github.com/google/go-cmp v0.3.0: cmp.Diff

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/google/go-cmp/cmp.Diff in pkg:golang/github.com/google/go-cmp@v0.3.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/google/go-cmp@v0.3.0
Demonstrate these symbols/APIs:
  - github.com/google/go-cmp/cmp.Diff

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:d121c1edf9238ae212bb2da358f3a6dac8b2dc0965162d3420a7725a5fd43cc2","contract":["cmp.Diff returns an empty string when comparing equal struct and slice values","cmp.Diff returns a non-empty human-readable diff naming differing fields when values differ","cmp.Diff supports cmpopts.IgnoreFields to exclude specified struct fields from comparison","cmp.Diff supports cmpopts.SortSlices for order-independent slice comparison","cmp.Diff respects custom cmp.Comparer options when computing differences","cmp.Diff supports cmp.AllowUnexported to compare structs containing unexported fields"],"goal":"verify github.com/google/go-cmp/cmp.Diff in pkg:golang/github.com/google/go-cmp@v0.3.0","kind":"HOW","packages":["pkg:golang/github.com/google/go-cmp@v0.3.0"],"schemaVersion":1,"symbols":["github.com/google/go-cmp/cmp.Diff"]},"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/google/go-cmp@v0.3.0"],"schemaVersion":1,"subject":"pkg:golang/github.com/google/go-cmp@v0.3.0","symbols":["github.com/google/go-cmp/cmp.Diff"],"verifierAdapter":"golang@1"}

module sample

go 1.21

require github.com/google/go-cmp v0.3.0

github.com/google/go-cmp v0.3.0 h1:crn/baboCvb5fXaQ0IJ1SGTsTVrWpDsCWC8EGETZijY=
github.com/google/go-cmp v0.3.0/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMywk6iLU=

{
  "schemaVersion": 1,
  "goal": "verify github.com/google/go-cmp/cmp.Diff in pkg:golang/github.com/google/go-cmp@v0.3.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/google/go-cmp@v0.3.0"
  ],
  "symbols": [
    "github.com/google/go-cmp/cmp.Diff"
  ]
}

package main

import (
	"fmt"
	"os"
	"strings"

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

type serviceConfig struct {
	Endpoint string
	Retries  int
	Internal int
}

type privateRecord struct {
	Label  string
	secret string
}

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

func runContract() error {
	// 1. cmp.Diff returns an empty string when comparing equal struct and slice values
	cfgA := serviceConfig{Endpoint: "localhost:8080", Retries: 3, Internal: 10}
	cfgB := serviceConfig{Endpoint: "localhost:8080", Retries: 3, Internal: 10}
	if diff := cmp.Diff(cfgA, cfgB); diff != "" {
		return fmt.Errorf("expected empty diff for equal structs, got: %s", diff)
	}
	if diff := cmp.Diff([]string{"a", "b"}, []string{"a", "b"}); diff != "" {
		return fmt.Errorf("expected empty diff for equal slices, got: %s", diff)
	}

	// 2. cmp.Diff returns a non-empty human-readable diff naming differing fields when values differ
	cfgC := serviceConfig{Endpoint: "localhost:8080", Retries: 5, Internal: 10}
	diffOut := cmp.Diff(cfgA, cfgC)
	if diffOut == "" {
		return fmt.Errorf("expected non-empty diff when struct fields differ")
	}
	if !strings.Contains(diffOut, "Retries") {
		return fmt.Errorf("expected diff output to mention differing field Retries, got: %s", diffOut)
	}

	// 3. cmp.Diff supports cmpopts.IgnoreFields to exclude specified struct fields from comparison
	cfgIgnored := serviceConfig{Endpoint: "localhost:8080", Retries: 3, Internal: 42}
	if cmp.Diff(cfgA, cfgIgnored) == "" {
		return fmt.Errorf("expected non-empty diff when Internal field differs without IgnoreFields")
	}
	if diff := cmp.Diff(cfgA, cfgIgnored, cmpopts.IgnoreFields(serviceConfig{}, "Internal")); diff != "" {
		return fmt.Errorf("expected empty diff when Internal field is ignored, got: %s", diff)
	}

	// 4. cmp.Diff supports cmpopts.SortSlices for order-independent slice comparison
	sliceX := []int{30, 10, 20}
	sliceY := []int{10, 20, 30}
	if cmp.Diff(sliceX, sliceY) == "" {
		return fmt.Errorf("expected non-empty diff for differently ordered slices without SortSlices")
	}
	lessInt := func(a, b int) bool { return a < b }
	if diff := cmp.Diff(sliceX, sliceY, cmpopts.SortSlices(lessInt)); diff != "" {
		return fmt.Errorf("expected empty diff with cmpopts.SortSlices, got: %s", diff)
	}

	// 5. cmp.Diff respects custom cmp.Comparer options when computing differences
	foldComparer := cmp.Comparer(func(a, b string) bool {
		return strings.EqualFold(strings.TrimSpace(a), strings.TrimSpace(b))
	})
	if diff := cmp.Diff(" Example ", "example", foldComparer); diff != "" {
		return fmt.Errorf("expected empty diff with custom case-folding Comparer, got: %s", diff)
	}

	// 6. cmp.Diff supports cmp.AllowUnexported to compare structs containing unexported fields
	rec1 := privateRecord{Label: "item", secret: "v1"}
	rec2 := privateRecord{Label: "item", secret: "v1"}
	rec3 := privateRecord{Label: "item", secret: "v2"}
	if diff := cmp.Diff(rec1, rec2, cmp.AllowUnexported(privateRecord{})); diff != "" {
		return fmt.Errorf("expected empty diff for equal unexported fields with AllowUnexported, got: %s", diff)
	}
	if diff := cmp.Diff(rec1, rec3, cmp.AllowUnexported(privateRecord{})); diff == "" {
		return fmt.Errorf("expected non-empty diff for differing unexported fields with AllowUnexported")
	}

	return nil
}