Support rebar3 auto in relx's dev_mode release

[gleber]

It would be nice to be able to add rebar3_auto to a relx release which has dev_mode enabled and let it rebuild files in the running release.

[vans163]

What is the difference between working in a relx release in dev_mode vs working in development mode with rebar3_auto outside a release?

If the reason is convincing enough it could be looked into.

[lucafavatella]

What is the difference between working in a relx release in dev_mode vs working in development mode with rebar3_auto outside a release?

Templating of sys.config and/or vm.args.

[vans163]

@lucafavatella Is it possible to get some more details of what is happening now, and what should be the expected behavior?

[lucafavatella]

@vans163 An OTP release built with rebar3 can benefit from "overlays" for creating directories, copying files and instantiating file templates in the release. The most typical use is templating of sys.config and vm.args.

Off the top of my head (I moved away from my attempt yesterday):

• Working in a relx release in dev_mode executes overlays e.g. instantiates sys.config and vm.args, but code is not automatically reloaded on recompilation;
• Working in development mode with rebar3_auto outside a release does not execute overlays hence is unusable of the OTP release code does not have (or cannot have) defaults for the configuration parameters; if OTP release has defaults for the configuration parameters though rebar3_auto provided code reloading on recompilation.

[vans163]

@lucafavatella Il look into this, but from the top of my head recompilation leverages rebar_agent:do(compile).

If rebar_agent is not picking up changes when the sources change, then it needs to be made to play better with dev_mode relx releases.

Otherwise rebar3_auto is not picking up the changed files.

[vans163]

Give this a new try please, v0.5.1 uses r3:do(compile) now