<Option<&'static str>, Error> {
         if self.state != State::Element {
             return Err(Error::UnexpectedState("invalid state for element start"));
         }
 
-        let prefix = match ns == self.default_ns {
-            true => {
+        let prefix = match (ns == self.default_ns, self.prefixes.get(ns)) {
+            (true, _) => {
                 self.output.write_fmt(format_args!("<{name}"))?;
                 None
             }
-            // In the case of scalars, we can use the prefix instead of setting a
-            // default namespace (since there are no child elements that will
-            // expect the default namespace to be set).
-            false => match (scalar, self.prefixes.get(ns)) {
-                (false, _) | (true, None) => {
-                    self.output
-                        .write_fmt(format_args!("<{name} xmlns=\"{ns}\""))?;
-                    None
-                }
-                (true, Some(&prefix)) => {
-                    self.output.write_fmt(format_args!("<{prefix}:{name}"))?;
-                    Some(prefix)
-                }
-            },
+            (false, Some(prefix)) => {
+                self.output.write_fmt(format_args!("<{prefix}:{name}"))?;
+                Some(*prefix)
+            }
+            _ => {
+                self.output
+                    .write_fmt(format_args!("<{name} xmlns=\"{ns}\""))?;
+                None
+            }
         };
 
         self.state = State::Attribute;