Move all bash custom completions to Go

[marckhouzam]

What type of PR is this?

/kind feature

What this PR does / why we need it:

Based on #93714, this PR finishes removing all bash completion scripting and replaces it fully with Go completions.

Advantages:

• easier maintenance of custom completions
• ability to write Go tests for custom completions
• allow to eventually move to native zsh completion
• allow Fish shell completion PR (add kubectl fish shell completion #92989) to fully support all of kubectl's custom completions
• removes lack of portability of bash scripts
• will allow to improve existing custom completions and add other ones

Which issue(s) this PR fixes:

Fixes kubernetes/kubectl#882

Special notes for your reviewer:

The PR is based on top of @knight42 great work of #93714. However, it has been mostly refactored when included with the rest of the PR.

The pattern that the PR follows is:

• main completion functions are added in their matching files:
  • completion of api resource names: apiresources.go#CompGetResourceList(...)
  • completion of individual resources: get.go#CompGetResource(...)
• a new completion.go file is added to the util package with the new completion code
• the Cobra ValidArgsFunction field is added to every cobra command that was part of the bash __kubectl_custom_func. Each ValidArgsFunction calls the util package.
• flag completion for --namespace, --context, --user, --cluster which are global was added in cmd.go
• flag completion for --clusterrole which is limited to the create clusterrolebinding command was added in create_clusterrolebinding.go
• go tests are added in the util package in completion_tests.go

Test the new completion code

• build kubectl from source

make WHAT=cmd/kubectl

• generate completion code

# zsh
source <(./_output/bin/kubectl completion zsh)

# bash
source <(./_output/bin/kubectl completion bash)

• use it
  Please note that for the new completion code to work, one must use the new kubectl on the command-line.

./_output/bin/kubectl get [TAB]
# debug
./_output/bin/kubectl __complete get ""<ENTER>

./_output/bin/kubectl describe -n kube-system pod [TAB]

Does this PR introduce a user-facing change?:

Regression:

Custom completions don't work following concatenated short flags, e.g., kubectl exec -it <TAB>.
This will be fixed in the next Cobra release: spf13/cobra#1258

Only minor changes:

• File completion is now disabled for the Go completions as it does not make sense for these cases
• Completion for the cp command works slightly differently; instead of doing file completion all the time, which I found to be very verbose, I have used the same solution that helm implemented, which is to only show / and ./ to indicate file completion is valid, and then to trigger full file completion once the user starts typing something. You can try this by comparing: ./_output/bin/kubectl cp <TAB> and ./_output/bin/kubectl cp /tmp/<TAB>
• Invalid command-lines will not lead to completions, for example:
  kubectl autoscale deployment --max NaN <TAB>
  will trigger file completion (that is what Cobra does when there is an error in the command-line) instead of accepting the invalid flag value and continuing with completion.

Shell completion has been migrated to Cobra's go solution.  `kubectl` is now smarter about disabling file completion when it does not apply.  Furthermore, completion for the `cp` command does not show all files unless the user has started typing something.

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[k8s-ci-robot]

Hi @marckhouzam. Thanks for your PR.

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[marckhouzam]

I've added instructions on how to test, taken from #93714

You may be interested @brianpursley @eddiezane @knight42 @WLun001

[soltysh]

/ok-to-test
/assign

[marckhouzam]

As for the tests, I'll wait for confirmation if testing individual commands for completion is or is not required, before cleaning up.

The tests should not keep delaying this PR, so I reverted the original commit which added the tests, and I wrote a few tests in the util package in completion_tests.go as suggested by @brianpursley. The original tests are still available in the commit history for reference.

Also, as a way to maybe to stir up some momentum, I moved to native zsh completion and removed all that extra hack-y shell code (see 77bb053).
With this, zsh gets completion descriptions:

$ source _output/bin/kubectl completion zsh
$ _output/bin/kubectl p<TAB>
patch         -- Update field(s) of a resource
plugin        -- Provides utilities for interacting with plugins.
port-forward  -- Forward one or more local ports to a pod
proxy         -- Run a proxy to the Kubernetes API server

Hopefully, we can get this merged.
/cc @brianpursley @rikatz @eddiezane

[soltysh]

A few nits that can be addressed in a followup. Apologies for the delays in reviewing and thank you very much for this great effort to you @marckhouzam and @brianpursley and @phil9909 for reviews.
/lgtm
/approve

[soltysh]

You'd need to support both linux and windows paths, so \\ would need to be included here as well.

[soltysh]

Yeah, although I'd like to see this being continued in the near future.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: marckhouzam, soltysh

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[sttts]

😍

[marckhouzam]

Thanks @soltysh! I will soon address your comment.

Should I revert the change that moves zsh completion to being native from this PR and leave it for a different PR?
I'm asking because I believe the zsh change will require an update to the documentation; specifically, aliases will be handled automatically by zsh, unlike what is mentioned here: https://kubernetes.io/docs/tasks/tools/included/optional-kubectl-configs-zsh/

[marckhouzam]

Oh and there is still a regression with this change caused by spf13/cobra#1258

I'm still waiting for the next Cobra release: spf13/cobra#1388

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