From e5cfd05f49f0f5061497d2d38c6d76206ebf545c Mon Sep 17 00:00:00 2001
From: Yuriy Ostapenko <yuo@scalepoint.com>
Date: Thu, 8 Jun 2017 14:18:27 +0300
Subject: [PATCH] Cache assets similar to how the normal compilation does it

Previously extract-text-webpack-plugin emitted css assets every time anything else changed.
Injected assets were also not included in compilation hash calculation and caused some rebuilds to be hidden.
---
 index.js | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/index.js b/index.js
index 75ef6216..45bd56a0 100644
--- a/index.js
+++ b/index.js
@@ -4,6 +4,7 @@
 */
 var fs = require('fs');
 var ConcatSource = require("webpack-sources").ConcatSource;
+var CachedSource = require("webpack-sources").CachedSource;
 var async = require("async");
 var ExtractedModule = require("./ExtractedModule");
 var Chunk = require("webpack/lib/Chunk");
@@ -337,8 +338,22 @@ ExtractTextPlugin.prototype.apply = function(compiler) {
 					});
 
 					var file = (isFunction(filename)) ? filename(getPath) : getPath(filename);
-					
+
+					var cacheKey = "extracted " + file;
+					var chunkHash = loaderUtils.getHashDigest(source.source());
+					if(compilation.cache && compilation.cache[cacheKey] && compilation.cache[cacheKey].hash === chunkHash) {
+						source = compilation.cache[cacheKey].source;
+					} else {
+						if(compilation.cache) {
+							compilation.cache[cacheKey] = {
+								hash: chunkHash,
+								source: source = (source instanceof CachedSource ? source : new CachedSource(source))
+							};
+						}
+					}
+
 					compilation.assets[file] = source;
+					compilation.modifyHash(chunkHash);
 					chunk.files.push(file);
 				}
 			}, this);