Handle unit multiplication

src/units.rs

@@ -91,6 +91,11 @@ pub(crate) enum Unit {
     Unknown(String),
     /// Unspecified unit
     None,
+
+    /// Two units multiplied together
+    Mul(Box<Unit>, Box<Unit>),
+    /// A unit divided by another
+    Div(Box<Unit>, Box<Unit>),
 }
 
 #[derive(Debug, Copy, Clone, Eq, PartialEq)]
@@ -223,6 +228,8 @@ impl Into<String> for Unit {
             Unit::X => "x",
             Unit::Fr => "fr",
             Unit::None => "",
+            Unit::Mul(l, r) => return format!("{}*{}", l, r),
+            Unit::Div(l, r) => return format!("{}/{}", l, r),
             Unit::Unknown(ref s) => s,
         }
         .into()
@@ -269,6 +276,8 @@ impl fmt::Display for Unit {
             Unit::Fr => write!(f, "fr"),
             Unit::Unknown(s) => write!(f, "{}", s),
             Unit::None => write!(f, ""),
+            Unit::Mul(l, r) => write!(f, "{}*{}", l, r),
+            Unit::Div(l, r) => write!(f, "{}/{}", l, r),
         }
     }
 }

src/value/mod.rs

@@ -29,7 +29,13 @@ impl Display for Value {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
             Self::Important => write!(f, "!important"),
-            Self::Dimension(num, unit) => write!(f, "{}{}", num, unit),
+            Self::Dimension(num, unit) => match unit {
+                Unit::Mul(..) | Unit::Div(..) => {
+                    eprintln!("Error: {}{} isn't a valid CSS value.", num, unit);
+                    std::process::exit(1);
+                }
+                _ => write!(f, "{}{}", num, unit),
+            },
             Self::List(vals, sep) => write!(
                 f,
                 "{}",

src/value/ops.rs

@@ -200,19 +200,12 @@ impl Mul for Value {
             Self::Null => todo!(),
             Self::Dimension(num, unit) => match other {
                 Self::Dimension(num2, unit2) => {
-                    if unit2 != Unit::None && unit != Unit::None {
-                        return Err(format!(
-                            "{}{}*{} isn't a valid CSS value.",
-                            num * num2,
-                            unit,
-                            unit2
-                        )
-                        .into());
-                    }
-                    if unit == unit2 {
+                    if unit == Unit::None {
+                        Value::Dimension(num * num2, unit2)
+                    } else if unit2 == Unit::None {
                         Value::Dimension(num * num2, unit)
                     } else {
-                        todo!("unit conversions")
+                        Value::Dimension(num * num2, Unit::Mul(Box::new(unit), Box::new(unit2)))
                     }
                 }
                 _ => {

tests/units.rs

@@ -9,3 +9,28 @@ test!(unit_px, "a {\n  height: 1px;\n}\n");
 test!(unit_em, "a {\n  height: 1em;\n}\n");
 test!(unit_rem, "a {\n  height: 1rem;\n}\n");
 test!(unit_percent, "a {\n  height: 1%;\n}\n");
+test!(
+    unit_times_none,
+    "a {\n  color: 3px * 2;\n}\n",
+    "a {\n  color: 6px;\n}\n"
+);
+test!(
+    none_times_unit,
+    "a {\n  color: 2 * 3px;\n}\n",
+    "a {\n  color: 6px;\n}\n"
+);
+test!(
+    unit_fn_unit_times_none,
+    "a {\n  color: unit(1px * 1);\n}\n",
+    "a {\n  color: \"px\";\n}\n"
+);
+test!(
+    unit_fn_none_times_unit,
+    "a {\n  color: unit(1 * 1px);\n}\n",
+    "a {\n  color: \"px\";\n}\n"
+);
+test!(
+    unit_fn_unit_times_unit,
+    "a {\n  color: unit(1px*1px);\n}\n",
+    "a {\n  color: \"px*px\";\n}\n"
+);