Library code inside fesm2015/esm2015/_esm2015 directories has been downlevelled to ES2015 which will not have native async/await. As a result, code from those directories can be skipped from the additional checks as well as the downlevel processing. RxJS uses the `_esm2015` directory naming convention.
With this change we configure `webpack-dev-middleware` and `webpack-dev-server` to print errors to the console, which previously were not displayed. This is because both of these libraries log/emit errors using the logger and the compilation API.
Certain errors such as the one below, were being swallowed during `ng serve`.
```
An unhandled exception occurred: Prevent writing to file that only differs in casing or query string from already written file.
This will lead to a race-condition and corrupted files on case-insensitive file systems.
/home/circleci/ng/aio/dist/generated/docs/api/router/Routes.json
/home/circleci/ng/aio/dist/generated/docs/api/router/ROUTES.json
```
Tailwind now suppports an environment variable named `TAILWIND_MODE` with possible values of `build` and `watch`. If the variable has not been set, the tooling will now set the variable based on the builder's `watch` option.
The current stable version of `webpack-dev-server` does not fully handle Webpack 5's configuration options. In this case, the `target` option can now be an array. However, the array form is ignored by the dev server which can cause the live reload client code to not be included in the output bundles. To remedy this, the `injectClient` option is used when live reload is enabled which forces the client code to be included regardless of the `target` option.
The GC caching mode will remove any unused cache entries after each rebuild. This prevents old modules from being retained indefinitely during long-lived development sessions.
The Webpack 5 automatic public path support can cause an incorrect public path to be used to load assets and lazy loaded routes. The current logic relies on the last script element found at runtime in the application's index HTML which may not be related to the application scripts. Now if a `deployUrl` is not specified, the Webpack `publicPath` option is defaulted to an empty string which provides equivalent behavior to Webpack 4.
In Webpack 5, the Webpack callback must be used when Webpack is running in watch mode.
Related warning
```
.(node:6565) [DEP_WEBPACK_WATCH_WITHOUT_CALLBACK] DeprecationWarning: A 'callback' argument need to be provided to the 'webpack(options, callback)' function when the 'watch' option is set. There is no way to handle the 'watch' option without a callback.
```
Webpack 5 now uses a `chunkHash` hook that is accessible from `JavascriptModulesPlugin.getCompilationHooks()`. The `hashForChunk` hooks have been deprecated in Webpack 5.
TypeScript files had the potential to be processed twice by the build optimizer. This did not affect the output code but could lead to longer production build times. The build optimizer is now configured in one centralized location for both TypeScript and JavaScript files. The Webpack configuration partial for TypeScript support is also reduced to one common function for both AOT and JIT as a result.
While the builders when executed via the Angular CLI and their associated options are considered stable, the programmatic APIs are not considered officially supported and are not subject to the breaking change guarantees of SemVer.
The programmatic APIs for the builders are now explicitly marked as experimental. This allows the package to use a stable versioning scheme while also continuing to provide access to the experimental programmatic API elements of the package.
With the minimum version of Node.js now set to v12, the promise fs API can now be leveraged within the tooling.
This change also uses `copyFile` (with copy-on-write where available) to setup the the service worker files as well a streaming APIs to generate service worker hashes. Both of which improves performance and reduces memory usage.
A new build option named `inlineStyleLanguage` has been introduced that will allow a project to define the stylesheet language used in an application's inline component styles. Inline component styles are styles defined via the `styles` property within the Angular `Component` decorator. Both JIT and AOT mode are supported. However, JIT mode requires that inline styles only be string literals (compile-time partial evaluation is not supported in JIT mode). Currently supported language options are: `CSS` (default), `Sass`, `SCSS`, and `Less`. If the option is not specified, `CSS` will be used and enables existing projects to continue to function as expected.
In some scenarios in Webpack 5 percentage goes from 1 back to 0.99, ex: 0.99 -> 1 -> 0.99 -> 1. This causes the "complete" message to be displayed multiple times.
The internal Webpack configuration now includes support for style rules with MIME type conditions. This allows the data URIs generated for inline component CSS styles by the Angular Webpack plugin to be processed with the same loaders as file based styles.
