Mix archives: can I have several of Phoenix's (different versions) and use them concurrently?

You could install each in a different MIX_HOME. And switch to those when using different versions.

Oh, so this is like Ruby’s gemsets and OCaml’s OPAM’s switches? Cool, at least there’s a good workaround, thank you.

There‘s https://www.phoenixdiff.org/ for that as well.

But that’s just comparing different Phoenix versions?

EDIT: I am after comparing a project freshly generated by Phoenix’s generator, and an in-progress project that was earlier generated by the same version of the generator.

It seems that a little better granularity (and I suppose less file waste) can be achieved by utilizing the MIX_ARCHIVES env var, I’ll experiment and report back.

Confirmed that using the following commands yields slightly different projects and thus it can be used to “sandbox” using various mix archive-related commands (like phx.new and many others):

MIX_ARCHIVES="$HOME/.mix_phoenix-1.5.5" mix archive.install hex phx_new 1.5.5
mkdir ~/demo155
cd ~/demo155
MIX_ARCHIVES="$HOME/.mix_phoenix-1.5.5" mix phx.new demo

MIX_ARCHIVES="$HOME/.mix_phoenix-1.5.6" mix archive.install hex phx_new 1.5.6
mkdir ~/demo156
cd ~/demo156
MIX_ARCHIVES="$HOME/.mix_phoenix-1.5.6" mix phx.new demo

Doing diff -ur ~/demo155/demo ~/demo156/demo only shows differences between the secret_key_base and signing_salt variables (both irrelevant here) and – voila! – there are differences in mix.exs:

-      {:phoenix, "~> 1.5.5"},
+      {:phoenix, "~> 1.5.6"},

and:

-      {:phoenix_live_dashboard, "~> 0.2"},
+      {:phoenix_live_dashboard, "~> 0.3 or ~> 0.2.9"},

TL;DR: Using the MIX_ARCHIVES env var works perfectly for my goal.

Many thanks to @NobbZ for pointing me in the right direction.