chore(lint): fix issues found in new golangci-lint

It looks like the GitHub Action doesn't have a pinned golangci-lint
version, so it's pulled in the latest (golangci-lint v1.54.0) which now
flags a few additional issues that it didn't previously.

Signed-off-by: Dominic Evans <dominic.evans@uk.ibm.com>

.golangci.yml

@@ -16,9 +16,8 @@ linters:
     - lll
     - misspell
     - nakedret
-    - structcheck
     - unparam
-    - varcheck
+    - unused
 
 linters-settings:
   dupl:

idgenerator/idgenerator_test.go

@@ -121,10 +121,9 @@ func TestRandomTimeStamped(t *testing.T) {
 
 	var latestTS uint64
 	for idx, traceID := range ids {
-		if new, old := traceID.High>>32, latestTS; new < old {
-			t.Errorf("[%d] expected a higher timestamp part in traceid but got: old: %d new: %d", idx, old, new)
+		if newVal, oldVal := traceID.High>>32, latestTS; newVal < oldVal {
+			t.Errorf("[%d] expected a higher timestamp part in traceid but got: old: %d new: %d", idx, oldVal, newVal)
 		}
 		latestTS = traceID.High >> 32
 	}
-
 }

middleware/http/client.go

@@ -108,7 +108,7 @@ func NewClient(tracer *zipkin.Tracer, options ...ClientOption) (*Client, error)
 }
 
 // DoWithAppSpan wraps http.Client's Do with tracing using an application span.
-func (c *Client) DoWithAppSpan(req *http.Request, name string) (res *http.Response, err error) {
+func (c *Client) DoWithAppSpan(req *http.Request, name string) (*http.Response, error) {
 	var parentContext model.SpanContext
 
 	if span := zipkin.SpanFromContext(req.Context()); span != nil {
@@ -120,13 +120,13 @@ func (c *Client) DoWithAppSpan(req *http.Request, name string) (res *http.Respon
 	zipkin.TagHTTPMethod.Set(appSpan, req.Method)
 	zipkin.TagHTTPPath.Set(appSpan, req.URL.Path)
 
-	res, err = c.Client.Do(
+	res, err := c.Do(
 		req.WithContext(zipkin.NewContext(req.Context(), appSpan)),
 	)
 	if err != nil {
 		zipkin.TagError.Set(appSpan, err.Error())
 		appSpan.Finish()
-		return
+		return res, err
 	}
 
 	if c.httpTrace {

reporter/amqp/amqp_test.go

@@ -77,19 +77,15 @@ func TestRabbitClose(t *testing.T) {
 	}
 }
 
-func setupRabbit(t *testing.T, address string) (conn *amqp.Connection, ch *amqp.Channel, close func()) {
+func setupRabbit(t *testing.T, address string) (*amqp.Connection, *amqp.Channel, func()) {
 	var err error
-	conn, err = amqp.Dial(address)
+	conn, err := amqp.Dial(address)
 	failOnError(t, err, "Failed to connect to RabbitMQ")
 
-	ch, err = conn.Channel()
+	ch, err := conn.Channel()
 	failOnError(t, err, "Failed to open a channel")
 
-	close = func() {
-		conn.Close()
-		ch.Close()
-	}
-	return
+	return conn, ch, func() { conn.Close(); ch.Close() }
 }
 
 func setupConsume(t *testing.T, ch *amqp.Channel) <-chan amqp.Delivery {
@@ -139,7 +135,7 @@ func testEqual(t *testing.T, want *model.SpanModel, have *model.SpanModel) {
 
 func makeNewSpan(methodName string, traceID, spanID, parentSpanID uint64, debug bool) *model.SpanModel {
 	timestamp := time.Now()
-	var parentID = new(model.ID)
+	parentID := new(model.ID)
 	if parentSpanID != 0 {
 		*parentID = model.ID(parentSpanID)
 	}