docs: notes on migrating to PWA with Angular 9 (#215)

Co-authored-by: Marcus Schmidt <MarSchmidt@intershop.com>

docs/check-dead-links.js

@@ -98,6 +98,7 @@ glob('**/*.md')
           !link.includes('github.com') &&
           !link.includes('repository.intershop.de') &&
           !link.includes('support.intershop.com') &&
+          !link.includes('azurewebsites.net') &&
           !link.includes('github.com/intershop/intershop-pwa/commit')
       )
       .sort();

docs/guides/migrations.md

@@ -7,6 +7,45 @@ kb_sync_latest_only
 
 # Migrations
 
+## 0.19.1 to 0.20
+
+We upgraded from Angular 8 to version 9 and activated the new rendering engine Ivy with this (following the [official upgrade guide](https://update.angular.io/#8.0:9.0l3)).
+This was a major upgrade and comes with some changes:
+
+- The following changes are available for cherry-picking in one commit:
+
+  - Angular no longer supports the previously deprecated string syntax for lazy loaded modules. Change it to the [dynamic import format](https://angular.io/guide/deprecations#loadchildren-string-syntax).
+
+  - `server.ts` was partially rewritten to support SSR dev-server and serverless deployments. Building SSR is now supported by Angular CLI and explicit `webpack` builds were removed.
+
+  - `core-js` had a major upgrade to version 3, so `polyfill.ts` imports have changed.
+
+  - We temporarily replaced `@ngx-utils/cookies` with `ngx-utils-cookies-port` due to a [bug](https://github.com/ngx-utils/cookies/issues/20) when using Angular 9.1.
+
+  - `angular2-cookie-law` was replaced by `ngx-cookie-banner` for compatibility reasons. This comes with a styling overhaul.
+
+- Further commits contain necessary refactoring:
+
+  - `TestBed.get` in tests was deprecated in favor of the new type-safe `TestBed.inject`.
+
+  - The empty generic type for NgRx `Store` is now the default and does not have to be supplied. The TSLint rule `ngrx-use-empty-store-type` was adapted to apply this refactoring.
+
+  - We removed lazy loading with `@wishtack/reactive-component-loader` and replaced it with the native Angular 9 approach. If you have customized or created extensions, you will have to adapt the following:
+
+    - Extension export modules are no longer imported and exported in `SharedModule`, instead export them in `ShellModule`.
+
+    - Instead of pointing to the extension module with `ReactiveComponentLoaderModule` in the extension exports module, use the new provider for `LAZY_FEATURE_MODULE` pointing to the _extension store module_, if available. All further lazy loading is done by lazy components and lazy loaded pages. With this, the extension module should no longer import the extension store module.
+
+    - Lazy components should no longer be part of the repository as they can be auto-generated on `npm install`. Use the new decorator `@GenerateLazyComponent()` via the `lazy-component` schematic to generate lazy components. We currently do not support creating lazy components for components with `@Output()` decorated fields.
+
+    - Previous work-arounds in `<extension>-store.ts` and `<extension>-store.module.ts` for adding reducers of selecting the feature state are no longer necessary and can be refactored to standard approaches.
+
+  - We performed a major upgrade to `prettier` which comes with new code formatting for parts of the code.
+
+  - We replaced VSCode extension `stylelint-plus` with the official extension. Update the recommended extensions.
+
+  - We overhauled the integration of utility libraries for our custom schematics and TSLint rules. These libraries now get built when `npm install`ing the PWA and transpiled JavaScript sources are no longer part of version control. Also, they mainly reuse libraries from the project root now.
+
 ## 0.18 to 0.19
 
 We migrated from using [ngrx-router](https://github.com/amcdnl/ngrx-router) to the official and better supported [@ngrx/router-store](https://ngrx.io/guide/router-store).