Clean up ast.TIdTable type definition

[haxscramper]

ast defines TIdTable type that is used in several parts of the semantic pass. Type defined as follows:

  TIdPair* = object
    key*: PIdObj
    val*: RootRef

  TIdPairSeq* = seq[TIdPair]
  TIdTable* = object # the same as table[PIdent] of PObject
    counter*: int
    data*: TIdPairSeq

All the uses of the val: RootRef field are either converted to PType or PSym (result = PType(idTableGet(c.bindings, t)) etc.). This means RootRef can be easily replaced with

type
  PSymOrTyp = object
    case isSym*: bool
      of true:
        sym*: PSym

      of false:
        typ*: PType

This would not create any functional difference, but will clean up the code a little.

[alaviss]

This will make it a touch too expensive. Right now the field takes 8 bytes on a 64-bit machine. If we were to add a bool sentinel, alignment will cause this to inflate to 16 bytes, which doubles the memory usage...

As much as I hate it, exploiting inheritance works better for this instance.

[alaviss]

We can tighten it up by making val to be PIdObj as well, as that is the common ancestor of PType and PSym.

[haxscramper]

All uses of the idTableGet are either PSym -> PSym or PType -> PType, which means we can make this procedure a generic, with the PIdObj for val