Merge pull request #3221 from justin808/patch-21

Update v6_upgrade.md

Author: guillaumebriday

docs/v6_upgrade.md

@@ -30,7 +30,7 @@ This means you have to configure integration with frameworks yourself, but webpa
 
 3. Rename `config/webpacker.yml` to `config/webpacker_old.yml`
 
-4. Uninstall the current version of `webpack-dev-server`: `yarn remove webpack-dev-server`
+4. Update `webpack-dev-server` to the current version, greater than 4.2, updating `package.json`.
 
 5. Upgrade the Webpacker Ruby gem and NPM package
 
@@ -57,7 +57,7 @@ Example going to a specific version:
 
 6. Update API usage of the view helpers by changing `javascript_packs_with_chunks_tag` and `stylesheet_packs_with_chunks_tag` to `javascript_pack_tag` and `stylesheet_pack_tag`. Ensure that your layouts and views will only have **at most one call** to `javascript_pack_tag` and **at most one call** to `stylesheet_pack_tag`. You can now pass multiple bundles to these view helper methods. If you fail to changes this, you may experience performance issues, and other bugs related to multiple copies of React, like [issue 2932](https://github.com/rails/webpacker/issues/2932).  If you expose jquery globally with `expose-loader,` by using `import $ from "expose-loader?exposes=$,jQuery!jquery"` in your `app/javascript/application.js`, pass the option `defer: false` to your `javascript_pack_tag`.
 
-7. If you are using any integrations like `css`, `React` or `TypeScript`. Please see https://github.com/rails/webpacker#integrations section on how they work in v6.
+7. If you are using any integrations like `css`, `postcss`, `React` or `TypeScript`. Please see https://github.com/rails/webpacker#integrations section on how they work in v6.
 
 8. Copy over any custom webpack config from `config/webpack_old`. Common code previously called 'environment' should be changed to 'base', and import `environment` changed to `webpackConfig`.
 
@@ -81,9 +81,7 @@ Example going to a specific version:
   }
   ```
 
-11. Remove `postcss.config.js` if you don't use `PostCSS`.
-
-12. `extensions` was removed from the `webpacker.yml` file. Move custom extensions to your configuration by merging an object like this. For more details, see docs for [Webpack Configuration](https://github.com/rails/webpacker/blob/master/README.md#webpack-configuration)
+11. `extensions` was removed from the `webpacker.yml` file. Move custom extensions to your configuration by merging an object like this. For more details, see docs for [Webpack Configuration](https://github.com/rails/webpacker/blob/master/README.md#webpack-configuration)
 
   ```js
   {
@@ -93,19 +91,19 @@ Example going to a specific version:
   }
   ```
 
-13. Some dependencies were removed in [PR 3056](https://github.com/rails/webpacker/pull/3056). If you see the error: `Error: Cannot find module 'babel-plugin-macros'`, or similar, then you need to `yarn add <dependency>` where <dependency> might include: `babel-plugin-macros`, `case-sensitive-paths-webpack-plugin`, `core-js`, `regenerator-runtime`. Or you might want to remove your dependency on those.
+12. Some dependencies were removed in [PR 3056](https://github.com/rails/webpacker/pull/3056). If you see the error: `Error: Cannot find module 'babel-plugin-macros'`, or similar, then you need to `yarn add <dependency>` where <dependency> might include: `babel-plugin-macros`, `case-sensitive-paths-webpack-plugin`, `core-js`, `regenerator-runtime`. Or you might want to remove your dependency on those.
 
-14. If `bin/yarn` does not exist, create an executable [yarn](https://github.com/rails/webpacker/blob/master/lib/install/bin/yarn) file in your `/bin` directory.
+13. If `bin/yarn` does not exist, create an executable [yarn](https://github.com/rails/webpacker/blob/master/lib/install/bin/yarn) file in your `/bin` directory.
 
-15. Remove overlapping dependencies from your `package.json` and rails/webpacker's `package.json`. For example, don't include `webpack` directly as that's a dependency of rails/webpacker.
+14. Remove overlapping dependencies from your `package.json` and rails/webpacker's `package.json`. For example, don't include `webpack` directly as that's a dependency of rails/webpacker.
 
-16. Review the new default's changes to `webpacker.yml` and `config/webpack`. Consider each suggested change carefully, especially the change to have your `source_entry_path` be at the top level of your `source_path`.
+15. Review the new default's changes to `webpacker.yml` and `config/webpack`. Consider each suggested change carefully, especially the change to have your `source_entry_path` be at the top level of your `source_path`.
 
-17. Make sure that you can run `bin/webpack` without errors.
+16. Make sure that you can run `bin/webpack` without errors.
 
-18. Try running `RAILS_ENV=production bin/rails assets:precompile`. If all goes well, don't forget to clean the generated assets with `bin/rails assets:clobber`.
+17. Try running `RAILS_ENV=production bin/rails assets:precompile`. If all goes well, don't forget to clean the generated assets with `bin/rails assets:clobber`.
 
-19. Try your app!
+18. Try your app!
 
 ## Examples of v5 to v6