Add unsafe sub- type definitions

[fgarcia]

TypeScript Version: 2.8.3

Search Terms:

• explicit cast
• require cast
• unsafe type

Code

function queryOutsideWorld(queryName) : unsafe {
   // ... some fetch() or RPC call
  // ... some JSON.parse()
  // ... extract body with random interface
  return someRandomData
}

// fail
let data = queryOutsideWorld('user-profile')

// ok
let data: UserProfile = queryOutsideWorld('user-profile')

Related Issues:

#10715
#22716
#9999

I've read similar issues and the closest one is the unknown type #10715. However I believe there is room for a less complex solution.

Currently if I fetch something from the outside world I must do some kind of runtime validation and cast to a known type / interface. If I start looking for common functionality I will be forced to create functions and even libraries that must return any but I would like a way return a value and force the programmer to do an explicit cast.

In my example I've used a new type keyword as a basic example, but I would rather like to have something where I can define unsafe subtypes such has:

// global.d.ts
type Unsafe extends any as unsafe
type RiskyAny extends any;

if (process.env.NODE_ENV === 'production') {
  type RiskyAny extends any as unsafe;
}

This would enable a second case. I want to prototype code/ideas in a non very strict environment, and only increase the typing-strictness later, if/when the library "matures". There is code that is OK to have type any in development, but in production (or at a more mature version) it will have to go away before other any types

[mhegazy]

looks like a duplicate of #10715

[typescript-bot]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.