syncs: delete WaitGroup and use sync.WaitGroup.Go in Go 1.25

Our own WaitGroup wrapper type was a prototype implementation
for the Go method on the standard sync.WaitGroup type.
Now that there is first-class support for Go,
we should migrate over to using it and delete syncs.WaitGroup.

Updates #cleanup
Updates tailscale/tailscale#16330

Change-Id: Ib52b10f9847341ce29b4ca0da927dc9321691235
Signed-off-by: Joe Tsai <joetsai@digital-static.net>

6 files changed, 9 insertions, 26 deletions

diff --git a/cmd/containerboot/egressservices.go b/cmd/containerboot/egressservices.go
index 71141f17a..64ca0a13a 100644
--- a/cmd/containerboot/egressservices.go
+++ b/cmd/containerboot/egressservices.go
@@ -18,6 +18,7 @@ import (
 	"reflect"
 	"strconv"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/fsnotify/fsnotify"
@@ -26,7 +27,6 @@ import (
 	"tailscale.com/kube/egressservices"
 	"tailscale.com/kube/kubeclient"
 	"tailscale.com/kube/kubetypes"
-	"tailscale.com/syncs"
 	"tailscale.com/tailcfg"
 	"tailscale.com/util/httpm"
 	"tailscale.com/util/linuxfw"
@@ -666,8 +666,7 @@ func (ep *egressProxy) waitTillSafeToShutdown(ctx context.Context, cfgs *egresss
 		return
 	}
 	log.Printf("Ensuring that cluster traffic for egress targets is no longer routed via this Pod...")
-	wg := syncs.WaitGroup{}
-
+	var wg sync.WaitGroup
 	for s, cfg := range *cfgs {
 		hep := cfg.HealthCheckEndpoint
 		if hep == "" {
diff --git a/cmd/tailscale/cli/file.go b/cmd/tailscale/cli/file.go
index 6f3aa40b5..e0879197e 100644
--- a/cmd/tailscale/cli/file.go
+++ b/cmd/tailscale/cli/file.go
@@ -20,6 +20,7 @@ import (
 	"path"
 	"path/filepath"
 	"strings"
+	"sync"
 	"sync/atomic"
 	"time"
 	"unicode/utf8"
@@ -32,7 +33,6 @@ import (
 	"tailscale.com/envknob"
 	"tailscale.com/ipn/ipnstate"
 	"tailscale.com/net/tsaddr"
-	"tailscale.com/syncs"
 	"tailscale.com/tailcfg"
 	tsrate "tailscale.com/tstime/rate"
 	"tailscale.com/util/quarantine"
@@ -176,7 +176,7 @@ func runCp(ctx context.Context, args []string) error {
 			log.Printf("sending %q to %v/%v/%v ...", name, target, ip, stableID)
 		}
 
-		var group syncs.WaitGroup
+		var group sync.WaitGroup
 		ctxProgress, cancelProgress := context.WithCancel(ctx)
 		defer cancelProgress()
 		if isatty.IsTerminal(os.Stderr.Fd()) {
diff --git a/cmd/tailscale/depaware.txt b/cmd/tailscale/depaware.txt
index b121a411f..02ffec0ea 100644
--- a/cmd/tailscale/depaware.txt
+++ b/cmd/tailscale/depaware.txt
@@ -140,7 +140,7 @@ tailscale.com/cmd/tailscale dependencies: (generated by github.com/tailscale/dep
      💣 tailscale.com/net/tshttpproxy                                from tailscale.com/clientupdate/distsign+
         tailscale.com/paths                                          from tailscale.com/client/local+
      💣 tailscale.com/safesocket                                     from tailscale.com/client/local+
-        tailscale.com/syncs                                          from tailscale.com/cmd/tailscale/cli+
+        tailscale.com/syncs                                          from tailscale.com/control/controlhttp+
         tailscale.com/tailcfg                                        from tailscale.com/client/local+
         tailscale.com/tempfork/spf13/cobra                           from tailscale.com/cmd/tailscale/cli/ffcomplete+
         tailscale.com/tka                                            from tailscale.com/client/local+
diff --git a/feature/taildrop/delete.go b/feature/taildrop/delete.go
index 0b7259879..8b03a125f 100644
--- a/feature/taildrop/delete.go
+++ b/feature/taildrop/delete.go
@@ -12,7 +12,6 @@ import (
 	"time"
 
 	"tailscale.com/ipn"
-	"tailscale.com/syncs"
 	"tailscale.com/tstime"
 	"tailscale.com/types/logger"
 )
@@ -33,7 +32,7 @@ type fileDeleter struct {
 	byName map[string]*list.Element
 
 	emptySignal chan struct{} // signal that the queue is empty
-	group       syncs.WaitGroup
+	group       sync.WaitGroup
 	shutdownCtx context.Context
 	shutdown    context.CancelFunc
 	fs          FileOps // must be used for all filesystem operations
diff --git a/syncs/syncs.go b/syncs/syncs.go
index cf0be919b..e85b474c9 100644
--- a/syncs/syncs.go
+++ b/syncs/syncs.go
@@ -402,19 +402,3 @@ func (m *Map[K, V]) Swap(key K, value V) (oldValue V) {
 	mak.Set(&m.m, key, value)
 	return oldValue
 }
-
-// WaitGroup is identical to [sync.WaitGroup],
-// but provides a Go method to start a goroutine.
-type WaitGroup struct{ sync.WaitGroup }
-
-// Go calls the given function in a new goroutine.
-// It automatically increments the counter before execution and
-// automatically decrements the counter after execution.
-// It must not be called concurrently with Wait.
-func (wg *WaitGroup) Go(f func()) {
-	wg.Add(1)
-	go func() {
-		defer wg.Done()
-		f()
-	}()
-}
diff --git a/syncs/syncs_test.go b/syncs/syncs_test.go
index 2439b6068..d99c3d1a9 100644
--- a/syncs/syncs_test.go
+++ b/syncs/syncs_test.go
@@ -7,6 +7,7 @@ import (
 	"context"
 	"io"
 	"os"
+	"sync"
 	"testing"
 	"time"
 
@@ -98,7 +99,7 @@ func TestMutexValue(t *testing.T) {
 		t.Errorf("Load = %v, want %v", v.Load(), now)
 	}
 
-	var group WaitGroup
+	var group sync.WaitGroup
 	var v2 MutexValue[int]
 	var sum int
 	for i := range 10 {
@@ -237,7 +238,7 @@ func TestMap(t *testing.T) {
 
 	t.Run("LoadOrStore", func(t *testing.T) {
 		var m Map[string, string]
-		var wg WaitGroup
+		var wg sync.WaitGroup
 		var ok1, ok2 bool
 		wg.Go(func() { _, ok1 = m.LoadOrStore("", "") })
 		wg.Go(func() { _, ok2 = m.LoadOrStore("", "") })