[CMake] DESTDIR behaviour with different variable name

[Tomasz Grobelny]

On Tue, 12 Apr 2011 03:44:04 +0200, Michael Hertling <mhertling at online.de>
wrote:
> On 04/11/2011 10:42 PM, Tomasz Grobelny wrote:
>> On Monday 11 April 2011 21:55:48 Alexander Neundorf wrote:
>>> 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 $DESTDIR/opt/foo.
>>> So they will not have a correct RPATH.
>>> You really should set CMAKE_INSTALL_PREFIX.
>>>
>> I'd like to. But CMAKE_INSTALL_PREFIX does not get recomputed when I
>> change
>> MYDESTDIR and try to do "make install" again. Or at least I don't know
>> how to
>> make it behave this way.
>> Besides, I don't use RPATH (at least not explicitely, hopefully cmake
is
>> not
>> doing anything nasty behind the scenes).
> 
> But some day, you might want to use RPATH features as they are very
> convenient in certain situations, or you might want to incorporate
> the installation prefix or derivatives like CMAKE_INSTALL_PREFIX/lib
> /${PROJECT_NAME} in your binaries which can be quite convenient, too.
> Moreover, you can hardly prevent your project's users to use RPATH on
> their own, see the CMAKE_INSTALL_RPATH/CMAKE_BUILD_WITH_INSTALL_RPATH
> variables, e.g. In this regard, using the DESTDIR Makefile/environment
> variable bears the risk of subtle failures and isn't worth the effort,
> IMO. Thus, you should take Alex's warning absolutely seriously, or in
> other words: Changing the installation prefix does invalidate your
> already built targets, so you do need to reconfigure and rebuild.
> 
> Anyway, see [1] for a chance to add "DESTDIR=$MYDESTDIR" to the
> generated Makefiles, provided that you are using GNU Make, but
> even this won't work as expected since DESTDIR is hard-coded
> in CMake, AFAIK, and due to other reasons.
> 
> [1] http://www.mail-archive.com/cmake@cmake.org/msg34344.html
> 
Somewhat hackish (especially this \$\(firstword \$\(MAKEFILE_LIST\)\)
part). I've just come up with another solution (probably not less hackish,
but simpler and working):
set(CMAKE_INSTALL_PREFIX "\$ENV{MYDESTDIR}")
-- 
Regards,
Tomasz Grobelny