fixup! fix: disable realContentHash optimization in app target

Author: haoqunjiang

packages/@vue/cli-service/lib/config/app.js

@@ -33,8 +33,15 @@ module.exports = (api, options) => {
         .filename(outputFilename)
         .chunkFilename(outputFilename)
 
-    webpackConfig.optimization
-      .set('realContentHash', false)
+    const webpack = require('webpack')
+    const { semver } = require('@vue/cli-shared-utils')
+    const webpackMajor = semver.major(webpack.version)
+    if (webpackMajor !== 4) {
+      // FIXME: a temporary workaround to get accurate contenthash in `applyLegacy`
+      // Should use a better fix per discussions at <https://github.com/jantimon/html-webpack-plugin/issues/1554#issuecomment-753653580>
+      webpackConfig.optimization
+        .set('realContentHash', false)
+    }
 
     // code splitting
     if (process.env.NODE_ENV !== 'test') {