Apply go fix to simplify using modern features

This patch contains the result of running `go fix ./...`, which applies
simplifications that make use of modern language features.

There are no logic or behaviour changes.

test/util/conngen/conngen.go

@@ -1,5 +1,4 @@
 //go:build !coverage
-// +build !coverage
 
 // SMTP connection generator, for testing purposes.
 package main

test/util/coverhtml/coverhtml.go

@@ -1,5 +1,4 @@
 //go:build !coverage
-// +build !coverage
 
 // Generate an HTML visualization of a Go coverage profile.
 // Serves a similar purpose to "go tool cover -html", but has a different
@@ -25,7 +24,7 @@ var (
 	notes  = flag.String("notes", "", "notes to add at the beginning (HTML)")
 )
 
-func errorf(f string, a ...interface{}) {
+func errorf(f string, a ...any) {
 	fmt.Printf(f, a...)
 	os.Exit(1)
 }

test/util/fexp/fexp.go

@@ -1,5 +1,4 @@
 //go:build !coverage
-// +build !coverage
 
 // Fetch an URL, and check if the response matches what we expect.
 //
@@ -187,12 +186,12 @@ func mkTransport(caCert string) http.RoundTripper {
 	}
 }
 
-func fatalf(s string, a ...interface{}) {
+func fatalf(s string, a ...any) {
 	fmt.Fprintf(os.Stderr, s, a...)
 	os.Exit(1)
 }
 
-func errorf(s string, a ...interface{}) {
+func errorf(s string, a ...any) {
 	fmt.Fprintf(os.Stderr, s, a...)
 	exitCode = 1
 }

test/util/generate_cert/generate_cert.go

@@ -1,5 +1,4 @@
 //go:build !coverage
-// +build !coverage
 
 // Utility to generate self-signed certificates.
 // It generates a self-signed x509 certificate and key pair, and writes them
@@ -34,7 +33,7 @@ var (
 		"Should this cert be its own CA?")
 )
 
-func fatalf(f string, a ...interface{}) {
+func fatalf(f string, a ...any) {
 	fmt.Printf(f, a...)
 	os.Exit(1)
 }
@@ -71,8 +70,8 @@ func main() {
 		tmpl.IsCA = true
 	}
 
-	hosts := strings.Split(*host, ",")
-	for _, h := range hosts {
+	hosts := strings.SplitSeq(*host, ",")
+	for h := range hosts {
 		if ip := net.ParseIP(h); ip != nil {
 			tmpl.IPAddresses = append(tmpl.IPAddresses, ip)
 		} else {

test/util/loadgen/loadgen.go

@@ -1,5 +1,4 @@
 //go:build !coverage
-// +build !coverage
 
 // SMTP load generator, for testing purposes.
 package main

test/util/minidns/minidns.go

@@ -1,5 +1,4 @@
 //go:build !coverage
-// +build !coverage
 
 // minidns is a trivial DNS server used for testing.
 //
@@ -63,11 +62,9 @@ func main() {
 	srv.loadZones(zonesFile)
 
 	var wg sync.WaitGroup
-	wg.Add(1)
-	go func() {
-		defer wg.Done()
+	wg.Go(func() {
 		srv.listenAndServeUDP(*addr)
-	}()
+	})
 	go func() {
 		defer wg.Done()
 		srv.listenAndServeTCP(*addr)

test/util/smtpc/smtpc.go

@@ -101,7 +101,7 @@ func loadConfig() {
 	}
 	notnil(err)
 
-	for _, line := range strings.Split(string(data), "\n") {
+	for line := range strings.SplitSeq(string(data), "\n") {
 		k, v, ok := strings.Cut(line, " ")
 		if !ok {
 			continue