[CMake] Adding explicit dependencies to a target

[Petr Kmoch]

Hi Tarjei.

add_custom_command() has a DEPENDS argument where you can list any number
of files which will act as dependencies for the custom command. So you
could extend your custom command like this:

add_custom_command(
  OUTPUT ... #as before
  COMMAND ... #as before
  MAIN_DEPENDENCY a.idl
  DEPENDS b.idl c.idl
  ... # rest as before
)

You have to keep in mind that this gets processed at configure time - if
you change the #include-s used in a.idl, you have to modify the CMakeList
and re-run CMake to get the changes picked up.

It should also be possible to use the IMPLICIT_DEPENDS argument of
add_custom_command() to request the C or C++ dependency scanner to run on
the file, moving the dependency detection to build time. But that only
works for Makefile generators.

Petr


On Thu, May 8, 2014 at 9:16 AM, Tarjei Knapstad
<tarjei.knapstad at gmail.com>wrote:

> In our project we are generating code from CORBA IDL files by adding a
> custom command that generates C++ code from the IDL files and a library
> target that depends on the generated output. This works as expected,
> however IDL supports include directives which are (naturally) not picked up
> as dependencies by CMake. To give an example:
>
> a.idl:
> --------------------
> #include "b.idl"
> #include "c.idl"
> ---------------------
>
> Here the file a.idl file includes b.idl and c.idl. The file a.idl is given
> as input to the custom command that processes IDL files into C++, but if I
> change b.idl or c.idl then the target is not rebuilt. Is it possible to add
> b.idl and c.idl as explicit dependencies in some way so that my target is
> rebuilt if these files change? I've made various attempts with
> add_custom_target() and add_dependencies() as well as
> set_source_files_properties() without any luck.
>
> Regards,
> --
> Tarjei
>
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