[CMake] if(ON) not considered true?

[frodak17]

$ cmake --version
cmake version 3.13.2

$ cmake -S src -B testON
ON is ON
-- Configuring done
-- Generating done
-- Build files have been written to:...

$ cat src/CMakeLists.txt
cmake_minimum_required(VERSION 3.12)

project(sample C)

if(ON)
  message("ON is ON")
endif()

What version are you using?

On Sat, Jan 26, 2019 at 10:39 AM Mario Emmenlauer <mario at emmenlauer.de>
wrote:

>
> Dear All,
>
> I'm plagued by an issue that I do not understand. An if-statement
> (in a package configuration file) evaluates ON to false:
>
> IF(ON)
>     ...some code here
> ENDIF()
>
> The part inside IF is *not* executed. Replacing ON by TRUE does not
> help, only replacing it by 1 helps. Is this correct behaviour? I can
> not understand this from the documentation. The docs seem to say "ON"
> would be a valid token for true:
> https://cmake.org/cmake/help/v3.6/command/if.html
>
> The full user story is that in the package configuration I'd like to
> treat shared libraries specially, so I use "IF(@BUILD_SHARED_LIBS@)".
> The user configures the build with
>
>     cmake -DBUILD_SHARED_LIBS=ON .
>
> so the package configuration gets resolved to "IF(ON)". I have not
> too much control about the way users specify the options, so I'd
> like to solve this on my end. If options should not keep the value
> "ON", how can I cleanly resolve them to the corresponding number 0/1?
>
> Am I doing something wrong?
>
> All the best,
>
>     Mario Emmenlauer
>
>
> --
> BioDataAnalysis GmbH, Mario Emmenlauer     Tel. Office: +49-89-74677203
> Balanstr. 43                   mailto: memmenlauer * biodataanalysis.de
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