Cmake build in specific order

Question

I'm trying to create a JNI jar with CMake. For that the following has to be done in the appropriate order:

1. compile .class files
2. generate .h headers
3. build native library
4. jar everything

where

1. is done with add_jar() (I prefered that at custom_command)
2. is done with add_custom_command(TARGET ...)
3. is done with add_library()
4. is done with add_custom_command(TARGET ...) (because -C option is not supported by add_jar)

How can I ensure that the proper order is followed? I get errors sometimes on the first run.

add_custom_command has a POST/PRE build option, but add_jar and add_library does not. The add_custom_command that does not have the argument TARGET has the DEPENDS option, should I use that?

Is there a way of telling add_library to wait for the 2. custom command to have been ran?

Answer 1

I guess the error is that you're calling add_library with source files which don't yet exist during the first run of CMake?

If so, you can set the GENERATED property on those source files using the set_source_files_properties command. This lets CMake know that it's OK for those files to not exist at configure-time (when CMake runs), but that they will exist at build-time.

To ensure that the add_jar command executes before add_library, create a dependency on the add_jar target using add_dependencies. To ensure that the add_custom_command command executes before add_library, have the custom command use the TARGET ... PRE_BUILD options.

For example, if your list of sources for the lib is held in a variable called ${Srcs}, you can do:

# Allow 'Srcs' to not exist at configure-time
set_source_files_properties(${Srcs} PROPERTIES GENERATED TRUE)
add_library(MyLib ${Srcs})

# compile .class files
add_jar(MyJarTarget ...)

# generate .h headers
add_custom_command(TARGET MyLib PRE_BUILD COMMAND ...)

# Force 'add_jar' to be built before 'MyLib'
add_dependencies(MyLib MyJarTarget)