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

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:sha256:7d37737f17a26d17106a63e6e206cb9d3530ffd86126e674d677877b80b81688","contract":["errors.New creates an error value returning the exact provided message string from Error()","errors.New creates distinct error values with unequal pointers for identical message strings","errors.New captures a stack trace at the call site accessible via the StackTrace() method","errors.New formats with %s and %v to output only the error message","errors.New formats with %+v to output the error message followed by the stack trace frames"],"goal":"verify github.com/pkg/errors.New 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.New"]},"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.New"],"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"
)

// validateInput checks if the input is valid, returning an error created by errors.New.
func validateInput(input string) error {
	if input == "" {
		return errors.New("input must not be empty")
	}
	return nil
}

func main() {
	err := validateInput("")
	if err != nil {
		fmt.Printf("Validation error: %v\n", err)
		fmt.Printf("Error with stack trace:\n%+v\n", err)
	}
}

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

package main

import (
	"fmt"
	"os"
	"strings"

	"github.com/pkg/errors"
)

type stackTracer interface {
	StackTrace() errors.StackTrace
}

func main() {
	if err := runContract(); err != nil {
		fmt.Fprintf(os.Stderr, "Contract verification failed: %v\n", err)
		os.Exit(1)
	}
	fmt.Println("All github.com/pkg/errors.New contract assertions passed successfully.")
}

func runContract() error {
	// 1. errors.New creates an error value returning the exact provided message string from Error()
	msg := "failed to perform operation"
	err := errors.New(msg)
	if err == nil {
		return fmt.Errorf("expected errors.New to return a non-nil error")
	}
	if err.Error() != msg {
		return fmt.Errorf("expected Error() to return %q, got %q", msg, err.Error())
	}

	emptyErr := errors.New("")
	if emptyErr.Error() != "" {
		return fmt.Errorf("expected Error() for empty message to return %q, got %q", "", emptyErr.Error())
	}

	// 2. errors.New creates distinct error values with unequal pointers for identical message strings
	err1 := errors.New("identical message")
	err2 := errors.New("identical message")
	if err1 == err2 {
		return fmt.Errorf("expected distinct pointers for consecutive errors.New calls, but err1 == err2")
	}

	// 3. errors.New captures a stack trace at the call site accessible via the StackTrace() method
	tracer, ok := err.(stackTracer)
	if !ok {
		return fmt.Errorf("expected error returned by errors.New to implement stackTracer")
	}
	frames := tracer.StackTrace()
	if len(frames) == 0 {
		return fmt.Errorf("expected non-empty stack trace frames")
	}

	// 4. errors.New formats with %s and %v to output only the error message
	formattedS := fmt.Sprintf("%s", err)
	if formattedS != msg {
		return fmt.Errorf("expected %%s to format as %q, got %q", msg, formattedS)
	}
	formattedV := fmt.Sprintf("%v", err)
	if formattedV != msg {
		return fmt.Errorf("expected %%v to format as %q, got %q", msg, formattedV)
	}

	// 5. errors.New formats with %+v to output the error message followed by the stack trace frames
	formattedPlusV := fmt.Sprintf("%+v", err)
	if !strings.HasPrefix(formattedPlusV, msg) {
		return fmt.Errorf("expected %%+v to start with message %q, got %q", msg, formattedPlusV)
	}
	if !strings.Contains(formattedPlusV, "contract.go") {
		return fmt.Errorf("expected %%+v to contain source file name 'contract.go', got %q", formattedPlusV)
	}

	return nil
}