[bug] zsh shell completion throw error

[sunny0826]

Hi, i noticed this issue is only for fish and powershell but I have some problems with completion also on zsh.
For example on tab after kubecm I get that last option:

11:32  76% ❯ kubecm
add                                                            -- Add KubeConfig to $HOME/.kube/config
alias                                                          -- Generate alias for all contexts
clear                                                          -- Clear lapsed context, cluster and user
completion                                                     -- Generate completion script
create                                                         -- Create new KubeConfig(experiment)
delete                                                         -- Delete the specified context from the kubeconfig
help                                                           -- Help about any command
list                                                           -- List KubeConfig
merge                                                          -- Merge the KubeConfig files in the specified directory
namespace                                                      -- Switch or change namespace interactively
rename                                                         -- Rename the contexts of kubeconfig
switch                                                         -- Switch Kube Context interactively
version                                                        -- Print version info
:4                                                             Completion ended with directive: ShellCompDirectiveNoFileComp

It also happen with any other commands but the error is sometime different:

11:32  76% ❯ kubecm list
:0                                                          Completion ended with directive: ShellCompDirectiveDefault

I enabled the completion with kubecm completion zsh > "${fpath[1]}/_kubecm" and zsh version is zsh 5.8 (x86_64-ubuntu-linux-gnu), don't know if it matters but I also use oh-my-zsh.

Originally posted by @gpstuff in #76 (comment)

[sunny0826]

@gpstuff thx for you feedback

[burmanm]

This is a bug in the cobra completions, not in kubecm. I created a ticket and a PR..

spf13/cobra#1667

[marckhouzam]

The problem is probably that kubecm redirects stderr to stdout, which will break the shell completion system.
This has happened to others before 😄.
I believe this happens here:

kubecm/cmd/root.go

Line 53 in ba2a539

cli.rootCmd.SetOutput(os.Stdout)

The SetOutput() function sets stderr and stdout to point to the same place. That function is deprecated in favor of the two functions SetOut() and SetErr() as you can see here: https://github.com/spf13/cobra/blob/master/command.go#L250-L268

If you really want to have stderr print to stdout, then you need to change it just for the __complete command within a PersistentPreRun

You can see some documentation about this here: https://github.com/spf13/cobra/blob/master/shell_completions.md#debugging

Making this difference between stderr and stdout for shell completion allows to print debugging information to stderr without breaking the completion scripts.

[sunny0826]

@marckhouzam @burmanm Thx for your feedback, this should be a historical problem and I will try to fix this issue.