gopkg.in/errgo.v2 v2.1.0: errors.New

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 gopkg.in/errgo.v2/fmt/errors.New in pkg:golang/gopkg.in/errgo.v2@v2.1.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/gopkg.in/errgo.v2@v2.1.0
Demonstrate these symbols/APIs:
  - gopkg.in/errgo.v2/fmt/errors.New
Required runtime conditions:
  - ecosystem: golang
  - language: go
  - packageManager: go@1.26.6
  - runtime: go@1.26.6

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:sha256:7d893ab4b1c143fcaacb53075ada232a65f080f0130c013c637e5e589ed205bc","contract":["errors.New returns a non-nil error with the specified message string","errors.New with an empty string returns an error whose Error method returns \u003cno error\u003e","errors.New returns an error whose Cause is nil and errors.Cause returns the error itself","errors.New returns an error implementing Wrapper with matching Message and nil Underlying","errors.New returns an error implementing Locator recording caller file and line information"],"goal":"verify gopkg.in/errgo.v2/fmt/errors.New in pkg:golang/gopkg.in/errgo.v2@v2.1.0","kind":"HOW","packages":["pkg:golang/gopkg.in/errgo.v2@v2.1.0"],"schemaVersion":1,"symbols":["gopkg.in/errgo.v2/fmt/errors.New"]},"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/gopkg.in/errgo.v2@v2.1.0"],"schemaVersion":1,"subject":"pkg:golang/gopkg.in/errgo.v2@v2.1.0","symbols":["gopkg.in/errgo.v2/fmt/errors.New"],"verifierAdapter":"golang@1"}

module sample

go 1.26.6

require gopkg.in/errgo.v2 v2.1.0

github.com/kr/pretty v0.1.0 h1:L/CwN0zerZDmRFUapSPitk6f+Q3+0za1rQkzVuMiMFI=
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 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 h1:qIbj1fsPNlZgppZ+VLlY7N33q108Sa+fhmuc+sWQYwY=
gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
gopkg.in/errgo.v2 v2.1.0 h1:0vLT13EuvQ0hNvakwLuFZ/jYrLp5F3kcWHXdRggjCE8=
gopkg.in/errgo.v2 v2.1.0/go.mod h1:hNsd1EY+bozCKY1Ytp96fpM3vjJbqLJn88ws8XvfDNI=

package main

import (
	"fmt"

	"gopkg.in/errgo.v2/fmt/errors"
)

func main() {
	err := errors.New("operation failed")
	if err != nil {
		fmt.Printf("Created error: %v\n", err)
	}
}

{
  "schemaVersion": 1,
  "goal": "verify gopkg.in/errgo.v2/fmt/errors.New in pkg:golang/gopkg.in/errgo.v2@v2.1.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/gopkg.in/errgo.v2@v2.1.0"
  ],
  "symbols": [
    "gopkg.in/errgo.v2/fmt/errors.New"
  ],
  "runtimeConditions": {
    "ecosystem": "golang",
    "language": "go",
    "packageManager": "go@1.26.6",
    "runtime": "go@1.26.6"
  }
}

package main

import (
	"fmt"
	"os"
	"strings"

	"gopkg.in/errgo.v2/fmt/errors"
)

func main() {
	// Assertion 1: errors.New returns a non-nil error with the specified message string
	{
		msg := "disk quota exceeded"
		err := errors.New(msg)
		if err == nil {
			fmt.Fprintf(os.Stderr, "Assertion 1 failed: expected non-nil error, got nil\n")
			os.Exit(1)
		}
		if err.Error() != msg {
			fmt.Fprintf(os.Stderr, "Assertion 1 failed: expected message %q, got %q\n", msg, err.Error())
			os.Exit(1)
		}
	}

	// Assertion 2: errors.New with an empty string returns an error whose Error method returns <no error>
	{
		err := errors.New("")
		if err == nil {
			fmt.Fprintf(os.Stderr, "Assertion 2 failed: expected non-nil error, got nil\n")
			os.Exit(1)
		}
		if err.Error() != "<no error>" {
			fmt.Fprintf(os.Stderr, "Assertion 2 failed: expected '<no error>', got %q\n", err.Error())
			os.Exit(1)
		}
	}

	// Assertion 3: errors.New returns an error whose Cause is nil and errors.Cause returns the error itself
	{
		err := errors.New("root cause error")
		causer, ok := err.(errors.Causer)
		if !ok {
			fmt.Fprintf(os.Stderr, "Assertion 3 failed: error does not implement Causer interface\n")
			os.Exit(1)
		}
		if causer.Cause() != nil {
			fmt.Fprintf(os.Stderr, "Assertion 3 failed: expected nil cause, got %v\n", causer.Cause())
			os.Exit(1)
		}
		if errors.Cause(err) != err {
			fmt.Fprintf(os.Stderr, "Assertion 3 failed: expected errors.Cause to return the error itself\n")
			os.Exit(1)
		}
	}

	// Assertion 4: errors.New returns an error implementing Wrapper with matching Message and nil Underlying
	{
		msg := "wrapper test"
		err := errors.New(msg)
		wrapper, ok := err.(errors.Wrapper)
		if !ok {
			fmt.Fprintf(os.Stderr, "Assertion 4 failed: error does not implement Wrapper interface\n")
			os.Exit(1)
		}
		if wrapper.Message() != msg {
			fmt.Fprintf(os.Stderr, "Assertion 4 failed: expected Message() %q, got %q\n", msg, wrapper.Message())
			os.Exit(1)
		}
		if wrapper.Underlying() != nil {
			fmt.Fprintf(os.Stderr, "Assertion 4 failed: expected nil Underlying(), got %v\n", wrapper.Underlying())
			os.Exit(1)
		}
	}

	// Assertion 5: errors.New returns an error implementing Locator recording caller file and line information
	{
		msg := "location test"
		err := errors.New(msg)
		locator, ok := err.(errors.Locator)
		if !ok {
			fmt.Fprintf(os.Stderr, "Assertion 5 failed: error does not implement Locator interface\n")
			os.Exit(1)
		}
		file, line := locator.Location()
		if !strings.HasSuffix(file, "contract.go") {
			fmt.Fprintf(os.Stderr, "Assertion 5 failed: expected filename ending with contract.go, got %q\n", file)
			os.Exit(1)
		}
		if line <= 0 {
			fmt.Fprintf(os.Stderr, "Assertion 5 failed: expected positive line number, got %d\n", line)
			os.Exit(1)
		}
		details := errors.Details(err)
		if !strings.Contains(details, msg) || !strings.Contains(details, "contract.go") {
			fmt.Fprintf(os.Stderr, "Assertion 5 failed: details %q does not contain expected info\n", details)
			os.Exit(1)
		}
	}

	fmt.Println("PASS: all errors.New contract assertions passed")
}