Private Fields in .d.ts Files

#30829

• One issue is that .d.ts files are sometimes lossy because private fields omit their types.
  • We probe the structure
• The variance issue sounds like something we're not likely to address.
  • It's broken today for private, why change for #?
• Perhaps it makes sense to just include a single #_ declaration in the output if we're just erasing all details.
  • Why don't we just include the original privates in the class declarations?
    • Because you don't want 30 privates in your classes?
    • But that's the case for private properties today.
  • Do private fields affect incremental and project references?
    • Yes, but they probably shouldn't.
    • A point in favor of emitting a single private property?
• So #_?
  • #privateProperty just so people can search it online more easily.

Collisions of Imported Types

#31231

• Introducing an error when types conflict with local type names.

import { foo } from "./stuff";
export type foo = foo;

• Breaks legitimate errors in firebase-firestore, glimmer, skype, vscode.
  • VS Code examples seemed suspicious.
• The general pattern is useful when running with isolatedModules, but there's no reason to use the same name.
• This is a breaking change, but the break seems legitimate, existing code seems wrong, and the fix is simple.

@RyanCavanaugh has the other notes.