I'm trying to use Meson to build an executable that embeds another binary in its data section, using gas' incbin directive, something like this:

magic_bin_start:
    .incbin MAGIC_BIN_PATH
magic_bin_end:

For the purposes of the build, I just need the CPP macro MAGIC_BIN_PATH to be set to the build-time path of a file that was created by a custom_target. The following almost works:

magic_elf = executable(...)

objcopy = find_program('objcopy')

magic_bin = custom_target(
  'magic.bin',
  output: 'magic.bin',
  input: magic_elf,
  command: [objcopy, '-O', 'binary', '@INPUT@', '@OUTPUT@'],
)

executable(
  'myprog',
  files('myprog.cpp', 'magic_blob.S'),
  cpp_args: ['-DMAGIC_BIN_PATH="' + magic_bin.full_path() + '"'])

The problem with this is that it doesn't emit a dependency from myprog to the custom target (so magic.bin won't be created in a clean build, for example). This is apparently expected, because the manual for full_path() explicitly says "In most cases using the object itself will do the same job as this and will also allow Meson to setup inter-target dependencies correctly." However, if I do as suggested, I get an error:

../meson.build:19:0: ERROR: The `+` operator of str does not accept objects of type CustomTarget (<CustomTarget magic.bin@cus: ['/usr/bin/objcopy', '-O', 'binary',  '@INPUT@', '@OUTPUT@']>)