[CMake] externalproject_add and generating sources

[Nicholas Braden]

You'll also want to build your own project with ExternalProject, and use
the DEPENDS option to control build order. This ensures that all
dependencies are fully installed before your own project is even
configured. The project with all the ExternalProject calls is typically
called a superbuild, and effectively becomes an optional convenience to
building your own project.

On Thu, Jan 26, 2017 at 3:23 AM, David Jobet <david.jobet at free.fr> wrote:

> Hello,
>
> suppose I want to use protobuf and integrate it in my project with
> externalproject_add. (actually, I just have precompiled binaries and libs +
> header files, I don't have the full sources)
> Once the project has been 'built' (actually, installed by a custom
> rpm-like tool to a shared path), I can use the protoc compiler to generate
> protobuf c++ files (.pb.h and .pb.cpp files) from a .proto description file.
> I can add_dependencies so that the external project is built before
> projects depending on libprotobuf.a.
>
> However, I don't know how to do the same thing with .pb.h and .pb.cpp
> files which use a .proto file and the protoc compiler.
>
> make is fine with it, but ninja complains with an error like this :
> ninja: error: '/path_to_external_projects/protobuf/2.6.0.4/bin/protoc',
> needed by 'some_project/SomeFile.pb.h', missing and no known rule to make it
>
> how can I tell ninja that protoc is going to be provided by
> externalproject ?
> If I use byproducts, ninja is happy, but "ninja clean" deletes
> /path_to_external_projects/protobuf/2.6.0.4/bin/protoc.
> I don't want that to happen since /path_to_external_projects/protobuf/
> 2.6.0.4/bin/protoc is shared with other users.
>
> With regards
>
> David
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