From efaa33088bc890914fb9aa8a7994912cdccd2d23 Mon Sep 17 00:00:00 2001
From: ConnorSkees <39542938+ConnorSkees@users.noreply.github.com>
Date: Wed, 18 Mar 2020 10:14:35 -0400
Subject: [PATCH] Implement unit conversions in numeric subtraction

---
 src/value/ops.rs | 11 ++++++++++-
 tests/units.rs   | 10 ++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/src/value/ops.rs b/src/value/ops.rs
index 4faa25d..0f07328 100644
--- a/src/value/ops.rs
+++ b/src/value/ops.rs
@@ -123,8 +123,17 @@ impl Sub for Value {
                     }
                     if unit == unit2 {
                         Value::Dimension(num - num2, unit)
+                    } else 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_CONVERSION_TABLE[&unit.to_string()][&unit2.to_string()]
+                                    .clone(),
+                            unit,
+                        )
                     }
                 }
                 _ => todo!(),
diff --git a/tests/units.rs b/tests/units.rs
index 9634213..88888e3 100644
--- a/tests/units.rs
+++ b/tests/units.rs
@@ -54,6 +54,16 @@ test!(
     "a {\n  color: 10 + 10px;\n}\n",
     "a {\n  color: 20px;\n}\n"
 );
+test!(
+    unit_minus_none,
+    "a {\n  color: 10px - 10;\n}\n",
+    "a {\n  color: 0px;\n}\n"
+);
+test!(
+    none_minus_unit,
+    "a {\n  color: 10 - 10px;\n}\n",
+    "a {\n  color: 0px;\n}\n"
+);
 
 macro_rules! test_unit_addition {
     ($u1:ident, $u2:ident, $out:literal) => {