GitHub Action CI: Add Go source file format check (#6090)

https://github.com/XTLS/Xray-core/pull/6057#issuecomment-4364819830

And https://github.com/XTLS/Xray-core/pull/6149#issuecomment-4546876261

proxy/tun/stack_gvisor.go

@@ -69,7 +69,7 @@ func (t *stackGVisor) Start() error {
 	tcpForwarder := tcp.NewForwarder(ipStack, 0, 65535, func(r *tcp.ForwarderRequest) {
 		go func(r *tcp.ForwarderRequest) {
 			var wq waiter.Queue
-			var id = r.ID()
+			id := r.ID()
 
 			// Perform a TCP three-way handshake.
 			ep, err := r.CreateEndpoint(&wq)

proxy/tun/stack_gvisor_endpoint.go

@@ -68,7 +68,6 @@ func (e *LinkEndpoint) IsAttached() bool {
 }
 
 func (e *LinkEndpoint) Wait() {
-
 }
 
 func (e *LinkEndpoint) ARPHardwareType() header.ARPHardwareType {
@@ -91,7 +90,6 @@ func (e *LinkEndpoint) Close() {
 }
 
 func (e *LinkEndpoint) SetOnCloseAction(_ func()) {
-
 }
 
 func (e *LinkEndpoint) WritePackets(packetBufferList stack.PacketBufferList) (int, tcpip.Error) {

proxy/tun/tun_darwin.go

@@ -44,8 +44,10 @@ type DarwinTun struct {
 	ownsFd  bool // true for macOS (we created the fd), false for iOS (fd from system)
 }
 
-var _ Tun = (*DarwinTun)(nil)
-var _ GVisorDevice = (*DarwinTun)(nil)
+var (
+	_ Tun          = (*DarwinTun)(nil)
+	_ GVisorDevice = (*DarwinTun)(nil)
+)
 
 func NewTun(options *Config) (Tun, error) {
 	// Check if fd is provided via environment (iOS mode)

proxy/tun/tun_default.go

@@ -9,8 +9,7 @@ import (
 	"gvisor.dev/gvisor/pkg/tcpip/stack"
 )
 
-type DefaultTun struct {
-}
+type DefaultTun struct{}
 
 // DefaultTun implements Tun
 var _ Tun = (*DefaultTun)(nil)

proxy/tun/tun_freebsd.go

@@ -27,8 +27,10 @@ type FreeBSDTun struct {
 	mtu    uint32
 }
 
-var _ Tun = (*FreeBSDTun)(nil)
-var _ GVisorDevice = (*FreeBSDTun)(nil)
+var (
+	_ Tun          = (*FreeBSDTun)(nil)
+	_ GVisorDevice = (*FreeBSDTun)(nil)
+)
 
 // NewTun builds new tun interface handler
 func NewTun(options *Config) (Tun, error) {