github.com/pkg/errors v0.9.1: WithStack

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/pkg/errors.WithStack in pkg:golang/github.com/pkg/errors@v0.9.1
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/pkg/errors@v0.9.1
Demonstrate these symbols/APIs:
  - github.com/pkg/errors.WithStack

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:e32e9ebed31e68c946819a6930e7646024d319135a11558663e8eb2f68d1da94","contract":["errors.WithStack returns nil when passed a nil error","errors.WithStack preserves the underlying error message via Error()","errors.WithStack attaches a stack trace retrievable via StackTrace()","errors.WithStack produces a multi-line formatted trace with %+v containing file and line information","errors.WithStack allows recovering the root cause via errors.Cause"],"goal":"verify github.com/pkg/errors.WithStack in pkg:golang/github.com/pkg/errors@v0.9.1","kind":"HOW","packages":["pkg:golang/github.com/pkg/errors@v0.9.1"],"schemaVersion":1,"symbols":["github.com/pkg/errors.WithStack"]},"contractCommand":["go","run","./test"],"environment":{"arch":"amd64","compiler":"go","compilerVersion":"1.26.6","distro":"ubuntu","ecosystem":"golang","language":"go","languageVersion":"1.26.6","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/pkg/errors@v0.9.1"],"schemaVersion":1,"subject":"pkg:golang/github.com/pkg/errors@v0.9.1","symbols":["github.com/pkg/errors.WithStack"],"verifierAdapter":"golang@1"}

module sample

go 1.26.6

require github.com/pkg/errors v0.9.1

github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=

package main

import (
	"fmt"

	"github.com/pkg/errors"
)

func performOperation() error {
	baseErr := errors.New("underlying network failure")
	return errors.WithStack(baseErr)
}

func main() {
	err := performOperation()
	if err != nil {
		fmt.Printf("Standard error message: %s\n", err)
		fmt.Printf("Error with stack trace:\n%+v\n", err)

		rootCause := errors.Cause(err)
		fmt.Printf("Root cause: %v\n", rootCause)
	}
}

{
  "schemaVersion": 1,
  "goal": "verify github.com/pkg/errors.WithStack in pkg:golang/github.com/pkg/errors@v0.9.1",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/pkg/errors@v0.9.1"
  ],
  "symbols": [
    "github.com/pkg/errors.WithStack"
  ]
}

package main

import (
	"fmt"
	"os"
	"strings"

	"github.com/pkg/errors"
)

type stackTracer interface {
	StackTrace() errors.StackTrace
}

func triggerWithStack(err error) error {
	return errors.WithStack(err)
}

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

	// Assertion 2: errors.WithStack preserves the underlying error message via Error()
	baseErr := errors.New("database connection refused")
	wrappedErr := triggerWithStack(baseErr)
	{
		if wrappedErr == nil {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: wrapped error is nil\n")
			os.Exit(1)
		}
		if wrappedErr.Error() != "database connection refused" {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: expected %q, got %q\n", "database connection refused", wrappedErr.Error())
			os.Exit(1)
		}
	}

	// Assertion 3: errors.WithStack attaches a stack trace retrievable via StackTrace()
	{
		tracer, ok := wrappedErr.(stackTracer)
		if !ok {
			fmt.Fprintf(os.Stderr, "assertion 3 failed: wrapped error does not implement StackTrace()\n")
			os.Exit(1)
		}
		frames := tracer.StackTrace()
		if len(frames) == 0 {
			fmt.Fprintf(os.Stderr, "assertion 3 failed: stack trace frames are empty\n")
			os.Exit(1)
		}
	}

	// Assertion 4: errors.WithStack produces a multi-line formatted trace with %+v containing file and line information
	{
		formatted := fmt.Sprintf("%+v", wrappedErr)
		if !strings.Contains(formatted, "database connection refused") {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: formatted trace does not contain base error message\n")
			os.Exit(1)
		}
		if !strings.Contains(formatted, "contract.go") {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: formatted trace does not contain contract.go file reference\n")
			os.Exit(1)
		}
	}

	// Assertion 5: errors.WithStack allows recovering the root cause via errors.Cause
	{
		root := errors.Cause(wrappedErr)
		if root != baseErr {
			fmt.Fprintf(os.Stderr, "assertion 5 failed: expected root %v, got %v\n", baseErr, root)
			os.Exit(1)
		}
	}

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