Trees that Grow / D3609

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Trees that Grow / D3609

Alan & Kim Zimmerman
This is a heads up that D3609[1], the first step toward implementing Trees that Grow[2] for the hsSyn AST is about to land in master.

The key change is that it is replacing the HsSyn type parameter with one that is an index into a set of type families, enabling the extension points (for a future diff).

Any current work in progress branches will need a one-time search and replace of all type parameters as follows

RdrName  -> GhcPs
Name  -> GhcRs
Var -> GhcTc
Id -> GhcTcId

Any code that makes use of the GHC API and needs to compile with earlier versions too can do something like

      #if MIN_VERSION_ghc(8,3,0)
      type ParseI     = GhcPs
      type RenameI    = GhcRn
      type TypecheckI = GhcTc
      type ParseI     = RdrName
      type RenameI    = Name
      type TypecheckI = Var

and then replace the RdrName / Name / Var type params with ParseI / RenameI / TypecheckI.

A real world example is in ghc-exactprint[3]

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