On 23. Dec, 2009, at 13:28 , Marcel Loose wrote:
> On Wed, 2009-12-23 at 13:09 +0100, Michael Wild wrote:
>> On 23. Dec, 2009, at 12:08 , Marcel Loose wrote:
>>
>>> Hi all,
>>>
>>> I suggested this in the quite long thread "third party library
>>> dependencies", but it may have been overlooked. Hence, I started a new
>>> thread.
>>>
>>> Upon (re)reading the Mandriva page
>>> http://wiki.mandriva.com/en/Overlinking, I was thinking: maybe the issue
>>> of overlinking can be solved more or less the same way as pkg-config
>>> does: i.e. by defining private dependencies. This could be an extra
>>> option to target_link_libraries.
>>> Something like:
>>>
>>> target_link_libraries(mylib public1 public2 PRIVATE private1 private2)
>>>
>>> This would tell CMake that mylib directly depends on public1 and public2
>>> and should only link in these two libraries when these are shared
>>> object libraries; otherwise private1 and private2 would also need to be
>>> added on the link line.
>>>
>>> The big hurdle to take, of course, is to detect in a
>>> platform-independent way whether the given library is shared or static.
>>> However, a lot of this knowledge is already available in the diverse
>>> Modules/Platform macros, so my feeling is that this should be feasible.
>>>
>>> Best regards,
>>> Marcel Loose.
>>>
>>
>> You would also need a PUBLIC keyword, and then require that all
>> FindXXX.cmake modules prefix their libraries with PUBLIC and PRIVATE. If
>> only the PRIVATE libraries where prefixed, the following would not work if
>> A_LIBRARIES contains PRIVATE:
>>
>> find_package(A)
>> find_package(B)
>> add_library(C source.c)
>> target_link_libraries(C ${A_LIBRARIES} ${B_LIBRARIES})
>>
>> Because then all the B_LIBRARIES would be considered to be private "details"
>> of the public A_LIBRARIES... Also, there's no way to tell CMake which of the
>> private libraries belongs to which of the public libraries.
>>
>> I think it would be better if a FindXXX.cmake module marked the private
>> libraries as a property of the public libraries and then let CMake take it
>> from there (although as of now I wouldn't know on what to set the property,
>> except if the module created an IMPORTED target for each of the public
>> libraries, but that bears the possibility of target name collisions with the
>> importing project).
>>
>> Michael
>
> Hi Michael,
>
> I don't think you'll need to prefix the library names with either
> PRIVATE_ or PUBLIC_. CMake could figure out whether "public1" and
> "public2" are shared or static libraries. If they are shared libraries,
> then the libraries marked as private ("private1" and "private2") do not
> have to be linked in as well. Otherwise they must also be linked in. I
> assume that CMake keeps a list internally, of all dependent targets; the
> private libs should only be added to that internal list if the public
> libs are static libs.
>
> I don't completely understand your example. Are you suggesting that
> you'll run into trouble if you have a library named "PRIVATE"? I think
> name clashes will currently occur as well if I name my library "debug",
> "optimized", or "general".
>
> Maybe, it would be better if the FindXXX modules would handle this. On
> the other hand, you then depend on third parties to properly update
> their FindXXX modules, or have to rewrite them yourselves :-(
>
> Best regards,
> Marcel Loose.
>
No, it won't work. For example, if FindA.cmake does
set(A_LIBRARIES /some/path/libA.so
PRIVATE /some/other/path/libX.a /some/other/path/libY.a)
and FindB.cmake contains
# notice that this is a static library!
set(B_LIBRARIES /some/path/libB.a)
then the call
target_link_libraries(C ${A_LIBRARIES} ${B_LIBRARIES})
expands to (wrapped for legibility
target_link_libraries(C
/some/path/libA.so
PRIVATE /some/other/path/libX.a
/some/other/path/libY.a
/some/path/libB.a)
which is different in meaning from
target_link_libraries(C ${B_LIBRARIES} ${A_LIBRARIES})
which becomes
target_link_libraries(C
/some/path/libB.a
/some/path/libA.so
PRIVATE
/some/other/path/libX.a
/some/other/path/libY.a)
In the first case libB.a becomes marked as PRIVATE of libA.so! Not very nice if
you ask me ;-)
Michael
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