[CMake] DESTDIR behaviour with different variable name

[Alexander Neundorf]

On Monday 11 April 2011, Tomasz Grobelny wrote:
> On Mon, 11 Apr 2011 09:01:09 -0700, Tyler <tyler at cryptio.net> wrote:
> > On Mon, Apr 11, 2011 at 8:54 AM, Tomasz Grobelny
> >
> > <tomasz at grobelny.oswiecenia.net> wrote:
> >> Ok, but is there a way to achieve the same effect so that the user can
> >> type just "make install" and not know anything about DESTDIR
>
> environment
>
> >> variable (provided he knows about MYDESTDIR)? Maybe it is possible to
>
> put
>
> >> this "DESTDIR=$MYDESTDIR" in the generated Makefiles somehow...
> >
> > If I understand your use case right (which I might not as you haven't
> > described what you're trying to do, just how you're trying to do it),
> > maybe you can just override CMAKE_INSTALL_PREFIX.
> >
> > If you go this route, check the archives because of the whole
> > _INITIALIZED_TO_DEFAULT aspect of that particular cache variable.
>
> I already tried playing with CMAKE_INSTALL_PREFIX but the problem was that
> value of MYDESTDIR was read (and saved to CMAKE_INSTALL_PREFIX) only when
> configuring first time. That's why DESTDIR mechanism comes closer to what
> I'm trying to achieve. My use case is something like that:
> 1. User has some default MYDESTDIR to non writable location.
> 2. User executes "cmake . && make install".
> 3. The installation fails because user has no rights to $MYDESTDIR.
> 4. User changes MYDESTDIR to another location (writable this time).
> 5. User executes "make install" once again and it should succeed.
>
> Of course the user could set MYDESTDIR to correct location before building
> but people often forget that. Now the tricky part is that users are already
> used to this mechanism (for particular variable name, called MYDESTDIR
> here). So taking different environment variable instead of DESTDIR would
> allow me to minimize confusion among users. Otherwise I'll just tell them
> to set yet another variable (DESTDIR). But I would like to avoid that if at
> all possible.

DESTDIR has a different purpose.
Installing to DESTDIR does not necessarily lead to a working and correct 
installation, mainly when paths are involved, like e.g. RPATH settings.
Assuming that CMAKE_INSTALL_PREFIX would be /opt/foo, your executable might 
get /opt/foo/lib as RPATH, also when installed to $DESTDIR/opt/foo.
So they will not have a correct RPATH.
You really should set CMAKE_INSTALL_PREFIX.

Alex