Issue an error when a derived class precedes its base class

[Ryan Cavanaugh (RyanCavanaugh)]

Fixes #8633 and dozens of other reportings of this easily-detected error case

[Daniel Rosenwasser (DanielRosenwasser)]

Why are we only checking between base/derived? Basically any value-side reference to a class should be an error before its declaration.

[Nathan Shively-Sanders (sandersn)]

Can you reorder these classes to fix the error? I'd rather keep types and symbols around for tests that are not meant to exercise the new error.

[Nathan Shively-Sanders (sandersn)]

And probably some of the other tests too.

[Mohamed Hegazy (mhegazy)]

+1

[Mohamed Hegazy (mhegazy)]

👍

[mihailik]

Does this cover the ordering across files when used with -outFile? That is, Derived and Base are in different files, but when compiled into the single output the order can go a wrong way — is that also reported?

Also what about this case, will it be (incorrectly) reported as an error?

function some() {
  class Derived extends Base {
  }

  return new Derived(); 
}

class Base { }

Textually Derived is preceding the Base here, but it won't be cause any problems during execution.

My logic suggests ordering warnings should only apply if Derived and Base are top-level or namespace-level classes.

[Ryan Cavanaugh (RyanCavanaugh)]

Yep, this fix uses the function isBlockScopedNameDeclaredBeforeUse which knows how to handle both outFile ordering and "evaluated later" scenarios correctly. It's the same function we use to detect improper ordering / use of let variables so that logic should be pretty well ironed-out by now.