Set IN_NIX_SHELL=1 for tests

[booxter]

This helps isolating system-wide zsh instance running in tests from the broader system shell initialization for limited nix environments.

This fixes failures as reported here:
NixOS/nixpkgs#312692

[kovidgoyal]

What exactly does IN_NIX_SHELL do and can you please add a comment explaining what it does in basic_shell_env()

[kovidgoyal]

As far as I can tell from a quick google valid values for it are pure/impure and its effects are undefined, depending on individual pkgs. https://nix.dev/manual/nix/2.18/command-ref/nix-shell#env-IN_NIX_SHELL

[booxter]

It very well may be that this is not a correct fix. Let me describe what I'm trying to achieve and why this helps.

The reason why test suite fails is that while zsh in the nix build environment comes from an injected package, it still reads from /etc/zshenv. From the man page for zsh:

STARTUP/SHUTDOWN FILES
       Commands are first read from /etc/zshenv; **this cannot  be
       overridden**.   Subsequent behaviour is modified by the RCS
       and GLOBAL_RCS options; the former  affects  all  startup
       files, while the second only affects global startup files
       (those  shown  here  with an path starting with a /).  If
       one of the options is unset at any point, any  subsequent
       startup  file(s)  of  the  corresponding type will not be
       read.  It is also possible for  a  file  in  $ZDOTDIR  to
       re-enable  GLOBAL_RCS. Both RCS and GLOBAL_RCS are set by
       default.

So tests adding --noglobalrcs is not enough to isolate in-test zsh from the system.

And here is what is in /etc/zshenv (managed by nix-darwin):

$ cat /etc/zshenv
# /etc/zshenv: DO NOT EDIT -- this file has been generated automatically.
# This file is read for all shells.

# Only execute this file once per shell.
# But don't clobber the environment of interactive non-login children!
if [ -n "$__ETC_ZSHENV_SOURCED" ]; then return; fi
export __ETC_ZSHENV_SOURCED=1

# Don't execute this file when running in a pure nix-shell.
if test -n "$IN_NIX_SHELL"; then return; fi

if [ -z "$__NIX_DARWIN_SET_ENVIRONMENT_DONE" ]; then
  . /nix/store/5kgqn44swwbivdxx1gsvpkz1qcvfhq16-set-environment
fi



# Read system-wide modifications.
if test -f /etc/zshenv.local; then
  source /etc/zshenv.local
fi

If the variable is not set, my full zsh environment is initialized, which triggers the following command (comes from /nix/store/5kgqn44swwbivdxx1gsvpkz1qcvfhq16-set-environment):

/nix/store/0mnp04vh94qi0cir0qhy29dn675hmpj5-gnupg-2.4.5/bin/gpg-connect-agent --quiet updatestartuptty /bye > /dev/null

...which produces some errors on the screen and make the tests fail.

Setting IN_NIX_SHELL allows me to work around the issue since then my env is not initialized.

[booxter]

I'm looking at this a bit closer, and I wonder if perhaps the root of the issue is not in the test suite, or not even in zsh, but in the fact that nix-darwin configures its zshenv such that it may dump errors from gpg-connect-agent in some scenarios.

Here is where the command is injected into the env: https://github.com/LnL7/nix-darwin/blob/ac5694a0b855a981e81b4d9f14052e3ff46ca39e/modules/programs/gnupg.nix#L46

I wonder if it should be gpg-connect-agent --quiet updatestartuptty /bye > /dev/null 2>&1 (note the additional 2>&1) to suppress all errors.

Do you think I should do this instead?

[kovidgoyal]

Yes, generally speaking, having things that potentially spew errors in
global rc files is not a good idea. Lots of tools run shell scripts and
can be confused by errors that dont come from the script itself.

Closing as IMO this should be fixed in nix.