vrod
Get app versions at compile time?
I encountered this interesting thing while trying to add more info to Logger messages.
I can get the version of an app by running something like this:
:myapp
|> Application.spec()
|> Keyword.get(:vsn)
|> List.to_string()
However, I thought this calculation maybe is expensive, so I tried to save this at compile time by putting it into a module attribute:
@app_ver :myapp
|> Application.spec()
|> Keyword.get(:vsn)
|> List.to_string()
However I have noticed that Application.spec/1 returns nil at compile time. Is there a way to read and store an application version at compile time? Or is the version only known AFTER compilation?
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wojtekmach
You cannot access the application spec because your application is being compiled. Fortunately, you can access information about your Mix project like this:
defmodule Foo do
IO.inspect(Mix.Project.config()[:version])
end
wojtekmach
You can grab information about your deps in that project config too.
I believe the dep apps are automatically loaded (if not, you can Application.load/1 them) so you can definitely call Application.spec/1 and it will work 
vrod
I found solution to this: just add mix.lock to .formatter.exs:
[
inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}", "mix.lock"]
]
and then the above works!
jpcaruana
for me, this works very well:
{:ok, version} = :application.get_key(:myapp, :vsn)
Logger.info("Application xxx #{version}: started")cenotaph
I doubt any measurable performance drawbacks will occur with the following
<%= Application.get_env(:ex, :env) %>:<%= Application.spec(:ex, :vsn) %>
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