Rebar3 .app file pkg_name for hex and relx about relx

[tsloughter]

The package name is only use in rebar.config. In .app.src you use the application name.

[tsloughter]

Same for the list of applications in the release, as in the list of apps in {relx, [{release, {r, "1"}, [app_1]}]}. The only place package name is ever used is deps.

[choptastic]

Thanks, I hadn't noticed the {AppName, {pkg, PkgName}} option here: https://hex.pm/docs/rebar3_usage (hiding in plain sight)

It's notable that https://hex.pm/docs/rebar3_publish does specify that you can add pkg_name to the .app.src file, but it doesn't specifically mention that if you do that, you'll also need to specify the package name in rebar.config, otherwise bad things might happen.

I also see that the pkg_name term for the .app.src isn't specified anywhere on rebar3.org, and seems to only exist on hex.pm. I will contact the hex.pm team to suggest updates to the documentation, unless you happen to know if the documentation for hex.pm exists somewhere in a publicly editable state.

Thanks again.

[tsloughter]

Oooh, that is about naming the package you are publishing, not the dependency of a package. If you need to name your package different you put pkg_name in your .app.src like in the docs. But that is just publishing data.

[choptastic]

Indeed, but once that's done, it's not currently clear that doing so means you must also specify the package name explicitly in rebar deps as {AppName, {pkg, PkgName}}. That bit wasn't obvious (to me, anyway).

This was one of those situations where I wasn't really sure which app or config was at fault, since it's an interplay between rebar3, hex, and relx. But since the error itself manifested when making a release with relx, that's where I went with my questions.

So, in short, I've learned that:

1. Specifying {pkg_name, PackageName} in .app.src, means you must:
2. Specify {AppName, {pkg, PackageName}} in deps in rebar.config, otherwise:
3. relx will crash when making a release.

As this isn't a bug with relx, but can be a little difficult to troubleshoot if misconfigured, I propose some improved error messages with this PR: #893

Hopefully this is okay!

Thanks again for the help!

[tsloughter]

It should actually fail earlier than a release build. rebar3 should fail to build the application if you use {deps, [PackageName]}. So I'm not sure how you were able to get passed that?

[choptastic]

I'm not sure, but I'm not doing anything particularly crazy.

The package that set this off was erl_pipeline (with app name pipeline).

But I tested making a bare application and specifying erl_pipeline as the only dependency (where it should be {pipeline, {pkg, erl_pipeline}}), rebar3 compile pulls deps and compiles just fine.