How to specify an input *directory* for custom_target or generator?

[ShamrockLee]

When trying to specify a directory sample_hello.source as input for custom_target or generator.process, Meson complains

../test/samples/meson.build:8:0: ERROR: File sample_hello.source does not exist.

How can I feed a directory to my script and produce the output file with Meson?

[bruchar1]

A custom_target needs files as its input, because it needs to know which modified files will trigger the build.

For a generator, you can provide the arguments you want to the script, because it is triggered by its outputs. Therefore, you could provide a directory as an argument to your script.