build: Extract runCommand from main

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3160

build.go

@@ -167,32 +167,17 @@ func main() {
 
 	parseFlags()
 
-	switch goarch {
-	case "386", "amd64", "arm", "arm64", "ppc64", "ppc64le":
-		break
-	default:
-		log.Printf("Unknown goarch %q; proceed with caution!", goarch)
-	}
-
+	checkArchitecture()
 	goVersion, _ = checkRequiredGoVersion()
 
-	// Invoking build.go with no parameters at all is equivalent to "go run
-	// build.go install all" as that builds everything (incrementally),
+	// Invoking build.go with no parameters at all builds everything (incrementally),
 	// which is what you want for maximum error checking during development.
 	if flag.NArg() == 0 {
-		var tags []string
-		if noupgrade {
-			tags = []string{"noupgrade"}
-		}
-		install(targets["all"], tags)
-
-		vet("cmd", "lib")
-		lint("./cmd/...")
-		lint("./lib/...")
-		return
-	}
-
-	// Otherwise, with any command given but not a target, the target is
+		runCommand("install", targets["all"])
+		runCommand("vet", target{})
+		runCommand("lint", target{})
+	} else {
+		// with any command given but not a target, the target is
 		// "syncthing". So "go run build.go install" is "go run build.go install
 		// syncthing" etc.
 		targetName := "syncthing"
@@ -204,7 +189,20 @@ func main() {
 			log.Fatalln("Unknown target", target)
 		}
 
-	cmd := flag.Arg(0)
+		runCommand(flag.Arg(0), target)
+	}
+}
+
+func checkArchitecture() {
+	switch goarch {
+	case "386", "amd64", "arm", "arm64", "ppc64", "ppc64le":
+		break
+	default:
+		log.Printf("Unknown goarch %q; proceed with caution!", goarch)
+	}
+}
+
+func runCommand(cmd string, target target) {
 	switch cmd {
 	case "setup":
 		setup()