From 63e5da17c7b05f0b7b23bb47c1cc004ba0a1c648 Mon Sep 17 00:00:00 2001
From: David Lee <davidomundo@gmail.com>
Date: Sun, 16 Sep 2018 22:52:51 -0700
Subject: [PATCH] Don't process constant() and env(); fixes #34

---
 src/__tests__/index.js | 14 ++++++++++++++
 src/index.js           |  4 ++++
 2 files changed, 18 insertions(+)

diff --git a/src/__tests__/index.js b/src/__tests__/index.js
index 4741658..b6435a6 100644
--- a/src/__tests__/index.js
+++ b/src/__tests__/index.js
@@ -338,3 +338,17 @@ test(
   'calc( (1em - calc( 10px + 1em)) / 2)',
   '-5px'
 )
+
+test(
+  'should skip constant()',
+  testFixture,
+  'calc(constant(safe-area-inset-left))',
+  'calc(constant(safe-area-inset-left))'
+)
+
+test(
+  'should skip env()',
+  testFixture,
+  'calc(env(safe-area-inset-left))',
+  'calc(env(safe-area-inset-left))'
+)
diff --git a/src/index.js b/src/index.js
index d2de067..a67efa2 100644
--- a/src/index.js
+++ b/src/index.js
@@ -14,6 +14,10 @@ export default (value, precision = 5) => {
 
     // stringify calc expression and produce an AST
     const contents = valueParser.stringify(node.nodes)
+
+    // skip constant() and env()
+    if (contents.indexOf('constant') >= 0 || contents.indexOf('env') >= 0) return;
+
     const ast = parser.parse(contents)
 
     // reduce AST to its simplest form, that is, either to a single value