github.com/google/go-cmp v0.5.5: cmp.AllowUnexported

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/github.com/google/go-cmp@v0.5.5
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/google/go-cmp@v0.5.5
Demonstrate these symbols/APIs:
  - github.com/google/go-cmp/cmp.AllowUnexported

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:sha256:0428b637bf776bfedd0d27865caaa0e577e17542c094f45e7585e93014fb375b","contract":["cmp.Equal panics when comparing structs with unexported fields without cmp.AllowUnexported","cmp.AllowUnexported enables comparing structs with unexported fields for equality","cmp.Diff with cmp.AllowUnexported reports differences in unexported fields","cmp.AllowUnexported allows comparing nested structs with unexported fields when both types are specified","cmp.AllowUnexported panics when passed a non-struct type or pointer to struct"],"goal":"verify pkg:golang/github.com/google/go-cmp@v0.5.5","kind":"HOW","packages":["pkg:golang/github.com/google/go-cmp@v0.5.5"],"schemaVersion":1,"symbols":["github.com/google/go-cmp/cmp.AllowUnexported"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","language":"go","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/github.com/google/go-cmp@v0.5.5"],"schemaVersion":1,"subject":"pkg:golang/github.com/google/go-cmp@v0.5.5","symbols":["github.com/google/go-cmp/cmp.AllowUnexported"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.22

require github.com/google/go-cmp v0.5.5

github.com/google/go-cmp v0.5.5 h1:Khx7svrCpmxxtHBq5j2mp/xVjsi8hQMfNLvJFAlrGgU=
github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=

package sample

import (
	"fmt"

	"github.com/google/go-cmp/cmp"
)

// Credential holds public and unexported authentication information.
type Credential struct {
	Username string
	token    string
}

// NewCredential creates a Credential instance.
func NewCredential(username, token string) Credential {
	return Credential{
		Username: username,
		token:    token,
	}
}

// Session contains a session ID and an unexported Credential.
type Session struct {
	ID   int
	cred Credential
}

// NewSession creates a Session instance.
func NewSession(id int, cred Credential) Session {
	return Session{
		ID:   id,
		cred: cred,
	}
}

// CompareCredentials compares two Credential instances using cmp.AllowUnexported.
func CompareCredentials(a, b Credential) bool {
	return cmp.Equal(a, b, cmp.AllowUnexported(Credential{}))
}

// DiffCredentials returns the diff between two Credential instances using cmp.AllowUnexported.
func DiffCredentials(a, b Credential) string {
	return cmp.Diff(a, b, cmp.AllowUnexported(Credential{}))
}

// CompareSessions compares two Session instances allowing unexported fields of both Session and Credential.
func CompareSessions(a, b Session) bool {
	return cmp.Equal(a, b, cmp.AllowUnexported(Session{}, Credential{}))
}

// TryCompareWithoutAllow attempts to compare two Credentials without AllowUnexported and catches panic.
func TryCompareWithoutAllow(a, b Credential) (panicMsg string) {
	defer func() {
		if r := recover(); r != nil {
			panicMsg = fmt.Sprint(r)
		}
	}()
	cmp.Equal(a, b)
	return ""
}

// TryAllowUnexported attempts to construct cmp.AllowUnexported with given types and catches panic.
func TryAllowUnexported(types ...interface{}) (opt cmp.Option, panicMsg string) {
	defer func() {
		if r := recover(); r != nil {
			panicMsg = fmt.Sprint(r)
		}
	}()
	opt = cmp.AllowUnexported(types...)
	return opt, ""
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:golang/github.com/google/go-cmp@v0.5.5",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/google/go-cmp@v0.5.5"
  ],
  "symbols": [
    "github.com/google/go-cmp/cmp.AllowUnexported"
  ]
}

package main

import (
	"fmt"
	"os"
	"strings"

	"example.com/sample"
	"github.com/google/go-cmp/cmp"
)

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

func runContractTests() error {
	c1 := sample.NewCredential("alice", "token-123")
	c2 := sample.NewCredential("alice", "token-123")
	c3 := sample.NewCredential("alice", "token-456")

	// 1. cmp.Equal panics when comparing structs with unexported fields without cmp.AllowUnexported
	panicNoAllow := sample.TryCompareWithoutAllow(c1, c2)
	if panicNoAllow == "" {
		return fmt.Errorf("expected panic when comparing structs with unexported fields without AllowUnexported")
	}
	if !strings.Contains(panicNoAllow, "cannot handle unexported field") {
		return fmt.Errorf("expected 'cannot handle unexported field' in panic message, got: %s", panicNoAllow)
	}

	// 2. cmp.AllowUnexported enables comparing structs with unexported fields for equality
	opt := cmp.AllowUnexported(sample.Credential{})
	if !cmp.Equal(c1, c2, opt) {
		return fmt.Errorf("expected c1 and c2 to be equal with AllowUnexported")
	}
	if cmp.Equal(c1, c3, opt) {
		return fmt.Errorf("expected c1 and c3 to be unequal when unexported token differs")
	}

	// 3. cmp.Diff with cmp.AllowUnexported reports differences in unexported fields
	diffSame := cmp.Diff(c1, c2, opt)
	if diffSame != "" {
		return fmt.Errorf("expected empty diff for identical structs with AllowUnexported, got: %s", diffSame)
	}
	diffDiff := cmp.Diff(c1, c3, opt)
	if diffDiff == "" {
		return fmt.Errorf("expected non-empty diff for differing unexported token")
	}
	if !strings.Contains(diffDiff, "token-123") || !strings.Contains(diffDiff, "token-456") {
		return fmt.Errorf("expected diff to show differing token values, got: %s", diffDiff)
	}

	// 4. cmp.AllowUnexported allows comparing nested structs with unexported fields when both types are specified
	s1 := sample.NewSession(1, c1)
	s2 := sample.NewSession(1, c2)
	s3 := sample.NewSession(1, c3)
	sessionOpt := cmp.AllowUnexported(sample.Session{}, sample.Credential{})
	if !cmp.Equal(s1, s2, sessionOpt) {
		return fmt.Errorf("expected s1 and s2 to be equal when both Session and Credential are allowed")
	}
	if cmp.Equal(s1, s3, sessionOpt) {
		return fmt.Errorf("expected s1 and s3 to be unequal when nested token differs")
	}

	// 5. cmp.AllowUnexported panics when passed a non-struct type or pointer to struct
	_, panicPtr := sample.TryAllowUnexported(&sample.Credential{})
	if panicPtr == "" {
		return fmt.Errorf("expected panic when pointer to struct is passed to AllowUnexported")
	}
	if !strings.Contains(panicPtr, "invalid struct type") {
		return fmt.Errorf("expected 'invalid struct type' in panic message, got: %s", panicPtr)
	}

	_, panicNonStruct := sample.TryAllowUnexported(42)
	if panicNonStruct == "" {
		return fmt.Errorf("expected panic when non-struct int is passed to AllowUnexported")
	}
	if !strings.Contains(panicNonStruct, "invalid struct type") {
		return fmt.Errorf("expected 'invalid struct type' in panic message, got: %s", panicNonStruct)
	}

	return nil
}