If you do a fetchTree on a Git repository, whether the result contains
a revCount attribute should not depend on whether that repository
happens to be a shallow clone or not. That would complicate caching a
lot and would be semantically messy. So applying fetchTree/fetchGit to
a shallow repository is now an error unless you pass the attribute
'shallow = true'. If 'shallow = true', we don't return revCount, even
if the repository is not actually shallow.
Note that Nix itself is not doing shallow clones at the moment. But it
could do so as an optimisation if the user specifies 'shallow = true'.
Issue #2988.
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.
Note: like 'nix run', and unlike 'nix-shell', this takes an argv
vector rather than a shell command. So
nix dev-shell -c 'echo $PATH'
doesn't work. Instead you need to do
nix dev-shell -c bash -c 'echo $PATH'
The problem fixed: each nix-shell invocation creates a new temporary
directory (`/tmp/nix-shell-*`) and never cleans up.
And while I'm here, shellescape all variables inlined into the rcfile.
See what might happen without escaping:
$ export TZ="';echo pwned'"
$ nix-shell -p hello --run hello
pwned
Hello, world!
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
Robert Hensing
Maximilian Bosch