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Flag development guide

This guide covers best practices for defining and managing command-line flags in the DataRobot CLI.

Note: This guide is about command-line flags (e.g., --verbose, --output file.txt), not feature gates. For feature gates, see Feature gates.

Table of contents

Define flags clearly

Define flags at the beginning of your command function, using clear variable names:

// cmd/mycommand/cmd.go
var (
    myFlag bool
    count int
)

func Cmd() *cobra.Command {
    cmd := &cobra.Command{
        Use:   "mycommand",
        Short: "Description",
        RunE: func(cmd *cobra.Command, args []string) error {
            // Implementation
            return nil
        },
    }

    // Define flags (use singular flag names)
    cmd.Flags().BoolVar(&myFlag, "my-flag", false, "Description")
    cmd.Flags().IntVar(&count, "count", 0, "Description")

    return cmd
}

Global output-format pattern

--output-format is implemented as a shared flag strategy:

  • cmd/root.go registers it once as a persistent root flag via outputformat.AddPersistentFlag(...)
  • The root flag is inherited by all subcommands, so no per-command registration is needed
  • Commands that render text/JSON read the effective value via outputformat.GetFormat(cmd) to resolve format from CLI flags or environment variables

Use this pattern for output-aware commands:

import "github.com/datarobot/cli/internal/outputformat"

func Cmd() *cobra.Command {
    cmd := &cobra.Command{
        Use: "list",
        RunE: func(cmd *cobra.Command, _ []string) error {
            // --output-format is a global persistent flag; no local AddFlag needed.
            format := outputformat.GetFormat(cmd)
            return render(format)
        },
    }

    return cmd
}

Why GetFormat(cmd) instead of reading the variable directly:

  • It correctly handles local flag usage (dr <cmd> --output-format json)
  • It correctly handles inherited root usage (dr --output-format json <cmd>)
  • It respects environment variable overrides (DATAROBOT_CLI_OUTPUT_FORMAT)

PrintJSONEnvelope

When outputting JSON, use outputformat.PrintJSONEnvelope to wrap data in a consistent envelope:

if format == outputformat.OutputFormatJSON {
    outputs := make([]MyOutput, len(items))
    for i, item := range items {
        outputs[i] = MyOutput{/* ... */}
    }
    return outputformat.PrintJSONEnvelope(os.Stdout, "items", outputs)
}

The envelope format is {"<key>": <data>}, which ensures output is always a JSON object (never a bare array). This makes the output forward-compatible for adding metadata, pagination, or warnings without breaking callers.

JSON output purity

When the effective format is JSON, stdout must contain only valid JSON. Anything that would break dr <cmd> --output-format json | jq . (or ... 2>&1 | jq .) is a bug.

All non-JSON diagnostics belong on stderr, never stdout:

  • Cobra deprecation warnings (e.g. from MarkDeprecated / the legacy -o/--format shorthand)
  • Usage/help printed on error
  • Log lines, warnings, progress messages, update hints

Concretely:

  • Write JSON via fmt.Fprintln(cmd.OutOrStdout(), payload) or outputformat.PrintJSONEnvelope(os.Stdout, ...) — never mix in non-JSON fmt.Fprintln(cmd.OutOrStdout(), ...) calls on the JSON path.
  • Return errors from RunE so cobra routes them to stderr; do not print errors to stdout.
  • If you need to emit a deprecation/notice alongside JSON output, write it to cmd.ErrOrStderr().

Universal flags (forwarded to plugins)

Some root flags must be forwarded to plugin subprocesses as DATAROBOT_CLI_* environment variables so plugins can honour them (e.g. --debug → DATAROBOT_CLI_DEBUG=1). These are called universal flags.

How it works

Separation of concerns is strict:

Layer Responsibility
cmd/root.go Declares which flags are universal and what env var suffix they map to
internal/plugin Reads the annotations and injects env vars when launching a subprocess

The two sides share only one thing: the annotation key constant plugin.UniversalAnnotationKey = "plugin-universal".

Adding a universal flag

Call bindUniversal in the universal flags block in cmd/root.go — that is the only change required:

// cmd/root.go — universal flags block
bindUniversal("debug")
bindUniversal("disable-telemetry")
bindUniversal("my-new-flag")  // ← one line, done

bindUniversal does three things at once:

  1. Looks up the already-registered *pflag.Flag
  2. Binds it to viper (same as a plain viperx.BindPFlag call)
  3. Sets flag.Annotations["plugin-universal"] = []string{"MY_NEW_FLAG"} — the suffix is derived automatically from the flag name (uppercased, hyphens → underscores)

internal/plugin discovers annotated flags automatically when it builds the subprocess environment — no edits needed there.

How internal/plugin discovers them

cmd/plugin.RegisterPluginCommands passes the root command's persistent flagset to internal/plugin.SetRootFlags. From that point universalFlagEnv() (called inside buildPluginEnv) walks the flagset, finds any flag carrying a plugin-universal annotation, and emits DATAROBOT_CLI_<SUFFIX>=<value> into the subprocess environment.

What you must NOT do

  • Do not add a new flag name to universalFlagEnv in exec.go — the annotation on the flag drives discovery automatically.
  • Do not call internalPlugin.SetRootFlags from cmd/root.go — that call lives inside RegisterPluginCommands.

Mark flag groups

Use Cobra's flag group markers to enforce constraints on flag combinations. This provides better UX and clearer error messages.

