What does `runHook` do?

busti · June 29, 2021, 11:34pm

The function runHook is often used in packages, but there doesn’t seem to be documentation anywhere.
I have usually seen before and after package phases, i.e.:

installPhase = ''
  runHook preInstall

  foobar

  runHook postInstall
'';

Will those hooks not run unless they are called using runHook?
Can I create arbitrary hook names?

abathur · June 29, 2021, 11:59pm

github.com

nixOS/nixpkgs/blob/be4382dcb383cf6920a08e6a49aaf8cb18561979/pkgs/stdenv/generic/setup.sh#L15-L18

    
      
          # Run all hooks with the specified name in the order in which they
          # were added, stopping if any fails (returns a non-zero exit
          # code). The hooks for <hookName> are the shell function or variable
          # <hookName>, and the values of the shell array ‘<hookName>Hooks’.

busti · June 30, 2021, 12:02am

So if those hooks were not called in the phase script, they will not run, right?
I.e.

preInstall = ''
  echo "I will be called";
'';

installPhase = ''
  runHook preInstall
'';

postInstall = ''
  echo "I will NEVER be called";
'';

jtojnar · June 30, 2021, 12:12am

That’s right. See also nixpkgs-hammering/missing-phase-hooks.md at 6a4f88d82ab7d0a95cf21494896bce40f7a4ac22 · jtojnar/nixpkgs-hammering · GitHub

busti · June 30, 2021, 12:14am

Nice writeup. That’s pretty much what I was wondering. I am overriding a postInstall hook and it turns out that it is not being called in the original package.