Go CLI Cobra

Go CLI with Cobra

1 -- Architecture

Project Layout

cmd/harvx/main.go         # Minimal: call cmd.Execute() only
internal/
  cli/                     # Cobra command definitions
    root.go                # Root command, persistent flags
    generate.go            # generate subcommand
    version.go             # version subcommand
  config/                  # Config loading, validation
  discovery/               # Business logic (never in cli/)
  pipeline/                # Core pipeline logic

Rules

• Keep main.go minimal: parse nothing, call cmd.Execute(), exit.
• All Cobra commands live in internal/cli/ (or cmd/).
• Business logic lives in internal/ packages. Never put business logic in command files.
• Construct dependencies once at startup; inject into commands via closures or struct fields.
• Prefer RunE (returns error) over Run (panics or swallows errors).
• Centralize error handling at the top-level Execute() function.

// cmd/harvx/main.go -- minimal entry point
package main

import (
    "os"

    "github.com/harvx/harvx/internal/cli"
)

func main() {
    if err := cli.Execute(); err != nil {
        os.Exit(1)
    }
}

// internal/cli/root.go -- centralized error handling
package cli

import (
    "fmt"
    "os"

    "github.com/spf13/cobra"
)

func NewRootCmd() *cobra.Command {
    root := &cobra.Command{
        Use:   "harvx",
        Short: "Package codebases into LLM-optimized context",
    }
    root.AddCommand(newGenerateCmd())
    root.AddCommand(newVersionCmd())
    return root
}

func Execute() error {
    cmd := NewRootCmd()
    if err := cmd.Execute(); err != nil {
        fmt.Fprintf(os.Stderr, "Error: %v\n", err)
        return err
    }
    return nil
}

2 -- Command Design

Naming and Metadata

• Use clear verbs: list, get, create, delete, sync, generate.
• Use: include argument placeholders, e.g. get <id>.
• Short: one-line, user-facing summary.
• Long: include context, caveats, and when to use this command.
• Example: 3--6 concrete, copy-paste-ready examples.

Arguments and Flags

• Use positional args for the primary noun (the thing being acted on).
• Use flags for options and modifiers.
• Validate args with Cobra validators: cobra.ExactArgs(1), cobra.MaximumNArgs(1).
• Error messages should point to --help when input is invalid.

func newGenerateCmd() *cobra.Command {
    var opts generateOptions

    cmd := &cobra.Command{
        Use:   "generate [path]",
        Short: "Generate context document from a codebase",
        Long: `Generate an LLM-optimized context document from the target
repository. Discovers files, applies relevance tiers, counts tokens,
and renders output in Markdown or XML format.

If no path is given, uses the current directory.`,
        Example: `  # Generate from current directory
  harvx generate

  # Generate from a specific repo with output file
  harvx generate /path/to/repo -o context.md

  # Use a specific profile
  harvx generate -p minimal

  # JSON output for scripting
  harvx generate --output json`,
        Args: cobra.MaximumNArgs(1),
        RunE: func(cmd *cobra.Command, args []string) error {
            root := "."
            if len(args) > 0 {
                root = args[0]
            }
            return runGenerate(cmd.Context(), root, opts)
        },
    }

    cmd.Flags().StringVarP(&opts.OutputFile, "output-file", "o", "", "output file path")
    cmd.Flags().StringVarP(&opts.Profile, "profile", "p", "", "profile name or path")
    cmd.Flags().StringVar(&opts.Format, "format", "markdown", "output format (markdown|xml)")
    cmd.Flags().BoolVar(&opts.JSON, "json", false, "output structured JSON")

    return cmd
}

type generateOptions struct {
    OutputFile string
    Profile    string
    Format     string
    JSON       bool
}

3 -- Flags and Config Precedence

Precedence (highest to lowest)

1. Explicit CLI flags
2. Environment variables
3. Config file
4. Defaults

Define this precedence in one place and apply it everywhere.

Rules

• Persistent flags on the root command (e.g. --verbose, --config).
• Command-specific flags on that command only.
• Validate config early, fail fast with actionable messages.
• Env vars: consistent prefix (HARVX_), documented, treated as untrusted input.
• Support explicit --config path flag.

// Root-level persistent flags
func NewRootCmd() *cobra.Command {
    root := &cobra.Command{
        Use: "harvx",
        PersistentPreRunE: func(cmd *cobra.Command, args []string) error {
            return initConfig(cmd)
        },
    }
    root.PersistentFlags().StringVar(&cfgFile, "config", "", "config file path")
    root.PersistentFlags().BoolP("verbose", "v", false, "enable verbose output")
    root.PersistentFlags().StringP("log-level", "l", "info", "log level (debug|info|warn|error)")
    return root
}

// Config loading with precedence
func initConfig(cmd *cobra.Command) error {
    cfg, err := config.Load(config.LoadInput{
        Path:     cfgFile,             // flag
        EnvPrefix: "HARVX",           // env
        Defaults: config.Defaults(),   // defaults
    })
    if err != nil {
        return fmt.Errorf("load config: %w", err)
    }
    if err := cfg.Validate(); err != nil {
        return fmt.Errorf("invalid config: %w", err)
    }
    return nil
}

4 -- Errors and Exit Codes

Output Routing

• Human/machine output goes to stdout.
• Errors and diagnostics go to stderr.
• Never mix logs or debug output into stdout.

