[CMake] [ADD_CUSTOM_COMMAND] How to add source dependences to the target ouside of the command?

[Tristan Carel]

Hi dear maintainers, hi lucky users!!!

The module `UseSwig' provided in the version 2.4.3 provides a macro
named `SWIG_ADD_MODULE' to define a C/C++ library wrapped for one of
the targets supported by Swig. This macro uses the command
`ADD_CUSTOM_COMMAND' to define the rule as below:

wrapper.cxx: foo.i
     swig [too many options] foo.i

But `foo.i' can include other files (.i, .h, ...) so `wrapper.cxx' 's
build must depend to these other files too. I guess it can't be
specified by using the macros provided by the module `SWIG_ADD_MODULE'

So I tried to add dependences to the target `wrapper.cxx' in the "user
land" (I mean without patching the module `UseSWIG.cmake' :) but I
failed.

I guess there are two commands to add dependences to entities:
`ADD_DEPENDENCIES' and `SET_SOURCE_FILES_PROPERTIES'


Now a use case: a swig input file `foo.i' which includes the header
`foo.hh', I would like to simply have a rule like below:

wrapper.cxx: foo.i foo.hh
     swig [too many options] foo.i

I tried the following commands:

1.
ADD_DEPENDENCIES(wrapper.cxx foo.hh)
it doesn't work because `foo.hh' is a source file, so not considered
by CMake as a target.

2.
INCLUDE(AddFileDependencies)
ADD_FILE_DEPENDENCIES(foo.i foo.hh)
It compiles but doesn't work and I don't understand why. It should
generate something like:

wrapper.cxx: foo.i
     swig [too many options] foo.i

foo.i: foo.hh   # <--- not generated

Where am I wrong?


3.
ADD_FILE_DEPENDENCIES(wrapper.cxx foo.hh)
But it'is like if `wrappers.cxx' included `foo.hh' , isn't it? (so
it's not what I'm looking for).


Have you got an idea on how to proceed, CMake wizards?


Even if it can be done in the user land, the variable which contains
`wrapper.cxx' defined in the module `UseSWIG.cmake' is private
(internal to the module).

If there is not solution, it means that there's a lack in the module
`UseSWIG.cmake', isn't it?

--- Modules/UseSWIG.cmake.orig  2006-08-24 13:46:46.033254900 -0400
+++ Modules/UseSWIG.cmake       2006-08-24 14:06:31.525217000 -0400
@@ -7,6 +7,8 @@
 # All other macros are for internal use only.
 # To get the actual name of the swig module,
 # use: ${SWIG_MODULE_name_REAL_NAME}.
+# To add extra dependancies to the generated wrapper
+# use: ${SWIG_MODULE_name_EXTRA_DEPS}.
 # Set Source files properties such as CPLUSPLUS and SWIG_FLAGS to specify
 # special behavior of SWIG. Also global CMAKE_SWIG_FLAGS can be used to add
 # special flags to all swig calls.
@@ -145,6 +147,7 @@
       -o "${swig_generated_file_fullname}"
       "${swig_source_file_fullname}"
       MAIN_DEPENDENCY "${swig_source_file_fullname}"
+      DEPENDS ${SWIG_MODULE_${name}_EXTRA_DEPS}
       COMMENT "Swig source")
   ELSE(CMAKE_SWIG_OUTDIR)
     ADD_CUSTOM_COMMAND(
@@ -160,6 +163,7 @@
       -o "${swig_generated_file_fullname}"
       "${swig_source_file_fullname}"
       MAIN_DEPENDENCY "${swig_source_file_fullname}"
+      DEPENDS ${SWIG_MODULE_${name}_EXTRA_DEPS}
       COMMENT "Swig source")
   ENDIF(CMAKE_SWIG_OUTDIR)
   SET_SOURCE_FILES_PROPERTIES("${swig_generated_file_fullname}"


So in the user land, we have to do as below:
SET(SWIG_MODULE_foo_EXTRA_DEPS foo.hh)
SWIG_ADD_MODULE(foo PYTHON foo.i foo.hh foo.cc)


I think it's dirty because:
- It could be nicer with an option in the macro instead than with a
new variable.
- you can have multiple .i files in the same module:
SWIG_ADD_MODULE(foo PYTHON foo.i foo.hh foo.cc bar.i)
it will generate:
wrapper1.cxx: foo.i
   swig .... foo.i

wrapper1.cxx: bar.i
   swig .... bar.i

It means that the variable `SWIG_MODULE_foo_EXTRA_DEPS' has to
contains dependencies for both `foo.i' and `bar.i'.
==> Useless dependencies are created
  ==> The Swig modules will sometimes be compile uselessly.
Extra dependencies have to be specified for each swig file, so why not
use the new variable like below:
SET(SWIG_MODULE_foo_FILE_foo_EXTRA_DEPS foo.hh)
SET(SWIG_MODULE_foo_FILE_bar_EXTRA_DEPS bar.hh misc.i)
SWIG_ADD_MODULE(foo PYTHON foo.i foo.hh foo.cc)

--- UseSWIG.cmake.orig  2006-08-24 13:46:46.033254900 -0400
+++ UseSWIG.cmake       2006-08-24 17:54:42.675339800 -0400
@@ -7,6 +7,8 @@
 # All other macros are for internal use only.
 # To get the actual name of the swig module,
 # use: ${SWIG_MODULE_name_REAL_NAME}.
+# To add extra dependancies to a swig input file of a module
+# set: ${SWIG_MODULE_name_FILE_name_EXTRA_DEPS} before calling SWIG_ADD_MODULE.
 # Set Source files properties such as CPLUSPLUS and SWIG_FLAGS to specify
 # special behavior of SWIG. Also global CMAKE_SWIG_FLAGS can be used to add
 # special flags to all swig calls.
@@ -145,6 +147,7 @@
       -o "${swig_generated_file_fullname}"
       "${swig_source_file_fullname}"
       MAIN_DEPENDENCY "${swig_source_file_fullname}"
+      DEPENDS ${SWIG_MODULE_${name}_FILE_${swig_source_file_name_we}_EXTRA_DEPS}
       COMMENT "Swig source")
   ELSE(CMAKE_SWIG_OUTDIR)
     ADD_CUSTOM_COMMAND(
@@ -160,6 +163,7 @@
       -o "${swig_generated_file_fullname}"
       "${swig_source_file_fullname}"
       MAIN_DEPENDENCY "${swig_source_file_fullname}"
+      DEPENDS ${SWIG_MODULE_${name}_FILE_${swig_source_file_name_we}_EXTRA_DEPS}
       COMMENT "Swig source")
   ENDIF(CMAKE_SWIG_OUTDIR)
   SET_SOURCE_FILES_PROPERTIES("${swig_generated_file_fullname}"


Thank you by advance.
-- 
Tristan Carel