Can't generate release if config contains values set by an anonymous function about exrm

[pcewing]

I ran into this as well and I believe it's actually a limitation with Mix.Config.read!/1.

In distillery, that function is used to read the base configuration:
https://github.com/bitwalker/distillery/blob/master/lib/mix/lib/releases/assembler.ex#L558

Then it's merged with the release configuration and written:
https://github.com/bitwalker/distillery/blob/master/lib/mix/lib/releases/assembler.ex#L537

Observations

Create a new project and add a key to the config whose value is an anonymous function:

mix new potato && cd potato
echo "config :potato, my_var: fn -> :ok end" >> config/config.exs

Start an iex session, read the config, and notice the output:

iex> config = Mix.Config.read!("config/config.exs")
[potato: [my_var: #Function<12.3456789/0 in :erl_eval.expr/5>]]

Correct me if I'm wrong, but that function will only exist in the current BEAM instance. We can't serialize/write it and expect it to be valid during a subsequent execution of the program when we read it; it will be redefined at run time in the new BEAM instance.

Edit: Removing the last observation as I misunderstood the purpose of Mix.Config.persist/1.

[bitwalker]

@pcewing It's not actually a problem with Mix.Config.read!/1, as it is supposed to return the captured function. The issue is that we need to write a function in capture syntax to the sys.config file, so that when it is evaluated by the VM, we get a valid capture back. What happens now is we serialize the capture, which of course is invalid. It's something I have some ideas on how to tackle, but I'll be doing so in distillery rather than exrm.

[szabolcsmaj]

Thank you @bitwalker! I'll close this since directions are clear --> Switch to distillery