Would one-time self-replacing macro/compile-time-function instead of CLI generators be possible?

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There is an example in Ash Framework of adding a resource Album into Music domain
mix ash.gen.resource Tunez.Music.Album --extend postgres. It generates a new module Album and modifies Music module – adding the Album into the domain.

I wondered if it would be possible to rather have a compile-time function (macro-ish) that would replace itself this one time during compilation and modify other modules as needed? It would allow developers not to deal with CLI but just use Elixir functions instead in the IDE environment having its usual features (docs, autocompletion, etc.)

To make it a bit more clear, I am imagining something like:

  • Add add_resource "Artist", extend: "postgres" in the defmodule Tunez.Music.
  • During compilation, add_resource would get called replacing itself and modifying Tunez.Music module, and creating Tunez.Music.Artist module
    • It would add resource Tunez.Music.Artist in the resources do ... block.
  • Which means it would have to recompile Tunez.Music after the function add_resource was executed and add Tunez.Music.Artist to the compilation queue.

What do I expect? To hear where this idea breaks down and to learn something new from that about Elixir. (Or possibly, how to achieve this.)

Why am I asking: I am exploring Elixir and its ecosystem and libraries (looks all very promising). I like to learn about languages/frameworks by trying to push at their limits. I would like to have the natural Elixir interface to generate the code instead of dealing with CLI tools myself.

If feasible, I would try to do this to get my hands dirty.

Thanks.

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I think it would be technically doable, but would be relatively complex, and might be able to be done better via things like editor snippets etc. but yeah a macro could call arbitrary code at compile time, including code that replaces it in its own source file.

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Wouldn’t even need to be a macro. When there’s no AST to be replaced with other AST it could potentially even be a function call. Though not sure how much “context” one gets about where exactly a call originated to replace that line.

Should also be quick to “validate”

# lib/commands.ex
Mix.Task.run("ash.gen.resource", ["Tunez.Music.Album", "--extend", "postgres"])

File.write(__ENV__.file, File.stream!(__ENV__.file, :line) |> Enum.at(-1))
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