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

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.StringSliceVar 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.StringSliceVar

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:b210f768c02387015c439526c37ad3c93a3a5f7414cc1a2a980b340c2ab0976e","contract":["FlagSet.StringSliceVar retains default value when no flag arguments are parsed","FlagSet.StringSliceVar parses comma-separated flag argument and overrides default value","FlagSet.StringSliceVar accumulates values across multiple flag occurrences"],"goal":"verify FlagSet.StringSliceVar 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.StringSliceVar"]},"contractCommand":["go","run","./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.StringSliceVar"],"verifierAdapter":"golang@1"}

module example.com/sample

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 (
	"fmt"
	"os"

	"github.com/spf13/pflag"
)

// Config holds command-line options parsed via pflag.
type Config struct {
	Tags []string
}

// ParseFlags parses command-line arguments into a Config instance.
func ParseFlags(args []string) (*Config, error) {
	cfg := &Config{}
	fs := pflag.NewFlagSet("sample", pflag.ContinueOnError)
	fs.StringSliceVar(&cfg.Tags, "tags", []string{"default"}, "list of tags")

	if err := fs.Parse(args); err != nil {
		return nil, err
	}
	return cfg, nil
}

func main() {
	cfg, err := ParseFlags(os.Args[1:])
	if err != nil {
		fmt.Fprintf(os.Stderr, "error: %v\n", err)
		os.Exit(1)
	}
	fmt.Printf("Tags: %v\n", cfg.Tags)
}

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

package main

import (
	"fmt"
	"os"
	"reflect"

	"github.com/spf13/pflag"
)

func main() {
	// 1. FlagSet.StringSliceVar binds slice pointer and retains default value when no flag arguments are parsed
	{
		var tags []string
		fs := pflag.NewFlagSet("test-default", pflag.ContinueOnError)
		fs.StringSliceVar(&tags, "tags", []string{"alpha", "beta"}, "comma-separated tags")

		if err := fs.Parse([]string{}); err != nil {
			fmt.Fprintf(os.Stderr, "failed to parse empty args: %v\n", err)
			os.Exit(1)
		}
		expected := []string{"alpha", "beta"}
		if !reflect.DeepEqual(tags, expected) {
			fmt.Fprintf(os.Stderr, "expected default %v, got %v\n", expected, tags)
			os.Exit(1)
		}
	}

	// 2. FlagSet.StringSliceVar parses comma-separated flag argument and overrides default value
	{
		var tags []string
		fs := pflag.NewFlagSet("test-comma", pflag.ContinueOnError)
		fs.StringSliceVar(&tags, "tags", []string{"default"}, "comma-separated tags")

		if err := fs.Parse([]string{"--tags", "web,api,db"}); err != nil {
			fmt.Fprintf(os.Stderr, "failed to parse comma args: %v\n", err)
			os.Exit(1)
		}
		expected := []string{"web", "api", "db"}
		if !reflect.DeepEqual(tags, expected) {
			fmt.Fprintf(os.Stderr, "expected %v, got %v\n", expected, tags)
			os.Exit(1)
		}
	}

	// 3. FlagSet.StringSliceVar accumulates values across multiple flag occurrences
	{
		var tags []string
		fs := pflag.NewFlagSet("test-repeat", pflag.ContinueOnError)
		fs.StringSliceVar(&tags, "tags", nil, "comma-separated tags")

		if err := fs.Parse([]string{"--tags=prod", "--tags=stage,test"}); err != nil {
			fmt.Fprintf(os.Stderr, "failed to parse repeated args: %v\n", err)
			os.Exit(1)
		}
		expected := []string{"prod", "stage", "test"}
		if !reflect.DeepEqual(tags, expected) {
			fmt.Fprintf(os.Stderr, "expected %v, got %v\n", expected, tags)
			os.Exit(1)
		}
	}

	fmt.Println("PASS")
}