go.uber.org/multierr v1.5.0: Combine, Append, AppendInto

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 pkg:golang/go.uber.org/multierr@v1.5.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/go.uber.org/multierr@v1.5.0

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.

package sample

import (
	"errors"
	"testing"

	"go.uber.org/multierr"
)

func TestCombineErrors(t *testing.T) {
	// Combining nil errors produces nil
	if err := multierr.Combine(nil, nil); err != nil {
		t.Fatalf("expected nil when combining nil errors, got %v", err)
	}

	// Combining a single error returns that error
	singleErr := errors.New("single failure")
	if err := multierr.Combine(singleErr, nil); err != singleErr {
		t.Fatalf("expected single error preserved, got %v", err)
	}

	// Combining multiple errors merges them
	err1 := errors.New("first error")
	err2 := errors.New("second error")
	combined := multierr.Combine(err1, err2)
	if combined == nil {
		t.Fatal("expected combined error to be non-nil")
	}

	errList := multierr.Errors(combined)
	if len(errList) != 2 {
		t.Fatalf("expected 2 errors, got %d", len(errList))
	}
	if errList[0] != err1 || errList[1] != err2 {
		t.Fatalf("unexpected errors in combined list: %v", errList)
	}

	// Test ProcessBatch helper
	batchErr := ProcessBatch([]func() error{
		func() error { return nil },
		func() error { return errors.New("op1 failed") },
		func() error { return errors.New("op2 failed") },
	})
	if batchErr == nil {
		t.Fatal("expected batch error to be non-nil")
	}
	if len(multierr.Errors(batchErr)) != 2 {
		t.Fatalf("expected 2 errors from batch, got %d", len(multierr.Errors(batchErr)))
	}
}

func TestAppendErrors(t *testing.T) {
	var baseErr error

	// Appending nil to nil remains nil
	baseErr = multierr.Append(baseErr, nil)
	if baseErr != nil {
		t.Fatalf("expected nil error after appending nil, got %v", baseErr)
	}

	// Appending error to nil sets the error
	err1 := errors.New("step 1 failed")
	baseErr = multierr.Append(baseErr, err1)
	if baseErr != err1 {
		t.Fatalf("expected baseErr to be err1, got %v", baseErr)
	}

	// Appending second error creates multierr
	err2 := errors.New("step 2 failed")
	baseErr = multierr.Append(baseErr, err2)
	if len(multierr.Errors(baseErr)) != 2 {
		t.Fatalf("expected 2 errors after append, got %d", len(multierr.Errors(baseErr)))
	}

	// Test Pipeline helper
	pipelineErr := Pipeline([]func() error{
		func() error { return errors.New("step A") },
		func() error { return nil },
		func() error { return errors.New("step B") },
	})
	if len(multierr.Errors(pipelineErr)) != 2 {
		t.Fatalf("expected 2 errors from pipeline, got %d", len(multierr.Errors(pipelineErr)))
	}
}

func TestAppendInto(t *testing.T) {
	var accumulated error

	// Appending nil returns false and does not change error
	appended := multierr.AppendInto(&accumulated, nil)
	if appended || accumulated != nil {
		t.Fatalf("expected false and nil error on nil append, got appended=%v, err=%v", appended, accumulated)
	}

	// Appending non-nil returns true and modifies pointer
	err1 := errors.New("validation failed")
	appended = multierr.AppendInto(&accumulated, err1)
	if !appended || accumulated != err1 {
		t.Fatalf("expected true and err1, got appended=%v, err=%v", appended, accumulated)
	}

	// Appending another error modifies pointer to combined error
	err2 := errors.New("write failed")
	appended = multierr.AppendInto(&accumulated, err2)
	if !appended || len(multierr.Errors(accumulated)) != 2 {
		t.Fatalf("expected true and 2 errors, got appended=%v, count=%d", appended, len(multierr.Errors(accumulated)))
	}

