Fixes assertion failure if outputsToInstall is empty by defaulting to the "out"
output. That is, behavior between the following commands should be consistent:
$ nix build --no-link --json .#nothing-to-install-no-out
error: derivation '/nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-nothing-to-install-no-out.drv' does not have wanted outputs 'out'
$ nix build --no-link --file default.nix --json nothing-to-install-no-out
error: derivation '/nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-nothing-to-install-no-out.drv' does not have wanted outputs 'out'
Real-world example of this issue:
$ nix build --json .#.legacyPackages.aarch64-linux.texlive.pkgs.iwona
error: derivation '/nix/store/dj0h6b0pnlnan5nidnhqa0bmzq4rv6sx-iwona-0.995b.drv' does not have wanted outputs 'out'
$ git rev-parse HEAD
eee33247cf6941daea8398c976bd2dda7962b125
$ nix build --json --file . texlive.pkgs.iwona
nix: src/libstore/outputs-spec.hh:46: nix::OutputsSpec::Names::Names(std::set<std::__cxx11::basic_string<char> >&&): Assertion `!empty()' failed.
Aborted (core dumped)
I think it is bad for these reasons when `tests/` contains a mix of
functional and integration tests
- Concepts is harder to understand, the documentation makes a good
unit vs functional vs integration distinction, but when the
integration tests are just two subdirs within `tests/` this is not
clear.
- Source filtering in the `flake.nix` is more complex. We need to
filter out some of the dirs from `tests/`, rather than simply pick
the dirs we want and take all of them. This is a good sign the
structure of what we are trying to do is not matching the structure
of the files.
With this change we have a clean:
```shell-session
$ git show 'HEAD:tests'
tree HEAD:tests
functional/
installer/
nixos/
```
