replace max_args! macro with builtin method

src/args.rs

@@ -170,6 +170,27 @@ impl CallArgs {
     pub fn is_empty(&self) -> bool {
         self.0.is_empty()
     }
+
+    pub fn max_args(&self, max: usize) -> SassResult<()> {
+        let len = self.len();
+        if len > max {
+            let mut err = String::with_capacity(50);
+            err.push_str(&format!("Only {} argument", max));
+            if max != 1 {
+                err.push('s');
+            }
+            err.push_str(" allowed, but ");
+            err.push_str(&len.to_string());
+            err.push(' ');
+            if len == 1 {
+                err.push_str("was passed.")
+            } else {
+                err.push_str("were passed.")
+            }
+            return Err((err, self.span()).into());
+        }
+        Ok(())
+    }
 }
 
 pub(crate) fn eat_func_args<I: Iterator<Item = Token>>(

src/builtin/color/hsl.rs

@@ -428,7 +428,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "hue".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             match arg!(args, scope, super_selector, 0, "color") {
                 Value::Color(c) => Ok(Value::Dimension(c.hue(), Unit::Deg)),
                 v => Err((
@@ -442,7 +442,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "saturation".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             match arg!(args, scope, super_selector, 0, "color") {
                 Value::Color(c) => Ok(Value::Dimension(c.saturation(), Unit::Percent)),
                 v => Err((
@@ -456,7 +456,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "lightness".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             match arg!(args, scope, super_selector, 0, "color") {
                 Value::Color(c) => Ok(Value::Dimension(c.lightness(), Unit::Percent)),
                 v => Err((
@@ -470,7 +470,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "adjust-hue".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 2);
+            args.max_args(2)?;
             let color = match arg!(args, scope, super_selector, 0, "color") {
                 Value::Color(c) => c,
                 v => {
@@ -500,7 +500,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "lighten".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 2);
+            args.max_args(2)?;
             let color = match arg!(args, scope, super_selector, 0, "color") {
                 Value::Color(c) => c,
                 v => {
@@ -530,7 +530,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "darken".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 2);
+            args.max_args(2)?;
             let color = match arg!(args, scope, super_selector, 0, "color") {
                 Value::Color(c) => c,
                 v => {
@@ -560,7 +560,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "saturate".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 2);
+            args.max_args(2)?;
             if args.len() == 1 {
                 return Ok(Value::Ident(
                     format!(
@@ -607,7 +607,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "desaturate".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 2);
+            args.max_args(2)?;
             let color = match arg!(args, scope, super_selector, 0, "color") {
                 Value::Color(c) => c,
                 v => {
@@ -637,7 +637,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "grayscale".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             let color = match arg!(args, scope, super_selector, 0, "color") {
                 Value::Color(c) => c,
                 Value::Dimension(n, u) => {
@@ -660,7 +660,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "complement".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             let color = match arg!(args, scope, super_selector, 0, "color") {
                 Value::Color(c) => c,
                 v => {
@@ -677,7 +677,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "invert".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 2);
+            args.max_args(2)?;
             let weight = match arg!(
                 args,
                 scope,

src/builtin/color/opacity.rs

@@ -10,7 +10,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "alpha".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             match arg!(args, scope, super_selector, 0, "color") {
                 Value::Color(c) => Ok(Value::Dimension(c.alpha(), Unit::None)),
                 v => Err((
@@ -24,7 +24,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "opacity".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             match arg!(args, scope, super_selector, 0, "color") {
                 Value::Color(c) => Ok(Value::Dimension(c.alpha(), Unit::None)),
                 Value::Dimension(num, unit) => Ok(Value::Ident(
@@ -42,7 +42,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "opacify".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 2);
+            args.max_args(2)?;
             let color = match arg!(args, scope, super_selector, 0, "color") {
                 Value::Color(c) => c,
                 v => {
@@ -72,7 +72,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "fade-in".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 2);
+            args.max_args(2)?;
             let color = match arg!(args, scope, super_selector, 0, "color") {
                 Value::Color(c) => c,
                 v => {
@@ -102,7 +102,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "transparentize".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 2);
+            args.max_args(2)?;
             let color = match arg!(args, scope, super_selector, 0, "color") {
                 Value::Color(c) => c,
                 v => {
@@ -132,7 +132,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "fade-out".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 2);
+            args.max_args(2)?;
             let color = match arg!(args, scope, super_selector, 0, "color") {
                 Value::Color(c) => c,
                 v => {

