[cmake-developers] General Config.cmake file issue on ArchLinux

[Stephen Kelly]

Alexander Neundorf wrote:

> On Thursday 06 December 2012, Stephen Kelly wrote:
>> Alexander Neundorf wrote:
>> > Let's assume /opt/foo/lib/ is a symlink to /usr/local/lib/.
>> > The package has been installed to /opt/foo/ and is found via
>> > CMAKE_PREFIX_PATH in /opt/foo/lib/cmake/Foo/FooConfig.cmake.
>> > Now when going up to the prefix, we will come across /opt/foo/lib/,
>> > which is a symlink, but everything will be fine, since going up will
>> > take us to /opt/foo/, from where we can correctly descend again.
>> 
>> But that works only if you don't search for anything in bin/ or share/,
>> right (assuming there are not appropriately similiar(!) symlinks for
>> those too)?
> 
> Hmm, no ?
> 
> /opt/foo/lib/cmake/Foo/../../../share/ is /opt/foo/share/, which would be
> correct (when the package has been installed to /opt/foo/, as said above).

Ok. Now I'm even more confused. 

I thought /opt/foo/share/ is incorrect. Correct would be /usr/local/share. 

You are assuming that /opt/foo/share/ is a symlink to /usr/local/share, 
right? That's why I wrote 'assuming there are not appropriately similiar(!) 
symlinks for those too'. Isn't exactly that kind of assumption the source of 
the original problem on Arch? They have a symlink for lib, but not for bin.

Are you confused too? Am I making sense?

>> > , but here there would be no
>> > symlink (other than if it would be possible to test whether a directory
>> > is the destination of a symlink).
>> > 
>> > It's a problem if the symlinked location is not the location to which
>> > the package has been installed, but for whatever reason the symlinked
>> > location is found first.
>> 
>> Yes, exactly. If the symlinked location is found first, and the symlink
>> reaches into the prefix (so that all relative paths which have to reach
>> back though the prefix end up somewhere unexpected), then the relative
> 
> It doesn't matter whether the location which is found, has been found via
> the symlink or via a "normal" path. It matters whether the location where
> it has been found is in the correct prefix.

Right. 'Correct prefix' is a bit ambiguous though if there is a symlink for 
lib/, but not for anything else. Does that make sense? Do you agree?

> 
>> paths will not work as expected. If the symlinked Config file is found
>> first, then it appears that the installation was to a 'split prefix' -
>> partly in /opt/foo/ and partly in /usr/local/, which is something the
>> Config file will not expect.
> 
> Yes, I would even say that making a subdir in a prefix a symlink into a
> different prefix is generally bad (no matter whether it's from / into
> /usr/, or from /usr/local/ into /usr), because it destroys as we see the
> relative paths between the subdirs.

Yes.

Thanks,

Steve.