DedupePlugin cannot be cached

Author: sokra

lib/CachePlugin.js

@@ -18,7 +18,11 @@ CachePlugin.prototype.apply = function(compiler) {
 	} else {
 		var _this = this;
 		compiler.plugin("compilation", function(compilation) {
-			compilation.cache = _this.cache;
+			if(compilation.notCacheable) {
+				compilation.warnings.push(new Error("CachePlugin - Cache cannot be used because of: " + compilation.notCacheable))
+			} else {
+				compilation.cache = _this.cache;
+			}
 		});
 		compiler.plugin("run", function(compiler, callback) {
 			if(!compiler._lastCompilationFileDependencies) return callback();

lib/optimize/DedupePlugin.js

@@ -10,6 +10,7 @@ module.exports = DedupePlugin;
 
 DedupePlugin.prototype.apply = function(compiler) {
 	compiler.plugin("compilation", function(compilation) {
+		compilation.notCacheable = "DedupePlugin";
 
 		compilation.dependencyTemplates.set(TemplateArgumentDependency, new TemplateArgumentDependency.Template());