github.com/sourcegraph/conc v0.3.1-0.20240121214520-5f936abd7ae8: WaitGroup

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/sourcegraph/conc.WaitGroup in pkg:golang/github.com/sourcegraph/conc@v0.3.1-0.20240121214520-5f936abd7ae8
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/sourcegraph/conc@v0.3.1-0.20240121214520-5f936abd7ae8
Demonstrate these symbols/APIs:
  - github.com/sourcegraph/conc.WaitGroup

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:sha256:746d73223d609227d1559aa176ce28bcbc27266a3433d4666c1b29c1af602d2d","contract":["conc.NewWaitGroup initializes a valid WaitGroup pointer","WaitGroup.Go executes concurrent tasks and Wait blocks until all complete","WaitGroup.Wait propagates panics from spawned goroutines to the caller","WaitGroup.WaitAndRecover catches panics from child goroutines without re-panicking","WaitGroup.WaitAndRecover returns nil when all child goroutines finish successfully"],"goal":"verify github.com/sourcegraph/conc.WaitGroup in pkg:golang/github.com/sourcegraph/conc@v0.3.1-0.20240121214520-5f936abd7ae8","kind":"HOW","packages":["pkg:golang/github.com/sourcegraph/conc@v0.3.1-0.20240121214520-5f936abd7ae8"],"schemaVersion":1,"symbols":["github.com/sourcegraph/conc.WaitGroup"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","language":"go","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","packageManagerVersion":"1.26.6","runtime":"go","runtimeVersion":"1.26.6","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/github.com/sourcegraph/conc@v0.3.1-0.20240121214520-5f936abd7ae8"],"schemaVersion":1,"subject":"pkg:golang/github.com/sourcegraph/conc@v0.3.1-0.20240121214520-5f936abd7ae8","symbols":["github.com/sourcegraph/conc.WaitGroup"],"verifierAdapter":"golang@1"}

module sample

go 1.26.6

require github.com/sourcegraph/conc v0.3.1-0.20240121214520-5f936abd7ae8

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/sourcegraph/conc v0.3.1-0.20240121214520-5f936abd7ae8 h1:+jumHNA0Wrelhe64i8F6HNlS8pkoyMv5sreGx2Ry5Rw=
github.com/sourcegraph/conc v0.3.1-0.20240121214520-5f936abd7ae8/go.mod h1:3n1Cwaq1E1/1lhQhtRK2ts/ZwZEhjcQeJQ1RuC6Q/8U=
github.com/stretchr/testify v1.8.1 h1:w7B6lhMri9wdJUVmEZPGGhZzrYTPvgJArz7wNPgYKsk=
github.com/stretchr/testify v1.8.1/go.mod h1:w2LPCIKwWwSfY2zedu0+kehJoqGctiVI29o6fzry7u4=
gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

package main

import (
	"fmt"
	"sync/atomic"

	"github.com/sourcegraph/conc"
)

func main() {
	// 1. Basic concurrent task execution with WaitGroup
	var wg conc.WaitGroup
	var counter atomic.Int64

	for i := 0; i < 5; i++ {
		wg.Go(func() {
			counter.Add(1)
		})
	}
	wg.Wait()
	fmt.Printf("Completed %d concurrent tasks\n", counter.Load())

	// 2. Catching panics with WaitAndRecover
	var recoverWg conc.WaitGroup
	recoverWg.Go(func() {
		panic("task execution error")
	})

	recovered := recoverWg.WaitAndRecover()
	if recovered != nil {
		fmt.Printf("Caught panic via WaitAndRecover: %v\n", recovered.Value)
	}

	fmt.Println("conc.WaitGroup sample completed successfully.")
}

{
  "schemaVersion": 1,
  "goal": "verify github.com/sourcegraph/conc.WaitGroup in pkg:golang/github.com/sourcegraph/conc@v0.3.1-0.20240121214520-5f936abd7ae8",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/sourcegraph/conc@v0.3.1-0.20240121214520-5f936abd7ae8"
  ],
  "symbols": [
    "github.com/sourcegraph/conc.WaitGroup"
  ]
}

package main

import (
	"errors"
	"fmt"
	"os"
	"sync/atomic"

	"github.com/sourcegraph/conc"
	"github.com/sourcegraph/conc/panics"
)

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

func runContractTests() error {
	// 1. conc.NewWaitGroup initializes a valid WaitGroup pointer
	{
		wg := conc.NewWaitGroup()
		if wg == nil {
			return errors.New("conc.NewWaitGroup returned nil")
		}
	}

	// 2. WaitGroup.Go executes concurrent tasks and Wait blocks until all complete
	{
		var wg conc.WaitGroup
		var counter atomic.Int64
		numTasks := 20
		for i := 0; i < numTasks; i++ {
			wg.Go(func() {
				counter.Add(1)
			})
		}
		wg.Wait()
		if got := counter.Load(); got != int64(numTasks) {
			return fmt.Errorf("expected counter %d, got %d", numTasks, got)
		}
	}

	// 3. WaitGroup.Wait propagates panics from spawned goroutines to the caller
	{
		var wg conc.WaitGroup
		wg.Go(func() {
			panic("panic in child goroutine")
		})

		var panicked bool
		var panicVal any
		func() {
			defer func() {
				if r := recover(); r != nil {
					panicked = true
					panicVal = r
				}
			}()
			wg.Wait()
		}()

		if !panicked {
			return errors.New("expected WaitGroup.Wait to propagate panic, but it did not panic")
		}
		if rec, ok := panicVal.(*panics.Recovered); ok {
			if rec.Value != "panic in child goroutine" {
				return fmt.Errorf("expected panic value %q, got %v", "panic in child goroutine", rec.Value)
			}
		} else if panicVal != "panic in child goroutine" {
			return fmt.Errorf("unexpected panic value type or content: %v", panicVal)
		}
	}

	// 4. WaitGroup.WaitAndRecover catches panics from child goroutines without re-panicking
	{
		var wg conc.WaitGroup
		wg.Go(func() {
			panic("handled panic")
		})

		recovered := wg.WaitAndRecover()
		if recovered == nil {
			return errors.New("expected WaitAndRecover to return a non-nil Recovered object")
		}
		if recovered.Value != "handled panic" {
			return fmt.Errorf("expected recovered value %q, got %v", "handled panic", recovered.Value)
		}
	}

	// 5. WaitGroup.WaitAndRecover returns nil when all child goroutines finish successfully
	{
		var wg conc.WaitGroup
		var done atomic.Bool
		wg.Go(func() {
			done.Store(true)
		})

		recovered := wg.WaitAndRecover()
		if recovered != nil {
			return fmt.Errorf("expected nil recovered panic on clean run, got %v", recovered)
		}
		if !done.Load() {
			return errors.New("expected task to complete before WaitAndRecover returned")
		}
	}

	return nil
}