Implement modulo

src/value/mod.rs

@@ -147,6 +147,7 @@ impl Value {
                 Op::NotEqual => Ok(Self::bool(*lhs != *rhs)),
                 Op::Mul => *lhs * *rhs,
                 Op::Div => *lhs / *rhs,
+                Op::Rem => *lhs % *rhs,
                 _ => Ok(Self::BinaryOp(lhs, op, rhs)),
             },
             _ => Ok(self),

src/value/ops.rs

@@ -1,4 +1,4 @@
-use std::ops::{Add, Div, Mul, Sub};
+use std::ops::{Add, Div, Mul, Rem, Sub};
 
 use crate::common::QuoteKind;
 use crate::error::SassResult;
@@ -348,3 +348,37 @@ impl Div for Value {
         })
     }
 }
+
+impl Rem for Value {
+    type Output = SassResult<Self>;
+
+    fn rem(self, other: Self) -> Self::Output {
+        Ok(match self {
+            Value::Dimension(n, u) => match other {
+                Value::Dimension(n2, u2) => {
+                    if !u.comparable(&u2) {
+                        return Err(format!("Incompatible units {} and {}.", u2, u).into());
+                    }
+                    if u == u2 {
+                        Value::Dimension(n % n2, u)
+                    } else if u == Unit::None {
+                        Value::Dimension(n % n2, u2)
+                    } else if u2 == Unit::None {
+                        Value::Dimension(n % n2, u)
+                    } else {
+                        Value::Dimension(n, u)
+                    }
+                }
+                _ => {
+                    return Err(format!(
+                        "Undefined operation \"{} % {}\".",
+                        Value::Dimension(n, u),
+                        other
+                    )
+                    .into())
+                }
+            },
+            _ => return Err(format!("Undefined operation \"{} % {}\".", self, other).into()),
+        })
+    }
+}

tests/number.rs

@@ -50,3 +50,29 @@ test!(
 );
 test!(positive_float_leading_zero, "a {\n  color: 0.1;\n}\n");
 test!(negative_float_leading_zero, "a {\n  color: -0.1;\n}\n");
+
+test!(
+    px_mod_px,
+    "a {\n  color: 10px % 2px;\n}\n",
+    "a {\n  color: 0px;\n}\n"
+);
+test!(
+    px_mod_in,
+    "a {\n  color: 10px % 2in;\n}\n",
+    "a {\n  color: 10px;\n}\n"
+);
+test!(
+    px_mod_none,
+    "a {\n  color: 10px % 2;\n}\n",
+    "a {\n  color: 0px;\n}\n"
+);
+test!(
+    none_mod_px,
+    "a {\n  color: 10 % 2px;\n}\n",
+    "a {\n  color: 0px;\n}\n"
+);
+test!(
+    none_mod_none,
+    "a {\n  color: 10 % 2;\n}\n",
+    "a {\n  color: 0;\n}\n"
+);