force compiler warning if callback handles not captured

[jasonbeach]

force a compiler warning if callback handles are not captured.
clarify documentation to show that not capturing returned handles
will result in callbacks immediately being unregistered
see issue #1998
Signed-off-by: Jason Beach

[jasonbeach]

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

[alsora]

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

[jasonbeach]

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.

[alsora]

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

[jasonbeach]

all issues fixed. thanks.

[fujitatomoya]

lgtm

[fujitatomoya]

CI:

• Linux
• Linux-aarch64
• Windows

[clalancette]

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