Dialyzer error when checking Mix task

Questions / Help
,
1

I have a Mix task that extracts the version number of the project (for use in a build pipeline):

defmodule Mix.Tasks.VersionNumber do
  @moduledoc "Mix task to print the current version number to stdout"
  use Mix.Task

  @shortdoc "Print the current application version number"
  def run(_) do
    MyApp.MixProject.project |> Keyword.fetch!(:version) |> IO.puts
  end
end

This all works fine. However, when I run mix dialyzer on my project, I get an error:

$ mix dialyzer
Compiling 1 file (.ex)
Finding suitable PLTs
Checking PLT...
[:asn1, :castore, :certifi, :compiler, :connection, :cowboy, :cowboy_telemetry, :cowlib, 
:crypto, :dart_sass, :db_connection, :decimal, :ecto, :ecto_sql, :eex, :elixir, :esbuild, 
:expo, :file_system, :finch, :geo, :geo_postgis, :gettext, :hackney, :heroicons, :hpax, 
:httpoison, :idna, :jason, :kernel, :logger, :metrics, :mime, :mimerl, :mint, :mix, 
:nimble_options, :nimble_pool, :parse_trans, :phoenix, :phoenix_copy, :phoenix_ecto, 
:phoenix_html, :phoenix_live_dashboard, :phoenix_live_reload, :phoenix_live_view, 
:phoenix_pubsub, :phoenix_template, :plug, :plug_cowboy, ...]
PLT is up to date!
No :ignore_warnings opt specified in mix.exs and default does not exist.

Starting Dialyzer
[
  check_plt: false,
  init_plt: '/home/ian/projects/verna/myapp/_build/dev/dialyxir_erlang-25.1.2_elixir-1.14.2_deps-dev.plt',
  files: ['/home/ian/projects/verna/myapp/_build/dev/lib/myapp/ebin/Elixir.MyApp.LocationSearch.SearchResult.beam',
   '/home/ian/projects/verna/myapp/_build/dev/lib/myapp/ebin/Elixir.MyApp.beam',
   '/home/ian/projects/verna/myapp/_build/dev/lib/myapp/ebin/Elixir.MyApp.Application.beam',
   '/home/ian/projects/verna/myapp/_build/dev/lib/myapp/ebin/Elixir.MyApp.ReferenceData.LandRegistry.beam',
   '/home/ian/projects/verna/myapp/_build/dev/lib/myapp/ebin/Elixir.MyApp.Gettext.beam',
   ...],
  warnings: [:unknown]
]
Total errors: 1, Skipped: 0, Unnecessary Skips: 0
done in 0m4.56s
lib/mix/tasks/version_number.ex:7:unknown_function
Function MyApp.MixProject.project/0 does not exist.
________________________________________________________________________________
done (warnings were emitted)
Halting VM with exit status 2

At a guess, the problem is maybe related to project/0 being defined in an .exs file rather than .ex? Is there a way to either ignore the mix task in the Dialyzer analysis, or, better, help it to find the definition of project/0?

2

I’m having the same problem, did you ever find a solution?

3

We switched approach, so we dropped this task from our project.exs.

However, we did find ourselves having to ignore some other Dialyzer errors. The pattern for that is to create a ./.dialyzer-ignore.exs file, using the pattern:

[
{path, error},
]

So in theory, this should work:

# .dialyzer-ignore.exs
[
{"./project.exs", :unknown_function}
]

But I’ve not tested it, so ymmv.

Good luck!
Ian

4

Dialyzer depends on the compiler, so it’s definitely not going to see modules defined in .exs files.

That file will be loaded by Mix at runtime before running the task, so it doesn’t actually fail.

A better approach might be to use the built-in Mix machinery, specifically Mix.Project.config/0:

defmodule Mix.Tasks.VersionNumber do
  @moduledoc "Mix task to print the current version number to stdout"
  use Mix.Task

  @shortdoc "Print the current application version number"
  def run(_) do
    Mix.Project.config() |> Keyword.fetch!(:version) |> IO.puts
  end
end
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