Support executing ESM schematics

首先跟踪编译和执行自定义 schematics 的 Angular CLI 路径，然后将其与所引用的 Angular loadEsmModule() workaround 以及链接的 schematics 示例进行比较。完成标准是 ESM schematics 可以在不出现报告中的 CommonJS require() 错误的情况下执行，并且有针对该行为的测试覆盖。

🚀 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).