Ensure get_requires* hook is called before prepare_metadata*

[abravalheri]

As described in #3043, it seems that for some circumstances the prepare_metadata* hook is not called before get_requires*, which result in errors on Python 3.12b2 for the setuptools backend.

The changes implemented in this PR are:

• Add caching to the get_requires* and prepare_metadata* hooks in Pep517VirtualEnvPackager (these methods may be called multiple times).
• Ensure get_requires* is called and that the requirements are installed before prepare_metadata*.

This seem to be required according to PEP 517, see last phrase on the paragraph below (copied from the PEP):

get_requires_for_build_wheel
This hook MUST return an additional list of strings containing PEP 508 dependency specifications, above and beyond those specified in the pyproject.toml file, to be installed when calling the build_wheel or prepare_metadata_for_build_wheel hooks.

• ran the linter to address style issues (tox -e fix)
• wrote descriptive pull request text
• ensured there are test(s) validating the fix
• added news fragment in docs/changelog folder
• updated/extended the documentation

Fix #3043

[abravalheri]

Not sure yet how to test this change without a full blown integrated test using the Python 3.12 example in the issue.

This is the evidence that the PR works for the related issue:

> docker run --rm -it python:3.12.0b2-bullseye /bin/bash
mkdir -p /tmp/myproj/src/myproj
cd /tmp/myproj
touch src/myproj/__init__.py
cat <<EOF > pyproject.toml
[build-system]
requires = ["setuptools"]
build-backend = "setuptools.build_meta"
EOF
cat <<EOF >setup.cfg
[metadata]
name = myproj
version = 0.42
[options.extras_require]
testing = pytest
EOF
cat <<EOF >tox.ini
[tox]
envlist = default
isolated_build = True

[testenv]
extras = testing
commands = pytest {posargs}
EOF


mkdir -p tests/
echo "def test_hello(): assert True" > tests/test_hello.py

python -m pip install -U 'pip==23.1.2'
python -m pip install -U 'tox==4.6.2'
tox
# => FAIL code error: invalid command 'bdist_wheel' (1.91 seconds)

python -m pip install -U git+https://github.com/abravalheri/tox@issue-3043
tox -r
# => congratulations :) (6.21 seconds)

[gaborbernat]

The test should define an inline build backend that would fail prepare metadata if not called get requires first (write to some local file to save if called or not?) And triggered via a notest run xl🙏

[abravalheri]

Hi @gaborbernat, after checking the failures in the CI, I noticed that test_tox_install_pkg_sdist is already ensuring that prepare_metadata_for_build_wheel runs.

To fix this test I had to prepend a line with get_requires_for_build_wheel. This effectively assert that the get_requires* runs before prepare_metadata*. Would this be enough for the tests?

I am not sure in which circumstances the prepare_metadata_for_build_wheel is being triggered, but the test_tox_install_pkg_sdist seems to hit one of them... (I tried adding prepare_metadata_for_build_wheel to the inline backend test, but it does not seem to call this function).

[gaborbernat]

[abravalheri]

Thank you very much @gaborbernat