github.com/google/go-cmp v0.5.1: 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@v0.5.1
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/google/go-cmp@v0.5.1
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:sha256:36e0bb49f8191c762e6de7714edc49241ac781def48f2f124753f9f46a75ae10","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@v0.5.1","kind":"HOW","packages":["pkg:golang/github.com/google/go-cmp@v0.5.1"],"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@v0.5.1"],"schemaVersion":1,"subject":"pkg:golang/github.com/google/go-cmp@v0.5.1","symbols":["github.com/google/go-cmp/cmp.Diff"],"verifierAdapter":"golang@1"}

module sample

go 1.21

require github.com/google/go-cmp v0.5.1

require golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543 // indirect

github.com/google/go-cmp v0.5.1 h1:JFrFEBb2xKufg6XkJsJr+WbKb4FQlURi5RUcBveYu9k=
github.com/google/go-cmp v0.5.1/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 github.com/google/go-cmp/cmp.Diff in pkg:golang/github.com/google/go-cmp@v0.5.1",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/google/go-cmp@v0.5.1"
  ],
  "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 inventoryItem struct {
	Code     string
	Quantity int
	Revision int
}

type secretNote struct {
	Title   string
	content string
}

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

func verifyCmpDiff() error {
	// 1. cmp.Diff returns an empty string when comparing equal scalar, slice, map, and struct values
	aItem := inventoryItem{Code: "SKU-100", Quantity: 5, Revision: 1}
	bItem := inventoryItem{Code: "SKU-100", Quantity: 5, Revision: 1}
	if diff := cmp.Diff(aItem, bItem); diff != "" {
		return fmt.Errorf("expected empty diff for identical structs, got: %s", diff)
	}
	if diff := cmp.Diff([]int{10, 20, 30}, []int{10, 20, 30}); diff != "" {
		return fmt.Errorf("expected empty diff for identical slices, got: %s", diff)
	}

	// 2. cmp.Diff returns a non-empty human-readable diff when compared values differ
	cItem := inventoryItem{Code: "SKU-100", Quantity: 8, Revision: 1}
	diffStruct := cmp.Diff(aItem, cItem)
	if diffStruct == "" {
		return fmt.Errorf("expected non-empty diff when Quantity differs")
	}
	if !strings.Contains(diffStruct, "Quantity") {
		return fmt.Errorf("expected diff output to mention differing field Quantity, got: %s", diffStruct)
	}

	// 3. cmp.Diff supports cmpopts.IgnoreFields to exclude specified struct fields from comparison
	revItem := inventoryItem{Code: "SKU-100", Quantity: 5, Revision: 99}
	if cmp.Diff(aItem, revItem) == "" {
		return fmt.Errorf("expected non-empty diff when Revision differs without IgnoreFields")
	}
	if diff := cmp.Diff(aItem, revItem, cmpopts.IgnoreFields(inventoryItem{}, "Revision")); diff != "" {
		return fmt.Errorf("expected empty diff when Revision is ignored via cmpopts.IgnoreFields, got: %s", diff)
	}

	// 4. cmp.Diff supports cmpopts.SortSlices for order-independent slice comparison
	tagsA := []string{"zeta", "alpha", "beta"}
	tagsB := []string{"alpha", "beta", "zeta"}
	if cmp.Diff(tagsA, tagsB) == "" {
		return fmt.Errorf("expected non-empty diff for unordered slices without SortSlices")
	}
	lessStr := func(x, y string) bool { return x < y }
	if diff := cmp.Diff(tagsA, tagsB, cmpopts.SortSlices(lessStr)); diff != "" {
		return fmt.Errorf("expected empty diff with cmpopts.SortSlices, got: %s", diff)
	}

	// 5. cmp.Diff respects custom cmp.Comparer options when computing differences
	caseInsensitive := cmp.Comparer(func(x, y string) bool {
		return strings.EqualFold(strings.TrimSpace(x), strings.TrimSpace(y))
	})
	if diff := cmp.Diff(" GoLang ", " golang ", caseInsensitive); diff != "" {
		return fmt.Errorf("expected empty diff with case-insensitive Comparer, got: %s", diff)
	}

	// 6. cmp.Diff supports cmp.AllowUnexported to compare structs containing unexported fields
	note1 := secretNote{Title: "Memo", content: "alpha"}
	note2 := secretNote{Title: "Memo", content: "alpha"}
	note3 := secretNote{Title: "Memo", content: "beta"}
	if diff := cmp.Diff(note1, note2, cmp.AllowUnexported(secretNote{})); diff != "" {
		return fmt.Errorf("expected empty diff for equal unexported fields with AllowUnexported, got: %s", diff)
	}
	if diff := cmp.Diff(note1, note3, cmp.AllowUnexported(secretNote{})); diff == "" {
		return fmt.Errorf("expected non-empty diff for differing unexported fields with AllowUnexported")
	}

	return nil
}