Add support for `RUST_LOG` to the uv build backend. While we were
previously using logging statements in the uv build backend, they could
only be shown when when using the direct build fast path through uv, as
there was no tracing subscriber to write log messages out. This means no
debug logging when using the build backend through pip, `python -m
build`, an incompatible version of uv, or any other build frontend; No
option to figure why includes and excludes behave the way they do.
This PR closes this gap by adding a tracing subscriber. The only option
to enable it is `RUST_LOG`, as we don't have a CLI. The formatting style
is the same as for uv, and color is also support in the same way, albeit
only through anstream's support for TTYs and environment variables. We
recommend only `RUST_LOG=uv=debug` and `RUST_LOG=uv=verbose` in the
docs, but this can be used to debug into crates such as `glob`, too.
<img width="1008" height="325" alt="image"
src="https://github.com/user-attachments/assets/d33df219-750b-46a2-b3b4-8895aa137ab9"
/>
**Before**
```
$ pip wheel . -v [...]
Looking in links: /home/konsti/projects/uv/target/wheels/
Processing /home/konsti/projects/uv/scripts/packages/built-by-uv
Running command pip subprocess to install build dependencies
Looking in links: /home/konsti/projects/uv/target/wheels/
Processing /home/konsti/projects/uv/target/wheels/uv_build-0.8.13-py3-none-manylinux_2_39_x86_64.whl
Installing collected packages: uv_build
Successfully installed uv_build-0.8.13
Installing build dependencies ... done
Running command Getting requirements to build wheel
Getting requirements to build wheel ... done
Running command Preparing metadata (pyproject.toml)
Preparing metadata (pyproject.toml) ... done
Building wheels for collected packages: built-by-uv
Running command Building wheel for built-by-uv (pyproject.toml)
Error: Unsupported glob expression in: `tool.uv.build-backend.*-exclude`
Caused by:
Invalid character `!` at position 10 in glob: `**/build-*!$§%!½¼²¼³¬!§%$§%.h`. hint: Characters can be escaped with a backslash
error: subprocess-exited-with-error
× Building wheel for built-by-uv (pyproject.toml) did not run successfully.
│ exit code: 1
╰─> See above for output.
note: This error originates from a subprocess, and is likely not a problem with pip.
full command: /usr/bin/python3 /usr/lib/python3/dist-packages/pip/_vendor/pyproject_hooks/_in_process/_in_process.py build_wheel /tmp/tmpow1illc9
cwd: /home/konsti/projects/uv/scripts/packages/built-by-uv
Building wheel for built-by-uv (pyproject.toml) ... error
ERROR: Failed building wheel for built-by-uv
Failed to build built-by-uv
ERROR: Failed to build one or more wheels
```
**After**
```
$ RUST_LOG=uv=debug pip wheel . -v [...]
Looking in links: /home/konsti/projects/uv/target/wheels/
Processing /home/konsti/projects/uv/scripts/packages/built-by-uv
Running command pip subprocess to install build dependencies
Looking in links: /home/konsti/projects/uv/target/wheels/
Processing /home/konsti/projects/uv/target/wheels/uv_build-0.8.13-py3-none-manylinux_2_39_x86_64.whl
Installing collected packages: uv_build
Successfully installed uv_build-0.8.13
Installing build dependencies ... done
Running command Getting requirements to build wheel
Getting requirements to build wheel ... done
Running command Preparing metadata (pyproject.toml)
DEBUG Writing metadata files to /tmp/pip-modern-metadata-l_kh78cj
DEBUG Found PEP 639 license declarations, using METADATA 2.4
DEBUG License files match: `LICENSE-APACHE`
DEBUG License files match: `LICENSE-MIT`
DEBUG License files match: `third-party-licenses/PEP-401.txt`
Preparing metadata (pyproject.toml) ... done
Building wheels for collected packages: built-by-uv
Running command Building wheel for built-by-uv (pyproject.toml)
DEBUG Checking metadata directory /tmp/pip-modern-metadata-l_kh78cj/built_by_uv-0.1.0.dist-info
DEBUG Found PEP 639 license declarations, using METADATA 2.4
DEBUG License files match: `LICENSE-APACHE`
DEBUG License files match: `LICENSE-MIT`
DEBUG License files match: `third-party-licenses/PEP-401.txt`
DEBUG Writing wheel at /tmp/pip-wheel-bu6to9i7/built_by_uv-0.1.0-py3-none-any.whl
DEBUG Wheel excludes: ["__pycache__", "*.pyc", "*.pyo", "build-*!$§%!½¼²¼³¬!§%$§%.h", "/src/built_by_uv/not-packaged.txt"]
Error: Unsupported glob expression in: `tool.uv.build-backend.*-exclude`
Caused by:
Invalid character `!` at position 10 in glob: `**/build-*!$§%!½¼²¼³¬!§%$§%.h`. hint: Characters can be escaped with a backslash
error: subprocess-exited-with-error
× Building wheel for built-by-uv (pyproject.toml) did not run successfully.
│ exit code: 1
╰─> See above for output.
note: This error originates from a subprocess, and is likely not a problem with pip.
full command: /usr/bin/python3 /usr/lib/python3/dist-packages/pip/_vendor/pyproject_hooks/_in_process/_in_process.py build_wheel /tmp/tmpjrxou13a
cwd: /home/konsti/projects/uv/scripts/packages/built-by-uv
Building wheel for built-by-uv (pyproject.toml) ... error
ERROR: Failed building wheel for built-by-uv
Failed to build built-by-uv
ERROR: Failed to build one or more wheels
```
(There is no color in the above uv log statements, as pip doesn't
register as a TTY)
Fixes#12723
