Override a transitive emacs dependency

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4

The answer ended up being:

{ pkgs ? import <nixpkgs> {} }:
let
  myEmacs = pkgs.emacs;
  overrides = self: super: {
    flymake = super.flymake.override {
      elpaBuild = args: super.elpaBuild (args // {
        src = (builtins.fetchGit {
          url = "git@github.com:flymake/emacs-flymake.git";
          rev = "8701c806d5e8f4e2c6f7dea461273482ad89c029";
          ref = "master";
        }) + "/flymake.el";
      });
    };
  };
in
(pkgs.stdenv.mkDerivation {
  name = "debug-flymake-annoying-clutter";
  buildInputs = [
    (((pkgs.emacsPackagesGen myEmacs).overrideScope' overrides).emacsWithPackages (p: with p; [
      p.haskellMode
      p.flymake
    ]))
  ];
})

I now am left with an emacs bug, but in the emacs that nix profile produces you can M-x customize-group and see the run in place option is available!