.circleci: Add config to test against go1.18

.circleci/config.yml

@@ -1,6 +1,6 @@
 version: 2.1
 orbs:
-  go: circleci/go@0.2.0
+  go: circleci/go@1.7.1
   prometheus: prometheus/prometheus@0.16.0
 jobs:
   test:
@@ -17,8 +17,7 @@ jobs:
         type: boolean
         default: true
     docker:
-      - image: circleci/golang:<< parameters.go_version >>
-    working_directory: /go/src/github.com/prometheus/client_golang
+      - image: cimg/go:<< parameters.go_version >>
     steps:
       - checkout
       - when:
@@ -59,4 +58,10 @@ workflows:
           name: go-1-17
           go_version: "1.17"
           run_lint: true
+      - test:
+          name: go-1-18
+          go_version: "1.18"
+          run_lint: true
+          # Style and unused/missing packages are only checked against
+          # the latest supported Go version.
           run_style_and_unused: true

.github/workflows/golangci-lint.yml

@@ -20,6 +20,7 @@ jobs:
       - name: install Go
         uses: actions/setup-go@v2
         with:
+          # golangci-lint is not read for Go 1.18 (https://github.com/golangci/golangci-lint/issues/2649)
           go-version: 1.17.x
       - name: Lint
         uses: golangci/golangci-lint-action@v3.1.0

prometheus/gen_go_collector_metrics_set.go

@@ -38,8 +38,10 @@ func main() {
 		log.Fatal("requires Go version (e.g. go1.17) as an argument")
 	}
 	toolVersion := runtime.Version()
-	if majorVersion := toolVersion[:strings.LastIndexByte(toolVersion, '.')]; majorVersion != os.Args[1] {
-		log.Fatalf("using Go version %q but expected Go version %q", majorVersion, os.Args[1])
+	mtv := majorVersion(toolVersion)
+	mv != majorVersion(os.Args[1])
+	if mtv != mv {
+		log.Fatalf("using Go version %q but expected Go version %q", mtv, mv)
 	}
 	version, err := parseVersion(os.Args[1])
 	if err != nil {
@@ -93,6 +95,10 @@ func parseVersion(s string) (goVersion, error) {
 	return goVersion(i), err
 }
 
+func majorVersion(v string) string {
+	return v[:strings.LastIndexByte(v, '.')]
+}
+
 func rmCardinality() int {
 	cardinality := 0