Allow passing GeneratedList to generator.process

[nirbheek]

Sometimes you want to chain two generators one after the other; for instance while building assembly with MSVC, you need to use ml.exe but it doesn't do pre-processing, so you need to call cl.exe /EP /P /Fi@OUTPUT@ @INPUT@ to do the pre-processing, and then pass it to ml.exe /Fo @OUTPUT@ /c @INPUT@ to get compiled object code which can be added as sources to an executable or library.

This is not trivial to do (I tried) but shouldn't be too difficult. Also implementing it on the Visual Studio backend has the same problem that is causing the 113 generatorcustom test to fail there.

This is needed for building libffi with Meson without resorting to a wrapper script.

[msink]

File objects too - if generator is defined in submodule - paths are relative to that submodule.

bin2c.process('../../hello.zip') - works

bin2c.process(files('hello.zip')) - syntax error

[randy408]

Any updates on this? Wrapper scripts are not trivial to write when e.g. subproject executables are involved in a compilation chain.

[germandiagogomez]

I am finding the exact same use case as described by this issue.

[quackerd]

Same here. I needed to preprocess some ASM files which include C headers, then pass the generated ASM sources to the ASM generator. Now it doesn't work. Could be done with custom_targets but not clean.

[Volker-Weissmann]

Same here. I'm using gnu m4 and lemon. Unfortunately

lemongen.process(m4gen.process('myfile'))

fails with

ERROR: Generator arguments must be strings or files not <GeneratedListHolder: ['myfile']>.

[vinipsmaker]

I stumbled upon this issue while trying to consume the output of gperf as input for re2c before finally using the generated sources to build an executable.

[vinipsmaker]

What I wanted to do:

gperf_gen.process(re2c_gen.process(re2c_src))

What I had to do thanks to Meson's limitation regarding non-chainable generators:

pp_state = custom_target(
    'bc2_state.cpp',
    output : 'bc2_state.cpp',
    input : re2c_gen.process('src/state.ypp'),
    command : [
        emilua_gperf,
        '--assign', 'GPERF_BIN=' + find_program('gperf').full_path(),
        '@INPUT@', '@OUTPUT@',
    ],
)

Full example: https://gitlab.com/emilua/emilua/-/blob/63683c851b1701ac3827f183624f13c341d03156/meson.build