Support executing ESM schematics

まず、カスタム schematics をコンパイルして実行する Angular CLI の経路を追跡し、参照されている Angular の loadEsmModule() workaround およびリンクされた schematics の例と比較します。ESM schematics が報告されている CommonJS の require() エラーなしで実行でき、その動作をカバレッジで確認できれば完了です。

🚀 Feature request

Support schematics written in ES Modules. Currently only CommonJS schematics are supported.

Command (mark with an x)

• new
• build
• serve
• test
• e2e
• generate
• add
• update
• lint
• extract-i18n
• run
• config
• help
• version
• doc
• other: compiling custom schematics

Description

Currently custom (and official) schematics can execute only CommonJS code, but not ES Modules. This is problematic when you want to import an ES Module in your custom schematics, for example HtmlParser from @angular/compiler (which since ng13 is shipped only as ESM).

Problems with not supporting ESM:

The following error started to occur for our custom schematics in runtime, since we upgraded from ng12 to 13:
require() of ES Module <path-to-the-repo>/node_modules/@angular/compiler/fesm2015/compiler.mjs not supported. Instead change the require of <path-to-the-repo>/node_modules/@angular/compiler/fesm2015/compiler.mjs to a dynamic import() which is available in all CommonJS modules.

But the advised change of the static @angular/compiler to a dynamic import is cumbersome due to various reasons:

• it unnecessarily changes the our synchronous code to asynchronous code
• it induces passing down the compilerModule (result of await import(@angular/compiler)) as an argument down to all helper functions (example in angular repo)
• it requires a hacky workaround ticking the Typescript compiler so to avoid compiling the dynamic import() into the require() call - for more see the workaround function loadEsmModule() in angular repo . Btw. this function is not exported in public API, so we need to copy-paste it to our repo.

Describe the solution you'd like

Support executing ESM schematics .

Describe alternatives you've considered

Change the import of ESM to dynamic imports in our schematics code and deal with all its cumbersome consequences (described above).