src/builtin/color/other.rs

@@ -268,7 +268,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "ie-hex-str".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             let color = match arg!(args, scope, super_selector, 0, "color") {
                 Value::Color(c) => c,
                 v => {

src/builtin/color/rgb.rs

@@ -666,7 +666,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "red".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             match arg!(args, scope, super_selector, 0, "color") {
                 Value::Color(c) => Ok(Value::Dimension(c.red(), Unit::None)),
                 v => Err((
@@ -680,7 +680,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "green".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             match arg!(args, scope, super_selector, 0, "color") {
                 Value::Color(c) => Ok(Value::Dimension(c.green(), Unit::None)),
                 v => Err((
@@ -694,7 +694,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "blue".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             match arg!(args, scope, super_selector, 0, "color") {
                 Value::Color(c) => Ok(Value::Dimension(c.blue(), Unit::None)),
                 v => Err((
@@ -708,7 +708,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "mix".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 3);
+            args.max_args(3)?;
             let color1 = match arg!(args, scope, super_selector, 0, "color1") {
                 Value::Color(c) => c,
                 v => {

src/builtin/list.rs

@@ -12,7 +12,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "length".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             let len = match arg!(args, scope, super_selector, 0, "list") {
                 Value::List(v, ..) => Number::from(v.len()),
                 Value::Map(m) => Number::from(m.len()),
@@ -24,7 +24,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "nth".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 2);
+            args.max_args(2)?;
             let list = match arg!(args, scope, super_selector, 0, "list") {
                 Value::List(v, ..) => v,
                 Value::Map(m) => m.entries(),
@@ -71,7 +71,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "list-separator".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             Ok(Value::Ident(
                 match arg!(args, scope, super_selector, 0, "list") {
                     Value::List(_, sep, ..) => sep.name(),
@@ -85,7 +85,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "set-nth".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 3);
+            args.max_args(3)?;
             let (mut list, sep, brackets) = match arg!(args, scope, super_selector, 0, "list") {
                 Value::List(v, sep, b) => (v, sep, b),
                 Value::Map(m) => (m.entries(), ListSeparator::Comma, Brackets::None),
@@ -134,7 +134,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "append".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 3);
+            args.max_args(3)?;
             let (mut list, sep, brackets) = match arg!(args, scope, super_selector, 0, "list") {
                 Value::List(v, sep, b) => (v, sep, b),
                 v => (vec![v], ListSeparator::Space, Brackets::None),
@@ -179,7 +179,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "join".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 4);
+            args.max_args(4)?;
             let (mut list1, sep1, brackets) = match arg!(args, scope, super_selector, 0, "list1") {
                 Value::List(v, sep, brackets) => (v, sep, brackets),
                 Value::Map(m) => (m.entries(), ListSeparator::Comma, Brackets::None),
@@ -255,7 +255,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "is-bracketed".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             Ok(Value::bool(
                 match arg!(args, scope, super_selector, 0, "list") {
                     Value::List(.., brackets) => match brackets {
@@ -270,7 +270,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "index".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 2);
+            args.max_args(2)?;
             let list = match arg!(args, scope, super_selector, 0, "list") {
                 Value::List(v, ..) => v,
                 Value::Map(m) => m.entries(),

src/builtin/macros.rs

@@ -36,25 +36,6 @@ macro_rules! named_arg {
     };
 }
 
-macro_rules! max_args {
-    ($args:ident, $count:literal) => {
-        if $args.len() > $count {
-            let mut err = String::with_capacity(50);
-            err.push_str(&format!("Only {} argument", $count));
-            if $count != 1 {
-                err.push('s');
-            }
-            err.push_str(&format!(" allowed, but {} ", $args.len()));
-            if $args.len() == 1 {
-                err.push_str("was passed.")
-            } else {
-                err.push_str("were passed.")
-            }
-            return Err((err, $args.span()).into());
-        }
-    };
-}
-
 macro_rules! bound {
     ($args:ident, $name:literal, $arg:ident, $unit:ident, $low:literal, $high:literal) => {
         if $arg > Number::from($high) || $arg < Number::from($low) {

