add check before writing file

fix for facebook/create-react-app#1656

index.js

@@ -6,11 +6,13 @@ var fs = require("fs")
 var findCacheDir = require("find-cache-dir")
 var objectHash = require("object-hash")
 var os = require("os")
+var path = require('path')
 
 var engines = {}
 var rules = {}
 var cache = null
 var cachePath = null
+var cacheFallback =  path.join(os.tmpdir(), 'eslint-loader', 'cache.json')
 
 /**
  * linter
@@ -59,13 +61,23 @@ function lint(input, config, webpack) {
     res = engine.executeOnText(input, resourcePath, true)
 
     // Save new results in the cache
-    if (config.cache) {
+    if (config.cache && cachePath) {
       cache[resourcePath] = {
         hash: inputMD5,
         rules: rulesHash,
         res: res,
       }
-      fs.writeFileSync(cachePath, JSON.stringify(cache))
+      var cacheJson = JSON.stringify(cacheJson)
+      try {
+        safeWriteCache(cachePath)
+      } catch(e){
+        try {
+          cachePath = cacheFallback
+          safeWriteCache(cachePath)
+        } catch(e){
+          cache = false
+        }
+      }
     }
   }
 
@@ -181,7 +193,7 @@ module.exports = function(input, map) {
         thunk: true,
         create: true,
       })
-      cachePath = thunk("data.json") || os.tmpdir() + "/data.json"
+      cachePath = thunk("data.json") || cacheFallback
       try {
         cache = require(cachePath)
       }
@@ -197,3 +209,13 @@ module.exports = function(input, map) {
   lint(input, config, this)
   this.callback(null, input, map)
 }
+
+
+function safeWriteCache(cacheJson){
+  if (fs.existsSync(cachePath)){
+    fs.writeFileSync(cachePath, cacheJson)
+  } else {
+    fs.mkdirSync(path.dirname(cachePath))
+    fs.writeFileSync(cachePath, cacheJson)
+  }
+}