google.golang.org/appengine v1.2.0: MultiError, MultiError.Error

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 google.golang.org/appengine.MultiError in pkg:golang/google.golang.org/appengine@v1.2.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/google.golang.org/appengine@v1.2.0
Demonstrate these symbols/APIs:
  - google.golang.org/appengine.MultiError

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:sha256:9c47b2a9b8da6bc4cc95fd6b4859c7d4a916d3c100bf30707c9f870d54fe4110","contract":["appengine.MultiError with zero non-nil errors returns \"(0 errors)\" from Error()","appengine.MultiError with exactly one non-nil error returns that error's Error() string unchanged","appengine.MultiError with two non-nil errors returns \"\u003cfirst\u003e (and 1 other error)\"","appengine.MultiError with N\u003e2 non-nil errors returns \"\u003cfirst\u003e (and \u003cN-1\u003e other errors)\""],"goal":"verify google.golang.org/appengine.MultiError in pkg:golang/google.golang.org/appengine@v1.2.0","kind":"HOW","packages":["pkg:golang/google.golang.org/appengine@v1.2.0"],"schemaVersion":1,"symbols":["google.golang.org/appengine.MultiError","google.golang.org/appengine.MultiError.Error"]},"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/google.golang.org/appengine@v1.2.0"],"schemaVersion":1,"subject":"pkg:golang/google.golang.org/appengine@v1.2.0","symbols":["google.golang.org/appengine.MultiError","google.golang.org/appengine.MultiError.Error"],"verifierAdapter":"golang@1"}

module sample

go 1.26.6

require google.golang.org/appengine v1.2.0

require (
	github.com/golang/protobuf v1.2.0 // indirect
	golang.org/x/net v0.0.0-20180724234803-3673e40ba225 // indirect
	golang.org/x/sync v0.24.0 // indirect
)

github.com/golang/protobuf v1.2.0 h1:P3YflyNX/ehuJFLhxviNdFxQPkGK5cDcApsge1SqnvM=
github.com/golang/protobuf v1.2.0/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
golang.org/x/net v0.0.0-20180724234803-3673e40ba225 h1:kNX+jCowfMYzvlSvJu5pQWEmyWFrBXJ3PBy10xKMXK8=
golang.org/x/net v0.0.0-20180724234803-3673e40ba225/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
golang.org/x/sync v0.24.0 h1:iqiDrGoDgyuvAKrhLQthUEzU/R378N78gXbBjxed7oA=
golang.org/x/sync v0.24.0/go.mod h1:sUUOizhqBxiL6pEWpqNLUiaJn1ShEbZ6BBqskPbjZm0=
golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
google.golang.org/appengine v1.2.0 h1:S0iUepdCWODXRvtE+gcRDd15L+k+k1AiHlMiMjefH24=
google.golang.org/appengine v1.2.0/go.mod h1:xpcJRLb0r/rnEns0DIKYYv+WjYCduHsrkT7/EB5XEv4=

{
  "schemaVersion": 1,
  "goal": "verify google.golang.org/appengine.MultiError in pkg:golang/google.golang.org/appengine@v1.2.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/google.golang.org/appengine@v1.2.0"
  ],
  "symbols": [
    "google.golang.org/appengine.MultiError"
  ]
}

package main

import (
	"errors"
	"os"

	"google.golang.org/appengine"
)

func main() {
	var empty appengine.MultiError
	if empty.Error() != "(0 errors)" {
		os.Exit(1)
	}

	allNil := appengine.MultiError{nil, nil}
	if allNil.Error() != "(0 errors)" {
		os.Exit(1)
	}

	single := appengine.MultiError{nil, errors.New("first failure"), nil}
	if single.Error() != "first failure" {
		os.Exit(1)
	}

	two := appengine.MultiError{errors.New("first failure"), nil, errors.New("second failure")}
	if two.Error() != "first failure (and 1 other error)" {
		os.Exit(1)
	}

	three := appengine.MultiError{
		errors.New("first failure"),
		errors.New("second failure"),
		errors.New("third failure"),
	}
	if three.Error() != "first failure (and 2 other errors)" {
		os.Exit(1)
	}

	var errIface error = two
	if errIface.Error() != "first failure (and 1 other error)" {
		os.Exit(1)
	}
}