`extern` block uses type `u128`, which is not FFI-safe

[maspe36]

This new warning is causing CI to fail

warning: `extern` block uses type `u128`, which is not FFI-safe
    --> /home/sam/rust_ws/src/ros2_rust/rclrs_tests/target/debug/build/rclrs-8555e18c0c9bb180/out/rcl_bindings_generated.rs:6343:31
     |
6343 |         dynamic_type_builder: *mut rosidl_dynamic_typesupport_dynamic_type_builder_t,
     |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
     |
     = note: 128-bit integers don't currently have a known stable ABI

Seems to be coming from auto-generated idl code. Investigate and hopefully resolve

[esteve]

It's interesting that this only happens with rolling. As I see it, we have two options:

• disable the dynamic message feature (dyn_msg) from the clippy check
• disable the warning about u128 (via improper-ctypes) from the clippy check

I believe that disabling the check from clippy should be fine in our case, as we're not exposing this API.

@maspe36 what do you think?

[maspe36]

This is also happening with iron in my PR to add support for it. I'm trying to hunt down the root cause and depending on that it may indeed make sense to disable the warning or dynamic message feature from clippy.

The first build I found where this was failing the rolling build #974.

Current theory is that this is related to the version uptick in rosidl_generator_c from 3.3.1 to 4.1.1 as that is a major version change between builds #974 and #973. I'll keep digging

[maspe36]

Looks like this is cause by the new Runtime Interface Reflection feature (#215) in the rmw_implementation package.

However, the original type that is ultimately by translated by bindgen(?) to a u128 is defined here in the newly stabilized in Iron, rosidl_dynamic_typesupport package.

It seems like the dyn_msg feature is a custom feature we use and frankly I don't know much about cargo features. I think the best course would be to disable clippy lints for the auto generated bindgen code.

But... Isn't that what we're doing here? Safe to say I'm a bit lost

[esteve]

@maspe36 adding #![allow(improper_ctypes)] should suppress that warning (see https://github.com/CCExtractor/rusty_ffmpeg/pull/13/files). I'll build locally with that change and see if it works.

[maspe36]

Nothing for us to do at this time, but there has been some movement upstream which will eventually trickle down to us
rust-lang/rust#54341

[oriongonza]

u128 is already FFI safe: https://blog.rust-lang.org/2024/03/30/i128-layout-update.html

[maspe36]

Yup, this is now part of stable Rust as of May 2nd. To take advantage we will need to upgrade from 1.74 to 1.78.

Issue for this upgrade created here #398