Description

When building rclrs, the compiler emits warnings about rosidl_typesupport_c__get_* functions being declared with different signatures. This occurs because the same C functions are declared in two places with different Rust return types.

Example warning

warning: `rosidl_typesupport_c__get_message_type_support_handle__action_msgs__srv__CancelGoal_Response` redeclared with a different signature
    --> rclrs/src/rcl_bindings_generated_jazzy.rs:8579:5
     |
8579 | /     pub fn rosidl_typesupport_c__get_message_type_support_handle__action_msgs__srv__CancelGoal_Response(
8580 | |     ) -> *const rosidl_message_type_support_t;
     | |______________________________________________^ this signature doesn't match the previous declaration
     |
    ::: rclrs/src/vendor/action_msgs/srv.rs:244:9
     |
 244 | /         fn rosidl_typesupport_c__get_message_type_support_handle__action_msgs__srv__CancelGoal_Response(
 245 | |         ) -> *const std::ffi::c_void;
     | |_____________________________________- previously declared here
     |
     = note: expected `unsafe extern "C" fn() -> *const c_void`
                found `unsafe extern "C" fn() -> *const rosidl_message_type_support_t`

Affected functions (6 instances)

• rosidl_typesupport_c__get_message_type_support_handle__action_msgs__msg__GoalInfo
• rosidl_typesupport_c__get_message_type_support_handle__action_msgs__msg__GoalStatus
• rosidl_typesupport_c__get_message_type_support_handle__action_msgs__msg__GoalStatusArray
• rosidl_typesupport_c__get_message_type_support_handle__action_msgs__srv__CancelGoal_Request
• rosidl_typesupport_c__get_message_type_support_handle__action_msgs__srv__CancelGoal_Response
• rosidl_typesupport_c__get_service_type_support_handle__action_msgs__srv__CancelGoal

Root cause

The same rosidl_typesupport_c__get_* functions are being declared in two places:

1. rosidl_generator_rs generates extern declarations in the vendored message crates (e.g. vendor/action_msgs/srv.rs) with return type *const std::ffi::c_void
2. bindgen generates extern declarations in rcl_bindings_generated_*.rs with return type *const rosidl_message_type_support_t (or rosidl_service_type_support_t)

Both declarations are ABI-compatible at runtime (the pointer types have identical representation), but Rust's clashing_extern_declarations lint correctly flags the type-level inconsistency.

Proposed fix

Add blocklist patterns to the bindgen configuration in rclrs/build.rs to prevent bindgen from generating declarations for typesupport functions that are already provided by rosidl_generator_rs:

let bindings = bindgen::Builder::default()
    .header("src/rcl_wrapper.h")
    // ... existing configuration ...
    .blocklist_function("rosidl_typesupport_.*__get_message_type_support_handle.*")
    .blocklist_function("rosidl_typesupport_.*__get_service_type_support_handle.*")
    .blocklist_function("rosidl_typesupport_.*__get_action_type_support_handle.*")
    // ... rest of builder ...

This approach:

• Keeps typesupport declarations with their respective message crates where they semantically belong
• Prevents bindgen from duplicating them as a side effect of rcl headers including rosidl headers
• Uses regex patterns to avoid playing whack-a-mole as new message types are added

Pre-implementation checklist

• Verify rclrs doesn't directly call any bindgen-generated typesupport functions (should be going through message crate APIs)
• Grep for affected function names in rclrs source to confirm no direct usage

Testing

• Verify clean build with no clashing_extern_declarations warnings on Humble, Jazzy, and Rolling
• Run existing test suite to confirm no regressions

I'm happy to develop and submit a PR for this fix if it helps.