template strings in generator.process(extra_args) are not replaced

[apache-hb]

Describe the bug
providing a template string such as @CURRENT_SOURCE_DIR@ in the extra_args argument for generator.process does not replace the template string.

To Reproduce

gen = generator(find_program('echo'),
    arguments : [ 'hello', '@INPUT@', '@EXTRA_ARGS@' ]
)

gen.process('source', extra_args : [ '@BUILD_DIR@' ])

Expected behavior
the @BUILD_DIR@ in extra_args is substituted with the path to the build dir. currently it echos @BUILD_DIR@

system parameters

• meson 0.57.2
• ninja 1.10.0