From b91f0ef628a27892b5f83cacba610fd93ca22de6 Mon Sep 17 00:00:00 2001
From: Adam Wathan <adam.wathan@gmail.com>
Date: Fri, 9 Aug 2019 16:10:41 -0400
Subject: [PATCH] Ignore values not parseable by reduce-css-calc

---
 __tests__/negateValue.test.js | 14 ++++++++++++++
 src/util/negateValue.js       |  9 +++++++++
 src/util/resolveConfig.js     |  4 ++--
 3 files changed, 25 insertions(+), 2 deletions(-)
 create mode 100644 __tests__/negateValue.test.js
 create mode 100644 src/util/negateValue.js

diff --git a/__tests__/negateValue.test.js b/__tests__/negateValue.test.js
new file mode 100644
index 000000000..d382db6a4
--- /dev/null
+++ b/__tests__/negateValue.test.js
@@ -0,0 +1,14 @@
+import negateValue from '../src/util/negateValue'
+
+test('it negates numeric CSS values', () => {
+  expect(negateValue('5')).toEqual('-5')
+  expect(negateValue('10px')).toEqual('-10px')
+  expect(negateValue('18rem')).toEqual('-18rem')
+  expect(negateValue('-10')).toEqual('10')
+  expect(negateValue('-7ch')).toEqual('7ch')
+})
+
+test('it leaves keywords untouched', () => {
+  expect(negateValue('auto')).toEqual('auto')
+  expect(negateValue('cover')).toEqual('cover')
+})
diff --git a/src/util/negateValue.js b/src/util/negateValue.js
new file mode 100644
index 000000000..bf9111f3e
--- /dev/null
+++ b/src/util/negateValue.js
@@ -0,0 +1,9 @@
+import reduceCalc from 'reduce-css-calc'
+
+export default function(value) {
+  try {
+    return reduceCalc(`calc(${value} * -1)`)
+  } catch (e) {
+    return value
+  }
+}
diff --git a/src/util/resolveConfig.js b/src/util/resolveConfig.js
index 4406e4cd5..41e41526d 100644
--- a/src/util/resolveConfig.js
+++ b/src/util/resolveConfig.js
@@ -3,7 +3,7 @@ import isFunction from 'lodash/isFunction'
 import defaults from 'lodash/defaults'
 import map from 'lodash/map'
 import toPath from 'lodash/toPath'
-import reduceCalc from 'reduce-css-calc'
+import negateValue from './negateValue'
 
 const configUtils = {
   negative(scale) {
@@ -12,7 +12,7 @@ const configUtils = {
       .reduce(
         (negativeScale, key) => ({
           ...negativeScale,
-          [`-${key}`]: reduceCalc(`calc(${scale[key]} * -1)`),
+          [`-${key}`]: negateValue(scale[key]),
         }),
         {}
       )