Support executing ESM schematics

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#22,786 7 comments 61 reactions 0 assignees View on GitHub

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
35/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Stale
Tech stack
angular, typescript
Domain
cli

Research direction

Start by tracing the Angular CLI path that compiles and executes custom schematics, then compare it with the referenced Angular loadEsmModule() workaround and the linked schematic examples. Done means ESM schematics can execute without the reported CommonJS require() error, with coverage for that behavior.

Written by the indexing model from the issue text.

Description

area: @angular-devkit/schematics feature feature: under consideration

🚀 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).

Dominant language
TypeScript
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Merged PRs (30d)
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