all: use set.Set consistently instead of map[T]struct{}

I didn't clean up the more idiomatic map[T]bool with true values, at
least yet.  I just converted the relatively awkward struct{}-valued
maps.

Updates #cleanup

Change-Id: I758abebd2bb1f64bc7a9d0f25c32298f4679c14f
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

util/set/set.go

@@ -10,6 +10,9 @@ type Set[T comparable] map[T]struct{}
 // Add adds e to the set.
 func (s Set[T]) Add(e T) { s[e] = struct{}{} }
 
+// Delete removes e from the set.
+func (s Set[T]) Delete(e T) { delete(s, e) }
+
 // Contains reports whether s contains e.
 func (s Set[T]) Contains(e T) bool {
 	_, ok := s[e]

util/winutil/svcdiag_windows.go

@@ -14,6 +14,7 @@ import (
 	"golang.org/x/sys/windows/svc"
 	"golang.org/x/sys/windows/svc/mgr"
 	"tailscale.com/types/logger"
+	"tailscale.com/util/set"
 )
 
 // LogSvcState obtains the state of the Windows service named rootSvcName and
@@ -78,7 +79,7 @@ func walkServices(rootSvcName string, callback walkSvcFunc) error {
 		}
 	}()
 
-	seen := make(map[string]struct{})
+	seen := set.Set[string]{}
 
 	for err == nil && len(deps) > 0 {
 		err = func() error {
@@ -87,7 +88,7 @@ func walkServices(rootSvcName string, callback walkSvcFunc) error {
 
 			deps = deps[:len(deps)-1]
 
-			seen[curSvc.Name] = struct{}{}
+			seen.Add(curSvc.Name)
 
 			curCfg, err := curSvc.Config()
 			if err != nil {
@@ -97,7 +98,7 @@ func walkServices(rootSvcName string, callback walkSvcFunc) error {
 			callback(curSvc, curCfg)
 
 			for _, depName := range curCfg.Dependencies {
-				if _, ok := seen[depName]; ok {
+				if seen.Contains(depName) {
 					continue
 				}