setuptools downloads and builds a correct version of a dependency in the install-to-egg step, but then adds a different version not satisfying the requirement to easy_install.pth

[davidsarah]

In the attached install-to-egg build on the 'Eugen lenny' buildslave, the requirement for Twisted is >= 10.1.0.

setuptools downloads and builds Twisted 10.2:

Searching for Twisted>=10.1.0
Best match: Twisted 10.2.0
Downloading http://tahoe-lafs.org/source/tahoe-lafs/deps/tahoe-dep-sdists/Twisted-10.2.0.tar.bz2
Processing Twisted-10.2.0.tar.bz2
Running Twisted-10.2.0/setup.py -q bdist_egg --dist-dir /tmp/easy_install-QTimkw/Twisted-10.2.0/egg-dist-tmp-yBXrHn
[...]

but then it adds Twisted 8.1 to easy-install.pth, resulting in a failed Tahoe build:

Adding Twisted 8.1.0 to easy-install.pth file
[...]
Installed /home/tahoebuildslave/tahoebuildslave/Eugen lenny-amd64/build/egginstalldir/Twisted-8.1.0-py2.5-linux-x86_64.egg
error: Could not find required distribution Twisted>=10.1.0

Since we're installing to an egg rather than globally, there's no good reason why that shouldn't work even if Twisted 8.1 is installed single-version-externally-managed. But if that's not supported for some reason, it's still incorrect to build 10.2 and then fail with a misleading error message.

[davidsarah]

Copy of ​http://tahoe-lafs.org/buildbot/builders/Eugen%20lenny-amd64/builds/850/steps/install-to-egg/logs/stdio/text