How to create custom cross-compile overlay?

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4

I have a video demonstrating overlays here.

However, if you’re doing a packages set like darwin, you’ll want to do something like:

# xcode_overlay
final: prev: {
  darwin = prev.darwin // {
    xcode_10_2 = .... ;
    ...
  }
  lib = prev.lib // {
    systems.examples.iphone64 = prev.lib.systems.examples.iphone64 // {
      sdk = "...";
    };
    ...
  };
}

maybe you could also use lib.recusiveUpdate. Which should make this a little nicer as the // operator will only overwrite top-level attributes.