9c766a40cb broke logging from the
daemon, because commonChildInit is called when starting the build hook
in a vfork, so it ends up resetting the parent's logger. So don't
vfork.
It might be best to get rid of vfork altogether, but that may cause
problems, e.g. when we call an external program like git from the
evaluator.
Before the changes when building the whole system with
`contentAddressedByDefault = true;` we get many noninformative messages:
$ nix build -f nixos system --keep-going
...
warning: rewriting hashes in '/nix/store/...-clang-11.1.0.drv.chroot/nix/store/...-11.1.0'; cross fingers
warning: rewriting hashes in '/nix/store/...-clang-11.1.0.drv.chroot/nix/store/...-11.1.0-dev'; cross fingers
warning: rewriting hashes in '/nix/store/...-clang-11.1.0.drv.chroot/nix/store/...-11.1.0-python'; cross fingers
error: 2 dependencies of derivation '/nix/store/...-hub-2.14.2.drv' failed to build
warning: rewriting hashes in '/nix/store/...-subversion-1.14.1.drv.chroot/nix/store/...-subversion-1.14.1-dev'; cross fingers
warning: rewriting hashes in '/nix/store/...-subversion-1.14.1.drv.chroot/nix/store/...-subversion-1.14.1-man'; cross fingers
...
Let's downgrade these messages down to debug().
I had started the trend of doing `std::visit` by value (because a type
error once mislead me into thinking that was the only form that
existed). While the optomizer in principle should be able to deal with
extra coppying or extra indirection once the lambdas inlined, sticking
with by reference is the conventional default. I hope this might even
improve performance.
I found it somewhat confusing to have an error like
error: attribute 'getFlake' missing
if the required experimental-feature (`flakes`) is not enabled. Instead,
I'd expect Nix to throw an error just like it's the case when using e.g. `nix
flake` without `flakes` being enabled.
With this change, the error looks like this:
$ nix-instantiate -E 'builtins.getFlake "nixpkgs"'
error: Cannot call 'builtins.getFlake' because experimental Nix feature 'flakes' is disabled. You can enable it via '--extra-experimental-features flakes'.
at «string»:1:1:
1| builtins.getFlake "nixpkgs"
| ^
I didn't use `settings.requireExperimentalFeature` here on purpose
because this doesn't contain a position. Also, it doesn't seem as if we
need to catch the error and check for the missing feature here since
this already happens at evaluation time.
Alex Kladov
Maximilian Bosch