Print a friendly message if a tool is not available

See arduino#755

Author: cmaglie

Diff for: arduino/cores/tools.go

@@ -133,8 +133,10 @@ func (tr *ToolRelease) String() string {
 // RuntimeProperties returns the runtime properties for this tool
 func (tr *ToolRelease) RuntimeProperties() *properties.Map {
 	res := properties.NewMap()
-	res.Set("runtime.tools."+tr.Tool.Name+".path", tr.InstallDir.String())
-	res.Set("runtime.tools."+tr.Tool.Name+"-"+tr.Version.String()+".path", tr.InstallDir.String())
+	if tr.IsInstalled() {
+		res.Set("runtime.tools."+tr.Tool.Name+".path", tr.InstallDir.String())
+		res.Set("runtime.tools."+tr.Tool.Name+"-"+tr.Version.String()+".path", tr.InstallDir.String())
+	}
 	return res
 }
 

Diff for: commands/upload/upload.go

@@ -193,7 +193,11 @@ func runProgramAction(pm *packagemanager.PackageManager,
 	if requiredTools, err := pm.FindToolsRequiredForBoard(board); err == nil {
 		for _, requiredTool := range requiredTools {
 			logrus.WithField("tool", requiredTool).Info("Tool required for upload")
-			uploadProperties.Merge(requiredTool.RuntimeProperties())
+			if requiredTool.IsInstalled() {
+				uploadProperties.Merge(requiredTool.RuntimeProperties())
+			} else {
+				errStream.Write([]byte(fmt.Sprintf("Warning: tool '%s' is not installed. It might not be available for your OS.", requiredTool)))
+			}
 		}
 	}