Detect SETUPTOOLS_DEB_LAYOUT properly on non-debian systems.

[ahendrix]

Currently, SETUPTOOLS_DEB_LAYOUT defaults to ON. This beaks on non-debain-based systems such as OS X, Windows, Gentoo, Arch, Fedora, etc.

Is it possible to make SETUPTOOLS_DEB_LAYOUT default to OFF, and turn it on if a deb-specific file exists; perhaps /etc/debian_version ?

if(EXISTS /etc/debian_version) ...

[dirk-thomas]

For OS X and Windows the default value is actually OFF. Can you point to references for the above mentioned platforms which install layout they are using?

[ahendrix]

The default value should be OFF, and it should be ON only if the system is debian-based.

Manually turning off SETUPTOOLS_DEB_LAYOUT is mentioned at various points in the install instructions for all of them:

http://www.ros.org/wiki/groovy/Installation/Gentoo
http://www.ros.org/wiki/groovy/Installation/Fedora
http://www.ros.org/wiki/groovy/Installation/Arch

[tho-]

This commit makes it impossible to override the default (i.e. disable debian-layout on debian platforms)
Could it be converted back to an option? (even if autodetected)

[dirk-thomas]

Could you describe a use case where that is desired on a Debian platform?

[tho-]

As long as you install from sources, you do not have to follow debian rules. Since debian is the only system redefining the python default of 'site-packages', it adds superflous complexity to e.g. environment setup scripts that are shared amongst different arch. (e.g. PYTHONPATH=${HOME}/${MACHTYPE}-${OSTYPE}/lib/python2.7/site-packages would break, it would need a special case for debian). That's why I usually ignore debian's 'dist-packages' and configure a consistent setup.

Besides that, if you use another package system than dpkg/apt, you may want to stick to your package system strategy and it may not be the same as 'debian'. I often use pkgsrc to install my packages, and pkgsrc just sticks to the python default of installing to "sites-packages". I do have a few packages for ros in robotpkg, and robotpkg also has a "sites-packages" everywhere strategy. Of course I can have local patches in robotpkg for that, but it becomes a problem when mixing a vanilla .deb catkin with other robotpkg ros packages.

Autodetecting --install-layout is just fine as it is, but I feel that turing it into an option (as it's always been) adds no overhead and is more user-friendly in the end. Even on debian, distutils, for instance, has a user-tunable option :)