gopkg.in/errgo.v2 v2.1.0

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 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

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:b943174e9a48065e7fd65b4376babde3ffa4c2cc0b442d3e90b3480938230e47","contract":["errors.New creates an error with given message","errors.Wrap wraps an error and preserves error message","errors.Because attaches a specific cause and contextual message","errors.Cause returns the root cause of an error wrapped with Because","errors.Details formats caller stack details for wrapped errors","fmt/errors.Newf creates formatted errors","fmt/errors.Becausef attaches cause with formatted message"],"goal":"verify pkg:golang/gopkg.in/errgo.v2@v2.1.0","kind":"HOW","packages":["pkg:golang/gopkg.in/errgo.v2@v2.1.0"],"schemaVersion":1},"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","verifierAdapter":"golang@1"}

module example.com/sample

go 1.22

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"

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

func main() {
	// 1. Create a base error
	baseErr := errors.New("underlying database connection refused")
	fmt.Println("Base error:", baseErr)

	// 2. Wrap the error to capture caller location while hiding cause
	wrappedErr := errors.Wrap(baseErr)
	fmt.Println("Wrapped error:", wrappedErr)

	// 3. Attach a root cause with contextual explanation
	rootCause := errors.New("connection timeout")
	becauseErr := errors.Because(baseErr, rootCause, "failed query execution")
	fmt.Println("Because error:", becauseErr)
	fmt.Println("Extracted cause:", errors.Cause(becauseErr))

	// 4. Formatted errors with fmt/errors
	formattedErr := fmtErrors.Newf("request failed with status %d", 503)
	fmt.Println("Formatted error:", formattedErr)

	formattedWithCause := fmtErrors.Becausef(baseErr, rootCause, "service %s unavailable", "order-api")
	fmt.Println("Formatted with cause:", formattedWithCause)
	fmt.Println("Extracted cause:", fmtErrors.Cause(formattedWithCause))
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:golang/gopkg.in/errgo.v2@v2.1.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/gopkg.in/errgo.v2@v2.1.0"
  ]
}

package main

import (
	"fmt"
	"os"
	"strings"

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

func main() {
	if err := runContractTests(); err != nil {
		fmt.Fprintf(os.Stderr, "Contract test failed: %v\n", err)
		os.Exit(1)
	}
	fmt.Println("All errgo.v2 contract assertions passed.")
}

func runContractTests() error {
	// Assertion 1: errors.New creates an error with given message
	err1 := errors.New("operation failed")
	if err1 == nil || err1.Error() != "operation failed" {
		return fmt.Errorf("expected 'operation failed', got %v", err1)
	}

	// Assertion 2: errors.Wrap wraps an error and preserves error message
	errWrapped := errors.Wrap(err1)
	if errWrapped == nil || errWrapped.Error() != "operation failed" {
		return fmt.Errorf("expected wrapped 'operation failed', got %v", errWrapped)
	}

	// Assertion 3: errors.Because attaches a specific cause and contextual message
	rootCause := errors.New("disk full")
	errBecause := errors.Because(err1, rootCause, "failed to save")
	if errBecause == nil || errBecause.Error() != "failed to save: operation failed" {
		return fmt.Errorf("expected 'failed to save: operation failed', got %v", errBecause)
	}

	// Assertion 4: errors.Cause returns the root cause of an error wrapped with Because
	extractedCause := errors.Cause(errBecause)
	if extractedCause != rootCause {
		return fmt.Errorf("expected cause %v, got %v", rootCause, extractedCause)
	}

	// Assertion 5: errors.Details formats caller stack details for wrapped errors
	details := errors.Details(errBecause)
	if !strings.Contains(details, "failed to save") || !strings.Contains(details, "operation failed") {
		return fmt.Errorf("expected details to contain stack info, got: %s", details)
	}

	// Assertion 6: fmt/errors.Newf creates formatted errors
	errFmt := fmtErrors.Newf("code %d: %s", 404, "not found")
	if errFmt == nil || errFmt.Error() != "code 404: not found" {
		return fmt.Errorf("expected 'code 404: not found', got %v", errFmt)
	}

	// Assertion 7: fmt/errors.Becausef attaches cause with formatted message
	errFmtBecause := fmtErrors.Becausef(err1, rootCause, "request %d failed", 123)
	if errFmtBecause == nil || errFmtBecause.Error() != "request 123 failed: operation failed" {
		return fmt.Errorf("expected 'request 123 failed: operation failed', got %v", errFmtBecause)
	}
	if fmtErrors.Cause(errFmtBecause) != rootCause {
		return fmt.Errorf("expected cause %v, got %v", rootCause, fmtErrors.Cause(errFmtBecause))
	}

	return nil
}