Implement builtin function round()

src/builtin/math.rs

@@ -6,11 +6,16 @@ use crate::value::{Number, Value};
 
 pub(crate) fn register(f: &mut BTreeMap<String, Builtin>) {
     decl!(f "percentage", |args, _| {
-        let arg = dbg!(arg!(args, 0, "number").eval());
-        let num = match arg {
+        let num = match arg!(args, 0, "number").eval() {
             Value::Dimension(n, Unit::None) => n * Number::from(100),
             _ => todo!("expected unitless number in builtin function `percentage()`")
         };
         Some(Value::Dimension(num, Unit::Percent))
     });
+    decl!(f "round", |args, _| {
+        match arg!(args, 0, "number").eval() {
+            Value::Dimension(n, u) => Some(Value::Dimension(n.round(), u)),
+            _ => todo!("expected number in builtin function `round()`")
+        }
+    });
 }

tests/math.rs

@@ -18,3 +18,13 @@ test!(
     "a {\n  color: percentage(2);\n}\n",
     "a {\n  color: 200%;\n}\n"
 );
+test!(
+    rounds_down,
+    "a {\n  color: round(10.4px);\n}\n",
+    "a {\n  color: 10px;\n}\n"
+);
+test!(
+    rounds_up,
+    "a {\n  color: round(10.6px);\n}\n",
+    "a {\n  color: 11px;\n}\n"
+);