gopkg.in/yaml.v2 v2.3.0: yaml.Marshal, yaml.Unmarshal

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 pkg:golang/gopkg.in/yaml.v2@v2.3.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/gopkg.in/yaml.v2@v2.3.0

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:ff3fab15bf28fbcaea4b745b561eada3a9b34bf18cae910d3101565b96a92a6a","contract":["yaml.Unmarshal unmarshals valid YAML bytes into a struct with yaml struct tags","yaml.Marshal serializes a Go struct into valid YAML bytes","yaml.Unmarshal unmarshals nested maps and slices into typed struct fields","yaml.Unmarshal returns an error when parsing malformed YAML syntax","yaml.Marshal respects omitempty tag by omitting zero-value fields"],"goal":"verify pkg:golang/gopkg.in/yaml.v2@v2.3.0","kind":"HOW","packages":["pkg:golang/gopkg.in/yaml.v2@v2.3.0"],"schemaVersion":1,"symbols":["yaml.Marshal","yaml.Unmarshal"]},"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/gopkg.in/yaml.v2@v2.3.0"],"schemaVersion":1,"subject":"pkg:golang/gopkg.in/yaml.v2@v2.3.0","symbols":["yaml.Marshal","yaml.Unmarshal"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.22.0

require gopkg.in/yaml.v2 v2.3.0

gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
gopkg.in/yaml.v2 v2.3.0 h1:clyUAQHOM3G0M3f5vQj7LuJrETvjVot3Z5el9nffUtU=
gopkg.in/yaml.v2 v2.3.0/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=

package main

import (
	"fmt"
	"os"

	"gopkg.in/yaml.v2"
)

// Config represents a sample application configuration.
type Config struct {
	Name    string            `yaml:"name"`
	Port    int               `yaml:"port"`
	Debug   bool              `yaml:"debug,omitempty"`
	Tags    []string          `yaml:"tags,omitempty"`
	Options map[string]string `yaml:"options,omitempty"`
}

// ParseConfig unmarshals YAML data into a Config struct.
func ParseConfig(data []byte) (*Config, error) {
	var cfg Config
	if err := yaml.Unmarshal(data, &cfg); err != nil {
		return nil, fmt.Errorf("failed to unmarshal yaml: %w", err)
	}
	return &cfg, nil
}

// SerializeConfig marshals a Config struct into YAML bytes.
func SerializeConfig(cfg *Config) ([]byte, error) {
	data, err := yaml.Marshal(cfg)
	if err != nil {
		return nil, fmt.Errorf("failed to marshal yaml: %w", err)
	}
	return data, nil
}

func main() {
	sampleYAML := `
name: sample-app
port: 8080
debug: true
tags:
  - web
  - api
options:
  env: production
`
	cfg, err := ParseConfig([]byte(sampleYAML))
	if err != nil {
		fmt.Fprintf(os.Stderr, "Error: %v\n", err)
		os.Exit(1)
	}
	fmt.Printf("Loaded config: name=%s, port=%d, debug=%t\n", cfg.Name, cfg.Port, cfg.Debug)

	out, err := SerializeConfig(cfg)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Error: %v\n", err)
		os.Exit(1)
	}
	fmt.Println("Marshaled YAML:")
	fmt.Println(string(out))
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:golang/gopkg.in/yaml.v2@v2.3.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/gopkg.in/yaml.v2@v2.3.0"
  ],
  "symbols": [
    "yaml.Marshal",
    "yaml.Unmarshal"
  ]
}

package main

import (
	"fmt"
	"os"
	"reflect"
	"strings"

	"gopkg.in/yaml.v2"
)

type ServerConfig struct {
	Host    string            `yaml:"host"`
	Port    int               `yaml:"port"`
	Enabled bool              `yaml:"enabled"`
	Secret  string            `yaml:"secret,omitempty"`
	Routes  []string          `yaml:"routes,omitempty"`
	Meta    map[string]string `yaml:"meta,omitempty"`
}

func main() {
	// Assertion 1: yaml.Unmarshal unmarshals valid YAML bytes into a struct with yaml struct tags
	yamlInput := []byte("host: localhost\nport: 9000\nenabled: true\n")
	var srv ServerConfig
	if err := yaml.Unmarshal(yamlInput, &srv); err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: yaml.Unmarshal failed: %v\n", err)
		os.Exit(1)
	}
	if srv.Host != "localhost" || srv.Port != 9000 || !srv.Enabled {
		fmt.Fprintf(os.Stderr, "FAIL: yaml.Unmarshal struct fields mismatch: %+v\n", srv)
		os.Exit(1)
	}

	// Assertion 2: yaml.Marshal serializes a Go struct into valid YAML bytes
	srvToMarshal := ServerConfig{
		Host:    "example.com",
		Port:    8080,
		Enabled: true,
	}
	marshaledBytes, err := yaml.Marshal(&srvToMarshal)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: yaml.Marshal failed: %v\n", err)
		os.Exit(1)
	}
	if !strings.Contains(string(marshaledBytes), "host: example.com") || !strings.Contains(string(marshaledBytes), "port: 8080") {
		fmt.Fprintf(os.Stderr, "FAIL: yaml.Marshal output missing expected content:\n%s\n", string(marshaledBytes))
		os.Exit(1)
	}

	// Assertion 3: yaml.Unmarshal unmarshals nested maps and slices into typed struct fields
	nestedYAML := []byte("host: 127.0.0.1\nport: 3000\nenabled: false\nroutes:\n  - /api/v1\n  - /health\nmeta:\n  tier: backend\n  region: us-east\n")
	var nestedSrv ServerConfig
	if err := yaml.Unmarshal(nestedYAML, &nestedSrv); err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: yaml.Unmarshal nested YAML failed: %v\n", err)
		os.Exit(1)
	}
	expectedRoutes := []string{"/api/v1", "/health"}
	if !reflect.DeepEqual(nestedSrv.Routes, expectedRoutes) {
		fmt.Fprintf(os.Stderr, "FAIL: yaml.Unmarshal routes mismatch: got %v, want %v\n", nestedSrv.Routes, expectedRoutes)
		os.Exit(1)
	}
	if nestedSrv.Meta["tier"] != "backend" || nestedSrv.Meta["region"] != "us-east" {
		fmt.Fprintf(os.Stderr, "FAIL: yaml.Unmarshal meta mismatch: got %v\n", nestedSrv.Meta)
		os.Exit(1)
	}

	// Assertion 4: yaml.Unmarshal returns an error when parsing malformed YAML syntax
	malformedYAML := []byte("host: [unclosed list\n  port: 8080\n")
	var malformedSrv ServerConfig
	if err := yaml.Unmarshal(malformedYAML, &malformedSrv); err == nil {
		fmt.Fprintf(os.Stderr, "FAIL: yaml.Unmarshal expected error for malformed YAML, got nil\n")
		os.Exit(1)
	}

	// Assertion 5: yaml.Marshal respects omitempty tag by omitting zero-value fields
	emptySecretSrv := ServerConfig{
		Host:    "app.local",
		Port:    443,
		Enabled: true,
		Secret:  "",
	}
	outWithOmit, err := yaml.Marshal(&emptySecretSrv)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: yaml.Marshal with omitempty failed: %v\n", err)
		os.Exit(1)
	}
	if strings.Contains(string(outWithOmit), "secret:") {
		fmt.Fprintf(os.Stderr, "FAIL: yaml.Marshal did not omit empty field secret:\n%s\n", string(outWithOmit))
		os.Exit(1)
	}

	fmt.Println("PASS: pkg:golang/gopkg.in/yaml.v2@v2.3.0 contract passed")
}