[CMake] Generate sources

[Mark Stijnman]

On Wed, Dec 16, 2015 at 2:29 PM, Layus <layus.on at gmail.com> wrote:

> Hi,
>
> I am looking for a way to share an archive of a partially compiled project
> to speedup compilation time and configuration hassle for the users.
>
> I have a project that works in two steps.
> First a source generator is built (based on clang) and generates some
> extra source files based on the existing source files.
> Then the normal compilation process takes places, building the application
> from both original and generated sources.
>
> <snip>


> Now, is it possible to distribute a source archive with the generated
> sources, in such a way that any user unpacking the archive and running
> cmake would not have to generate the extra sources ?
>
> This would be useful because
> i) the project is tricky to configure and
> ii) the generated sources are not dependent on the user config, so
> building the generator is just useless computation time on the user.
>
> The ideal scheme would be something like
>
>     [developper]
>     $ cmake -DCLANG=config
>     $ make generate
>     $ make package_source
>
>     [user]
>     $ unpack
>     $ cmake -DUSER=config
>     $ make # builds only the application, reusing the shipped generated
> sources.
>     $ make install
>
> ... but when the user runs cmake, he overwrites the generated Makefiles
> and the extra sources are generated again.
>
> Any idea ?
>
> layus.
>
> --
>

I'd probably just make it such that the CMake script automatically detects
the presence of the generated files, and if they don't exist, generate
them. For example:
1. Set a variable GENERATED_FOLDER to ${CMAKE_CURRENT_SOURCE_DIR}/generated
2. If ${GENERATED_FOLDER} doesn't exist, set it to
${CMAKE_CURRENT_BINARY_DIR}/generated instead, and set up the targets that
will generate the files in that folder.
3. Simply use the ${GENERATED_FOLDER} variable to add the generated files
to your application.
4. Set up the package_source target so that it packages the files from
${GENERATED_FOLDER} to a folder called "generated" (such that if a user
unpacks from there, they will end up in
${CMAKE_CURRENT_SOURCE_DIR}/generated), and you're done.
5. Recommended: add a check for the existence of target "generate", and if
so, set it as a dependency for your application and package_source.

This way, you don't need to remember what switches to use, or when to use
"make generate". If you need to make it possible for a user to force
generation, you can alter step 2 to also run when a command line option is
supplied.

Hope that helps,

Best regards Mark
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