How to implement flag auto-completion for command-line interfaces (CLIs) in Go?

To implement flag auto-completion for command-line interfaces (CLIs) in Go, you can use the complete package. This package provides functionalities for generating and managing auto-completions for flag-based commands.

Here is a step-by-step guide on how to implement flag auto-completion in Go for CLIs:

Install the complete package using the go get command:

go get github.com/posener/complete/v2

Import the necessary packages in your Go code:

import (
    "flag"
    "os"

    "github.com/posener/complete/v2"
)

Define the flags for your CLI using the flag package, as you would normally do:

var (
    flag1 = flag.String("flag1", "", "Description of flag1.")
    flag2 = flag.Int("flag2", 0, "Description of flag2.")
    // Define other flags
)

Initialize the auto-completion with the commands and flags using the complete package:

var commands = complete.Commands{
    // Define your commands and their descriptions here
    // For example:
    "command1": complete.Command{
        Args: complete.PredictNothing,
        Flags: complete.Flags{
            "--flag1": complete.PredictAnything,
            "--flag2": complete.PredictAnything,
            // Define other flags for this command
        },
    },
    // Define other commands
}

Create a function to generate and manage the auto-completions:

func runComplete(c *complete.Complete) {
    c.Complete("your-cli-name", os.Environ(), nil)
}

func main() {
    // ... Your CLI code ...

    // Generate and manage auto-completions only if the first argument is "complete"
    if len(os.Args) > 1 && os.Args[1] == "complete" {
        runComplete(complete.New(commands))
        return
    }

    // ... Rest of your CLI code ...
}

Build and install your CLI:

go install path/to/your/cli

Enable auto-completion for your CLI by adding the completion script to your shell. For Bash, add the following line to your ~/.bashrc or ~/.bash_profile file:

source $(your-cli-name complete)

That's it! With these steps, you have implemented flag auto-completion for your CLI in Go. Now, when users type your CLI name followed by a command and press the Tab key, they will see auto-completion suggestions for flag options.