Error Message Quality

• What failed + what was invalid + what is expected + how to fix.
• No stack traces by default.
• User errors: short message + help hint.
• System errors: actionable message + underlying error.

Exit Codes

func runGenerate(ctx context.Context, root string, opts generateOptions) error {
    // Validate early with helpful messages
    if opts.Format != "markdown" && opts.Format != "xml" {
        return fmt.Errorf(
            "unknown format %q (expected markdown or xml); see --help",
            opts.Format,
        )
    }

    result, err := pipeline.Run(ctx, pipeline.RunInput{
        Root:    root,
        Profile: opts.Profile,
    })
    if err != nil {
        return fmt.Errorf("generate %s: %w", root, err)
    }

    // Output routing: data to stdout
    if opts.JSON {
        return writeJSON(os.Stdout, result)
    }
    return writeText(os.Stdout, result)
}

5 -- Output Contracts

Modes

• Default: human-friendly text (tables, colors, summaries).
• Machine mode: --json or --output json for structured output.
• Quiet mode: --quiet suppresses success noise; only errors printed.

Rules

• Keep JSON schema stable; version if breaking changes needed.
• Define JSON output structs explicitly; never use map[string]any.
• Deterministic ordering for reproducible tests and scripts.
• Support piping: no interactive prompts unless --interactive is set.

// Explicit JSON output struct -- never map[string]any
type GenerateOutput struct {
    Files      []FileEntry `json:"files"`
    TotalFiles int         `json:"total_files"`
    Tokens     int         `json:"tokens"`
    Budget     int         `json:"budget"`
    Profile    string      `json:"profile"`
}

type FileEntry struct {
    Path   string `json:"path"`
    Tier   int    `json:"tier"`
    Tokens int    `json:"tokens"`
    Size   int64  `json:"size"`
}

func writeJSON(w io.Writer, out GenerateOutput) error {
    enc := json.NewEncoder(w)
    enc.SetIndent("", "  ")
    return enc.Encode(out)
}

6 -- Shell Completions

• Provide a completion subcommand for bash, zsh, fish, and powershell.
• Add custom completion for enum flags and resource names.
• Keep completion functions fast: no network calls, no heavy I/O.

func newCompletionCmd() *cobra.Command {
    return &cobra.Command{
        Use:   "completion [bash|zsh|fish|powershell]",
        Short: "Generate shell completion script",
        Args:  cobra.ExactArgs(1),
        ValidArgs: []string{"bash", "zsh", "fish", "powershell"},
        RunE: func(cmd *cobra.Command, args []string) error {
            switch args[0] {
            case "bash":
                return cmd.Root().GenBashCompletion(os.Stdout)
            case "zsh":
                return cmd.Root().GenZshCompletion(os.Stdout)
            case "fish":
                return cmd.Root().GenFishCompletion(os.Stdout, true)
            case "powershell":
                return cmd.Root().GenPowerShellCompletionWithDesc(os.Stdout)
            default:
                return fmt.Errorf("unsupported shell %q", args[0])
            }
        },
    }
}

// Custom completion for enum flags
cmd.RegisterFlagCompletionFunc("format", func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
    return []string{"markdown", "xml"}, cobra.ShellCompDirectiveNoFileComp
})

7 -- Dependency Injection Pattern

Wire dependencies at the root level and pass them into subcommands via closures or a shared app struct.

// App struct holds shared dependencies
type App struct {
    Logger *slog.Logger
    Config *config.Config
}

func NewRootCmd() *cobra.Command {
    app := &App{}

    root := &cobra.Command{
        Use: "harvx",
        PersistentPreRunE: func(cmd *cobra.Command, args []string) error {
            app.Logger = initLogger(cmd)
            cfg, err := config.Load(cfgFile)
            if err != nil {
                return err
            }
            app.Config = cfg
            return nil
        },
    }

    root.AddCommand(newGenerateCmd(app))
    root.AddCommand(newVersionCmd())
    return root
}

func newGenerateCmd(app *App) *cobra.Command {
    return &cobra.Command{
        Use:  "generate [path]",
        RunE: func(cmd *cobra.Command, args []string) error {
            svc := pipeline.New(pipeline.Options{
                Logger: app.Logger,
                Config: app.Config,
            })
            return svc.Run(cmd.Context(), args[0])
        },
    }
}

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