github.com/spf13/pflag v1.0.10: FlagSet.MarkHidden

# Pflag Hidden Flag Configuration

## Overview
This sample verifies the behavior of `FlagSet.MarkHidden` in `github.com/spf13/pflag`.

## Pinned Release
- Package: `github.com/spf13/pflag`
- Version: `v1.0.10`

## Observed Behavior
1. `FlagSet.MarkHidden` marks a registered flag with `flag.Hidden = true` and returns `nil`.
2. `FlagSet.MarkHidden` returns an error when called on a flag name that does not exist in the flag set.
3. `FlagSet.FlagUsages` excludes hidden flags from generated usage output while retaining visible flags.
4. Hidden flags remain fully functional for command-line argument parsing (`FlagSet.Parse`) and value assignment.

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify FlagSet.MarkHidden in pkg:golang/github.com/spf13/pflag@v1.0.10
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/spf13/pflag@v1.0.10
Demonstrate these symbols/APIs:
  - FlagSet.MarkHidden

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:0af6453dd167dbbb91d3ceda6daf3989f22c81bb7540a2fa64f8b1a2b6c54ade","contract":["FlagSet.MarkHidden marks an existing flag as hidden and returns nil error.","FlagSet.MarkHidden returns an error when called on an undefined flag name.","FlagSet.FlagUsages excludes flags marked as hidden from formatted usage output.","FlagSet.Parse successfully parses arguments for hidden flags and updates flag values."],"goal":"verify FlagSet.MarkHidden in pkg:golang/github.com/spf13/pflag@v1.0.10","kind":"HOW","packages":["pkg:golang/github.com/spf13/pflag@v1.0.10"],"schemaVersion":1,"symbols":["FlagSet.MarkHidden"]},"contractCommand":["go","test","./..."],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/github.com/spf13/pflag@v1.0.10"],"schemaVersion":1,"subject":"pkg:golang/github.com/spf13/pflag@v1.0.10","symbols":["FlagSet.MarkHidden"],"verifierAdapter":"golang@1"}

module example.com/pflag-hidden

go 1.22

require github.com/spf13/pflag v1.0.10

github.com/spf13/pflag v1.0.10 h1:4EBh2KAYBwaONj6b2Ye1GiHfwjqyROoF4RwYO+vPwFk=
github.com/spf13/pflag v1.0.10/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=

package main

import (
	"strings"
	"testing"

	"github.com/spf13/pflag"
)

func TestMarkHidden(t *testing.T) {
	fs := pflag.NewFlagSet("test_hidden", pflag.ContinueOnError)

	var visible string
	var secret string

	fs.StringVar(&visible, "visible", "default_visible", "a visible flag description")
	fs.StringVar(&secret, "secret", "default_secret", "a secret flag description")

	// 1. Verify MarkHidden marks the flag as hidden and returns nil error
	if err := fs.MarkHidden("secret"); err != nil {
		t.Fatalf("expected MarkHidden(secret) to succeed, got error: %v", err)
	}

	flag := fs.Lookup("secret")
	if flag == nil {
		t.Fatal("expected Lookup(secret) to find the flag")
	}
	if !flag.Hidden {
		t.Fatalf("expected flag.Hidden to be true, got %v", flag.Hidden)
	}

	// 2. Verify MarkHidden returns an error for undefined flags
	if err := fs.MarkHidden("nonexistent"); err == nil {
		t.Fatal("expected MarkHidden(nonexistent) to return an error, got nil")
	}

	// 3. Verify FlagUsages excludes hidden flags while keeping visible flags
	usages := fs.FlagUsages()
	if strings.Contains(usages, "secret") || strings.Contains(usages, "a secret flag description") {
		t.Fatalf("expected FlagUsages() to exclude hidden flag, got: %s", usages)
	}
	if !strings.Contains(usages, "visible") || !strings.Contains(usages, "a visible flag description") {
		t.Fatalf("expected FlagUsages() to include visible flag, got: %s", usages)
	}

	// 4. Verify FlagSet.Parse still accepts and parses hidden flags from arguments
	args := []string{"--secret=updated_secret", "--visible=updated_visible"}
	if err := fs.Parse(args); err != nil {
		t.Fatalf("unexpected parse error: %v", err)
	}

	if secret != "updated_secret" {
		t.Fatalf("expected secret to be 'updated_secret', got %q", secret)
	}
	if visible != "updated_visible" {
		t.Fatalf("expected visible to be 'updated_visible', got %q", visible)
	}
}

{
  "schemaVersion": 1,
  "goal": "verify FlagSet.MarkHidden in pkg:golang/github.com/spf13/pflag@v1.0.10",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/spf13/pflag@v1.0.10"
  ],
  "symbols": [
    "FlagSet.MarkHidden"
  ]
}