golang.org/x/sys v0.22.0: unix.Errno

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 golang.org/x/sys/unix.Errno in pkg:golang/golang.org/x/sys@v0.22.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/sys@v0.22.0
Demonstrate these symbols/APIs:
  - golang.org/x/sys/unix.Errno

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:sha256:851718a52a3c416fdfe0b8a8a11528c823666a414805b239436aa557779d396b","contract":["unix.Errno implements the error interface and formats standard error descriptions with Error()","unix.Errno matches standard library sentinel errors via errors.Is and implements Timeout and Temporary predicates","failed unix system calls return unix.Errno values that can be unwrapped and matched using errors.As and errors.Is"],"goal":"verify golang.org/x/sys/unix.Errno in pkg:golang/golang.org/x/sys@v0.22.0","kind":"HOW","packages":["pkg:golang/golang.org/x/sys@v0.22.0"],"schemaVersion":1,"symbols":["golang.org/x/sys/unix.Errno"]},"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/golang.org/x/sys@v0.22.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/sys@v0.22.0","symbols":["golang.org/x/sys/unix.Errno"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require golang.org/x/sys v0.22.0

golang.org/x/sys v0.22.0 h1:RI27ohtqKCnwULzJLqkv897zojh5/DwS/ENaMzUOaWI=
golang.org/x/sys v0.22.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=

package main

import (
	"errors"
	"fmt"
	"os"

	"golang.org/x/sys/unix"
)

func main() {
	var errENOENT unix.Errno = unix.ENOENT
	fmt.Printf("Errno value: %d, description: %s\n", errENOENT, errENOENT.Error())

	if errors.Is(errENOENT, os.ErrNotExist) {
		fmt.Println("unix.ENOENT matches os.ErrNotExist")
	}

	_, err := unix.Open("nonexistent_demo_file_xyz", unix.O_RDONLY, 0)
	if err != nil {
		var errno unix.Errno
		if errors.As(err, &errno) {
			fmt.Printf("unix.Open failed with unix.Errno: %d (%s)\n", errno, errno.Error())
		}
	}
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/sys/unix.Errno in pkg:golang/golang.org/x/sys@v0.22.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/sys@v0.22.0"
  ],
  "symbols": [
    "golang.org/x/sys/unix.Errno"
  ]
}

package main

import (
	"errors"
	"fmt"
	"io/fs"
	"os"

	"golang.org/x/sys/unix"
)

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

func runTests() error {
	// 1. unix.Errno implements the error interface and formats standard error descriptions with Error()
	var err interface{} = unix.ENOENT
	errVal, ok := err.(error)
	if !ok {
		return fmt.Errorf("expected unix.Errno to implement error interface")
	}
	if errVal.Error() != "no such file or directory" {
		return fmt.Errorf("expected unix.ENOENT.Error() to be 'no such file or directory', got %q", errVal.Error())
	}

	var existErr error = unix.EEXIST
	if existErr.Error() != "file exists" {
		return fmt.Errorf("expected unix.EEXIST.Error() to be 'file exists', got %q", existErr.Error())
	}

	if unix.Errno(2) != unix.ENOENT {
		return fmt.Errorf("expected unix.Errno(2) to equal unix.ENOENT")
	}

	// 2. unix.Errno matches standard library sentinel errors via errors.Is and implements Timeout and Temporary predicates
	if !errors.Is(unix.ENOENT, os.ErrNotExist) {
		return fmt.Errorf("expected errors.Is(unix.ENOENT, os.ErrNotExist) to be true")
	}
	if !errors.Is(unix.ENOENT, fs.ErrNotExist) {
		return fmt.Errorf("expected errors.Is(unix.ENOENT, fs.ErrNotExist) to be true")
	}
	if !errors.Is(unix.EEXIST, os.ErrExist) {
		return fmt.Errorf("expected errors.Is(unix.EEXIST, os.ErrExist) to be true")
	}
	if !errors.Is(unix.EACCES, os.ErrPermission) {
		return fmt.Errorf("expected errors.Is(unix.EACCES, os.ErrPermission) to be true")
	}
	if !errors.Is(unix.EPERM, os.ErrPermission) {
		return fmt.Errorf("expected errors.Is(unix.EPERM, os.ErrPermission) to be true")
	}

	if !unix.ETIMEDOUT.Timeout() {
		return fmt.Errorf("expected unix.ETIMEDOUT.Timeout() to be true")
	}
	if !unix.EINTR.Temporary() {
		return fmt.Errorf("expected unix.EINTR.Temporary() to be true")
	}
	if !unix.EAGAIN.Temporary() {
		return fmt.Errorf("expected unix.EAGAIN.Temporary() to be true")
	}

	// 3. failed unix system calls return unix.Errno values that can be unwrapped and matched using errors.As and errors.Is
	_, openErr := unix.Open("nonexistent_path_test_file_csx", unix.O_RDONLY, 0)
	if openErr == nil {
		return fmt.Errorf("expected unix.Open on nonexistent file to fail")
	}

	var errno unix.Errno
	if !errors.As(openErr, &errno) {
		return fmt.Errorf("expected errors.As to extract unix.Errno from unix.Open error")
	}
	if errno != unix.ENOENT {
		return fmt.Errorf("expected errno to be unix.ENOENT (2), got %d", errno)
	}
	if !errors.Is(openErr, unix.ENOENT) {
		return fmt.Errorf("expected errors.Is(openErr, unix.ENOENT) to be true")
	}
	if !errors.Is(openErr, os.ErrNotExist) {
		return fmt.Errorf("expected errors.Is(openErr, os.ErrNotExist) to be true")
	}

	return nil
}