FindBoost.cmake (Was: kdesupport-for-4.2 cmake error)

[Pau Garcia i Quiles]

On Sun, Jan 18, 2009 at 11:33 PM, Andreas Pakulat <apaku at gmx.de> wrote:

>> >> Parsing boost/version.hpp seems like the right way to do version
>> >> detection. From Boost 1.35.0 :
>> >
>> > But how do you find that _easily_? Boost installs its headers into
>> > <prefix>/include/boost-<version>/boost/, so we need the version to try to find
>> > boost. The only way to avoid that is writing platform specific cmake code
>> > that iterates for <includedir>/boost-* and checks in each one for a
>> > boost/version.hpp.
>>
>> FILE(GLOB ... ) and FILE( GLOB_RECURSE )...  to the rescue! Using the
>> globbing expressions "boost", "boost-*" and "Boost-*" would be
>> probably enough. Furthermore, you usually only have one version of
>> Boost installed, two or three tops, so FILE( GLOB/GLOB_RECURSE ...)
>> should not take long.
>
> The OP had 5 versions installed actually and in his case its even more
> complicated, because with globbing you might find boost 1.34 and use that
> (as the project works with that). That might or might not be ok for the
> user...

If you sort the result of FILE( GLOB ... ) so that the most recent
version comes first (i. e. 1.37.0 in this case), globbing would not be
any different from having a list of versions in FindBoost.cmake.

>> > This would be quite a bit more code, as <includedir> is
>> > different on each of the 3 major platforms.
>>
>> FindBoost.cmake is already long enough (638 lines in CMake 2.6.2), so
>> a hundred more lines are not a problem, IMHO.
>
> I'd say that this wouldn't increase readability or "understandability" of
> the module, but as only few people touch it thats probably true (i.e. not a
> real problem).

I'd say readability or understandability stopped being a problem in
FindBoost.cmake a long time ago ;-)

>> > IMNSHO we should either get Boost people to stop this insanity
>>
>> Good luck with that! On the other hand, this "insanity" allows for
>> different Boost versions to be co-installed.
>
> There are far better ways to do that.

Given that CMake is being added as a new build system for Boost, my
hopes are this would create and install some kind of
UseBoost-<version>.cmake.

>> > or just
>> > better document that projects using FindBoost should set
>> > Boost_ADDITIONAL_VERSIONS to a list of versions they know their project
>> > builds with.
>>
>> The problem with that is when a new version is out.
>
> Not really, if a project uses boost, one of its dev should _check_ that it
> still works with the newer version (As I said in the other mail,
> kdevplatform for example doesn't build with 1.37). And if he verified that,
> he can simply commit the change.
>
> IMHO you can't assume that your boost-using project will work just fine
> with a newer version.

The problem we face now is we do not even arrive that far in the "checklist":

1. Write application
2. Find Boost <- Here is were we fail now
3. Build my application with the found Boost version <- Here is where
we would fail if we parse version.hpp

-- 
Pau Garcia i Quiles
http://www.elpauer.org
(Due to my workload, I may need 10 days to answer)