write out error log when PrepareGraphDefs returnes PluginFaultError

agent/agent.go

@@ -2,6 +2,7 @@ package agent
 
 import (
 	"context"
+	"errors"
 	"time"
 
 	"github.com/mackerelio/mackerel-agent/checks"
@@ -98,7 +99,11 @@ func (agent *Agent) CollectGraphDefsOfPlugins() []*mkr.GraphDefsParam {
 
 	for _, g := range agent.PluginGenerators {
 		p, err := g.PrepareGraphDefs()
-		if err != nil {
+
+		var faultError *metrics.PluginFaultError
+		if errors.As(err, &faultError) {
+			logger.Errorf("Failed to fetch meta information from plugin %v; seems that the plugin has a bug: %v", g, err)
+		} else if err != nil {
 			logger.Debugf("Failed to fetch meta information from plugin %v (non critical); seems that this plugin does not have meta information: %v", g, err)
 		}
 		if p != nil {