[CMake] Problem with option() when in subdirectory

Discussion:

David Demelier

2011-09-18 12:15:54 UTC

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? :)

Cheers,

--
David Demelier

Alexander Neundorf

2011-09-18 12:32:33 UTC

Permalink

Post by David Demelier
Hello,
I noticed that option() values are not checked when the option() command
is under a add_subdirectory() target.
-- 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

Michael Wild

2011-09-18 12:42:49 UTC

Permalink

Post by Alexander Neundorf

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")

this way

Alexander Neundorf

2011-09-18 19:54:51 UTC

Permalink

Post by Michael Wild

Post by Alexander Neundorf

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...
set(BUILD_DEMOS OFF CACHE INTERNAL "Don't build demos")

Yes, you are completely right.

Alex

David Demelier

2011-09-21 19:50:43 UTC

Permalink

Post by Alexander Neundorf

Post by Michael Wild

Post by Alexander Neundorf

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...
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