Bash completion for subcommand flags

[mabelzhang]

🎉 New feature

Part of #1
Test with any or all of these subcommands (ign --commands shows these 11):

• plugin Bash completion for flags gz-plugin#81
• gui Bash completion for flags gz-gui#392
• topic service Bash completion for flags gz-transport#312
  • log is a third level subcommand and not yet implemented, see Bash completion for flags gz-transport#312 (comment). Adds the third level commands for the log gz-transport#451
• gazebo model Bash completion for flags gz-sim#1504
• msg Bash completion for flags gz-msgs#254
• launch Bash completion for flags gz-launch#167
• fuel also has three levels, and the third level subcommand might have to come later
• sdf Bash completion for flags sdformat#1042

Summary

Demonstration of tab completion for ign-gui (libraries, Ruby parsing) and ign-plugin (executables, CLI11 parsing).
When we are happy with these two, it is easy to extend to other ign-* libraries.

Doing tab completion this way means it's purely at the bash interaction level, independent of how the actual flags are parsed and executed. Regardless of whether the flag implementation is Ruby or CLI11, the tab completion happens before any of those are incurred. gui and plugin are chosen so that we validate that here.

I took the liberty of adding comments to the existing code, because it took me a long time to understand even with online tutorials, this being my first time writing a bash completion script. Thought the comments might help the next person.

This set of PRs is for functionality, and the bash scripts are manually sourced for now.
The scripts will need to be installed for tab completion to happen out of the box, which is more about infrastructure and will be in a separate PR.

Test it

1efb619 installs a single script to source everything:

. install/share/gz/gz.completion

Then you should get tab completion when you type ign <subcommand> -<tab>. See those PRs for sample outputs.

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[mabelzhang]

Do not merge this PR until we have a PR to install all the scripts and source them at once. Otherwise, this script will be calling functions that don't exist. This script is already being installed, so the new changes will probably break the original tab completion.

The other two PRs can be merged, as those scripts are new and not being used anywhere else.

[mabelzhang]

1efb619 adds installation, which is also added to the ign-gui and ign-plugin PRs.
Let me know if it's better to break off installation into separate PRs (it would be another set of 3 PRs, 1 in each repo).

Scripts are installed to the directory install/share/ignition/ignition.completion.d/, which are sourced by the script installed at install/share/ignition/ignition.completion.
The user needs to source it manually:

. install/share/ignition/ignition.completion

I don't know if the way I've written this script is the most secure way to source bash scripts. What if somebody adds a random script matching the name pattern to that directory?
I think it probably needs to be versioned too, like the Ruby scripts? If one version of a library adds a new flag, then the bash script will need to have that new flag just for that version.
If that turns out to be complicated, maybe it's better to break off installation into separate PRs to figure those things out.

Either way, this is probably still not compatible with https://github.com/ignition-release/ign-tools-release/pull/4/files . I think bash completion requires a single file. We probably still have to pipe all the repos' individual scripts to a single script before installing to /usr/share/bash-completion/completions/ign.

[mabelzhang]

To push this along before I'm gone next week, I've started opening PRs in more repos, following the installation method in this comment #87 (comment) that worked for gui and plugin.

[chapulina]

Just one last thing

[mabelzhang]

All PRs have now been opened for second-level flags.
All ready for another pass. The main change is that the flags are no longer hard coded in the tests.

Comments addressed

[scpeters]

I noticed the nightly builds are unstable since this was merged forward since the newly installed completion files are not handled by the current debian metadata

• https://build.osrfoundation.org/job/ign-tools2-debbuilder/150/

we should update the release repos for tools1 and tools2