This was broken because MountedSourceAccessor did not return a
fingerprint. Previously fingerprints were global to an accessor, but
with a MountedSourceAccessor the fingerprint can be different for each
mount point.
These got displayed as e.g.
«github:NixOS/nixpkgs/adaa24fbf46737f3f1b5497bf64bae750f82942e?narHash=sha256-qhFMmDkeJX9KJwr5H32f1r7Prs7XbQWtO0h3V0a0rFY%3D»/nix/store/x9wnkly3k1gkq580m90jjn32q9f05q2v-source/pkgs/stdenv/generic/source-stdenv.sh
Now we get
«github:NixOS/nixpkgs/adaa24fbf46737f3f1b5497bf64bae750f82942e?narHash=sha256-qhFMmDkeJX9KJwr5H32f1r7Prs7XbQWtO0h3V0a0rFY%3D»/pkgs/stdenv/generic/source-stdenv.sh
Judging by the comment for `makeEmptySourceAccessor` the prefix has
to be empty:
> Return a source accessor that contains only an empty root directory.
Fixes#13295.
(cherry picked from commit fba1bb0c13)
Previously it used the `ThreadPool` default,
i.e. `std:🧵:hardware_concurrency()`. But copying signatures is
not primarily CPU-bound so it makes more sense to use the
`http-connections` setting (since we're typically copying from/to a
binary cache).
(Actually, this adds a position field to *all* values.)
This allows improving the "inefficient double copy" warning by showing
where the source path came from in the source, e.g.
warning: Performing inefficient double copy of path '/home/eelco/Dev/patchelf/' to the store at /home/eelco/Dev/patchelf/flake.nix:30:17. This can typically be avoided by rewriting an attribute like `src = ./.` to `src = builtins.path { path = ./.; name = "source"; }`.
As it turns out using `std::regex` is actually the bottleneck
for root discovery. Just substituting `std::` -> `boost::`
makes root discovery twice as fast (3x if counting only userspace time).
Some rather ad-hoc measurements to motivate the switch:
(On master)
```
nix build github:nixos/nix/1e822bd4149a8bce1da81ee2ad9404986b07914c#nix-cli --out-link result-1e822bd4149a8bce1da81ee2ad9404986b07914c
taskset -c 2,3 hyperfine "result-1e822bd4149a8bce1da81ee2ad9404986b07914c/bin/nix store gc --dry-run --max 0"
Benchmark 1: result-1e822bd4149a8bce1da81ee2ad9404986b07914c/bin/nix store gc --dry-run --max 0
Time (mean ± σ): 481.6 ms ± 3.9 ms [User: 336.2 ms, System: 142.0 ms]
Range (min … max): 474.6 ms … 487.7 ms 10 runs
```
(After this patch)
```
taskset -c 2,3 hyperfine "result/bin/nix store gc --dry-run --max 0"
Benchmark 1: result/bin/nix store gc --dry-run --max 0
Time (mean ± σ): 254.7 ms ± 9.7 ms [User: 111.1 ms, System: 141.3 ms]
Range (min … max): 246.5 ms … 281.3 ms 10 runs
```
`boost::regex` is a drop-in replacement for `std::regex`, but much faster.
Doing a simple before/after comparison doesn't surface any change in behavior:
```
result/bin/nix store gc --dry-run -vvvvv --max 0 |& grep "got additional" | wc -l
result-1e822bd4149a8bce1da81ee2ad9404986b07914c/bin/nix store gc --dry-run -vvvvv --max 0 |& grep "got additional" | wc -l
```
(cherry picked from commit 3a1301cd6d)
Leverage #10766 to show how we can now resolve a store configuration
without actually opening the store for that resolved configuration.
Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>
Splicing the list element to the back can be done in
a much simpler and concise way without the need for
erasing and re-inserting the element. Doing it this
way is equivalent to just moving node pointers around,
whereas inserting/erasing allocates/deallocates new nodes.
The existing header is a bit too big. Now the following use-cases are
separated, and get their own headers:
- Using or implementing an arbitrary store: remaining `store-api.hh`
This is closer to just being about the `Store` (and `StoreConfig`)
classes, as one would expect.
- Opening a store from a textual description: `store-open.hh`
Opening an aribtrary store implementation like this requires some sort
of store registration mechanism to exists, but the caller doesn't need
to know how it works. This just exposes the functions which use such a
mechanism, without exposing the mechanism itself
- Registering a store implementation: `store-registration.hh`
This requires understanding how the mechanism actually works, and the
mechanism in question involves templated machinery in headers we
rather not expose to things that don't need it, as it would slow down
compilation for no reason.
