github.com/mitchellh/copystructure v1.2.0: Must

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 github.com/mitchellh/copystructure.Must in pkg:golang/github.com/mitchellh/copystructure@v1.2.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/mitchellh/copystructure@v1.2.0
Demonstrate these symbols/APIs:
  - github.com/mitchellh/copystructure.Must

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:sha256:9addcb5fa20043426b6311903722ea70ba9ba0b15eb31edb1e6ab21467ee3a86","contract":["copystructure.Must unwraps and returns the cloned value when error is nil","copystructure.Must returns an independent deep copy whose mutations do not affect the original source","copystructure.Must panics when error is non-nil","copystructure.Must returns nil when the input value is nil and error is nil"],"goal":"verify github.com/mitchellh/copystructure.Must in pkg:golang/github.com/mitchellh/copystructure@v1.2.0","kind":"HOW","packages":["pkg:golang/github.com/mitchellh/copystructure@v1.2.0"],"schemaVersion":1,"symbols":["github.com/mitchellh/copystructure.Must"]},"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/mitchellh/copystructure@v1.2.0"],"schemaVersion":1,"subject":"pkg:golang/github.com/mitchellh/copystructure@v1.2.0","symbols":["github.com/mitchellh/copystructure.Must"],"verifierAdapter":"golang@1"}

module sample

go 1.26.6

require github.com/mitchellh/copystructure v1.2.0

require github.com/mitchellh/reflectwalk v1.0.2 // indirect

github.com/mitchellh/copystructure v1.2.0 h1:vpKXTN4ewci03Vljg/q9QvCGUDttBOGBIa15WveJJGw=
github.com/mitchellh/copystructure v1.2.0/go.mod h1:qLl+cE2AmVv+CoeAwDPye/v+N2HKCj9FbZEVFJRxO9s=
github.com/mitchellh/reflectwalk v1.0.2 h1:G2LzWKi524PWgd3mLHV8Y5k7s6XUvT0Gef6zxSIeXaQ=
github.com/mitchellh/reflectwalk v1.0.2/go.mod h1:mSTlrgnPZtwu0c4WaC2kGObEpuNDbx0jmZXqmk4esnw=

package main

import (
	"fmt"

	"github.com/mitchellh/copystructure"
)

type Config struct {
	Name    string
	Options map[string]string
	Tags    []string
}

func main() {
	original := Config{
		Name: "base",
		Options: map[string]string{
			"env": "production",
		},
		Tags: []string{"server", "primary"},
	}

	// Must unwraps the result of Copy and panics if an error occurred
	cloned := copystructure.Must(copystructure.Copy(original)).(Config)

	cloned.Options["env"] = "staging"
	cloned.Tags[0] = "worker"

	fmt.Printf("Original env: %s, tags: %v\n", original.Options["env"], original.Tags)
	fmt.Printf("Cloned env:   %s, tags: %v\n", cloned.Options["env"], cloned.Tags)
}

{
  "schemaVersion": 1,
  "goal": "verify github.com/mitchellh/copystructure.Must in pkg:golang/github.com/mitchellh/copystructure@v1.2.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/mitchellh/copystructure@v1.2.0"
  ],
  "symbols": [
    "github.com/mitchellh/copystructure.Must"
  ]
}

package main

import (
	"errors"
	"fmt"
	"os"
	"reflect"

	"github.com/mitchellh/copystructure"
)

type Item struct {
	Key   string
	Data  map[string]int
	Tags  []string
	Child *Item
}

func main() {
	if err := runContract(); err != nil {
		fmt.Fprintf(os.Stderr, "Contract verification failed: %v\n", err)
		os.Exit(1)
	}
	fmt.Println("All copystructure.Must contract assertions passed successfully.")
}

func runContract() error {
	// Assertion 1: copystructure.Must unwraps and returns the cloned value when error is nil
	origMap := map[string]interface{}{
		"host": "localhost",
		"port": 8080,
		"meta": map[string]string{"region": "local"},
	}
	copied := copystructure.Must(copystructure.Copy(origMap))
	if !reflect.DeepEqual(origMap, copied) {
		return fmt.Errorf("expected copied value to equal original, got %#v", copied)
	}

	// Assertion 2: copystructure.Must returns an independent deep copy whose mutations do not affect the original source
	srcItem := Item{
		Key:  "root",
		Data: map[string]int{"count": 10},
		Tags: []string{"a", "b"},
		Child: &Item{
			Key:  "nested",
			Data: map[string]int{"level": 1},
		},
	}
	clonedItem := copystructure.Must(copystructure.Copy(srcItem)).(Item)
	clonedItem.Data["count"] = 99
	clonedItem.Tags[0] = "modified"
	clonedItem.Child.Data["level"] = 999

	if srcItem.Data["count"] != 10 {
		return fmt.Errorf("source Data map was mutated: expected 10, got %d", srcItem.Data["count"])
	}
	if srcItem.Tags[0] != "a" {
		return fmt.Errorf("source Tags slice was mutated: expected 'a', got %q", srcItem.Tags[0])
	}
	if srcItem.Child.Data["level"] != 1 {
		return fmt.Errorf("source Child struct pointer map was mutated: expected 1, got %d", srcItem.Child.Data["level"])
	}

	// Assertion 3: copystructure.Must panics when error is non-nil
	panicHappened := false
	expectedErr := errors.New("custom copy failure")
	func() {
		defer func() {
			if r := recover(); r != nil {
				panicHappened = true
				if err, ok := r.(error); ok {
					if err.Error() != expectedErr.Error() {
						panic(fmt.Sprintf("unexpected panic value error: %v", err))
					}
				}
			}
		}()
		_ = copystructure.Must(nil, expectedErr)
	}()
	if !panicHappened {
		return fmt.Errorf("expected copystructure.Must to panic when non-nil error is passed, but it did not panic")
	}

	// Assertion 4: copystructure.Must returns nil when the input value is nil and error is nil
	var nilPtr *Item
	clonedNil := copystructure.Must(copystructure.Copy(nilPtr))
	if clonedNil != nil {
		if !reflect.ValueOf(clonedNil).IsNil() {
			return fmt.Errorf("expected nil result for nil input, got %#v", clonedNil)
		}
	}
	rawNil := copystructure.Must(nil, nil)
	if rawNil != nil {
		return fmt.Errorf("expected nil result for (nil, nil), got %#v", rawNil)
	}

	return nil
}