fix(plugin): nilness findings (#7556)

Enable nilness linter in govet.

Plugin-by-plugin rationale:

- plugin/transfer: reuse error instead of shadowing it inside the for
  loop by declaring "ret" outside of the loop
- plugin/view: remove redundant err check
- plugin/dnstap: avoid possible nil dereference in error reporting
  path in setup test
- plugin/forward: prevent nil deference or empty-slice dereference on
  error paths in setup test

Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>

.golangci.yml

@@ -31,6 +31,9 @@ linters:
       - legacy
       - std-error-handling
   settings:
+    govet:
+      enable:
+        - nilness
     revive:
       rules:
         - name: blank-imports

plugin/dnstap/setup_test.go

@@ -111,7 +111,7 @@ func TestMultiDnstap(t *testing.T) {
 	handlers := dnsserver.GetConfig(c).Handlers()
 	d1, ok := handlers[0].(*Dnstap)
 	if !ok {
-		t.Fatalf("expected first plugin to be Dnstap, got %v", reflect.TypeOf(d1.Next))
+		t.Fatalf("expected first plugin to be Dnstap, got %v", reflect.TypeOf(handlers[0]))
 	}
 
 	if d1.io.(*dio).endpoint != "dnstap1.sock" {

plugin/forward/setup_test.go

@@ -112,7 +112,6 @@ func TestSetupTLS(t *testing.T) {
 	for i, test := range tests {
 		c := caddy.NewTestController("dns", test.input)
 		fs, err := parseForward(c)
-		f := fs[0]
 
 		if test.shouldErr && err == nil {
 			t.Errorf("Test %d: expected error but found %s for input %s", i, err, test.input)
@@ -128,6 +127,8 @@ func TestSetupTLS(t *testing.T) {
 			}
 		}
 
+		f := fs[0]
+
 		if !test.shouldErr && test.expectedServerName != "" && test.expectedServerName != f.tlsConfig.ServerName {
 			t.Errorf("Test %d: expected: %q, actual: %q", i, test.expectedServerName, f.tlsConfig.ServerName)
 		}
@@ -314,7 +315,7 @@ func TestMultiForward(t *testing.T) {
 	handlers := dnsserver.GetConfig(c).Handlers()
 	f1, ok := handlers[0].(*Forward)
 	if !ok {
-		t.Fatalf("expected first plugin to be Forward, got %v", reflect.TypeOf(f1.Next))
+		t.Fatalf("expected first plugin to be Forward, got %v", reflect.TypeOf(handlers[0]))
 	}
 
 	if f1.from != "1st.example.org." {

plugin/transfer/notify.go

@@ -39,10 +39,11 @@ func (t *Transfer) Notify(zone string) error {
 
 func sendNotify(c *dns.Client, m *dns.Msg, s string) error {
 	var err error
+	var ret *dns.Msg
 
 	code := dns.RcodeServerFailure
 	for range 3 {
-		ret, _, err := c.Exchange(m, s)
+		ret, _, err = c.Exchange(m, s)
 		if err != nil {
 			continue
 		}

plugin/view/setup.go

@@ -52,9 +52,6 @@ func parse(c *caddy.Controller) (*View, error) {
 					return v, err
 				}
 				v.progs = append(v.progs, prog)
-				if err != nil {
-					return nil, err
-				}
 				continue
 			default:
 				return nil, c.Errf("unknown property '%s'", c.Val())