	// Test CollectErrors helper
	var targetErr error
	hasErr := CollectErrors(&targetErr,
		func() error { return nil },
		func() error { return errors.New("action error") },
	)
	if !hasErr || targetErr == nil {
		t.Fatalf("expected hasErr=true and non-nil targetErr")
	}
}

func TestErrorsExtraction(t *testing.T) {
	// Inspect empty error
	if len(InspectErrors(nil)) != 0 {
		t.Fatal("expected 0 messages for nil error")
	}

	// Inspect single error
	single := errors.New("single error")
	msgs := InspectErrors(single)
	if len(msgs) != 1 || msgs[0] != "single error" {
		t.Fatalf("unexpected inspect result for single error: %v", msgs)
	}

	// Inspect combined errors
	combined := multierr.Combine(
		errors.New("err 1"),
		errors.New("err 2"),
		errors.New("err 3"),
	)
	msgs = InspectErrors(combined)
	if len(msgs) != 3 {
		t.Fatalf("expected 3 messages, got %d: %v", len(msgs), msgs)
	}
	if msgs[0] != "err 1" || msgs[1] != "err 2" || msgs[2] != "err 3" {
		t.Fatalf("unexpected messages: %v", msgs)
	}
}

{"case":{"caseId":"case:sha256:d8dac3e1e8a2eb6814a28e98a245ad65edee595d48485f87556b2c71e7a157e8","contract":["multierr.Combine merges multiple errors into a single error preserving all non-nil errors","multierr.Append appends a secondary error onto a primary error","multierr.AppendInto appends an error into a pointer destination and reports whether an error was added","multierr.Errors inspects and extracts the underlying slice of errors from a combined error"],"goal":"verify pkg:golang/go.uber.org/multierr@v1.5.0","kind":"HOW","packages":["pkg:golang/go.uber.org/multierr@v1.5.0"],"schemaVersion":1,"symbols":["multierr.Combine","multierr.Append","multierr.AppendInto","multierr.Errors"]},"contractCommand":["go","test","./..."],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","language":"go","libc":"glibc","libcVersion":"2.39","moduleSystem":"go.mod","os":"linux","osVersionBucket":"24","packageManager":"go","runtime":"go","runtimeVersion":"1.26.6","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/go.uber.org/multierr@v1.5.0"],"schemaVersion":1,"subject":"pkg:golang/go.uber.org/multierr@v1.5.0","symbols":["multierr.Combine","multierr.Append","multierr.AppendInto","multierr.Errors"],"verifierAdapter":"golang@1"}

