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

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.Locator 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.Locator

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:sha256:0fd36fec3917e7b2b5e77900f2a8ea156494e9186c69e8db545439d5493e4461","contract":["errors.New returns an error implementing errors.Locator","errors.Locator.Location returns caller file name and positive line number for errors.New","errors.Wrap returns an error implementing errors.Locator","custom error type implementing errors.Locator is recognized by errors.Locator interface","errors.Details formats location from errors.Locator into output string","standard error does not implement errors.Locator"],"goal":"verify gopkg.in/errgo.v2/errors.Locator 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.Locator"]},"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.Locator"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

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"
)

// CustomLocatedError demonstrates a custom error type implementing errors.Locator.
type CustomLocatedError struct {
	msg  string
	file string
	line int
}

func (e *CustomLocatedError) Error() string {
	return e.msg
}

func (e *CustomLocatedError) Location() (file string, line int) {
	return e.file, e.line
}

func main() {
	// Standard error created with errgo records caller location and implements errors.Locator
	err := errors.New("sample failure")
	if loc, ok := err.(errors.Locator); ok {
		file, line := loc.Location()
		fmt.Printf("errgo error location: %s:%d\n", file, line)
	}

	// Custom error implementing errors.Locator
	custom := &CustomLocatedError{
		msg:  "custom failure",
		file: "main.go",
		line: 42,
	}
	if loc, ok := interface{}(custom).(errors.Locator); ok {
		file, line := loc.Location()
		fmt.Printf("custom error location: %s:%d\n", file, line)
	}
}

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

package main

import (
	stderrors "errors"
	"fmt"
	"os"
	"strings"

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

// customLocatedError implements errors.Locator for testing.
type customLocatedError struct {
	msg  string
	file string
	line int
}

func (e *customLocatedError) Error() string {
	return e.msg
}

func (e *customLocatedError) Location() (file string, line int) {
	return e.file, e.line
}

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

func runContractTests() error {
	// Assertion 1: errors.New returns an error implementing errors.Locator
	err := errors.New("failed operation")
	loc, ok := err.(errors.Locator)
	if !ok {
		return fmt.Errorf("expected errors.New to return an error implementing errors.Locator")
	}

	// Assertion 2: errors.Locator.Location returns caller file name and positive line number for errors.New
	file, line := loc.Location()
	if file == "" || line <= 0 {
		return fmt.Errorf("expected non-empty file and positive line, got %s:%d", file, line)
	}
	if !strings.HasSuffix(file, "contract.go") {
		return fmt.Errorf("expected location file to end with contract.go, got %s", file)
	}

	// Assertion 3: errors.Wrap returns an error implementing errors.Locator
	wrapped := errors.Wrap(err)
	wrapLoc, ok := wrapped.(errors.Locator)
	if !ok {
		return fmt.Errorf("expected errors.Wrap to return an error implementing errors.Locator")
	}
	wrapFile, wrapLine := wrapLoc.Location()
	if wrapFile == "" || wrapLine <= 0 {
		return fmt.Errorf("expected non-empty wrapped location, got %s:%d", wrapFile, wrapLine)
	}

	// Assertion 4: custom error type implementing errors.Locator is recognized by errors.Locator interface
	custom := &customLocatedError{
		msg:  "disk quota exceeded",
		file: "storage.go",
		line: 88,
	}
	customLoc, ok := interface{}(custom).(errors.Locator)
	if !ok {
		return fmt.Errorf("expected custom error to implement errors.Locator")
	}
	cFile, cLine := customLoc.Location()
	if cFile != "storage.go" || cLine != 88 {
		return fmt.Errorf("expected storage.go:88, got %s:%d", cFile, cLine)
	}

	// Assertion 5: errors.Details formats location from errors.Locator into output string
	details := errors.Details(custom)
	expectedDetail := "[\n\t{storage.go:88: disk quota exceeded}\n]"
	if details != expectedDetail {
		return fmt.Errorf("expected details %q, got %q", expectedDetail, details)
	}

	// Assertion 6: standard error does not implement errors.Locator
	stdErr := stderrors.New("standard error")
	if _, ok := stdErr.(errors.Locator); ok {
		return fmt.Errorf("expected standard error not to implement errors.Locator")
	}

	return nil
}