python39Packages.pytest-xdist: add hook to add flags

[Artturin]

many of our packages have pytest-xdist in their inputs however
oftentimes the required flags aren't added to pytest flags
since we dont use tox and other frameworks

some examples of improvements
(my pc has ryzen 9 5900x)
hypothesis 11m:15s on hydra -> <1m on my pc
hypothesmith 8m on my pc -> <1m on my pc

the whole graph from pytest-xdist (tested by adding postPatch with true to xdist)
time nix build ".#python3Packages.hypothesmith"
19m:57s -> 9m:13s

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 22.05 Release Notes (or backporting 21.11 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
  • (Release notes changes) Ran nixos/doc/manual/md-to-db.sh to update generated release notes
• Fits CONTRIBUTING.md.

[FRidh]

Not relevant right now, but in case checkInputs gets split into a checkNativeInputs and checkInputs we may need to have this library in both in order to have the hook run. Though I am not sure about that.

[SuperSandro2000]

I think this will be very valuable. Thank you!

[roberth]

Doesn't this duplicate what happens in the setup hook?

[Artturin]

i don't think the setup hook is used at this point yet?

[Artturin]

just tested and yep its not used at this point

if i apply the following the build fails with
python3.9-pytest-xdist> substitute(): ERROR: file '/nix/store/q4qj7q82vrxfwnmymyhdwxid0sr0rjnn-hook' does not exist

diff --git a/pkgs/development/python-modules/pytest-xdist/default.nix b/pkgs/development/python-modules/pytest-xdist/default.nix
index 75fd066c76d..ae23bf3f31b 100644
--- a/pkgs/development/python-modules/pytest-xdist/default.nix
+++ b/pkgs/development/python-modules/pytest-xdist/default.nix
@@ -1,4 +1,5 @@
 { lib
+, makeSetupHook
 , buildPythonPackage
 , fetchPypi
 , pythonOlder
@@ -12,6 +13,10 @@
 , pexpect
 }:
 
+let
+  setupHook' = makeSetupHook {} ./setup-hook.sh;
+in
+
 buildPythonPackage rec {
   pname = "pytest-xdist";
   version = "2.5.0";
@@ -26,11 +31,9 @@ buildPythonPackage rec {
   buildInputs = [
     pytest
   ];
-  checkInputs = [ pytestCheckHook filelock pexpect ];
+  checkInputs = [ pytestCheckHook filelock pexpect setupHook' ];
   propagatedBuildInputs = [ execnet pytest-forked psutil ];
 
-  pytestFlagsArray = [ "-n $NIX_BUILD_CORES" "--forked" ]; # pytest can already use xdist at this point
-
   # access file system
   disabledTests = [
     "test_distribution_rsyncdirs_example"
@@ -43,7 +46,7 @@ buildPythonPackage rec {
     "test_internal_errors_propagate_to_controller"
   ];
 
-  setupHook = ./setup-hook.sh;
+  setupHook = setupHook';
 
   meta = with lib; {
     description = "Pytest xdist plugin for distributed testing and loop-on-failing modes";

[mweinelt]

I think this is a reasonable change and we can test it in #166489 if you rebase onto that.

[roberth]

I don't usually package python, so I'll unsubscribe after my superficial observation earlier.