[cmake-developers] [PATCH] FindBoost: Add imported targets

[Ruslan Baratov]

On 17-Nov-15 15:48, Roger Leigh wrote:
> On 17/11/2015 07:53, Ruslan Baratov wrote:
>> On 16-Nov-15 21:01, rleigh at codelibre.net wrote:
>>> I have attached a patch to add imported targets to FindBoost, in the 
>>> form
>>> of Boost::<component> (e.g. Boost::date_time) or Boost::Boost as a
>>> generic
>>> interface library for header-only components.
>> Since it's `Boost::date_time` I expect that it will be `Boost::boost`
>> (lowercase).
>
> Yes, I've merged most of the previous work Brad pointed to yesterday, 
> and this included this change.
>
>> On 16-Nov-15 21:39, Brad King wrote:
>>> On 11/16/2015 09:26 AM, Florent Castelli wrote:
>>>> But one there’s one thing that comes to mind. Some compiled libraries
>>>> have dependencies on other compiled libraries.
>>>> Don’t you think it would make sense to teach FindBoost about those
>>>> so we link everything properly?
>>>>
>>>> And also maybe add the native dependencies for some modules that
>>>> have one like maybe pthread or openssl.
>>>> Though, this might be hard to get right in a cross platform way.
>>> Please look at adding these.  The imported targets should come
>>> with all usage requirements as if they were provided by upstream
>>> Boost.  It may be tricky to get right on all platforms but if we
>>> do not do it then application code will have to do it instead.
>>>
>>
>> One tricky part about it is that dependency can be optional. I.e.
>> Boost::iostreams may or may not depends on ZLIB/BZip2. Such information
>> is known only by build procedure. I.e. should be installed by b2 itself
>> or by wrapped ExternalProject_Add instructions.
>
> For the specific case of the zlib/bzip2 dependencies, this is only the 
> case when using the static libraries?  It's not exposed via the 
> headers is it?
I'm not sure about all aspects it's not my main point anyway :) I'm 
saying that this kind of information can be installed by CMake project 
and I can predict that it will be hard to achieve the same in 
FindBoost.cmake when build already done and this info is lost.

>
> Looking at the information embedded in the sources for use with 
> autolinking, we could certainly process the headers for the requested 
> components and pull out the referenced libraries.  This would get us 
> all of the header dependencies without hardcoding anything ourselves, 
> which would make it work with arbitrary versions of boost without 
> having to hardcode the differences between Boost versions.
>
> Fully supporting static linking would be much more difficult.  As you 
> say, it depends upon how Boost was built. 
...

> Full support here would need to wait for the upstream to generate this 
> data at build time?
This is a best option but not necessary. As I said earlier if you're 
using wrapper to install boost (like ExternalProject_Add) you can add 
some extra files which will hold this info.

Ruslan