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

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/errors.Wrap 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/errors.Wrap

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:c0c4806d97bff0bb8d75a91c7c01bad1f1641261e5f7f93a990c8db2c3af5747","contract":["errors.Wrap returns nil when given a nil error","errors.Wrap returns a non-nil error wrapping the provided error","errors.Wrap preserves the message of the underlying error","errors.Wrap hides the underlying cause so errors.Cause returns the wrapped error itself","errors.Wrap implements errors.Wrapper with the underlying error","errors.Wrap records the caller location implementing errors.Locator"],"goal":"verify gopkg.in/errgo.v2/errors.Wrap 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/errors.Wrap"]},"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/gopkg.in/errgo.v2@v2.1.0"],"schemaVersion":1,"subject":"pkg:golang/gopkg.in/errgo.v2@v2.1.0","symbols":["gopkg.in/errgo.v2/errors.Wrap"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.23

require gopkg.in/errgo.v2 v2.1.0

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=
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"
	"io"

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

// ReadConfig demonstrates wrapping an error with source location tracking using errors.Wrap.
func ReadConfig() error {
	// Simulate an underlying error, e.g., io.EOF
	err := io.EOF
	return errors.Wrap(err)
}

func main() {
	if err := ReadConfig(); err != nil {
		fmt.Printf("Error: %v\n", err)
		fmt.Printf("Cause: %v\n", errors.Cause(err))
	}
}

{
  "schemaVersion": 1,
  "goal": "verify gopkg.in/errgo.v2/errors.Wrap 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/errors.Wrap"
  ]
}

package main

import (
	"fmt"
	"os"

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

func main() {
	// 1. errors.Wrap returns nil when given a nil error
	if err := errors.Wrap(nil); err != nil {
		fmt.Fprintf(os.Stderr, "assertion 1 failed: expected nil, got %v\n", err)
		os.Exit(1)
	}

	// 2. errors.Wrap returns a non-nil error wrapping the provided error
	underlying := errors.New("underlying failure")
	wrapped := errors.Wrap(underlying)
	if wrapped == nil {
		fmt.Fprintf(os.Stderr, "assertion 2 failed: expected non-nil error\n")
		os.Exit(1)
	}

	// 3. errors.Wrap preserves the message of the underlying error
	if wrapped.Error() != underlying.Error() {
		fmt.Fprintf(os.Stderr, "assertion 3 failed: expected %q, got %q\n", underlying.Error(), wrapped.Error())
		os.Exit(1)
	}

	// 4. errors.Wrap hides the underlying cause so errors.Cause returns the wrapped error itself
	if cause := errors.Cause(wrapped); cause != wrapped {
		fmt.Fprintf(os.Stderr, "assertion 4 failed: expected cause to be wrapped error %v, got %v\n", wrapped, cause)
		os.Exit(1)
	}

	// 5. errors.Wrap implements errors.Wrapper with the underlying error
	wrapper, ok := wrapped.(errors.Wrapper)
	if !ok {
		fmt.Fprintf(os.Stderr, "assertion 5 failed: wrapped error does not implement errors.Wrapper\n")
		os.Exit(1)
	}
	if wrapper.Underlying() != underlying {
		fmt.Fprintf(os.Stderr, "assertion 5 failed: expected underlying %v, got %v\n", underlying, wrapper.Underlying())
		os.Exit(1)
	}

	// 6. errors.Wrap records the caller location implementing errors.Locator
	locator, ok := wrapped.(errors.Locator)
	if !ok {
		fmt.Fprintf(os.Stderr, "assertion 6 failed: wrapped error does not implement errors.Locator\n")
		os.Exit(1)
	}
	file, line := locator.Location()
	if file == "" || line == 0 {
		fmt.Fprintf(os.Stderr, "assertion 6 failed: expected valid file and line, got file=%q line=%d\n", file, line)
		os.Exit(1)
	}

	fmt.Println("All contract assertions passed.")
}