Implement unitless builtin function

src/builtin/meta.rs

@@ -2,6 +2,7 @@ use std::collections::BTreeMap;
 
 use super::Builtin;
 use crate::common::QuoteKind;
+use crate::units::Unit;
 use crate::value::Value;
 
 pub(crate) fn register(f: &mut BTreeMap<String, Builtin>) {
@@ -48,4 +49,12 @@ pub(crate) fn register(f: &mut BTreeMap<String, Builtin>) {
         let value = arg!(args, 0, "value");
         Some(Value::Ident(value.kind().to_owned(), QuoteKind::None))
     });
+    decl!(f "unitless", |args| {
+        let number = arg!(args, 0, "number");
+        match number {
+            Value::Dimension(_, Unit::None) => Some(Value::True),
+            Value::Dimension(_, _) => Some(Value::False),
+            _ => Some(Value::True)
+        }
+    });
 }

tests/meta.rs

@@ -123,3 +123,18 @@ test!(
     "a {\n  color: type-of(hi + bye)\n}\n",
     "a {\n  color: string;\n}\n"
 );
+test!(
+    unitless_px,
+    "a {\n  color: unitless(1px)\n}\n",
+    "a {\n  color: false;\n}\n"
+);
+test!(
+    unitless_num,
+    "a {\n  color: unitless(1)\n}\n",
+    "a {\n  color: true;\n}\n"
+);
+test!(
+    unitless_string,
+    "a {\n  color: unitless(foo)\n}\n",
+    "a {\n  color: true;\n}\n"
+);