Merge pull request webpack#6627 from Hoten/feat-uglifyjs-default-sourcemap

defaults: set source map option for UglifyJs to true if SourceMapDevToolPlugin exists

Author: sokra

lib/WebpackOptionsDefaulter.js

@@ -264,10 +264,14 @@ class WebpackOptionsDefaulter extends OptionsDefaulter {
 				apply: compiler => {
 					// Lazy load the uglifyjs plugin
 					const UglifyJsPlugin = require("uglifyjs-webpack-plugin");
+					const SourceMapDevToolPlugin = require("./SourceMapDevToolPlugin");
 					new UglifyJsPlugin({
 						cache: true,
 						parallel: true,
-						sourceMap: options.devtool && /source-?map/.test(options.devtool)
+						sourceMap:
+							(options.devtool && /source-?map/.test(options.devtool)) ||
+							(options.plugins &&
+								options.plugins.some(p => p instanceof SourceMapDevToolPlugin))
 					}).apply(compiler);
 				}
 			}