src/builtin/map.rs

@@ -8,7 +8,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "map-get".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 2);
+            args.max_args(2)?;
             let key = arg!(args, scope, super_selector, 1, "key");
             let map = match arg!(args, scope, super_selector, 0, "map") {
                 Value::Map(m) => m,
@@ -27,7 +27,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "map-has-key".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 2);
+            args.max_args(2)?;
             let key = arg!(args, scope, super_selector, 1, "key");
             let map = match arg!(args, scope, super_selector, 0, "map") {
                 Value::Map(m) => m,
@@ -46,7 +46,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "map-keys".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             let map = match arg!(args, scope, super_selector, 0, "map") {
                 Value::Map(m) => m,
                 Value::List(v, ..) if v.is_empty() => SassMap::new(),
@@ -68,7 +68,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "map-values".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             let map = match arg!(args, scope, super_selector, 0, "map") {
                 Value::Map(m) => m,
                 Value::List(v, ..) if v.is_empty() => SassMap::new(),
@@ -90,7 +90,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "map-merge".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 2);
+            args.max_args(2)?;
             let mut map1 = match arg!(args, scope, super_selector, 0, "map1") {
                 Value::Map(m) => m,
                 Value::List(v, ..) if v.is_empty() => SassMap::new(),

src/builtin/math.rs

@@ -13,7 +13,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "percentage".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             let num = match arg!(args, scope, super_selector, 0, "number") {
                 Value::Dimension(n, Unit::None) => n * Number::from(100),
                 v @ Value::Dimension(..) => {
@@ -43,7 +43,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "round".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             match arg!(args, scope, super_selector, 0, "number") {
                 Value::Dimension(n, u) => Ok(Value::Dimension(n.round(), u)),
                 v => Err((
@@ -60,7 +60,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "ceil".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             match arg!(args, scope, super_selector, 0, "number") {
                 Value::Dimension(n, u) => Ok(Value::Dimension(n.ceil(), u)),
                 v => Err((
@@ -77,7 +77,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "floor".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             match arg!(args, scope, super_selector, 0, "number") {
                 Value::Dimension(n, u) => Ok(Value::Dimension(n.floor(), u)),
                 v => Err((
@@ -94,7 +94,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "abs".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             match arg!(args, scope, super_selector, 0, "number") {
                 Value::Dimension(n, u) => Ok(Value::Dimension(n.abs(), u)),
                 v => Err((
@@ -111,7 +111,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "comparable".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 2);
+            args.max_args(2)?;
             let unit1 = match arg!(args, scope, super_selector, 0, "number1") {
                 Value::Dimension(_, u) => u,
                 v => {
@@ -147,7 +147,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "random".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             let limit = match arg!(args, scope, super_selector, 0, "limit" = Value::Null) {
                 Value::Dimension(n, _) => n,
                 Value::Null => {

