Design Meeting Notes, 7/28/2021

[DanielRosenwasser]

Overriding libs and @types/web

#44795

• Underlying idea here is to take parts of the DOM API and put them into @types
  • Have already started shipping @types/web.
  • Enables you to avoid breaking changes around the DOM when upgrading TypeScript versions.
• But now we need to give a way to disable the DOM types.
  • You can already remove dom from the lib field in tsconfig.json.
  • However, packages can have a /// <reference lib="dom">
• One solution is a pragma of some sort - tell the compiler "no no, it's over here."
• Another is a tsconfig.json option that overrides.
• Pragma has implications
  • Have to watch for its addition/removal and that can modify the current project. Means that you have to load/unload files.
  • Global "pollution" along the same lines of
  • Can do tsconfig.json first and then do a pragma; easy path there. Pragma is undoable.
• Already have to modify the tsconfig.json if you need to remove the DOM - seems like you should just put all of this in the tsconfig.json.
• Have the full picture of the world, seems like it's doable.
• MSBuild context with no tsconfig?
  • Can add a specific MSBuild option.
• Seems like we're leaning with a tsconfig flag.
• [[Bike-shedding tsconfig options]]
• Big cliff in your configuration
  • Everything works
  • User installs @types/web
  • "OH NO ERRORS" 😭
  • User removes lib: dom
  • 😊👍
• How do we expect people to do dependency management?
  • peerDependency?
    • Really don't want people to declare it as a dependency.
• What if someone /// <reference types="web"> or /// <reference types="@types/web">
  • Can stop people from doing it in DefinitelyTyped
  • Can also give an error in TypeScript itself.
• Can also use Node.js policies to override.
  • https://nodejs.org/api/policy.html
  • Seems confusing.
  • Yarn overrides can do some of this.
• Do we see people doing this beyond just @types/web?
  • People may want their own "strict" version of the standard libraries.
  • People may want some subset of libraries like for SES.
  • Globals that conflict between libraries
• Conclusions
  • Ship as tsconfig setting first.
  • Iterate on the prototype.