github.com/google/go-cmp v0.6.0: 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@v0.6.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/google/go-cmp@v0.6.0
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 Item struct {
	ID   int
	Name string
}

type Catalog struct {
	Category string
	Items    []Item
	Metadata map[string]*string
}

func TestPathContract(t *testing.T) {
	var pathStrings []string
	var foundIDStructField bool
	var foundSliceIndex bool
	var foundMapIndex bool
	var foundIndirect bool
	var pathsVisited int

	captureOpt := cmp.FilterPath(func(p cmp.Path) bool {
		pathsVisited++

		// Contract: cmp.Path represents the sequence of PathStep operations during value tree traversal.
		if len(p) == 0 {
			t.Errorf("expected non-empty 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) == p.Last()")
		}
		if p.Index(0) == nil {
			t.Errorf("expected non-nil root step at index 0")
		}

		// Contract: cmp.Path.String formats the path representation of the current traversal step.
		pathStr := p.String()
		pathStrings = append(pathStrings, pathStr)

		// Record step strings
		steps := sample.GetPathStepStrings(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 {
			if sf.Name() == "ID" {
				foundIDStructField = true
				if !strings.Contains(pathStr, "ID") {
					t.Errorf("expected path string %q to contain 'ID'", pathStr)
				}
				if last.Type() != reflect.TypeOf(0) {
					t.Errorf("expected ID field type int, got %v", last.Type())
				}
			}
		}

		if _, ok := last.(cmp.SliceIndex); ok {
			foundSliceIndex = true
		}

		if _, ok := last.(cmp.MapIndex); ok {
			foundMapIndex = true
		}

		if _, ok := last.(cmp.Indirect); ok {
			foundIndirect = true
		}

		return false
	}, cmp.Ignore())

	val1 := "v1"
	val2 := "v2"
	c1 := Catalog{
		Category: "books",
		Items: []Item{
			{ID: 1, Name: "Algorithms"},
			{ID: 2, Name: "Compilers"},
		},
		Metadata: map[string]*string{
			"env": &val1,
		},
	}
	c2 := Catalog{
		Category: "books",
		Items: []Item{
			{ID: 10, Name: "Algorithms"},
			{ID: 20, Name: "Compilers"},
		},
		Metadata: map[string]*string{
			"env": &val2,
		},
	}

	// Traverse with filter option
	_ = cmp.Equal(c1, c2, captureOpt)

	if pathsVisited == 0 {
		t.Fatalf("expected to visit paths during traversal, visited 0")
	}
	if !foundIDStructField {
		t.Errorf("expected to find StructField 'ID' during traversal")
	}
	if !foundSliceIndex {
		t.Errorf("expected to find SliceIndex step during traversal")
	}
	if !foundMapIndex {
		t.Errorf("expected to find MapIndex step during traversal")
	}
	if !foundIndirect {
		t.Errorf("expected to find Indirect step during traversal")
	}

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

	if !cmp.Equal(c1, c2, ignoreID, ignoreEnv) {
		t.Errorf("expected c1 and c2 to be equal when ignoring field 'ID' and map key 'env'")
	}

	if cmp.Equal(c1, c2) {
		t.Errorf("expected c1 and c2 to be unequal without ignoring differing fields")
	}
}

{"case":{"caseId":"case:sha256:00c6e83f36f9277d17456c4da63ccc28e1b8c3773c402f6a0e242c0f75d4d2c5","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@v0.6.0","kind":"HOW","packages":["pkg:golang/github.com/google/go-cmp@v0.6.0"],"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@v0.6.0"],"schemaVersion":1,"subject":"pkg:golang/github.com/google/go-cmp@v0.6.0","symbols":["github.com/google/go-cmp/cmp.Path"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.22

require github.com/google/go-cmp v0.6.0

github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=

package sample

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

// FilterByLastStep creates a cmp.Option that applies opt only when the terminal step
// of cmp.Path satisfies the provided 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 specified name
// using cmp.Path and its terminal StructField step.
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())
}

// GetPathStepStrings extracts the string representation of every PathStep in a cmp.Path.
func GetPathStepStrings(p cmp.Path) []string {
	strs := make([]string, len(p))
	for i := 0; i < len(p); i++ {
		strs[i] = p.Index(i).String()
	}
	return strs
}

{
  "schemaVersion": 1,
  "goal": "verify github.com/google/go-cmp/cmp.Path in pkg:golang/github.com/google/go-cmp@v0.6.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/google/go-cmp@v0.6.0"
  ],
  "symbols": [
    "github.com/google/go-cmp/cmp.Path"
  ]
}