From 159b66ac724fbbb08a1d8cb776a1a03f8471563c Mon Sep 17 00:00:00 2001
From: Michael Ciniawsky <michael.ciniawsky@gmail.com>
Date: Tue, 9 May 2017 13:17:49 +0200
Subject: [PATCH] fix(index): don't fail on 'sourceMap: false' && emit a
 warning instead, when previous map found (`options.sourceMap`)

---
 lib/index.js | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/lib/index.js b/lib/index.js
index a4da252c..6fbf9869 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -127,8 +127,12 @@ module.exports = function loader (css, map) {
       css = this.exec(css, this.resource)
     }
 
-    if (typeof map === 'string') map = JSON.parse(map)
-    if (map && map.mappings) options.map.prev = map
+    if (!sourceMap && map) {
+      this.emitWarning(`\n\n ⚠️  PostCSS Loader\n\nPrevious source map found, but options.sourceMap isn't set, this way the loader will discard the source map enterily for performance reasons, see https://github.com/postcss/postcss-loader#sourcemap for more info on the subject\n\n`)
+    }
+
+    if (sourceMap && typeof map === 'string') map = JSON.parse(map)
+    if (sourceMap && map) options.map.prev = map
 
     return postcss(plugins)
       .process(css, options)