allow comma separated bracketed list in function args

src/args.rs

@@ -180,6 +180,10 @@ pub(crate) fn eat_call_args<I: Iterator<Item = Token>>(
                     return Ok(CallArgs(args));
                 }
                 TokenKind::Symbol(Symbol::Comma) => break,
+                TokenKind::Symbol(Symbol::OpenSquareBrace) => {
+                    val.push(tok);
+                    val.extend(read_until_close_square_brace(toks));
+                }
                 TokenKind::Symbol(Symbol::OpenParen) => {
                     val.push(tok);
                     val.extend(read_until_close_paren(toks));
@@ -225,3 +229,24 @@ fn read_until_close_paren<I: Iterator<Item = Token>>(toks: &mut Peekable<I>) ->
     }
     v
 }
+
+fn read_until_close_square_brace<I: Iterator<Item = Token>>(toks: &mut Peekable<I>) -> Vec<Token> {
+    let mut v = Vec::new();
+    let mut scope = 0;
+    for tok in toks {
+        match tok.kind {
+            TokenKind::Symbol(Symbol::CloseSquareBrace) => {
+                if scope <= 1 {
+                    v.push(tok);
+                    return v;
+                } else {
+                    scope -= 1;
+                }
+            }
+            TokenKind::Symbol(Symbol::OpenSquareBrace) => scope += 1,
+            _ => {}
+        }
+        v.push(tok)
+    }
+    v
+}

src/value/parse.rs

@@ -281,7 +281,11 @@ impl Value {
                 if let Some(tok) = toks.peek() {
                     if tok.is_symbol(Symbol::CloseSquareBrace) {
                         toks.next();
-                        return Ok(Value::List(Vec::new(), ListSeparator::Space, Brackets::Bracketed));
+                        return Ok(Value::List(
+                            Vec::new(),
+                            ListSeparator::Space,
+                            Brackets::Bracketed,
+                        ));
                     }
                 }
                 let inner = Self::from_tokens(toks, scope, super_selector)?;

tests/functions.rs

@@ -68,3 +68,8 @@ test!(
     "@function f() {\n  @return g();\n}\n@function g() {\n  @return false;\n}\na {\n  color: f();\n  color: g();\n}\n",
     "a {\n  color: false;\n  color: false;\n}\n"
 );
+test!(
+    square_bracket_comma_separated,
+    "@function foo($a) {\n  @return $a;\n}\n\na {\n  color: foo([a, b]);\n}\n",
+    "a {\n  color: [a, b];\n}\n"
+);