Unused options for buildout: 'extends'.

[pumazi]

Providing 'buildout:extends=<cfgs>' via the command line does not work as the documentation would suggest. The testcase is provided as an attachment.

I run the following command (after a bootstrap, of course): """bin/buildout -c master.cfg buildout:extends+=extender.cfg\nversions.cfg buildout:package-name=dummy buildout:develop=src/dummy"""

A fake package, called dummy, is provided as a test package, which pulls in the jsonrpc2 package (randomly found on PyPI) as a dependency.

The intended result is a buildout that both adds z3c.checkversions (in extender.cfg) and pins the version of jsonrpc2 (in versions.cfg). Neither of these changes take place.