Credo ignore existing errors

I want to add Credo to an existing project, and of course, when it runs it flags a lot of problems. What I want to know is there a built-in way to cause Credo to ignore the known issues, but report an error on new issues that may come up? That way the existing issues can be handled over time while we prevent any more issues from happening

I am not aware of anything Credo does to remember results of prior runs, but it does allow you to ignore specific lines or files, if you are willing able to go through the code and apply those exceptions.

You can use ReviewDog to filter out failures limiting them to only the errors in current diff.

As a kind of a workaround, you could use git to select only files that changed relative to the base branch for credo checks. It’s still coarse grained but allows for incrementally improving credo compliance of the code base (however that assumes branch-based workflow so YMMV).

NOTE: I didn’t run this code (it’s a heavily edited and simplified version of an existing solution). It should give an idea though.

defmodule Mix.Tasks.Credo.Ci do
  use Mix.Task

  @impl true
  def run(_) do
    if System.cmd("git", ["rev-parse", "--abbrev-ref", "HEAD"]) == {"master", 0} do"credo", [])
      {head_sha, 0} = System.cmd("git", ["rev-parse", "HEAD"])

      {closest_ancestor_sha, 0} =
        System.cmd("git", [

      {diff, 0} = System.cmd("git", ["diff", "--name-only", String.trim(closest_ancestor_sha)])

      files =
        |> String.split("\n")
        |> Enum.filter(&(&1 =~ ~r/(lib|test).*\.exs?/))
        |> Enum.flat_map(&["--files-included", &1])

      unless files == [] do"credo", ["-C", config_name | files])