Uncrustify seems to be complaining about something, but I can't figure out what or how to fix it. Guidance would be appreciated.

PR looks good to me.

The uncrustify output is the following

include/rclcpp/parameter_event_handler.hpp
+++ include/rclcpp/parameter_event_handler.hpp.uncrustify
@@ -89,2 +89,2 @@
- * Note: the object returned from add_parameter_callback must be captured or the callback will 
- * be immediately unregistered. 
+ * Note: the object returned from add_parameter_callback must be captured or the callback will
+ * be immediately unregistered.
@@ -159 +159 @@
- * the callback will immediately be unregistered. 
+ * the callback will immediately be unregistered.
@@ -198,2 +198,2 @@
-   * Note: if the returned callback handle smart pointer is not captured, the callback is 
-   * immediatedly unregistered. A compiler warning should be generated to warn of this. 
+   * Note: if the returned callback handle smart pointer is not captured, the callback is
+   * immediatedly unregistered. A compiler warning should be generated to warn of this.
@@ -227 +227 @@
-   * of this. 
+   * of this.

The problem is that you have trailing whitespaces at the end of the comments.
Make sure that lines don't end in a whitespace.
P. S. Try highlithing the uncrustify log and you will see that the current lines have a whitespace, while the suggested ones do not.. Unfortunately it's not evident unless you highlight it or paste it in an editor that shows whitespaces

what's the typical workflow you follow for using uncrustify? I normally use clangd and for that there's a .clangd / .clang-format / .clang-tidy file in the top level of the repo. For uncrustify, it looks like it takes a .cfg file to define the formatting, but I couldn't find one in the repo.

Ros projects like this do not invoke uncrustify directly, but rather they use the "ament_uncrustify" wrapper.
Among the other features, this wrapper comes with a configuration file https://github.com/ament/ament_lint/blob/master/ament_uncrustify/ament_uncrustify/configuration/ament_code_style.cfg

all issues fixed. thanks.

CI:

• Linux
• Linux-aarch64
• Windows

This was approved and has green CI, so I'm going ahead and merging it.