src/builtin/meta.rs

@@ -12,7 +12,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "if".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 3);
+            args.max_args(3)?;
             if arg!(args, scope, super_selector, 0, "condition").is_true(args.span())? {
                 Ok(arg!(args, scope, super_selector, 1, "if-true"))
             } else {
@@ -23,7 +23,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "feature-exists".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             match arg!(args, scope, super_selector, 0, "feature") {
                 Value::Ident(s, _) => match s.as_str() {
                     // A local variable will shadow a global variable unless
@@ -57,7 +57,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "unit".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             let unit = match arg!(args, scope, super_selector, 0, "number") {
                 Value::Dimension(_, u) => u.to_string(),
                 v => {
@@ -77,7 +77,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "type-of".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             let value = arg!(args, scope, super_selector, 0, "value");
             Ok(Value::Ident(
                 value.kind(args.span())?.to_owned(),
@@ -88,7 +88,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "unitless".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             match arg!(args, scope, super_selector, 0, "number") {
                 Value::Dimension(_, Unit::None) => Ok(Value::True),
                 Value::Dimension(_, _) => Ok(Value::False),
@@ -99,7 +99,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "inspect".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             Ok(Value::Ident(
                 arg!(args, scope, super_selector, 0, "value").inspect(args.span())?,
                 QuoteKind::None,
@@ -109,7 +109,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "variable-exists".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             match arg!(args, scope, super_selector, 0, "name") {
                 Value::Ident(s, _) => Ok(Value::bool(scope.var_exists(&s))),
                 v => Err((
@@ -123,7 +123,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "global-variable-exists".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             match arg!(args, scope, super_selector, 0, "name") {
                 Value::Ident(s, _) => Ok(Value::bool(global_var_exists(&s))),
                 v => Err((
@@ -137,7 +137,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "mixin-exists".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 2);
+            args.max_args(2)?;
             match arg!(args, scope, super_selector, 0, "name") {
                 Value::Ident(s, _) => Ok(Value::bool(scope.mixin_exists(&s))),
                 v => Err((
@@ -151,7 +151,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "function-exists".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 2);
+            args.max_args(2)?;
             match arg!(args, scope, super_selector, 0, "name") {
                 Value::Ident(s, _) => Ok(Value::bool(
                     scope.fn_exists(&s) || GLOBAL_FUNCTIONS.contains_key(&s),
@@ -167,7 +167,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "get-function".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 3);
+            args.max_args(3)?;
             let name = match arg!(args, scope, super_selector, 0, "name") {
                 Value::Ident(s, _) => s,
                 v => {

src/builtin/string.rs

@@ -15,7 +15,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "to-upper-case".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             match arg!(args, scope, super_selector, 0, "string") {
                 Value::Ident(i, q) => Ok(Value::Ident(i.to_ascii_uppercase(), q)),
                 v => Err((
@@ -32,7 +32,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "to-lower-case".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             match arg!(args, scope, super_selector, 0, "string") {
                 Value::Ident(i, q) => Ok(Value::Ident(i.to_ascii_lowercase(), q)),
                 v => Err((
@@ -49,7 +49,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "str-length".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             match arg!(args, scope, super_selector, 0, "string") {
                 Value::Ident(i, _) => Ok(Value::Dimension(
                     Number::from(i.chars().count()),
@@ -69,7 +69,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "quote".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             match arg!(args, scope, super_selector, 0, "string") {
                 Value::Ident(i, _) => Ok(Value::Ident(i, QuoteKind::Quoted)),
                 v => Err((
@@ -86,7 +86,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "unquote".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 1);
+            args.max_args(1)?;
             match arg!(args, scope, super_selector, 0, "string") {
                 i @ Value::Ident(..) => Ok(i.unquote()),
                 v => Err((
@@ -103,7 +103,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "str-slice".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 3);
+            args.max_args(3)?;
             let (string, quotes) = match arg!(args, scope, super_selector, 0, "string") {
                 Value::Ident(s, q) => (s, q),
                 v => {
@@ -207,7 +207,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "str-index".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 2);
+            args.max_args(2)?;
             let s1 = match arg!(args, scope, super_selector, 0, "string") {
                 Value::Ident(i, _) => i,
                 v => {
@@ -245,7 +245,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "str-insert".to_owned(),
         Builtin::new(|mut args, scope, super_selector| {
-            max_args!(args, 3);
+            args.max_args(3)?;
             let (s1, quotes) = match arg!(args, scope, super_selector, 0, "string") {
                 Value::Ident(i, q) => (i, q),
                 v => {
@@ -349,7 +349,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
         "unique-id".to_owned(),
         Builtin::new(|args, _, _| {
-            max_args!(args, 0);
+            args.max_args(0)?;
             let mut rng = thread_rng();
             let string = std::iter::repeat(())
                 .map(|()| rng.sample(Alphanumeric))