always honor keeppreviousinstall setting

[smoors]

needed for installing software in a bwrap namespace, where we bind mount the software installdir (name/version) of each software that will be installed by EB.

this in turn requires setting keeppreviousinstall to True, because removing a bind mounted directory is not possible. we currently set this in the parse hook (would be useful to have a build option for this).

EB currently hard sets keeppreviousinstall to False if buildininstalldir is True, which breaks the bwrap installation, for example for ecBuild.

this PR prints a big warning instead of changing keeppreviousinstall.

see also #4110

[boegel]

@smoors Hmm, it seems rather intrusive to change this behaviour, is this really the only way?

keepreviousinstall and buildininstalldir are fundamentally incompatible, so I'm not keen on just printing a warning here and pretending it'll all work out well

[smoors]

@smoors Hmm, it seems rather intrusive to change this behaviour, is this really the only way?

keepreviousinstall and buildininstalldir are fundamentally incompatible, so I'm not keen on just printing a warning here and pretending it'll all work out well

i agree that it's an intrusive change, but we really need a way to avoid cleaning up the installdir when building in the installdir. otherwise we have to modify each easyconfig that uses buildininstalldir.

the alternative would be to add another parameter to enforce this, e.g. keeppreviousbuild, would you prefer that?

[boegel]

@smoors Hmm, it seems rather intrusive to change this behaviour, is this really the only way?
keepreviousinstall and buildininstalldir are fundamentally incompatible, so I'm not keen on just printing a warning here and pretending it'll all work out well

i agree that it's an intrusive change, but we really need a way to avoid cleaning up the installdir when building in the installdir. otherwise we have to modify each easyconfig that uses buildininstalldir.

the alternative would be to add another parameter to enforce this, e.g. keeppreviousbuild, would you prefer that?

Maybe that makes more sense, yes. That way we're at least not changing existing behavior.

Though it still feels a bit off somehow...

[smoors]

another solution would be to only remove the contents of the installdir, but not the installdir itself. with bwrap, the installdir will appear empty anyway, so that will be very fast.

[smoors]

alternative implementation with new param forcekeeppreviousinstall in #4890

[smoors]

thinking more about this, i think the best solution is to add a build option to indicate that the installdir is mounted in a new namespace. that makes it clear why we are doing this, and this option can be used by the eb wrapper to install with bwrap. it will also allow fixing the Tarball easyblock, which needs self.cfg['install_type'] = 'merge', again to avoid removing the installdir.

[smoors]

closing in favor of #4894