[CMake] Build Library from Thrift generated files

[Eric Noulard]

2013/9/4 Pascal Bach <pasci.bach at gmail.com>:
> Hello Eric
>
> On Wed, Sep 4, 2013 at 11:26 AM, Eric Noulard <eric.noulard at gmail.com> wrote:
>>
>> 2013/9/4 Pascal Bach <pasci.bach at gmail.com>:
>> > Hello everybody
>> >
>> > I'm trying to build a library from source files that are generated at build
>> > time. The setup is the following.
>> >
>> > Inputfiles (Service.thrift)   -> Thrift Compiler/Generator -> Several
>> > generated files (gen-cpp/Service.h, gen-cpp/Service.cpp, gen-cpp/Types.h,
>> > [possibly more] -> Build Library -> Library (thrift-service.so)
>>
>> Unknown source file name is just painful.
>>
>> Can't the thrift generator tell you the name of the files he will generate?
>> Something like:
>> thrift --generated-file-list Service.thrift
>>
>> or may be you can teach him the name of the flie you want?
>
> Currently there is no way toget just a list of the generated output
> file. One idea that I had was to just run the
> process once to get a list of the generated output files and then
> throw the files away. If I wrap this in a function
> it would be similar to the generated-file-list. But it seems like a waste to me.
>
> Because the output of the generator is dependent on the content of the
> file it is not possible to specify an output file, only an output
> directory.
>
>>
>> If neither of this apply then you'll have to discover the source file yourself
>> (and file a feature request to thrift compiler guys :-] ).
>>
>>
>> > The idea is to rebuild the library whenever one of the Service.thrift file
>> > changes.
>> > The problem is that I don't know the output of the generated files in
>> > advanced so I like to use all the files generated by the generator and pack
>> > them in a library.
>> >
>> > I tried to use add_custom_command() but as I don't know what's the output of
>> > the generator I didn't succeed.
>>
>> May be you can use a 2 steps approach.
>> Your custom command should generate
>>
>> 1) the source file
>> 2) a cmake file which contains the list of the generated sources files,
>>     the OUTPUT of the custom command will be that file.
>>
>> add_custom_command(OUTPUT ${CMAKE_CURRENT_SOURCE_DIR}/ThriftGeneratedFiles.cmake
>>                                    COMMAND thrift ARGS -o
>> ${CMAKE_CURRENT_SOURCE_DIR}/ThriftGenerated Service.thrift
>>                                    COMMAND ${CMAKE_COMMAND} ARGS
>> -DSRCDIR=${CMAKE_CURRENT_SOURCE_DIR}/ThriftGenerated -P
>> ${CMAKE_CURRENT_SOURCE_DIR}/GetThriftGeneratedFiles.cmake
>>                                    DEPENDS Service.thrift)
>>
>> # This will include the file if it exists
>> include( ${CMAKE_CURRENT_SOURCE_DIR}/ThriftGeneratedFiles.cmake OPTIONAL)
>>
>> Now the script "GetThriftGeneratedFiles.cmake" should be a CMake scripts which
>> knows that "SRCDIR" contains all the generated files, from which it can build
>> ThriftGeneratedFiles.cmake.
>>
>> In the end ThriftGeneratedFiles.cmake content may be something like:
>>
>> set(THRIFTGEN_SRC
>>       gen-cpp/Service.h, gen-cpp/Service.cpp, gen-cpp/Types.h)
>>
>> add_library(thrift-service
>>                 ${THRIFTGEN_SRC})
>>
>> You may have to initially build twice in order to bootstrap the
>> missing "ThriftGeneratedFiles.cmake".
>>
>> I did not test this scheme but I guess it should work.
>>
>
> Your suggestion is interesting.
> What I don't understand is what triggers the
> ThriftGeneratedFiles.cmake to be recreated. Is it right that this file
> gets recreated whenever a .thift file changes?

Yes because it is the output of the add_custom_command
which DEPENDS on the thrift file.

> I will try to implement something like this tomorrow and see if can
> get it to work.

Ok.


-- 
Erk
L'élection n'est pas la démocratie -- http://www.le-message.org