This gives us a concrete place to put the new resolver code and
resolver-specific modules (`resolution.resolver`).
The reason for another level of hierarchy compared to other modules
is to allow us to move other modules here as they
become implementation details of the legacy resolver. Examples I
have in mind are: `req.req_set`, `req.req_install`,
`req.constructors`, and `operations.prepare`.
* Make ParsedLine record the type of line
* Split handle_line to allow passing arguments only where needed
* Remove unneeded attributes from ParsedRequirement
This makes the resolver interface simpler by returning a brand new
RequirementSet vs mutating the one that was input to the function, and
will let us specialize RequirementSet for the different use cases.
Previously we were writing a delete marker file which is checked in
InstallRequirement.remove_temporary_source which is only invoked if the
user did not pass --no-clean (and a PreviousBuildDirError was not
raised). Since our TempDirectory machinery now respects these conditions
we can just wrap our source directory in that instead of using this
ad-hoc mechanism for tracking our delete preference.
This will let us clean up a lot of dead code that only existed for this
use case.
As we introduce stricter metadata parsing, we will need to ensure that
the wheel files used in our tests are compliant (except in the specific
way that we're testing against).
Currently we have a large number of test cases relying on undocumented or
under-documented wheel files that have various inconsistencies
(incorrect name, missing fields) that are unrelated to the features
actually under test.
With a new wheel builder helper function, we will be able to replace all
of our instances of pre-built wheel test fixtures with dynamically-generated
files in code that are correct by default.
_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.
