Undefined function Mix.env/0

[ghost]

Environment

Tested on three different machines/environments.

• Elixir & Erlang/OTP versions (elixir --version): 1) Erlang Solutions apt repository for ubuntu (in docker)

  
  Erlang/OTP 23 [erts-11.0.2] [source] [64-bit] [smp:6:6] [ds:6:6:10] [async-threads:1] [hipe]

Elixir 1.10.4 (compiled with Erlang/OTP 22)

2) Windows 10 Pro 1909 with Elixir installer

Erlang/OTP 23 [erts-11.0] [64-bit] [smp:6:6] [ds:6:6:10] [async-threads:1]

Elixir 1.10.4 (compiled with Erlang/OTP 21)

3) Elixir docker image

Erlang/OTP 22 [erts-10.7.2.1] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:1] [hipe]

Elixir 1.10.4 (compiled with Erlang/OTP 22)

* Which version of Dialyxir are you using? (cat mix.lock | grep dialyxir):
1.0.0

### Current behavior
When running `mix dialyzer` on my phoenix project with `MIX_ENV=dev`, I get on all three environments the same error:

Total errors: 1, Skipped: 0, Unnecessary Skips: 0 done in 0m6.08s :0:unknown_function Function Mix.env/0 does not exist.

---

done (warnings were emitted) Halting VM with exit status 2

Format raw says only (unhelpful-wise):

{:warn_unknown, {[], 0}, {:unknown_function, {Mix, :env, 0}}}

### Expected behavior
No errors. Project compiles without any errors or warnings and runs without any problems. All `Mix.env()` usages are valid, I'm running a mix release without any crashes.

[jeremyjh]

If you are using mix application at runtime, you need to included it in your extra_applications key in your mix.exs. We're not encouraged to use Mix at runtime in our applications, since it is a build tool. If you are using mix release you probably don't want to be using Mix.env().

[ghost]

I'm not running Mix at runtime, it's used completely at compile time for conditional compilation.

[romenigld]

I fixed the Dialyzer warnings with the unquote macro doing this:

if unquote(Mix.env() == :prod) do