[CMake] How to skip steps and use default values in ExternalProject_Add command?

[Petr Kmoch]

No idea on this one. The trick I showed is "vanilla CMake," a direct
consequence of the CMake parsing & string processing algorithm. What you're
asking is about the internals of ExternalProject_Add, of which I know
nothing.

Petr

On Thu, May 21, 2015 at 1:43 PM, Cedric Doucet <cedric.doucet at inria.fr>
wrote:

>
> Hi Petr!
>
> Thank you for the trick: it's very powerful!
>
> Does this mean that these two calls are equivalent if I write: set(the_configure_command
> CONFIGURE_COMMAND)?
>
> ExternalProject_Add(${${LIBRARY}_LOWERNAME}
>   PREFIX ${${LIBRARY}_PREFIX}
>   URL ${${LIBRARY}_URL}
>   ${the_configure_command}
> )
>
> ExternalProject_Add(${${LIBRARY}_LOWERNAME}
>   PREFIX ${${LIBRARY}_PREFIX}
>   URL ${${LIBRARY}_URL}
> )
>
> I guess the default value of CONFIGURE_COMMAND will be used, right?
>
> Cédric
>
>
> ------------------------------
>
> *De: *"Petr Kmoch" <petr.kmoch at gmail.com>
> *À: *"Cedric Doucet" <cedric.doucet at inria.fr>
> *Cc: *cmake at cmake.org
> *Envoyé: *Jeudi 21 Mai 2015 13:33:27
> *Objet: *Re: [CMake] How to skip steps and use default values in
> ExternalProject_Add command?
>
>
> Hi Cedric.
>
> When doing things like that, remember that CMake's "named arguments" are
> arguments just like any other. So you can easily obtain them from variable
> expansion; something like this:
>
> if(${LIBRARY}_CONFIGURE_COMMAND)
>   set(the_configure_command CONFIGURE_COMMAND
> ${${LIBRARY}_CONFIGURE_COMMAND})
> else()
>   set(the_configure_command "")
> endif()
>
> ExternalProject_Add(${${LIBRARY}_LOWERNAME}
>   PREFIX ${${LIBRARY}_PREFIX}
>   URL ${${LIBRARY}_URL}
>   ${the_configure_command}
>   BUILD_COMMAND ${${LIBRARY}_BUILD_COMMAND}
>   INSTALL_COMMAND ${${LIBRARY}_INSTALL_COMMAND}
> )
>
> The same trick can be applied to any other command you need to
> conditionally exclude, of course.
>
> Petr
>
> On Thu, May 21, 2015 at 1:10 PM, Cedric Doucet <cedric.doucet at inria.fr>
> wrote:
>
>> Hello,
>>
>> I would like to loop on a list of libraries to download and install, by
>> calling the ExternalProject_Add command for each of these libraries.
>> To do that, I need to define some commands for each library, like
>> CONFIGURE_COMMAND, BUILD_COMMAND and INSTALL_COMMAND.
>> These commands may differ from one library to another; for example, some
>> of them may be based on make, or autoconfig, or cmake, etc.
>> Furthermore, some of these libraries may not need to be built.
>>
>> What is the good way to skip some steps?
>> Is it possible to use default values for some commands?
>>
>> The problem in my situation is that I have to fill in each command since
>> I want to design way of downloading and installing third party libraries.
>> To be clear, I wrote a loop which looks like this:
>>
>> ==========================================================================
>> foreach(LIBRARY IN LISTS NOT_FOUND_LIBRARIES)
>>     ExternalProject_Add(${${LIBRARY}_LOWERNAME}
>>                                        PREFIX ${${LIBRARY}_PREFIX}
>>                                        URL ${${LIBRARY}_URL}
>>                                        CONFIGURE_COMMAND
>> ${${LIBRARY}_CONFIGURE_COMMAND}
>>                                        BUILD_COMMAND
>> ${${LIBRARY}_BUILD_COMMAND}
>>                                        INSTALL_COMMAND
>> ${${LIBRARY}_INSTALL_COMMAND}
>>                                      )
>> endforeach(LIBRARY)
>> ==========================================================================
>>
>> However, if a library is based on cmake, I do not need to specify
>> commands for configuration and building.
>> Is it possible to say that the default value of CONFIGURE_COMMAND will be
>> used for example?
>> The only way I know to do that is to suppress the line
>> defining CONFIGURE_COMMAND but I can't do that since other libraries may
>> need to define it.
>>
>> To skip steps, I replace the corresponding command by 'ls' but it's not
>> very clean.
>> That is to say, the value of ${LIBRARY}_CONFIGURE_COMMAND is 'ls' when I
>> want to skip the configuration step.
>>
>> Thank you very much for your help.
>>
>> Cédric
>>
>>
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>
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