preprocess and custom_target results in ninja dependency error

[julianneswinoga]

Describe the bug
Using compiler .preprocess() and custom_target() results in ninja dependency error but not a meson error:

ninja: error: '/tmp/meson_preprocessor_bug/buildDir/preprocessor_0.p/lscript.pp.ld', needed by 'lscript.pp.strip.ld', missing and no known rule to make it

yet afaik the dependency chain should be:

lscript.ld < lscript.pp.ld < lscript.pp.strip.ld < exe
^source      ^preprocess     ^strip_lscript.sh

To Reproduce

project('my_project', 'c')

preprocesssed_lscript = meson.get_compiler('c').preprocess(
    'lscript.ld',
    output: '@[email protected]',
)[0]

linker_script_tgt = custom_target(
    'lscript',
    input: preprocesssed_lscript.full_path(),
    output: '@[email protected]',
    command: [files('strip_lscript.sh'), '@INPUT@', '@OUTPUT@'],
    depends: [preprocesssed_lscript],
)
linker_script_dep = declare_dependency(sources: [linker_script_tgt])
output_file = linker_script_tgt.full_path()
add_project_link_arguments(['-T', f'@output_file@'], language: 'c')

executable('exe', ['main.c'], dependencies: [linker_script_dep])

results in

The Meson build system
Version: 1.6.0
Source dir: /tmp/meson_preprocessor_bug
Build dir: /tmp/meson_preprocessor_bug/buildDir
Build type: native build
Project name: my_project
Project version: undefined
C compiler for the host machine: ccache cc (gcc 11.4.0 "cc (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0")
C linker for the host machine: cc ld.bfd 2.38
Host machine cpu family: x86_64
Host machine cpu: x86_64
meson.build:8: WARNING: Source item '/tmp/meson_preprocessor_bug/buildDir/preprocessor_0.p/lscript.pp.ld' cannot be converted to File object, because it is a generated file. This will become a hard error in meson 2.0.
Build targets in project: 3

Found ninja-1.10.1 at /usr/bin/ninja
INFO: autodetecting backend as ninja
INFO: calculating backend command to run: /usr/bin/ninja -C /tmp/meson_preprocessor_bug/buildDir -j 16 -v
ninja: Entering directory `/tmp/meson_preprocessor_bug/buildDir'
ninja: error: '/tmp/meson_preprocessor_bug/buildDir/preprocessor_0.p/lscript.pp.ld', needed by 'lscript.pp.strip.ld', missing and no known rule to make it

(full repo: https://github.com/julianneswinoga/meson_preprocessor_bug)

Expected behavior
Dependency chain to be built correctly and build to start.

system parameters

• Plain native build
• OS: Ubuntu 22.04.5
• python --version: 3.10.12
• meson --version: 1.6.0
• ninja --version: 1.10.1