github.com/rogpeppe/go-internal v1.3.0: txtar.Format

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/rogpeppe/go-internal/txtar.Format in pkg:golang/github.com/rogpeppe/go-internal@v1.3.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/rogpeppe/go-internal@v1.3.0
Demonstrate these symbols/APIs:
  - github.com/rogpeppe/go-internal/txtar.Format

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:bb61c176f00810f6acf921665510b76eac9bc6befa940b689605411844f0b4fd","contract":["txtar.Format formats Archive struct into txtar text archive format with comment and delimited files","txtar.Format appends trailing newline to comment and file data if missing","txtar.Format returns empty byte slice for empty Archive with nil or empty comment and files","txtar.Format output is round-tripped identically by txtar.Parse"],"goal":"verify github.com/rogpeppe/go-internal/txtar.Format in pkg:golang/github.com/rogpeppe/go-internal@v1.3.0","kind":"HOW","packages":["pkg:golang/github.com/rogpeppe/go-internal@v1.3.0"],"schemaVersion":1,"symbols":["github.com/rogpeppe/go-internal/txtar.Format"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","language":"go","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","packageManagerVersion":"1.26.6","runtime":"go","runtimeVersion":"1.26.6","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/github.com/rogpeppe/go-internal@v1.3.0"],"schemaVersion":1,"subject":"pkg:golang/github.com/rogpeppe/go-internal@v1.3.0","symbols":["github.com/rogpeppe/go-internal/txtar.Format"],"verifierAdapter":"golang@1"}

module sample

go 1.26.6

require github.com/rogpeppe/go-internal v1.3.0

github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
github.com/rogpeppe/go-internal v1.3.0 h1:RR9dF3JtopPvtkroDZuVD7qquD0bnHlKSqaQhgwt8yk=
github.com/rogpeppe/go-internal v1.3.0/go.mod h1:M8bDsm7K2OlrFYOpmOWEs/qY81heoFRclV5y23lUDJ4=
gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
gopkg.in/errgo.v2 v2.1.0/go.mod h1:hNsd1EY+bozCKY1Ytp96fpM3vjJbqLJn88ws8XvfDNI=

package main

import (
	"fmt"

	"github.com/rogpeppe/go-internal/txtar"
)

func main() {
	archive := &txtar.Archive{
		Comment: []byte("Sample txtar archive\n"),
		Files: []txtar.File{
			{
				Name: "sample.txt",
				Data: []byte("txtar formatted file content\n"),
			},
		},
	}

	formatted := txtar.Format(archive)
	fmt.Printf("Formatted archive:\n%s", string(formatted))
}

{
  "schemaVersion": 1,
  "goal": "verify github.com/rogpeppe/go-internal/txtar.Format in pkg:golang/github.com/rogpeppe/go-internal@v1.3.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/rogpeppe/go-internal@v1.3.0"
  ],
  "symbols": [
    "github.com/rogpeppe/go-internal/txtar.Format"
  ]
}

package main

import (
	"bytes"
	"fmt"
	"os"

	"github.com/rogpeppe/go-internal/txtar"
)

func main() {
	if err := runContractTests(); err != nil {
		fmt.Fprintf(os.Stderr, "Contract test failure: %v\n", err)
		os.Exit(1)
	}
	fmt.Println("All contract assertions passed.")
}

func runContractTests() error {
	// 1. txtar.Format formats Archive struct into txtar text archive format with comment and delimited files
	{
		archive := &txtar.Archive{
			Comment: []byte("Package overview\n"),
			Files: []txtar.File{
				{
					Name: "a.txt",
					Data: []byte("file A contents\n"),
				},
				{
					Name: "sub/b.txt",
					Data: []byte("file B contents\n"),
				},
			},
		}

		got := txtar.Format(archive)
		expected := "Package overview\n-- a.txt --\nfile A contents\n-- sub/b.txt --\nfile B contents\n"
		if string(got) != expected {
			return fmt.Errorf("assertion 1 failed: got %q, expected %q", string(got), expected)
		}
	}

	// 2. txtar.Format appends trailing newline to comment and file data if missing
	{
		archive := &txtar.Archive{
			Comment: []byte("No trailing newline"),
			Files: []txtar.File{
				{
					Name: "c.txt",
					Data: []byte("No newline at EOF"),
				},
			},
		}

		got := txtar.Format(archive)
		expected := "No trailing newline\n-- c.txt --\nNo newline at EOF\n"
		if string(got) != expected {
			return fmt.Errorf("assertion 2 failed: got %q, expected %q", string(got), expected)
		}
	}

	// 3. txtar.Format returns empty byte slice for empty Archive with nil or empty comment and files
	{
		emptyArchive := &txtar.Archive{}
		got := txtar.Format(emptyArchive)
		if len(got) != 0 {
			return fmt.Errorf("assertion 3 failed: expected empty output, got %q (len %d)", string(got), len(got))
		}
	}

	// 4. txtar.Format output is round-tripped identically by txtar.Parse
	{
		original := &txtar.Archive{
			Comment: []byte("Roundtrip comment\n"),
			Files: []txtar.File{
				{
					Name: "file1.go",
					Data: []byte("package main\n"),
				},
				{
					Name: "file2.json",
					Data: []byte("{\"key\": \"val\"}\n"),
				},
			},
		}

		formatted := txtar.Format(original)
		parsed := txtar.Parse(formatted)

		if !bytes.Equal(parsed.Comment, original.Comment) {
			return fmt.Errorf("assertion 4 failed (comment mismatch): got %q, expected %q", string(parsed.Comment), string(original.Comment))
		}
		if len(parsed.Files) != len(original.Files) {
			return fmt.Errorf("assertion 4 failed (files count mismatch): got %d files, expected %d", len(parsed.Files), len(original.Files))
		}
		for i := range original.Files {
			if parsed.Files[i].Name != original.Files[i].Name {
				return fmt.Errorf("assertion 4 failed (file %d name mismatch): got %q, expected %q", i, parsed.Files[i].Name, original.Files[i].Name)
			}
			if !bytes.Equal(parsed.Files[i].Data, original.Files[i].Data) {
				return fmt.Errorf("assertion 4 failed (file %d data mismatch): got %q, expected %q", i, string(parsed.Files[i].Data), string(original.Files[i].Data))
			}
		}
	}

	return nil
}