Fixed: Don't reduce expression containing CSS variables. (MoOx#9)

This fixes cssnano/cssnano#168.

Author: ben-eb

index.js

@@ -51,8 +51,9 @@ function reduceCSSCalc(value, decimalPrecision) {
 
     var units = getUnitsInExpression(expression)
 
-    // If multiple units let the expression be (i.e. browser calc())
-    if (units.length > 1) {
+    // If the expression contains multiple units or CSS variables,
+    // then let the expression be (i.e. browser calc())
+    if (units.length > 1 || expression.indexOf("var(") > -1) {
       return functionIdentifier + "(" + expression + ")"
     }
 

test/index.js

@@ -102,6 +102,7 @@ test("ignore unrecognized values", function(t) {
 
   t.equal(reduceCSSCalc("calc(calc(4px + 8px) + calc(var(--foo) + 10px) + calc(10% * 20%))"), "calc(12px + calc(var(--foo) + 10px) + 2%)", "ignore unrecognized nested call")
 
+  t.equal(reduceCSSCalc("calc(100% - var(--my-var))"), "calc(100% - var(--my-var))", "should not try to reduce 100% - var");
   t.end()
 })