[cmake-developers] using ocaml with cmake

[Brad King]

Alexander Neundorf wrote:
> in KDE we have kalzium, which uses an OCaml library.
> We managed to get it compile, but not very nice until now.
> OCaml comes with a tool ocamldep, which parses the ocaml source files for 
> dependencies and generates a "depend" file which can be included in a 
> Makefile.
> How can we do the dependency checking with CMake ?
> We could load the depend file and try to parse it in CMake.
> Or we would have to implement an ocaml dependency parser in CMake.
> Are there other options ?

What's really missing is a way to specify custom dependency scanners for
custom commands and new languages.  The real bottleneck to this is how
to get Visual Studio projects to do the scanning and load the
dependencies.  Currently C and C++ dependencies are automatically
handled by the VS IDE, but there does not seem to be a way even through
the GUI to specify dependency scanning for custom build rules.

One solution would be to write a VS IDE plugin to implement support for
a whole new "language" which is used by CMake to drive custom commands.
 This would probably be a major undertaking though.

What we've done in the past is to use a hack to get the dependencies in
place.  As part of the custom command for running an ocaml rule run the
dependency scanner along with your own custom tool to convert the output
to a MyCustomDepends<rule-id>.cmake file.  In the file write

SET(MY_OCAML_DEPENDS_<rule-id>
  /path/to/dep1
  /path/to/dep2
  ...
)

Then in the CMakeLists.txt file do

INCLUDE(${CMAKE_CURRENT_BINARY_DIR}/MyCustomDepends<rule-id.cmake OPTIONAL)
ADD_CUSTOM_COMMAND(
  OUTPUT some_output
  DEPENDS explicit_dependencies ${MY_OCAML_DEPENDS_<rule-id>}
  COMMAND ocaml ...
  COMMAND ocamldep ...
  COMMAND convert-depends-to-cmake-file
)

The first time the rule will run because the output doesn't exist.
After that CMake will re-run before the next build and include the
dependencies.

-Brad