[CMake] Generating include files

[Florent Castelli]

On 20/05/2017 13:32, Urs Thuermann wrote:
> Yes, but not directly. The executable depends on the object file, and
> the object file depends on the (created) source file.  Since "depends
> on" is transitive, the executable also depends on the source file.
>
> Still, I would prefer to write add_executable(foo foo.o) and have
> cmake determine that foo.o depends on foo.c like in make.

But "foo.o" is an intermediate file, an implementation detail that isn't 
cross-platform when CMake wants to work everywhere.
You shouldn't try to express that, it is just wrong.

The proper solution for CMake that works cross-platform is the one 
expressed before with another target that generates only the headers and 
your executable depending on it.
You can't really have the header generated in the same target that is 
using them as that doesn't port well to some build systems that are more 
high level (aka not Make or Ninja). Files will sometimes fail to 
preprocess. Since your foo.c file can be preprocessed before the data 
has been generated and build tools can't extract the dependency 
information automatically as they usually do.
That preprocessing step needs to always work for most build tool, if it 
doesn't they'll just fail the build and they won't check if it did fail 
because that's a file generated in the same target.

Another solution is just not to have that weird requirement to compile 
it "static". From what I understand, you had it as a .c file and 
included it. So you know the object that is exported and its type.
You could just decouple your files using an extern declaration, this way 
you can compile them both in parallel without an actual compile 
dependency from foo.c to tab.c, but instead use a link dependency.

/Florent