Mutually exclusive flags

Prevent users from using incompatible flags together:

// Only one of these flags can be used
cmd.MarkFlagsMutuallyExclusive("list", "versions", "version")

When multiple flags are used together, users get a clear error:

Error: if any flags in the group [list versions version] are set none of the others can be; list version were all set

Use cases:

  • Different operation modes (e.g., --list all vs --versions for specific)
  • Conflicting output levels (e.g., --silent vs --verbose)
  • Incompatible actions (e.g., --parallel vs --watch)

Required together

If any flag in a group is used, all must be used:

// If --name is used, --version, --url, --sha256, and --release-date must also be used
cmd.MarkFlagsRequiredTogether("name", "version", "url", "sha256", "release-date")

Use cases:

  • Flags that form a complete set of parameters (e.g., all fields required for a record)
  • Flags that depend on each other for validity

One required

At least one flag from a group must be provided:

// User must provide either --output or --stdout
cmd.MarkFlagsOneRequired("output", "stdout")

Use cases:

  • Required operation modes where user must choose one
  • Output destination selection

Combining constraints

You can combine multiple constraints on the same flags:

// User must pick ONE of these approaches
cmd.MarkFlagsRequiredTogether("name", "version", "url", "sha256", "release-date")
cmd.MarkFlagsMutuallyExclusive("from-file", "name")
cmd.MarkFlagsMutuallyExclusive("from-file", "version")
cmd.MarkFlagsMutuallyExclusive("from-file", "url")
cmd.MarkFlagsMutuallyExclusive("from-file", "sha256")
cmd.MarkFlagsMutuallyExclusive("from-file", "release-date")

This pattern means:

  • Either use --from-file alone
  • Or use all five manual flags together
  • But never mix them

See the Cobra Command documentation for complete API reference.

Flag naming conventions

  • Use singular names — template, dependency, plugin (not templates, dependencies, plugins)
  • Plural aliases are acceptable for backward compatibility
  • Use lowercase with hyphens — --my-flag (not --myFlag or --my_flag)
  • Provide both short and long forms when appropriate:
cmd.Flags().BoolVarP(&force, "force", "f", false, "Force operation")
  • Be descriptive — Flag descriptions should explain the purpose and any side effects
  • Document defaults — If a flag has a non-obvious default value, mention it in the description

Examples from the codebase

Task run command (cmd/task/run/cmd.go)

// Incompatible operations
cmd.MarkFlagsMutuallyExclusive("parallel", "watch")

Rationale: Cannot run multiple tasks in parallel while watching files for changes.

Plugin install command (cmd/plugin/install/cmd.go)

// Different operation modes
cmd.MarkFlagsMutuallyExclusive("list", "versions", "version")

Rationale:

  • --list shows all available plugins
  • --versions shows available versions for one plugin
  • --version specifies an exact version to install

These are fundamentally different operations that can't coexist.

Self plugin add command (cmd/self/plugin/add/cmd.go)

// Manual flags must be used together
cmd.MarkFlagsRequiredTogether("name", "version", "url", "sha256", "release-date")

// But mutually exclusive with file-based approach
cmd.MarkFlagsMutuallyExclusive("from-file", "name")
cmd.MarkFlagsMutuallyExclusive("from-file", "version")
cmd.MarkFlagsMutuallyExclusive("from-file", "url")
cmd.MarkFlagsMutuallyExclusive("from-file", "sha256")
cmd.MarkFlagsMutuallyExclusive("from-file", "release-date")

Rationale: Users can either:

  1. Load all plugin metadata from a JSON file (--from-file)
  2. Specify all fields manually (requires all five flags together)

Best practices

  1. Add constraints at flag definition time — Mark flag groups before returning the command:
func Cmd() *cobra.Command {
    cmd := &cobra.Command{ /* ... */ }

    // Define flags
    cmd.Flags().BoolVar(...)
    cmd.Flags().StringVar(...)

    // Mark constraints AFTER all flags are defined
    cmd.MarkFlagsMutuallyExclusive("flag1", "flag2")

    return cmd
}

  1. Consider shell completion — Cobra automatically hides mutually exclusive flags from completion once one is selected, improving UX.

  2. Write clear descriptions — Help users understand why flags are incompatible:

cmd.Flags().BoolVar(&parallel, "parallel", false, "Run tasks in parallel (cannot be used with --watch)")
cmd.Flags().BoolVar(&watch, "watch", false, "Watch files and re-run (cannot be used with --parallel)")
  1. Test flag combinations — Verify that your constraints work as expected:
# Should error: incompatible flags
dr mycommand --flag1 --flag2

# Should work: one flag only
dr mycommand --flag1

Viper binding rules

The CLI deliberately limits which flags are bound to viper. Subcommand flags (such as --yes, --all, --if-needed) must not be bound via viperx.BindPFlag, and cmd/root.go does not bulk-bind subcommand flags either. Doing so would slurp those flag values into viper.AllSettings() and risk persisting them to drconfig.yaml on the next config write.

Outside internal/config/..., all viper interaction goes through the internal/config/viperx wrapper, which omits WriteConfig, SafeWriteConfig, and BindPFlags by design. Direct github.com/spf13/viper imports are blocked by depguard.

Quick rules for new flags:

  • Transient flags (per-invocation): read directly via cmd.Flags().GetBool(...). Do not bind to viper.
  • Env-var override needed? Register only the env var with viperx.BindEnv(key, "DATAROBOT_CLI_…") and OR the two sources in your handler:
yesFlag, _ := cmd.Flags().GetBool("yes")
yes := yesFlag || viperx.GetBool("yes")
  • Sticky CLI preferences (rare): bind via viperx.BindPFlag and add the key to config.PersistableKeys in internal/config/write.go.

For full details and test patterns, see the Configuration guide.

See also