module sample

go 1.26.6

require go.uber.org/multierr v1.5.0

require go.uber.org/atomic v1.6.0 // indirect

github.com/BurntSushi/toml v0.3.1 h1:WXkYYl6Yr3qBf1K79EBnL4mak0OimBfB0XUf9Vl28OQ=
github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
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/google/renameio v0.1.0/go.mod h1:KWCgfxg9yswjAJkECMjeO8J8rahYeXnNhOm40UhjYkI=
github.com/kisielk/gotool v1.0.0/go.mod h1:XhKaO+MFFWcvkIS/tQcRk01m1F5IRFswLeQ+oQHNcck=
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=
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/rogpeppe/go-internal v1.3.0/go.mod h1:M8bDsm7K2OlrFYOpmOWEs/qY81heoFRclV5y23lUDJ4=
github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
github.com/stretchr/testify v1.3.0 h1:TivCn/peBQ7UY8ooIcPgZFpTNSz0Q2U6UrFlUfqbe0Q=
github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
go.uber.org/atomic v1.6.0 h1:Ezj3JGmsOnG1MoRWQkPBsKLe9DwWD9QeXzTRzzldNVk=
go.uber.org/atomic v1.6.0/go.mod h1:sABNBOSYdrvTF6hTgEIbc7YasKWGhgEQZyfxyTvoXHQ=
go.uber.org/multierr v1.5.0 h1:KCa4XfM8CWFCpxXRGok+Q0SS/0XBhMDbHHGABQLvD2A=
go.uber.org/multierr v1.5.0/go.mod h1:FeouvMocqHpRaaGuG9EjoKcStLC43Zu/fmqdUMPcKYU=
go.uber.org/tools v0.0.0-20190618225709-2cfd321de3ee h1:0mgffUl7nfd+FpvXMVz4IDEaUSmT1ysygQC7qYo7sG4=
go.uber.org/tools v0.0.0-20190618225709-2cfd321de3ee/go.mod h1:vJERXedbb3MVM5f9Ejo0C68/HhF8uaILCdgjnY+goOA=
golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
golang.org/x/crypto v0.0.0-20190510104115-cbcb75029529/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
golang.org/x/lint v0.0.0-20190930215403-16217165b5de h1:5hukYrvBGR8/eNkX5mdUezrA6JiaEZDtJb9Ei+1LlBs=
golang.org/x/lint v0.0.0-20190930215403-16217165b5de/go.mod h1:6SW0HCj/g11FgYtHlgUYUwCkIfeOF89ocIRzGO/8vkc=
golang.org/x/mod v0.0.0-20190513183733-4bf6d317e70e/go.mod h1:mXi4GBBbnImb6dmsKGUJ2LatrhH/nqhxcFungHvyanc=
golang.org/x/net v0.0.0-20190311183353-d8887717615a/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
golang.org/x/tools v0.0.0-20190311212946-11955173bddd/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
golang.org/x/tools v0.0.0-20190621195816-6e04913cbbac/go.mod h1:/rFqwRUd4F7ZHNgwSSTFct+R/Kf4OFW1sUzUTQQTgfc=
golang.org/x/tools v0.0.0-20191029041327-9cc4af7d6b2c/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
golang.org/x/tools v0.0.0-20191029190741-b9c20aec41a5 h1:hKsoRgsbwY1NafxrwTs+k64bikrLBkAgPir1TNCj3Zs=
golang.org/x/tools v0.0.0-20191029190741-b9c20aec41a5/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
gopkg.in/errgo.v2 v2.1.0/go.mod h1:hNsd1EY+bozCKY1Ytp96fpM3vjJbqLJn88ws8XvfDNI=
honnef.co/go/tools v0.0.1-2019.2.3 h1:3JgtbtFHMiCmsznwGVTUWbgGov+pVqnlf1dEJTNAXeM=
honnef.co/go/tools v0.0.1-2019.2.3/go.mod h1:a3bituU0lyd329TUQxRnasdCoJDkEUEAqEt0JzvZhAg=

package sample

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

// ProcessBatch executes multiple operations and combines any returned errors into a single error.
func ProcessBatch(operations []func() error) error {
	var errs []error
	for _, op := range operations {
		if err := op(); err != nil {
			errs = append(errs, err)
		}
	}
	return multierr.Combine(errs...)
}

// Pipeline executes a sequence of steps, accumulating any errors encountered.
func Pipeline(steps []func() error) error {
	var combined error
	for _, step := range steps {
		if err := step(); err != nil {
			combined = multierr.Append(combined, err)
		}
	}
	return combined
}

// CollectErrors invokes actions and records errors directly into the target accumulator.
func CollectErrors(target *error, actions ...func() error) bool {
	var hadError bool
	for _, action := range actions {
		if multierr.AppendInto(target, action()) {
			hadError = true
		}
	}
	return hadError
}

// InspectErrors returns all individual error messages from a potentially combined multierr.
func InspectErrors(err error) []string {
	var messages []string
	for _, subErr := range multierr.Errors(err) {
		if subErr != nil {
			messages = append(messages, subErr.Error())
		}
	}
	return messages
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:golang/go.uber.org/multierr@v1.5.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/go.uber.org/multierr@v1.5.0"
  ]
}