go.uber.org/multierr v1.11.0: Combine

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 go.uber.org/multierr.Combine in pkg:golang/go.uber.org/multierr@v1.11.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/go.uber.org/multierr@v1.11.0
Demonstrate these symbols/APIs:
  - go.uber.org/multierr.Combine

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:sha256:53216c78373058defba4d0e52396e034ccbe4a43333351b4729cdd399946a8b6","contract":["multierr.Combine returns nil when all arguments are nil or empty","multierr.Combine returns the single non-nil error when only one non-nil error is passed","multierr.Combine combines multiple distinct errors into a single error preserving error count and messages","multierr.Combine flattens nested combined errors into a single flat error slice"],"goal":"verify go.uber.org/multierr.Combine in pkg:golang/go.uber.org/multierr@v1.11.0","kind":"HOW","packages":["pkg:golang/go.uber.org/multierr@v1.11.0"],"schemaVersion":1,"symbols":["go.uber.org/multierr.Combine"]},"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/go.uber.org/multierr@v1.11.0"],"schemaVersion":1,"subject":"pkg:golang/go.uber.org/multierr@v1.11.0","symbols":["go.uber.org/multierr.Combine"],"verifierAdapter":"golang@1"}

module example.com/multierr-sample

go 1.26.6

require go.uber.org/multierr v1.11.0

github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5CcY=
github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
go.uber.org/multierr v1.11.0 h1:blXXJkSxSSfBVBlC76pxqeO+LN3aDfLQo+309xJstO0=
go.uber.org/multierr v1.11.0/go.mod h1:20+QtiLqy0Nd6FdQB9TLXag12DsQkrbs3htMFfDN80Y=
gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

package multierrsample

import (
	"go.uber.org/multierr"
)

// CombineErrors wraps multierr.Combine to combine multiple errors into a single error.
func CombineErrors(errs ...error) error {
	return multierr.Combine(errs...)
}

// InspectErrors returns all individual errors contained within a combined error.
func InspectErrors(err error) []error {
	return multierr.Errors(err)
}

{
  "schemaVersion": 1,
  "goal": "verify go.uber.org/multierr.Combine in pkg:golang/go.uber.org/multierr@v1.11.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/go.uber.org/multierr@v1.11.0"
  ],
  "symbols": [
    "go.uber.org/multierr.Combine"
  ]
}

package main

import (
	"errors"
	"fmt"
	"os"

	sample "example.com/multierr-sample"
	"go.uber.org/multierr"
)

func main() {
	// Assertion 1: multierr.Combine returns nil when all arguments are nil or empty
	if err := multierr.Combine(); err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: expected nil for empty Combine, got %v\n", err)
		os.Exit(1)
	}
	if err := multierr.Combine(nil, nil, nil); err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: expected nil for nil errors, got %v\n", err)
		os.Exit(1)
	}
	if err := sample.CombineErrors(nil, nil); err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: sample wrapper expected nil, got %v\n", err)
		os.Exit(1)
	}

	// Assertion 2: multierr.Combine returns the single non-nil error when only one non-nil error is passed
	errSingle := errors.New("single error")
	if got := multierr.Combine(nil, errSingle, nil); got != errSingle {
		fmt.Fprintf(os.Stderr, "FAIL: expected %v, got %v\n", errSingle, got)
		os.Exit(1)
	}
	if got := sample.CombineErrors(errSingle); got != errSingle {
		fmt.Fprintf(os.Stderr, "FAIL: sample wrapper expected %v, got %v\n", errSingle, got)
		os.Exit(1)
	}

	// Assertion 3: multierr.Combine combines multiple distinct errors into a single error preserving error count and messages
	err1 := errors.New("first error")
	err2 := errors.New("second error")
	err3 := errors.New("third error")
	combined := multierr.Combine(err1, err2, err3)
	if combined == nil {
		fmt.Fprintln(os.Stderr, "FAIL: expected non-nil combined error")
		os.Exit(1)
	}
	errs := multierr.Errors(combined)
	if len(errs) != 3 {
		fmt.Fprintf(os.Stderr, "FAIL: expected 3 errors, got %d\n", len(errs))
		os.Exit(1)
	}
	if errs[0] != err1 || errs[1] != err2 || errs[2] != err3 {
		fmt.Fprintf(os.Stderr, "FAIL: errors in slice do not match original errors\n")
		os.Exit(1)
	}
	sampleErrs := sample.InspectErrors(combined)
	if len(sampleErrs) != 3 {
		fmt.Fprintf(os.Stderr, "FAIL: sample InspectErrors expected 3 errors, got %d\n", len(sampleErrs))
		os.Exit(1)
	}

	// Assertion 4: multierr.Combine flattens nested combined errors into a single flat error slice
	err4 := errors.New("fourth error")
	nested := multierr.Combine(combined, err4)
	nestedErrs := multierr.Errors(nested)
	if len(nestedErrs) != 4 {
		fmt.Fprintf(os.Stderr, "FAIL: expected 4 errors after flattening, got %d\n", len(nestedErrs))
		os.Exit(1)
	}
	if nestedErrs[3] != err4 {
		fmt.Fprintf(os.Stderr, "FAIL: expected 4th error to match err4\n")
		os.Exit(1)
	}

	fmt.Println("PASS: all multierr.Combine contract assertions verified")
}