Add unit function

src/builtin/meta.rs

@@ -1,6 +1,7 @@
 use std::collections::BTreeMap;
 
 use super::Builtin;
+use crate::common::QuoteKind;
 use crate::value::Value;
 
 pub(crate) fn register(f: &mut BTreeMap<String, Builtin>) {
@@ -35,4 +36,12 @@ pub(crate) fn register(f: &mut BTreeMap<String, Builtin>) {
             _ => Some(Value::False),
         }
     });
+    decl!(f "unit", |args| {
+        let number = arg!(args, 0, "number");
+        let unit = match number {
+            Value::Dimension(_, u) => u.to_string(),
+            _ => String::new()
+        };
+        Some(Value::Ident(unit, QuoteKind::Double))
+    });
 }

tests/meta.rs

@@ -38,3 +38,23 @@ test!(
     "a {\n  color: feature-exists($feature: at-error)\n}\n",
     "a {\n  color: true;\n}\n"
 );
+test!(
+    unit_px,
+    "a {\n  color: unit(1px)\n}\n",
+    "a {\n  color: \"px\";\n}\n"
+);
+test!(
+    unit_none,
+    "a {\n  color: unit(1)\n}\n",
+    "a {\n  color: \"\";\n}\n"
+);
+test!(
+    unit_non_numeric,
+    "a {\n  color: unit(red)\n}\n",
+    "a {\n  color: \"\";\n}\n"
+);
+test!(
+    unit_named_args,
+    "a {\n  color: unit($number: 1px)\n}\n",
+    "a {\n  color: \"px\";\n}\n"
+);