5 files changed, 24 insertions, 5 deletions
diff --git a/tvix/eval/src/builtins/to_xml.rs b/tvix/eval/src/builtins/to_xml.rs
index 250891b60d99..f23cb22db3d9 100644
--- a/tvix/eval/src/builtins/to_xml.rs
+++ b/tvix/eval/src/builtins/to_xml.rs
@@ -90,15 +90,22 @@ fn value_variant_to_xml<W: Write>(w: &mut EventWriter<W>, value: &Value) -> Resu
 
             match &c.lambda.formals {
                 Some(formals) => {
+                    let mut attrspat = XmlEvent::start_element("attrspat");
                     if formals.ellipsis {
-                        w.write(XmlEvent::start_element("attrspat").attr("ellipsis", "1"))?;
-                        w.write(XmlEvent::end_element())?;
+                        attrspat = attrspat.attr("ellipsis", "1");
+                    }
+                    if let Some(ref name) = &formals.name {
+                        attrspat = attrspat.attr("name", name.as_str());
                     }
 
+                    w.write(attrspat)?;
+
                     for arg in formals.arguments.iter() {
                         w.write(XmlEvent::start_element("attr").attr("name", arg.0.as_str()))?;
                         w.write(XmlEvent::end_element())?;
                     }
+
+                    w.write(XmlEvent::end_element())?;
                 }
                 None => {
                     // TODO(tazjin): tvix does not currently persist function
diff --git a/tvix/eval/src/compiler/mod.rs b/tvix/eval/src/compiler/mod.rs
index 4bb734290c3e..53a99a453d9e 100644
--- a/tvix/eval/src/compiler/mod.rs
+++ b/tvix/eval/src/compiler/mod.rs
@@ -973,9 +973,16 @@ impl Compiler<'_> {
     ///    cases.
     fn compile_param_pattern(&mut self, pattern: &ast::Pattern) -> (Formals, CodeIdx) {
         let span = self.span_for(pattern);
-        let set_idx = match pattern.pat_bind() {
-            Some(name) => self.declare_local(&name, name.ident().unwrap().to_string()),
-            None => self.scope_mut().declare_phantom(span, true),
+
+        let (set_idx, pat_bind_name) = match pattern.pat_bind() {
+            Some(name) => {
+                let pat_bind_name = name.ident().unwrap().to_string();
+                (
+                    self.declare_local(&name, pat_bind_name.clone()),
+                    Some(pat_bind_name),
+                )
+            }
+            None => (self.scope_mut().declare_phantom(span, true), None),
         };
 
         // At call time, the attribute set is already at the top of the stack.
@@ -1126,6 +1133,7 @@ impl Compiler<'_> {
                 arguments,
                 ellipsis,
                 span,
+                name: pat_bind_name,
             }),
             throw_idx,
         )
diff --git a/tvix/eval/src/tests/nix_tests/notyetpassing/eval-okay-xml.exp.xml b/tvix/eval/src/tests/nix_tests/eval-okay-xml.exp.xml
index 20099326cc96..20099326cc96 100644
--- a/tvix/eval/src/tests/nix_tests/notyetpassing/eval-okay-xml.exp.xml
+++ b/tvix/eval/src/tests/nix_tests/eval-okay-xml.exp.xml
diff --git a/tvix/eval/src/tests/nix_tests/notyetpassing/eval-okay-xml.nix b/tvix/eval/src/tests/nix_tests/eval-okay-xml.nix
index 9ee9f8a0b4f5..9ee9f8a0b4f5 100644
--- a/tvix/eval/src/tests/nix_tests/notyetpassing/eval-okay-xml.nix
+++ b/tvix/eval/src/tests/nix_tests/eval-okay-xml.nix
diff --git a/tvix/eval/src/value/function.rs b/tvix/eval/src/value/function.rs
index 8131cffa0230..7592e3d64164 100644
--- a/tvix/eval/src/value/function.rs
+++ b/tvix/eval/src/value/function.rs
@@ -18,6 +18,10 @@ pub(crate) struct Formals {
 
     /// The span of the formals themselves, to use to emit errors
     pub(crate) span: Span,
+
+    /// Optionally tracks a name for all function arguments (args@ style).
+    /// Used by toXML.
+    pub(crate) name: Option<String>,
 }
 
 impl Formals {