ci: add go vet to test stage (!99)

* Add `go vet` to the test stage of the Gitlab CI/CD pipeline
* Fix issues raised by `go vet`

https://gitlab.com/hectorjsmith/fail2ban-prometheus-exporter/-/merge_requests/99

.gitlab-ci.yml

@@ -19,6 +19,13 @@ format:
   script:
     - make check/fmt
 
+vet:
+  extends: .go_template
+  stage: test
+  allow_failure: true
+  script:
+    - make vet
+
 test:
   extends: .go_template
   stage: test

Makefile

@@ -20,6 +20,11 @@ update:
 test: download
 	go test ./... -v -race
 
+# Look for "suspicious constructs" in source code
+.PHONY: vet
+vet: download
+	go vet ./...
+
 # Format code
 .PHONY: fmt
 fmt: download

exporter.go

@@ -53,7 +53,7 @@ func main() {
 }
 
 func handleGracefulShutdown() {
-	var signals = make(chan os.Signal)
+	var signals = make(chan os.Signal, 1)
 
 	signal.Notify(signals, syscall.SIGTERM)
 	signal.Notify(signals, syscall.SIGINT)