## Summary
I believe `zlib-rs` is now a better choice on ARM and x86, so I'm just
going to assume it's a better choice everywhere. It's much easier to
build (removes our CMake dependency), and in my benchmarking, it's
substantially faster on ARM and faster or ~exactly even on my x86
Windows machine.
We migrated to `zlib-rs` once before (#9184); however, I later reverted
it as I learned that they were only doing compile-time feature
detection, and so `zlib-rs` was meaningfully slower on x86. They now
perform runtime feature detection:
https://trifectatech.org/blog/zlib-rs-is-faster-than-c/.
To benchmark, I wrote a script to create a local Simple API-compliant
registry (see the commit history) for a single package. Then I ran the
`install-cold` benchmark against that registry to install NumPy.
On ARM:
```
❯ uv run resolver --uv-pip-path ../../zlib-ng --uv-pip-path ../../zlib-rs \
--benchmark install-cold \
req.txt --warmup 10 --min-runs 30
Benchmark 1: ../../zlib-ng (install-cold)
Time (mean ± σ): 165.7 ms ± 34.7 ms [User: 64.4 ms, System: 93.2 ms]
Range (min … max): 141.8 ms … 293.2 ms 30 runs
Benchmark 2: ../../zlib-rs (install-cold)
Time (mean ± σ): 150.9 ms ± 16.2 ms [User: 57.4 ms, System: 86.4 ms]
Range (min … max): 135.3 ms … 202.4 ms 30 runs
Summary
../../zlib-rs (install-cold) ran
1.10 ± 0.26 times faster than ../../zlib-ng (install-cold)
```
I benchmarked this about 100 times on my Windows machine and found it
difficult to conclude anything beyond "They're nearly the same". Here's
an example:
```
PS C:\Users\crmar\workspace\puffin> hyperfine --prepare "uv venv" "zlib-rs.exe pip sync ./scripts/benchmark/req.txt" "zlib-ng.exe pip sync ./scripts/benchmark/req.txt" "zlib-rs.exe pip sync ./scripts/benchmark/req.txt" "zlib-ng.exe pip sync ./scripts/benchmark/req.txt" --runs 10 --warmup 5
Benchmark 1: zlib-rs.exe pip sync ./scripts/benchmark/req.txt
Time (mean ± σ): 240.6 ms ± 10.8 ms [User: 6.1 ms, System: 92.2 ms]
Range (min … max): 229.4 ms … 267.9 ms 10 runs
Benchmark 2: zlib-ng.exe pip sync ./scripts/benchmark/req.txt
Time (mean ± σ): 241.3 ms ± 6.2 ms [User: 7.7 ms, System: 90.6 ms]
Range (min … max): 233.9 ms … 252.1 ms 10 runs
Benchmark 3: zlib-rs.exe pip sync ./scripts/benchmark/req.txt
Time (mean ± σ): 242.8 ms ± 7.7 ms [User: 6.2 ms, System: 23.4 ms]
Range (min … max): 236.1 ms … 262.8 ms 10 runs
Benchmark 4: zlib-ng.exe pip sync ./scripts/benchmark/req.txt
Time (mean ± σ): 245.9 ms ± 5.7 ms [User: 1.5 ms, System: 59.4 ms]
Range (min … max): 240.9 ms … 257.3 ms 10 runs
Summary
zlib-rs.exe pip sync ./scripts/benchmark/req.txt ran
1.00 ± 0.05 times faster than zlib-ng.exe pip sync ./scripts/benchmark/req.txt
1.01 ± 0.06 times faster than zlib-rs.exe pip sync ./scripts/benchmark/req.txt
1.02 ± 0.05 times faster than zlib-ng.exe pip sync ./scripts/benchmark/req.txt
```
Closes#11885.
From PEP 517:
```python
def prepare_metadata_for_build_wheel(metadata_directory, config_settings=None):
...
```
> Must create a .dist-info directory containing wheel metadata inside
the specified metadata_directory (i.e., creates a directory like
{metadata_directory}/{package}-{version}.dist-info/).
```python
def build_wheel(wheel_directory, config_settings=None, metadata_directory=None):
...
```
> If the build frontend has previously called
prepare_metadata_for_build_wheel and depends on the wheel resulting from
this call to have metadata matching this earlier call, then it should
provide the path to the created .dist-info directory as the
metadata_directory argument.
Notice that the `metadata_directory` is different for the both hooks:
For `prepare_metadata_for_build_wheel` is doesn't contain the
`.dist-info` directory as final segment, for `build_wheel` it does.
Previously, the code assumed that both directories didn't contain the
`.dist-info` for both cases.
Checked with:
```
maturin build
uv init test-uv-build-backend --build-backend uv
cd test-uv-build-backend
uv build --sdist --preview
cd ..
UV_PREVIEW=1 pip install test-uv-build-backend/dist/test_uv_build_backend-0.1.0.tar.gz --no-index --find-links target/wheels/ -v --no-cache-dir
```
Fixes#9969
It used to report:
```
» mypy
python/uv/_build_backend.py:40: error: Incompatible types in assignment (expression has type "list[str]", variable has type "CompletedProcess[bytes]") [assignment]
python/uv/_build_backend.py:41: error: Value of type "CompletedProcess[bytes]" is not indexable [index]
python/uv/_build_backend.py:46: error: Value of type "CompletedProcess[bytes]" is not indexable [index]
Found 3 errors in 1 file (checked 6 source files)
```
So, I had to fix this problem by renaming the `result` var.