Add fzf-based interactive selection to ros2cli commands

[tonynajjar]

Description

This PR adds optional fuzzy search functionality to ros2cli commands using fzf, inspired by the ros2-aliases project. When arguments are omitted from commands, an interactive fzf selector is launched instead of throwing an error.

Commands enhanced:

• ros2 topic echo - Select topic interactively
• ros2 topic hz - Select topic interactively
• ros2 topic info - Select topic interactively
• ros2 topic bw - Select topic interactively
• ros2 topic pub - Select topic interactively
• ros2 node info - Select node interactively
• ros2 service call - Select service interactively
• ros2 param get - Cascading selection (node → parameter)
• ros2 interface show - Select interface interactively

Implementation:

• Added interactive_select() helper function in ros2cli/helpers.py
• Made positional arguments optional (nargs='?') in affected verbs
• Added fzf as an execution dependency in ros2cli/package.xml
• Maintains 100% backward compatibility - all existing command usage still works

Is this user-facing behavior change?

Yes. Users can now omit arguments and use fuzzy search instead:

Before:

ros2 topic echo /my_topic_name  # Must know exact topic name

After:

ros2 topic echo                  # Launches fzf to select from available topics
ros2 topic echo /my_topic_name   # Still works as before

If fzf is not installed, users get a clear error message directing them to install via rosdep.

Did you use Generative AI?

Yes, GitHub Copilot was used

Additional Information

• Requires fzf: Added as dependency in package.xml but dependent on Add fzf ros/rosdistro#49148
• No breaking changes: All existing CLI usage remains unchanged
• Graceful degradation: Clear error message if fzf is missing

[tonynajjar]

This PR still needs some testing and refinement but before I iterate further I'd like to know if you would merge this idea in. Thanks
@ahcorde @fujitatomoya
You can see a gif demo in https://github.com/tonynajjar/ros2-aliases

[fujitatomoya]

@tonynajjar generally i like this enhancement, thanks 🚀

there are several comments that i think we need to address but overall i think this is gonna be better user-experience for ROS 2 users and developers.

we already have type completion via shell command prompt but tab completion requires us to know the prefix and type sequentially from the beginning, while fzf lets us match any part of the name in any order (e.g., typing "wrist depth" finds /arm/wrist_camera/depth/image_raw). fzf also provides visual browsing of all available options with real-time filtering, making it ideal for exploring unfamiliar systems or when you only remember fragments of a name.

before fixing up my comments, let's hear out more feedback on this 👍

[fujitatomoya]

does it miss tty detection? no check for whether stdin/stdout is a tty? i think this will cause scripts and CI/CD pipelines to hang, if it meets this case. related to this issue, fzf reads keyboard input from /dev/tty, not stdin. however, when ros2cli commands are piped or redirected, fzf may not be able to access the tty properly?

the followings are pseudo code,

    # Check if we're in an interactive terminal
    if not sys.stdin.isatty() or not sys.stdout.isatty():
        print('Error: Interactive selection requires a TTY terminal.', 
              file=sys.stderr)
        return None

and

try:
    # fzf needs direct access to /dev/tty for keyboard input
    tty = open('/dev/tty', 'r')
    process = subprocess.Popen(
        ['fzf', '--prompt', prompt + ' ', '--height', '40%', '--reverse'],
        stdin=subprocess.PIPE,
        stdout=subprocess.PIPE,
        stderr=tty,  # fzf uses stderr for display
        text=True
    )
    # ...
finally:
    tty.close()

[fujitatomoya]

We do not need to have any signal control here when opening the child process? If the user presses Ctrl+C, this may leave the terminal in a bad state or not clean up properly... maybe we can add try/except statement to catch the KeyboardInterrupt to call process.terminate()?

import signal

try:
    stdout, _ = process.communicate(input='\n'.join(items))
except KeyboardInterrupt:
    process.terminate()
    process.wait()
    return None

[fujitatomoya]

besides that, i would add the timeout just in case if fzf hangs for some reason, the entire command hangs indefinitely.

[fujitatomoya]

i believe this is redundant. i would do the following instead to check fzf availability.

import shutil

if shutil.which('fzf') is None:
    print('Error: fzf is not installed...', file=sys.stderr)
    return None

[fujitatomoya]

Catching all exceptions hides bugs and makes debugging harder.

Suggested change

	except Exception as e:
	print(f'Error during interactive selection: {e}', file=sys.stderr)
	return None
	except (OSError, subprocess.SubprocessError) as e:
	print(f'Error during interactive selection: {e}', file=sys.stderr)
	return None

[tonynajjar]

Thanks for the feedback @fujitatomoya . Like you said I will start working on your comments once I get another opinion on the general idea, to make sure this can ultimately get merged in

[tonynajjar]

Maybe @ahcorde you can give your general opinion on the feature and I can continue to iterate with @fujitatomoya? Thanks!