From 31d7bbf622fc701552cc72678ccf2c56165eaf9a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jonas=20Sch=C3=A4fer?= <jonas@zombofant.net>
Date: Fri, 18 Apr 2025 19:42:42 +0200
Subject: [PATCH] xso: discard xml:lang implicitly

Because this attribute may occur in random places, it makes no sense
failing on it. We discard it after attribute processing though, so it
can still be captured by structs which are explicitly interested in it.
---
 parsers/src/util/macro_tests.rs | 17 +++++++++++++++++
 xso-proc/src/compound.rs        |  6 +++++-
 xso/ChangeLog                   |  5 +++++
 3 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/parsers/src/util/macro_tests.rs b/parsers/src/util/macro_tests.rs
index 70bbffb90979a522a5c35ed135f3353cbb7aa87f..a477ed9495478865fcdc96bb0bcaa984cbf01d69 100644
--- a/parsers/src/util/macro_tests.rs
+++ b/parsers/src/util/macro_tests.rs
@@ -139,6 +139,23 @@ fn empty_unexpected_attribute() {
     }
 }
 
+#[test]
+#[cfg_attr(
+    feature = "disable-validation",
+    should_panic = "unexpected result: Ok("
+)]
+fn empty_ignores_xml_lang() {
+    #[allow(unused_imports)]
+    use core::{
+        option::Option::{None, Some},
+        result::Result::{Err, Ok},
+    };
+    match parse_str::<Empty>("<foo xmlns='urn:example:ns1' xml:lang='bar'/>") {
+        Ok(Empty) => (),
+        other => panic!("unexpected result: {:?}", other),
+    }
+}
+
 #[test]
 #[cfg_attr(
     feature = "disable-validation",
diff --git a/xso-proc/src/compound.rs b/xso-proc/src/compound.rs
index bf149119932d4e15b4785cbe673fd3edfba1ee2f..d91fa8c3a5244afcb623e17d61faec5974d8ea0b 100644
--- a/xso-proc/src/compound.rs
+++ b/xso-proc/src/compound.rs
@@ -396,7 +396,11 @@ impl Compound {
             }
         }
 
-        let mut discard_attr = TokenStream::default();
+        // We always implicitly discard the `xml:lang` attribute. Its
+        // processing is handled using the `#[xml(language)]` meta.
+        let mut discard_attr = quote! {
+            let _ = #attrs.remove(::xso::exports::rxml::Namespace::xml(), "lang");
+        };
         for (xml_namespace, xml_name) in self.discard_attr.iter() {
             let xml_namespace = match xml_namespace {
                 Some(v) => v.to_token_stream(),
diff --git a/xso/ChangeLog b/xso/ChangeLog
index f00527a662f386444d2c3609f7d0dd369a4aed61..002c8236c57d6ac501b4c36082f22fcb618c8282 100644
--- a/xso/ChangeLog
+++ b/xso/ChangeLog
@@ -12,6 +12,11 @@ Version NEXT:
 
         This change overall allows for more flexibility in the implementation
         of text codecs.
+      - `xml:lang` attributes are now silently discarded during
+        deserialisation unless captured by `#[xml(attribute = "xml:lang")]` or
+        equivalent. This is because `xml:lang` is special as per
+        XML 1.0 § 2.12 and it is generally preferable to allow it to occur
+        anywhere in the document.
     * Added
       - Support for child elements in derive macros. Child elements may also
         be wrapped in Option or Box or in containers like Vec or HashSet.