add better required subtool enforcing

gxutil/pm.go

@@ -299,12 +299,12 @@ func (pm *PM) InitPkg(dir, name, lang string, setup func(*Package)) error {
 }
 
 func CheckForHelperTools(lang string) {
-	_, err := exec.LookPath("gx-" + lang)
-	if err == nil {
+	p, err := getSubtoolPath(lang)
+	if err == nil && p != "" {
 		return
 	}
 
-	if strings.Contains(err.Error(), "file not found") {
+	if p == "" || strings.Contains(err.Error(), "file not found") {
 		Log("notice: no helper tool found for", lang)
 		return
 	}
@@ -615,6 +615,14 @@ func resolveDepName(pkg *Package, out interface{}, dir, name string, checked map
 
 	return ErrUnrecognizedName
 }
+func IsSubtoolInstalled(env string) (bool, error) {
+	p, err := getSubtoolPath(env)
+	if err != nil {
+		return false, err
+	}
+
+	return p != "", nil
+}
 
 func getSubtoolPath(env string) (string, error) {
 	if env == "" {

main.go

@@ -49,6 +49,16 @@ func LoadPackageFile(path string) (*gx.Package, error) {
 		pkg.GxVersion = gx.GxVersion
 	}
 
+	if pkg.SubtoolRequired {
+		found, err := gx.IsSubtoolInstalled(pkg.Language)
+		if err != nil {
+			return nil, err
+		}
+		if !found {
+			return nil, fmt.Errorf("package requires a subtool (gx-%s) and none was found.", pkg.Language)
+		}
+	}
+
 	return &pkg, nil
 }