Erlang parse transform to add -vsn attributes from (e.g.) git.

By default, an Erlang module has a vsn attribute that's the MD5 checksum of the module. You'd probably prefer something easier to read, such as 1.0.2. You can control this version by adding a -vsn module attribute, for example:

-module(foo).
-vsn("1.0.2").

% ...

But that's tedious. So we wrote a parse transform that allows you to set the version attribute at build time.

Add it to your rebar.config file, as follows:

{deps, [
    {vsn_transform, ".*",
        {git, "https://github.com/rlipscombe/vsn_transform.git"}}
]}.

{erl_opts, [
    {parse_transform, vsn_transform},
    {vsn_command, "git describe --tags"}
]}.

Obviously, you can change the command as needed. You might want to use git rev-parse --short HEAD, for example.

Note that the parse transform runs the command once for each file being compiled, which can sometimes be slow. If you'd prefer, you can set the version explicitly:

    {vsn, "1.0.2"}

You lose some flexibility, because the value's now hard-coded in rebar.config. If you'd prefer to use an environment variable, create a rebar.config.script file. See examples/rebar_script_example.

You can check it with the following:

lists:map(
    fun({Mod, Path}) ->
        Vsn = proplists:get_value(vsn, Mod:module_info(attributes)),
        {Mod, Vsn}
    end, code:all_loaded()).

Or with:

beam_lib:version("path/to/some.beam").

Apache 2.0