Add downstream integration test for hercules-ci/gitignore

[Profpatsch]

In hercules-ci/gitignore.nix#32 we noticed that using readDir (and searching for .gitignore files outside of the project directory) would watch way to many directories recursively. hercules-ci/gitignore.nix#33 should fix that, but we have to confirm.

[curiousleo]

More context: #211 (comment), #211 (comment)

[curiousleo]

I haven't been able to repro with a simplistic setup.

Setup

# default.nix
{ pkgs ? import <nixpkgs> {} }:
let
  gitignoreSrc = pkgs.fetchFromGitHub { 
    owner = "hercules-ci";
    repo = "gitignore";
    # rev = "f9e996052b5af4032fe6150bba4a6fe4f7b9d698";
    # sha256 = "sha256:0jrh5ghisaqdd0vldbywags20m2cxpkbbk5jjjmwaw0gr8nhsafv";
    rev = "f9525682432c116edfb390482dcc7f72ae3df64b"; # before "don't readDir the store"
    sha256 = "sha256:1iy502qi8ljj7c31vsjb75vnrbfkpc2pnfq85j33zvnr2li3kb4i";
  };
  inherit (import gitignoreSrc { inherit (pkgs) lib; }) gitignoreSource;
in
  pkgs.stdenv.mkDerivation {
    name = "hercules-gitignore-test";
    src = gitignoreSource ./.;
  }

# Makefile
install:
        echo 'Done'

and shell.nix is a soft link to default.nix.

As a sanity check, this succeeds:

$ nix-build .

Result

In neither case did lorri start watching / or /nix or /nix/store.

[curiousleo]

straceing this, it looks to me like the readDirs stop at the Git repo boundary in either case, except for special files like $HOME/.gitconfig and $XDG_CONFIG_DIR/git/config.

If there is a $HOME/.gitconfig then lorri will watch its parent directory, $HOME, and that may already lead to watcher issues.

This does not explain why users were seeing / and /nix being watched by lorri. But it does point to a problem that is not solved by hercules-ci/gitignore.nix#32.

---

Aside: why does lorri watch the parent directory? From https://docs.rs/notify/5.0.0-pre.1/notify/trait.Watcher.html#tymethod.watch:

On some platforms, if the path is renamed or removed while being watched, behaviour may be unexpected. [...] If less surprising behaviour is wanted one may non-recursively watch the parent directory as well and manage related events.

Possibly related: #232