Not embracing package extensions

[johnnychen94]

This is a memo to get some agreement on why I don't want to introduce the new package extension mechanism for ImageIO (and FileIO).

• Compatibility:
  • we want downstream users to refrain from managing the compatibility of different backends
  • package authors that only want minimal jpeg support can use JpegTurbo and maintain the compatibility themselves
• workflow:
  • we don't want our users to remember every image IO backend name to trigger the wrapper module loading, we want our users to remember only ImageIO and FileIO.load/FileIO.save.
  • A common workflow is (v1.9) pkg> add ImageIO FileIO and every project above it just works (without needing to add them repeatedly). The package extension doesn't support this workflow IIUC. (CRef: allow loading extensions when a trigger is loaded from below the parent's load path JuliaLang/julia#49701)

[timholy]

Agreed! For exactly the reasons you cite.

[dpinol]

Would it make sense to make an exception for sixel? It's a pain that it depends on REPL, which takes so long to compile