workdir for custom_target

[georgmu]

Hi,

having a workdir parameter for custom_target() would be very handy.

I have a project which is a lot of C, but also some go, which currently uses cmake. Compiling the go stuff is done through custom targets.
Since go build only works in the source tree, but allows writing the output somewhere else, the custom target in cmake looks something like this:

add_custom_target(goprog
  COMMAND go build -mod=vendor -o ${CMAKE_CURRENT_BINARY_DIR}/goprog
  WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
)

With meson, it is not possible to specify a workdir for such a scenario. The only alternative I see is to introduce a script which takes the souce and target directory as arguments and does the computation itself (using readlink -f).

I think such a change should be possible by using absolute paths to replace @INPUT@, @OUTPUT@ and similar placeholders if workdir is set (instead of the rel_to_builddir()).

Any thoughts about this idea?

[mcb2003]

Another example of where this could be useful: I'm building a project that uses Lua, and documenting both the Lua and C code with LDoc. I tried the following custom_target to build the documentation:

  docs = custom_target('docs',
    command: [ldoc, '-d', '@OUTDIR@/doc', '@SOURCE_DIR@'],
    output: 'doc',
    install: true,
    install_dir: get_option('datadir') / 'doc' / meson.project_name(),
  )

But unfortunately, LDoc gets confused and can't find the files it's looking for, like README.md, as it's looking for a relative path as specified in config.ld:

-- ...
topics = {"README.md"}
file = "lege"
examples = "examples"

I suppose I could canonicalize the paths in config.ld, but since Lua doesn't ship with a function for doing so, that may be more complex than it seems. In fact, with the above command LDoc can't even find config.ld -- I tried passing other flags to ldoc, such as -b and -c, which changed the behaviour somewhat (I was able to specify the exact path to config.ld), but in the end, LDoc just won't work unless it's run from the source directory.