We warn instead of erroring out when --build-option is present
when doing a PEP 517 build. There is no strong reason to error
out, and this will avoid backward compatibility issues when we
support build options in requirement files and installation.
The typing module has been available since Python 3.5. Guarding the
import has been unnecessary since dropping Python 2.
Some guards remain to either:
- Avoid circular imports
- Importing objects that are also guarded by typing.TYPE_CHECKING
- Avoid mypy_extensions dependency
The stdlib module has been available since Python 3.5 and the
TYPE_CHECKING constant has been available since 3.5.2.
By using stdlib, this removes the need for pip to maintain its own
Python 2 typing compatibility shim.
check_binary_allowed is only used to check
if a wheel needs to be built in 'pip install' mode.
It mixed format control and pep517 mode check.
We change it so it checks allowed formats only,
which leads to better readability of _should_build().
The condition "never cache if pip install would not have built"
can be simplified to "do not cache editable requirements".
This is easier to read, and avoid a double warning if the 'wheel'
package is not installed.
_should_cache is only called by _get_cache_dir.
In pip install mode, _get_cache_dir is never called when
check_binary_allowed returns False because in that case
should_build_for_install_command has returned False before
and the build was skipped.
In pip wheel mode, check_binary_allowed always returns True
(because it is not passed to the build function).
So _should_cache can use _always_true for check_binary_allowed.
*Alternative*
Alternatively, we could have passed check_binary_allowed
to build in pip wheel mode. The only difference is that wheels built
locally from *legacy* packages would then not be cached,
when pip wheel is used with --no-binary.
The only purpose of _collect_buildset is now
to compute the cache directory to use
for a given requirements. This is better
computed one by one in the build loop.
Actual installation has been using the wheel file directly for some
time. The last piece that required an unpacked wheel was metadata. Now
that it uses the wheel file directly, we can remove the unpacking after
build.
We unconditionally update the requirement
link with the build wheel (in cache), so
when build() will return build success as
well as build failure, the caller can obtain
the built wheel by looking at req.local_file_path
