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 cmp.AllowUnexported in 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:
  - 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.

package main

import (
	"strings"
	"testing"

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

type sampleStruct struct {
	Exported   string
	unexported int
}

type nestedChild struct {
	secret string
}

type nestedParent struct {
	Name  string
	child nestedChild
}

// TestAllowUnexportedPanicWithoutOption verifies that comparing unexported fields without AllowUnexported panics.
func TestAllowUnexportedPanicWithoutOption(t *testing.T) {
	a := sampleStruct{Exported: "A", unexported: 42}
	b := sampleStruct{Exported: "A", unexported: 42}

	defer func() {
		r := recover()
		if r == nil {
			t.Fatalf("expected panic when comparing unexported fields without AllowUnexported, got nil")
		}
		errMsg := ""
		if err, ok := r.(error); ok {
			errMsg = err.Error()
		} else if s, ok := r.(string); ok {
			errMsg = s
		}
		if !strings.Contains(errMsg, "cannot handle unexported field") {
			t.Fatalf("unexpected panic message: %v", r)
		}
	}()

	_ = cmp.Equal(a, b)
}

// TestAllowUnexportedEqual verifies that AllowUnexported enables equality comparison for identical unexported fields.
func TestAllowUnexportedEqual(t *testing.T) {
	a := sampleStruct{Exported: "test", unexported: 100}
	b := sampleStruct{Exported: "test", unexported: 100}

	opt := cmp.AllowUnexported(sampleStruct{})
	if !cmp.Equal(a, b, opt) {
		t.Fatalf("expected structs to be equal with AllowUnexported, diff: %s", cmp.Diff(a, b, opt))
	}
}

// TestAllowUnexportedDiff verifies that AllowUnexported detects differences in unexported fields.
func TestAllowUnexportedDiff(t *testing.T) {
	a := sampleStruct{Exported: "test", unexported: 100}
	b := sampleStruct{Exported: "test", unexported: 200}

	opt := cmp.AllowUnexported(sampleStruct{})
	if cmp.Equal(a, b, opt) {
		t.Fatalf("expected structs with different unexported fields to not be equal")
	}

	diff := cmp.Diff(a, b, opt)
	if !strings.Contains(diff, "unexported") {
		t.Fatalf("diff should mention unexported field, got: %s", diff)
	}
}

// TestAllowUnexportedNested verifies that AllowUnexported can configure multiple struct types simultaneously.
func TestAllowUnexportedNested(t *testing.T) {
	p1 := nestedParent{
		Name:  "parent",
		child: nestedChild{secret: "hidden-value"},
	}
	p2 := nestedParent{
		Name:  "parent",
		child: nestedChild{secret: "hidden-value"},
	}
	p3 := nestedParent{
		Name:  "parent",
		child: nestedChild{secret: "different-value"},
	}

	opts := cmp.AllowUnexported(nestedParent{}, nestedChild{})

	if !cmp.Equal(p1, p2, opts) {
		t.Fatalf("expected identical nested structs to be equal, diff: %s", cmp.Diff(p1, p2, opts))
	}

	if cmp.Equal(p1, p3, opts) {
		t.Fatalf("expected differing nested structs to not be equal")
	}
}

// TestAllowUnexportedNonStructPanic verifies that passing non-struct types causes AllowUnexported to panic.
func TestAllowUnexportedNonStructPanic(t *testing.T) {
	defer func() {
		r := recover()
		if r == nil {
			t.Fatalf("expected panic when passing non-struct to AllowUnexported, got nil")
		}
	}()

	_ = cmp.AllowUnexported(sampleStruct{}, &sampleStruct{})
}

{"case":{"caseId":"case:sha256:be08fed01486aeade615b5c528cfa9ced4f0562d8208f5e6425d6225d50f5445","contract":["cmp.AllowUnexported permits equality comparisons of structs with unexported fields that otherwise cause cmp.Equal and cmp.Diff to panic.","cmp.AllowUnexported enables cmp.Equal to report true for identical unexported field values and false when unexported field values differ.","cmp.AllowUnexported detects and reports differences in unexported fields when generating diff strings via cmp.Diff.","cmp.AllowUnexported accepts multiple struct types in a single option to allow recursive comparison of nested structs containing unexported fields.","cmp.AllowUnexported panics when passed a non-struct type or pointer to a struct."],"goal":"verify cmp.AllowUnexported in 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":["cmp.AllowUnexported"]},"contractCommand":["go","test","./..."],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","language":"go","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","runtime":"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":["cmp.AllowUnexported"],"verifierAdapter":"golang@1"}

module example.com/cmpunexported

go 1.23

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 h1:E7g+9GITq07hpfrRu66IVDexMakfv52eLZ2CXBWiKr4=
golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=

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