Add testcase for services with buffer in the response only

[mathias-luedtke]

Description

This PR add a test case that shows that cpplint checks fail for generated code for services that have buffers in their response, but not in the request.
The same issue should happen for actions.

The tests will fail with:

- rosidl_generator_py.cpplint_rosidl_generated_py build/include_order [4] (/ws/build/rosidl_generator_py/rosidl_generator_py/rosidl_generator_py/srv/_get_buffer_s.c:83)
  <<< failure message
    Found C system header after other header. Should be: _get_buffer_s.h, c system, c++ system, other.
  >>>

Is this user-facing behavior change?

No

Did you use Generative AI?

No

Additional Information

This issue was introduced by #250

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[skyegalaxy]

@adbidwai to take a look

[adbidwai]

Hi, I can take a look at this. Thanks!

[fujitatomoya]

I do not think we can take this without fixes, because this generates intentionally red test.

[mathias-luedtke]

I do not think we can take this without fixes, because this generates intentionally red test.

I can add the fix as well, but I need to know which option you do prefer (see #264)

[mathias-luedtke]

@fujitatomoya: Which fix would you prefer?

• silence build/include_order in the cpplint checks
• always include <stdint.h>
• more complicated fix: add stdint.h in the request/goal part, if the parts use buffers

[fujitatomoya]

I'd say that the best option we got here is to hoist the include to the top-of-file system-header block, conditionally at the interface level with checking that interface requires the header. but i guess that perfectly acceptable fallback: always include <stdint.h> in the top block if that makes the complicatoin. I was thinking about the compile-time concern but stdint.h is one of the smallest headers in the standard library. what do you think?

[mathias-luedtke]

I'd say that the best option we got here is to hoist the include to the top-of-file system-header block, conditionally at the interface level with checking that interface requires the header.

I came up with mathias-luedtke@620a026
However, I am not convinced..

but i guess that perfectly acceptable fallback: always include <stdint.h>

It turns out that Python.h already includes it, so it should not affect compile time.
-> We could even drop the stdint.h include and it still passes.

Furthermore - depending on the message type - the generated code already uses the types from stdint.h without including them explicitly.

IMHO always including stdint.h is the better fix: it is simple and maintainable.
And it allows us to drop the has_buffer_fields handling, which should make up for any (negligible) include overhead.