how to make a dep between custom_target() and preprocess()?

[stsp]

I have this code:

plt_inc = custom_target('plt.inc',
  output: 'plt.inc',
  input: tct,
  command: [PD, '3', '@INPUT@'],
  capture: true)
cpp = meson.get_compiler('c')
sfiles = cpp.preprocess(['plt.S'],
  output: '@[email protected]',
  dependencies: declare_dependency(
    compile_args: ['-D__ASSEMBLER__']))

Both targets work properly separately,
when started by hands in a needed order.
But I need to make sure plt_inc is built
before running the preprocessor for plt.S.
No matter what I do, this ordering is not
achieved.
How can I do that?

[stsp]

For example if I do this:

sfiles = cpp.preprocess('plt.S', plt_inc,
  output: '@[email protected]',
  dependencies: declare_dependency(
    compile_args: ['-D__ASSEMBLER__']))

Or this:

sfiles = cpp.preprocess('plt.S',
  output: '@[email protected]',
  dependencies: declare_dependency(
    compile_args: ['-D__ASSEMBLER__'],
    sources: plt_inc))

Then in both cases I get this:

ERROR: Multiple producers for Ninja target "src/preprocessor_0.p/plt.s". Please rename your targets.

Any other attempt to feed plt_inc
to preprocess() lead to other errors,
and no success.

[bruchar1]

I already answered in #12715. This is current not possible. We would need to add a depends keyword to compiler.preprocess. It is probably not there simply because nobody had a need for it before...

Alternatively, you could manually invoke the preprocessor using a custom_target.