How to switch between local or Hex dependency?

This may not work for you but taking inspiration from Doggo, I package the demo app alongside the library in the same repo. While there some annoyances around grepping and how some editor tools handle nested mix.exs, it’s generally really convenient for everyone: 1) You can simply leave the dep as {:my_lib, path: ".."} in your demo’s mix.exs, 2) the demo repo is source controlled alongside the lib, and 3) when users only have to clone one repo to get everything.

I can imagine this isn’t always viable so I’m also interested in other options.

I do this in the demo for one of my projects, in “mix.exs”:

defp deps do
  [
    {:phoenix, "~> 1.7.14"},
    ...,
    my_lib_dep()
  ]
end

defp my_lib_dep() do
    if File.exists?(Path.join(__DIR__, "../my_lib/mix.exs")) do
      {:my_lib, path: "../my_lib"}
    else
      {:my_lib, "~> 0.1.0"}
    end
end

Or you can append an entire list to the end if you have multiple deps. The nice thing about “mix.exs” is that it’s code, and is executed every time you run mix.

I didn’t do it this way because it feels wrong to reach out into an unsuspecting user’s filesystem to execute code (at least from an unsanctioned directory). While I’m fully aware it’s super edge case, you never know what people have on their machines. For example, maybe they clone the example app into a directory where a long time ago they were experimenting with a mix project with the same name as your lib. Confusion ensues. It’s certainly an option, but I wish there was a more “official” way.

If you don’t like that option, you can always use a environment variable to achieve the same, the important point is as @Nicodemus mentioned: you can execute elixir code inside of mix.exs, which is a very powerful concept.

@BartOtten already mentioned the env variable approach which I do like better. I’m certainly aware mix.exs is just code which I thought was implied by my saying I already considered @Nicodemus’s approach (well, same goes for checking an env var, really).

Indeed, after reading it again I misunderstood the question.

Addressing your previous concerns, just opening a project with a LSP carries risk of executing stuff you are unaware of, especially since elixir metaprogramming allows execution of code at compile-time.

Current implementation is like this. I did commit an .envrc file which sets the path. It seems checking path existence is the only ‘fully native’ solution. Combining it with env override and a warning might hit the sweet spot.

defp routex_dep() do
    if path = System.get_env("ROUTEX_PATH") do
      IO.puts(">> !! USING LOCAL ROUTEX PATH !! <<")
      {:routex, path: path}
    else
      {:routex, ">= 0.0.0"}
    end
  end

If the solution works without many hitches, what is inherently wrong with it?

I guess you could use a mix task to ask the user the default option before he starts the project, but I don’t see that as a much better approach.

Not much. But as I can imagine others having the same use case, I wondered if there would be a better way.

And because I rather have a minimum of helper apps (such as direnv).

—nvm—..