fix: resolve the ?addr=:port shorthand against the primary host

Author: NotAFlightRisk

url.go

@@ -23,10 +23,11 @@ func ParseURL(str string) (opt ClientOption, err error) {
 	if err != nil {
 		return opt, err
 	}
+	fallbackHost := u.Host
 	parseAddr := func(hostport string) (host string, addr string) {
 		host, port, _ := net.SplitHostPort(hostport)
 		if host == "" {
-			host = u.Host
+			host = fallbackHost
 		}
 		if host == "" {
 			host = "localhost"
@@ -52,6 +53,7 @@ func ParseURL(str string) (opt ClientOption, err error) {
 	}
 	if opt.InitAddress == nil {
 		host, addr := parseAddr(u.Host)
+		fallbackHost = host
 		opt.InitAddress = []string{addr}
 		if opt.TLSConfig != nil {
 			opt.TLSConfig.ServerName = host

url_test.go

@@ -35,6 +35,12 @@ func TestParseURL(t *testing.T) {
 	if opt, err := ParseURL("redis://?addr=:6380&addr=:6381"); err != nil || opt.InitAddress[0] != "localhost:6379" || opt.InitAddress[1] != "localhost:6380" || opt.InitAddress[2] != "localhost:6381" {
 		t.Fatalf("unexpected %v %v", opt, err)
 	}
+	if opt, err := ParseURL("redis://cache:6379?addr=:6380"); err != nil || opt.InitAddress[0] != "cache:6379" || opt.InitAddress[1] != "cache:6380" {
+		t.Fatalf("unexpected %v %v", opt, err)
+	}
+	if opt, err := ParseURL("redis://[::1]:6379?addr=:6380"); err != nil || opt.InitAddress[0] != "[::1]:6379" || opt.InitAddress[1] != "[::1]:6380" {
+		t.Fatalf("unexpected %v %v", opt, err)
+	}
 	if opt, err := ParseURL("redis://myhost:1234"); err != nil || opt.InitAddress[0] != "myhost:1234" {
 		t.Fatalf("unexpected %v %v", opt, err)
 	}