Fix trailing comma of function call in math mode (#2772)

crates/typst-syntax/src/ast.rs

@@ -1571,6 +1571,16 @@ impl<'a> Args<'a> {
     pub fn items(self) -> impl DoubleEndedIterator<Item = Arg<'a>> {
         self.0.children().filter_map(SyntaxNode::cast)
     }
+
+    /// Whether there is a comma at the end.
+    pub fn trailing_comma(self) -> bool {
+        self.0
+            .children()
+            .rev()
+            .skip(1)
+            .find(|n| !n.kind().is_trivia())
+            .is_some_and(|n| n.kind() == SyntaxKind::Comma)
+    }
 }
 
 /// An argument to a function call.

crates/typst/src/eval/call.rs

@@ -26,6 +26,8 @@ impl Eval for ast::FuncCall<'_> {
         let in_math = in_math(callee);
         let callee_span = callee.span();
         let args = self.args();
+        let trailing_comma = args.trailing_comma();
+
         if vm.engine.route.exceeding() {
             bail!(span, "maximum function call depth exceeded");
         }
@@ -133,6 +135,9 @@ impl Eval for ast::FuncCall<'_> {
                 }
                 body += arg;
             }
+            if trailing_comma {
+                body += TextElem::packed(',');
+            }
             return Ok(Value::Content(
                 callee.display().spanned(callee_span)
                     + LrElem::new(TextElem::packed('(') + body + TextElem::packed(')'))

tests/typ/math/call.typ

@@ -0,0 +1,7 @@
+// Test function calls that aren't typst functions
+
+---
+$ pi(a) $
+$ pi(a,) $
+$ pi(a,b) $
+$ pi(a,b,) $