github.com/google/go-cmp v0.5.7: cmp.Path

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.Path in pkg:golang/github.com/google/go-cmp@v0.5.7
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/google/go-cmp@v0.5.7
Demonstrate these symbols/APIs:
  - github.com/google/go-cmp/cmp.Path

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 sample_test

import (
	"reflect"
	"strings"
	"testing"

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

type Entry struct {
	Code  int
	Label string
}

type Record struct {
	Group   string
	Entries []Entry
	Tags    map[string]*string
}

func TestPathContract(t *testing.T) {
	var visited int
	var sawCodeField bool
	var sawSliceStep bool
	var sawMapStep bool
	var sawIndirectStep bool

	inspectOpt := cmp.FilterPath(func(p cmp.Path) bool {
		visited++

		// Contract: cmp.Path represents the sequence of PathStep operations during value tree traversal
		if len(p) == 0 {
			t.Errorf("expected non-empty cmp.Path during traversal")
			return false
		}

		// Contract: cmp.Path.Last returns the terminal PathStep in the traversal path
		last := p.Last()
		if last == nil {
			t.Errorf("expected non-nil Last() for Path of length %d", len(p))
			return false
		}

		// Contract: cmp.Path.Index returns the PathStep at the specified index from the root
		if p.Index(len(p)-1) != last {
			t.Errorf("expected p.Index(len(p)-1) to equal p.Last()")
		}
		if p.Index(0) == nil {
			t.Errorf("expected non-nil root step at index 0")
		}

		// Contract: cmp.Path.String formats the human-readable path representation of the current step
		fullStr := p.String()
		if len(p) > 1 && fullStr == "" {
			t.Errorf("expected non-empty p.String() for path length %d", len(p))
		}

		steps := sample.CollectStepStrings(p)
		if len(steps) != len(p) {
			t.Errorf("expected %d step strings, got %d", len(p), len(steps))
		}

		if sf, ok := last.(cmp.StructField); ok && sf.Name() == "Code" {
			sawCodeField = true
			if !strings.Contains(fullStr, "Code") {
				t.Errorf("expected path string %q to contain 'Code'", fullStr)
			}
			if last.Type() != reflect.TypeOf(0) {
				t.Errorf("expected Code field type int, got %v", last.Type())
			}
		}

		if _, ok := last.(cmp.SliceIndex); ok {
			sawSliceStep = true
		}
		if _, ok := last.(cmp.MapIndex); ok {
			sawMapStep = true
		}
		if _, ok := last.(cmp.Indirect); ok {
			sawIndirectStep = true
		}

		return false
	}, cmp.Ignore())

	tagA := "alpha"
	tagB := "beta"
	r1 := Record{
		Group: "core",
		Entries: []Entry{
			{Code: 1, Label: "First"},
			{Code: 2, Label: "Second"},
		},
		Tags: map[string]*string{
			"stage": &tagA,
		},
	}
	r2 := Record{
		Group: "core",
		Entries: []Entry{
			{Code: 100, Label: "First"},
			{Code: 200, Label: "Second"},
		},
		Tags: map[string]*string{
			"stage": &tagB,
		},
	}

	_ = cmp.Equal(r1, r2, inspectOpt)

	if visited == 0 {
		t.Fatalf("expected cmp.Path traversal to visit steps, got 0")
	}
	if !sawCodeField {
		t.Errorf("expected to observe StructField 'Code' on cmp.Path")
	}
	if !sawSliceStep {
		t.Errorf("expected to observe SliceIndex step on cmp.Path")
	}
	if !sawMapStep {
		t.Errorf("expected to observe MapIndex step on cmp.Path")
	}
	if !sawIndirectStep {
		t.Errorf("expected to observe Indirect step on cmp.Path")
	}

	// Contract: cmp.FilterPath evaluates cmp.Path predicates to selectively apply comparison options
	ignoreCode := sample.IgnoreStructField("Code")
	ignoreStage := sample.FilterByLastStep(func(step cmp.PathStep) bool {
		mi, ok := step.(cmp.MapIndex)
		return ok && mi.Key().String() == "stage"
	}, cmp.Ignore())

	if !cmp.Equal(r1, r2, ignoreCode, ignoreStage) {
		t.Errorf("expected r1 and r2 to be equal when ignoring 'Code' field and 'stage' map key")
	}
	if cmp.Equal(r1, r2) {
		t.Errorf("expected r1 and r2 to differ without cmp.Path filtering options")
	}
}

{"case":{"caseId":"case:sha256:6fe2f4b015e3adf18e9d378dea00702dc283f655595d02fe74a7285e4f075f23","contract":["cmp.Path represents the sequence of PathStep operations during value tree traversal","cmp.Path.String formats the human-readable path representation of the current step","cmp.Path.Last returns the terminal PathStep in the traversal path","cmp.Path.Index returns the PathStep at the specified index from the root","cmp.FilterPath evaluates cmp.Path predicates to selectively apply comparison options"],"goal":"verify github.com/google/go-cmp/cmp.Path in pkg:golang/github.com/google/go-cmp@v0.5.7","kind":"HOW","packages":["pkg:golang/github.com/google/go-cmp@v0.5.7"],"schemaVersion":1,"symbols":["github.com/google/go-cmp/cmp.Path"]},"contractCommand":["go","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@v0.5.7"],"schemaVersion":1,"subject":"pkg:golang/github.com/google/go-cmp@v0.5.7","symbols":["github.com/google/go-cmp/cmp.Path"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.21

require github.com/google/go-cmp v0.5.7

github.com/google/go-cmp v0.5.7 h1:81/ik6ipDQS2aGcBfIN5dHDB36BwrStyeAQquSYCV4o=
github.com/google/go-cmp v0.5.7/go.mod h1:n+brtR0CgQNWTVd5ZUFpTBC8YFBDLK/h/bpaJ8/DtOE=
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=

package sample

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

// FilterByLastStep returns a cmp.Option that applies opt when the terminal step
// of cmp.Path matches the given predicate.
func FilterByLastStep(predicate func(step cmp.PathStep) bool, opt cmp.Option) cmp.Option {
	return cmp.FilterPath(func(p cmp.Path) bool {
		if len(p) == 0 {
			return false
		}
		return predicate(p.Last())
	}, opt)
}

// IgnoreStructField returns a cmp.Option that ignores struct fields with the given name
// by inspecting the terminal StructField step on cmp.Path.
func IgnoreStructField(fieldName string) cmp.Option {
	return FilterByLastStep(func(step cmp.PathStep) bool {
		sf, ok := step.(cmp.StructField)
		return ok && sf.Name() == fieldName
	}, cmp.Ignore())
}

// CollectStepStrings returns the formatted string of each PathStep in p using Index.
func CollectStepStrings(p cmp.Path) []string {
	out := make([]string, len(p))
	for i := 0; i < len(p); i++ {
		out[i] = p.Index(i).String()
	}
	return out
}

{
  "schemaVersion": 1,
  "goal": "verify github.com/google/go-cmp/cmp.Path in pkg:golang/github.com/google/go-cmp@v0.5.7",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/google/go-cmp@v0.5.7"
  ],
  "symbols": [
    "github.com/google/go-cmp/cmp.Path"
  ]
}