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

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.Errorf 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.Errorf

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:c199fd087125082c3d641cb6fac52fc9ea2b2b90e253d646c4e82851bd1c478b","contract":["errors.Errorf returns non-nil error","errors.Errorf formats message with formatted arguments","errors.Errorf attaches stack trace"],"goal":"verify github.com/pkg/errors.Errorf 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.Errorf"]},"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/github.com/pkg/errors@v0.9.1"],"schemaVersion":1,"subject":"pkg:golang/github.com/pkg/errors@v0.9.1","symbols":["github.com/pkg/errors.Errorf"],"verifierAdapter":"golang@1"}

module sample

go 1.26.6

require github.com/pkg/errors v0.9.1 // indirect

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"
)

// FormatUserError creates a formatted error with context using errors.Errorf.
func FormatUserError(code int, reason string) error {
	return errors.Errorf("operation failed (code %d): %s", code, reason)
}

func main() {
	err := FormatUserError(404, "item not found")
	if err != nil {
		fmt.Printf("Formatted error: %v\n", err)
	}
}

{
  "schemaVersion": 1,
  "goal": "verify github.com/pkg/errors.Errorf 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.Errorf"
  ]
}

package main

import (
	"fmt"
	"os"
	"strings"

	"github.com/pkg/errors"
)

func main() {
	err := errors.Errorf("request failed with status %d: %s", 500, "internal error")
	if err == nil {
		fmt.Fprintf(os.Stderr, "contract violation: errors.Errorf returned nil\n")
		os.Exit(1)
	}

	expectedMsg := "request failed with status 500: internal error"
	if err.Error() != expectedMsg {
		fmt.Fprintf(os.Stderr, "contract violation: expected message %q, got %q\n", expectedMsg, err.Error())
		os.Exit(1)
	}

	stackOutput := fmt.Sprintf("%+v", err)
	if !strings.Contains(stackOutput, "contract.go") {
		fmt.Fprintf(os.Stderr, "contract violation: stack trace does not contain source file: %s\n", stackOutput)
		os.Exit(1)
	}

	fmt.Printf("contract passed: errors.Errorf produces expected formatted error and stack trace\n")
}