A wish: create rel file about relx

[tsloughter]

Is the creation of the bin scripts that big of an issue? With dev mode {dev_mode, true}. relx will use links for setting up the lib directory, so it is doing much less, but will still generate the bin scripts.

[saleyn]

Well, there are cases when a developer just needs to create the rel/boot script without any other side effects. In this case relx is very helpful at figuring out the dependencies and the content of the *.rel file, but the fact that it doesn't have an option of not producing any other side effects is a bit troublesome. Not every application installation is embedded, and there are cases when release management is not needed, so it would be very helpful to have an option of just producing a rel file.

[tsloughter]

Right, if you set generate_start_script to false, include_erts to false and dev_mode to true you will only be generating the rel/boot/script files and linking to the libs.

[saleyn]

Ideally there should be a way of creating just a release file without links or any other artifacts, e.g.:
{providers, [rlx_prv_config, rlx_prv_release, rlx_prv_discover]}.
{include_erts, false}.
{dev_mode, nolinks}.
{generate_start_script, false}.
{generate_release_script, "priv/myproject.rel"}.

This would just create a single "priv/myproject.rel" file, without anything else under "_rel". In some simple projects not involving release handling this is all that is needed.

[jwilberding]

@tsloughter Do you think we should do this?

[nuex]

I think it would be cool if relx provided an API for doing things like this. Then you could build tools that use relx programmatically.

I'm looking through the code to work out how a .rel file gets generated.

[jwilberding]

@nuex do you have any update on this? I do agree on making relx more programmatic, will have to think out how to best do that.

[tsloughter]

You already can use it programmatically to just get the .rel file. The function rlx_release:metadata/1 returns the terms that make up the rel file. The provider rlx_prv_release will resolve the release so you have the release record to pass to rlx_release:metadata/1.

[saleyn]

Could you put a small example use case in the wiki?

[tsloughter]

I'll need to do a page on using the relx api, for now these are the commands I tested to verify in a shell that this works:

State = rlx_state:new([], []),
{ok, State1} = lists:foldl(fun rlx_config:load_terms/2, 
                          {ok, State}, [{release, {rel_a, "0.0.1"}, [app_a]}, 
                                       {lib_dirs, ["_build/default/lib"]}, 
                                       {default_release, {rel_a, "0.0.1"}}]),
AllProviders = rlx_state:providers(State1),
Providers = providers:get_target_providers(resolve_release, AllProviders),
{ok, State2} = lists:foldl(fun(ProviderName, {ok, StateAcc}) -> 
                                   Provider = providers:get_provider(ProviderName, rlx_state:providers(StateAcc)), 
                                   providers:do(Provider, StateAcc) 
                           end, {ok, State1}, Providers),
Release = rlx_state:get_realized_release(State2, rel_a, "0.0.1"),
rlx_release:metadata(Release).