... has invalid version ~> Version_1 or ~> Version_2

[starbelly]

Originally reported by ulfa in Supersonido/rebar_mix#6

Hi,

I am trying to use rebar3_mix, but when ich declare a dependency like
{timex, "~> 3.5"} rebar3 tries to download the dependencies from timex.

But the dependency of the timex package tzdata is declared in the mix.exs as {:tzdata, "~> 0.1.8 or ~> 0.5"} and I think rebar3 can't manage this.

[starbelly]

Confirmed. This, is due to rebar not supporting these type of constraints. This PR (draft) attempts to resolve this by migrating to verl in rebar3 : erlang/rebar3#2785

[filmor]

It was an attempt, but this stuff is really complicated :/

I'm trying it again now entirely independent of verl by first attempting to introduce a distinction between requirements and versions in rebar3.

/EDIT: And I think I already wrote this somewhere else: In my opinion, this is the single most critical issue for rebar3/elixir compatibility, having different resolution algorithms for deps and even incompatible requirement formats.