Having JSON.stringify(expr) return string | undefined

#38574

• We approved an issue about JSON.stringify potentially returning undefined.
  • JSON.stringify(function() {}) -> undefined
  • JSON.stringify(undefined) -> undefined
  • JSON.stringify(Symbol()) -> undefined
  • JSON.stringify({ toJSON() {} }) -> 🤷‍♀️
  • JSON.stringify(?????) -> string
• Thinking
  • JSON.stringify(object | undefined) -> string | undefined
  • JSON.stringify(any) -> string
• What are the goals?
• Should've said it was string | undefined from the beginning, but strictNullChecks came later and we didn't wanna break people.
• Fixing this is a fool's errand.
• Won't fix?
  • Can't fix, won't fix, don't know how to fix.
  • The cure is worse than the disease.

Upper Bounds of Types Resolved to any

#38555
#29571

• Should we specially interpret function fn<T extends U>(arg: T) when U is a type that resolves to any?
  • Substituting a type with any ideally shouldn't break existing code.
  • But users were using this to say "from the outside, I'm sound, from the inside I'm not".
• Using any as a type constraint is a foot-gun.
  • But any itself is a foot-gun.
• What about syntactic any being different?
  • Could give an error on syntactic any: "you mean unknown"
  • Seems strange.
• extends any might be meaningful, but 50% of the time that meaning might not be obvious to people, causes more bugs.
• Conclusion
  • Reconsider with more feedback
  • No plans for servicing release

Emitting empty export lists, and other fun problems with bundlers

webpack/webpack#10889

• Do we need to start emitting export {}?

  • Maybe not for empty modules.

• We're not emitting export {} for value-ful modules though.

  export type Yadda = any;
  
  var a = 10;
  
  export { };

  • Affects other stuff (e.g. strict mode)
  • We also don't emit anything in empty files when alwaysStrict is on.
    • Because we assume that, well, it's a module.

• Weird because we emit export {} for .d.ts files.

• Conclusion

  • Don't restore export * behavior
  • Evaluate where export {} may need to be injected.