Fix errcheck warnings in cmd/tools (#3729)

Author: MichaelSnowden

cmd/tools/copyright/licensegen.go

@@ -137,7 +137,10 @@ func (task *addLicenseHeaderTask) handleFile(path string, fileInfo os.FileInfo,
 	if err := scanner.Err(); err != nil {
 		return err
 	}
-	f.Close()
+	err = f.Close()
+	if err != nil {
+		return err
+	}
 
 	if strings.Contains(firstLine, licenseHeaderPrefix) {
 		return nil // file already has the copyright header

cmd/tools/rpcwrappers/main.go

@@ -52,22 +52,22 @@ type (
 
 var (
 	services = []service{
-		service{
+		{
 			name:            "frontend",
 			clientType:      reflect.TypeOf((*workflowservice.WorkflowServiceClient)(nil)),
 			clientGenerator: generateFrontendOrAdminClient,
 		},
-		service{
+		{
 			name:            "admin",
 			clientType:      reflect.TypeOf((*adminservice.AdminServiceClient)(nil)),
 			clientGenerator: generateFrontendOrAdminClient,
 		},
-		service{
+		{
 			name:            "history",
 			clientType:      reflect.TypeOf((*historyservice.HistoryServiceClient)(nil)),
 			clientGenerator: generateHistoryClient,
 		},
-		service{
+		{
 			name:            "matching",
 			clientType:      reflect.TypeOf((*matchingservice.MatchingServiceClient)(nil)),
 			clientGenerator: generateMatchingClient,
@@ -102,12 +102,17 @@ var (
 	}
 )
 
+func panicIfErr(err error) {
+	if err != nil {
+		panic(err)
+	}
+}
+
 func writeTemplatedCode(w io.Writer, service service, text string) {
-	t := template.Must(template.New("code").Parse(text))
-	t.Execute(w, map[string]string{
+	panicIfErr(template.Must(template.New("code").Parse(text)).Execute(w, map[string]string{
 		"ServiceName":        service.name,
 		"ServicePackagePath": service.clientType.Elem().PkgPath(),
-	})
+	}))
 }
 
 func pathToField(t reflect.Type, name string, path string, maxDepth int) string {
@@ -231,8 +236,7 @@ func writeTemplatedMethod(w io.Writer, service service, impl string, m reflect.M
 		}
 	}
 
-	t := template.Must(template.New("code").Parse(text))
-	t.Execute(w, fields)
+	panicIfErr(template.Must(template.New("code").Parse(text)).Execute(w, fields))
 }
 
 func writeTemplatedMethods(w io.Writer, service service, impl string, text string) {
@@ -412,12 +416,13 @@ func callWithFile(f func(io.Writer, service), service service, filename string,
 	if err != nil {
 		panic(err)
 	}
-	fmt.Fprintf(w, "%s\n// Code generated by cmd/tools/rpcwrappers. DO NOT EDIT.\n", licenseText)
-	f(w, service)
-	err = w.Close()
-	if err != nil {
+	defer func() {
+		panicIfErr(w.Close())
+	}()
+	if _, err := fmt.Fprintf(w, "%s\n// Code generated by cmd/tools/rpcwrappers. DO NOT EDIT.\n", licenseText); err != nil {
 		panic(err)
 	}
+	f(w, service)
 }
 
 func readLicenseFile(path string) string {