Fix empty 2-d math args with whitespace/trivia (#3786)

Co-authored-by: Laurenz <laurmaedje@gmail.com>

1 files changed, 14 insertions, 1 deletions

diff --git a/crates/typst-syntax/src/parser.rs b/crates/typst-syntax/src/parser.rs
index ffbd7266..e61618e0 100644
--- a/crates/typst-syntax/src/parser.rs
+++ b/crates/typst-syntax/src/parser.rs
@@ -592,10 +592,23 @@ fn math_args(p: &mut Parser) {
     p.wrap(m, SyntaxKind::Args);
 }
 
+/// Wrap math function arguments in a "Math" SyntaxKind to combine adjacent expressions
+/// or create blank content.
+///
+/// We don't wrap when `exprs == 1`, as there is only one expression, so the grouping
+/// isn't needed, and this would change the type of the expression from potentially
+/// non-content to content.
+///
+/// Note that `exprs` might be 0 if we have whitespace or trivia before a comma i.e.
+/// `mat(; ,)` or `sin(x, , , ,)`. This would create an empty Math element before that
+/// trivia if we called `p.wrap()` -- breaking the expected AST for 2-d arguments -- so
+/// we instead manually wrap to our current marker using `p.wrap_within()`.
 fn maybe_wrap_in_math(p: &mut Parser, arg: Marker, named: Option<Marker>) {
     let exprs = p.post_process(arg).filter(|node| node.is::<ast::Expr>()).count();
     if exprs != 1 {
-        p.wrap(arg, SyntaxKind::Math);
+        // Convert 0 exprs into a blank math element (so empty arguments are allowed).
+        // Convert 2+ exprs into a math element (so they become a joined sequence).
+        p.wrap_within(arg, p.marker(), SyntaxKind::Math);
     }
 
     if let Some(m) = named {