pex does not resolve the same version as pip for llvmlite 0.29.0

[tibonihoo]

When trying to use the documented pattern of collecting wheels with pip and then using the wheelhouse with --no-index for pex generation of a project, I came across a blocking issue due to a difference in which pex and pip resolved the package name for the 0.29.0 version of llvmlite.

Please find below the sequence of commands that "minimally" reproduce the issue (along with showing the versions of the various tools involved):

~/shared/Development $mkdir pex-repro
~/shared/Development $cd pex-repro/
~/shared/Development/pex-repro $python3.6 -m venv venv-linux
~/shared/Development/pex-repro $source venv-linux/bin/activate
(venv-linux) ~/shared/Development/pex-repro $python -m pip install --upgrade pip
(...)
Successfully installed pip-19.2.2
(venv-linux) ~/shared/Development/pex-repro $python -m pip install --upgrade pex
(...)
Successfully installed pex-1.6.10
(venv-linux) ~/shared/Development/pex-repro $python -m pip freeze
pex==1.6.10
(venv-linux) ~/shared/Development/pex-repro $python -m pip wheel -w wheelhouseDir "llvmlite>=0.29.0,<0.30.0"
(...)
  Saved ./wheelhouseDir/llvmlite-0.29.0-1-cp36-cp36m-manylinux1_x86_64.whl
Skipping llvmlite, due to already being wheel.
(venv-linux) ~/shared/Development/pex-repro $python -m pex -f wheelhouseDir --no-index --disable-cache "llvmlite>=0.29.0,<0.30.0" -o test.pex
Could not satisfy all requirements for llvmlite<0.30.0,>=0.29.0:
    llvmlite<0.30.0,>=0.29.0

For reference and comparison, using pex directly with the same requirement and allowing it to resolve the reference from the package index directly works:

(venv-linux) ~/shared/Development/pex-repro $python -m pex -f wheelhouseDir -i https://pypi.org/simple/ -vv --disable-cache "llvmlite>=0.29.0,<0.30.0
" -o test.pex
pex: Warning, using a UrllibContext which is known to be flaky.
pex: Please build pex with the requests module for more reliable downloads.
pex: Building pex :: Resolving distributions :: Fetching https://files.pythonhosted.org/packages/09/f1/4fa99c2079132da8694361fb9a19094616f1ba2c2eae610379e7539pex: Building pex :: Resolving distributions :: Fetching https://files.pythonhosted.org/packages/09/f1/4fa99c2079132da8694361fb9a19094616f1ba2c2eae610379e75394575f/llvmlite-0.29.0-cp36-cp36m-manylinux1_x86_64.whl#sha256=bd68e01f1444e38983a364ad1810bdaf3eb59ca1fe8aff4a33cc17a90cb9fcdb :: Fetching https://files.pythonhosted.org/packages/09/f1/4fa99c2079132da8694361fb9a19094616f1ba2c2eae610379e75394575f/llvmlite-0.29.0-cp36-cp36m-manylinux1_x86_64.whl#sha256=bd68e01f1444e3pex: Building pex :: Resolving distributions :: Translating /tmp/tmp6utook28/llvmlite-0.29.0-cp36-cp36m-manylinux1_x86_64.whl into distribution                                                                                                                                                                                                                                                                                                                                             llvmlite<0.30.0,>=0.29.0 -> llvmlite 0.29.0
pex: Building pex: 9075.3ms
pex:   Resolving interpreters: 5.7ms
pex:   Resolving distributions: 9065.0ms
pex:     Fetching https://files.pythonhosted.org/packages/09/f1/4fa99c2079132da8694361fb9a19094616f1ba2c2eae610379e75394575f/llvmlite-0.29.0-cp36-cp36m-manylinux1_x86_64.whl#sha256=bd68e01f1444e38983a364ad1810bdaf3eb59ca1fe8aff4a33cc17a90cb9fcdb: 5689.0ms
pex:       Fetching https://files.pythonhosted.org/packages/09/f1/4fa99c2079132da8694361fb9a19094616f1ba2c2eae610379e75394575f/llvmlite-0.29.0-cp36-cp36m-manylinux1_x86_64.whl#sha256=bd68e01f1444e38983a364ad1810bdaf3eb59ca1fe8aff4a33cc17a90cb9fcdb: 5688.5ms
pex:     Translating /tmp/tmp6utook28/llvmlite-0.29.0-cp36-cp36m-manylinux1_x86_64.whl into distribution: 2.6ms
Saving PEX file to test.pex

As a summary of what happened:

• pip resolved: llvmlite-0.29.0-1-cp36-cp36m-manylinux1_x86_64.whl
• pex resolved: llvmlite-0.29.0-cp36-cp36m-manylinux1_x86_64.whl

So it seems the extra -1 in the august release of llvmlite for version 0.29.0 triggered the discrepancy.

I can understand that the llvmlite naming is possibly breaking some typical assumption on package name and versionning, but the discrepancy between pex and pip is what is really bothering me here as it breaks the "build wheelhouse -> build pex from wheelhouse" workflow.

Am I missing an option that would help having a version resolution that better matches pip ?

As last notes of context about my real use case (for the sake of completeness):

• llvmlite is a dependency of an external dependency and I don't have much ways to impose any restriction on its exact version.
• I do need to constraint the set of wheels pex will use (so the "pex from wheelhouse" features makes a lot of sense for me)

[tibonihoo]

My current workaround to this issue is to use pex --cache-dir ... to force pex to collect my external dependencies' wheels (thus replacing pip wheel -w ...) in the provided cache directory and to then provide this cache directory as an extra wheelhouse to another call to pex.

Obviously this way of relying on a tool's caching strategy is a fairly bad practice, so I'm also wondering if there are more reliable ways to deal with this issue with the current version of the tool.