When perlSupport = false, we will set NO_PERL=1, and build Git without Perl support. This is a build option that Git supports. However, Git's test suite still requires a Perl to be available to run the tests, and we did not provide one. The tests respect PERL_PATH, and if it is not set, they default to /usr/bin/perl.

Before this commit, if we set perlSupport = false, then no Perl would be available to the package, and so the tests would default to /usr/bin/perl. When building without a sandbox, that could still work,
even though there is no perl on the path, because the tests defaulted to an absolute path.

You can reproduce this issue as follows:

nix-build -E 'let pkgs = (import ./default.nix) {}; in pkgs.git.override { perlSupport = false; }'

I just ran into this when trying to build pkgs.git from an old version of Nixpkgs that I was able to build just fine in the past, and today it would not build any more, complaining when running the tests:

make -C t/ all
make[1]: Entering directory '/build/git-2.18.0/t'
rm -f -r 'test-results'
/nix/store/czx8vkrb9jdgjyz8qfksh10vrnqa723l-bash-4.4-p23/bin/bash: /usr/bin/perl: No such file or directory

In the past the sandbox was not enabled by default, so then it worked for me. But now that it is enabled, my host's (not NixOS) /usr/bin/perl is no longer accessible, and the build fails.

The solution is to explicitly set PERL_PATH when running the tests. This almost works, except that there appears to be a bug in the test for git request-pull. That command is a Bash script that calls Perl at some point, so it requires Perl, and therefore it cannot be supported when NO_PERL=1. But that particular test does not check whether Git was compiled with Perl support (other tests do include that check), and that makes the test fail:

t5150-request-pull.sh ..............................
not ok 4 - pull request after push
not ok 5 - request asks HEAD to be pulled
not ok 6 - pull request format
not ok 7 - request-pull ignores OPTIONS_KEEPDASHDASH poison
not ok 9 - pull request with mismatched object
not ok 10 - pull request with stale object
Dubious, test returned 1 (wstat 256, 0x100)
Failed 6/10 subtests

This output makes sense if you look at t5150-request-pull.sh. Test 1 and 2 are setup steps. Test 3 does call request-pull, but it expects the command to fail, and it cannot distinguish between the command exiting with a nonzero exit code, or failing to start it at all. So test 3 passes for the wrong reasons. Test 4 through 10 all call request-pull, so they fail.

The quick workaround here is to disable the test. I will look into upstreaming a patch that makes the test skip itself when Perl is disabled.

Motivation for this change

Without sandbox, setting perlSupport = false creates an implicit dependency on the host system. With sandbox, building with perlSupport = false fails.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nix-review --run "nix-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

I also verified that this does not introduce a Perl dependency in the closure with nix-store -qR.

Notify maintainers

cc @peti @the-kenny @wmertens @globin

Also, @bgamari, as the author of perlSupport, you might be interested in this.