[CMake] Problem with option() when in subdirectory

[David Demelier]

On 18/09/2011 21:54, Alexander Neundorf wrote:
> On Sunday, September 18, 2011 02:42:49 PM Michael Wild wrote:
>> On 09/18/2011 02:32 PM, Alexander Neundorf wrote:
>>> On Sunday, September 18, 2011 02:15:54 PM David Demelier wrote:
>>>> Hello,
>>>>
>>>> I noticed that option() values are not checked when the option() command
>>>> is under a add_subdirectory() target.
>>>>
>>>> Example:
>>>>
>>>>
>>>> -- a's CMakeLists.txt --
>>>> project(a C)
>>>>
>>>> set(BUILD_DEMOS OFF)
>>>> add_subdirectory(extern/b)
>>>>
>>>> -- extern/b's CMakeLists.txt --
>>>> project(b C)
>>>>
>>>> option(BUILD_DEMOS "Enable the demos build" ON)
>>>>
>>>> if (BUILD_DEMOS)
>>>>
>>>> 	...
>>>>
>>>> endif ()
>>>>
>>>> Then when building the project a it will also enter the if BUILD_DEMOS
>>>> conditional.
>>>>
>>>> What can I do now? :)
>>>
>>> The values of options are stored in the cache.
>>> In your toplevel file, OFF is put in the cache.
>>> Then, in the subdir, the variable of BUILD_DEMOS is already in the cache,
>>> so it is not overridden with ON, but keeps the value which is in the
>>> cache.
>>>
>>> Does that help ?
>>>
>>> Alex
>>
>> Alex, you mis-read his code. In the top-level CMakeLists.txt file
>> BUILD_DEMOS is *not* put in the cache, which is why it is overridden by
>> the option() call *the first time round*, but not afterwards which makes
>> for very confusing behaviour.
>>
>> In general, it is safe to override a cached variable with a uncached
>> variable, but the other way round is asking for trouble...
>>
>> It would be better to do in a/CMakeLists.txt:
>>
>> set(BUILD_DEMOS OFF CACHE INTERNAL "Don't build demos")
>
> Yes, you are completely right.
>
> Alex
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Thanks a lot! This solved my problem :)

Cheers,

-- 
David Demelier