In
nix-instantiate --dry-run '<nixpkgs/nixos/release-combined.nix>' -A nixos.tests.simple.x86_64-linux
this reduces time spent in unparse() from 9.15% to 4.31%. The main
culprit was appending characters one at a time to the destination
string. Even though the string has enough capacity, push_back() still
needs to check this on every call.
Worktrees[1] are a feature of git which allow you to check out a ref in
a different directory.
While playing around with flakes I realized that git repositories in a
worktree checkout break when trying to build a flake:
```
$ git worktree add ../nixpkgs-flakes nixpkgs-flakes
$ cd ../nixpkgs-flakes
$ nix build .#hello
error: opening directory '/home/ma27/Projects/nixpkgs-flakes/.git/refs/heads': Not a directory
```
This issue has been fixed by determining with `git rev-parse --git-common-dir`
where the actual `.git` directory is.
Please note that this issue only exists on the `flakes` branch, fetching
worktree checkouts with Nix master seems to work fine.
[1] https://git-scm.com/docs/git-worktree
The ssh client is lazily started by the first worker thread, that
requires a ssh connection. To avoid the ssh client to be killed, when
the worker process is stopped, do not set PR_SET_PDEATHSIG.
Brings the functionality of ssh-ng:// in sync with the legacy ssh://
implementation. Specifying the remote store uri enables various useful
things. eg.
$ nix copy --to ssh-ng://cache?remote-store=file://mnt/cache --all
When computing a lock file, we now respect the lock files of flake
inputs. This is important for usability / reproducibility. For
example, the 'nixops' flake depends on the 'nixops-aws' and
'nixops-hetzner' repositories. So when the 'nixops' flake is used in
another flake, we want the versions of 'nixops-aws' and
'nixops-hetzner' locked by the the 'nixops' flake because those
presumably have been tested.
This can lead to a proliferation of versions of flakes like 'nixpkgs'
(since every flake's lock file could depend on a different version of
'nixpkgs'). This is not a major issue when using Nixpkgs overlays or
NixOS modules, since then the top-level flake composes those
overlays/modules into *its* version of Nixpkgs and all other versions
are ignored. Lock file computation has been made a bit more lazy so it
won't try to fetch all those versions of 'nixpkgs'.
However, in case it's necessary to minimize flake versions, there now
are two input attributes that allow this. First, you can copy an input
from another flake, as follows:
inputs.nixpkgs.follows = "dwarffs/nixpkgs";
This states that the calling flake's 'nixpkgs' input shall be the same
as the 'nixpkgs' input of the 'dwarffs' input.
Second, you can override inputs of inputs:
inputs.nixpkgs.url = github:edolstra/nixpkgs/<hash>;
inputs.nixops.inputs.nixpkgs.url = github:edolstra/nixpkgs/<hash>;
or equivalently, using 'follows':
inputs.nixpkgs.url = github:edolstra/nixpkgs/<hash>;
inputs.nixops.inputs.nixpkgs.follows = "nixpkgs";
This states that the 'nixpkgs' input of the 'nixops' input shall be
the same as the calling flake's 'nixpkgs' input.
Finally, at '-v' Nix now prints the changes to the lock file, e.g.
$ nix flake update ~/Misc/eelco-configurations/hagbard
inputs of flake 'git+file:///home/eelco/Misc/eelco-configurations?subdir=hagbard' changed:
updated 'nixpkgs': 'github:edolstra/nixpkgs/7845bf5f4b3013df1cf036e9c9c3a55a30331db9' -> 'github:edolstra/nixpkgs/03f3def66a104a221aac8b751eeb7075374848fd'
removed 'nixops'
removed 'nixops/nixops-aws'
removed 'nixops/nixops-hetzner'
removed 'nixops/nixpkgs'
