[Elastic Agent] Cleaner output of inspect command (elastic#18405)

* no stack on inspect warnings

x-pack/elastic-agent/CHANGELOG.asciidoc

@@ -56,3 +56,4 @@
 - Do not require unnecessary configuration {pull}18003[18003]
 - Use nested objects so fleet can handle metadata correctly {pull}18234[18234]
 - Enable debug log level for Metricbeat and Filebeat when run under the Elastic Agent. {pull}17935[17935]
+- More clear output of inspect command {pull}18405[18405]

x-pack/elastic-agent/pkg/agent/application/introspect_config_cmd.go

@@ -53,7 +53,7 @@ func (c *IntrospectConfigCmd) introspectConfig() error {
 	if err != nil {
 		return err
 	} else if fleetConfig == nil {
-		return errors.New("no fleet config retrieved yet")
+		return fmt.Errorf("no fleet config retrieved yet")
 	}
 
 	return printMapStringConfig(fleetConfig)

x-pack/elastic-agent/pkg/agent/application/introspect_output_cmd.go

@@ -13,7 +13,6 @@ import (
 	"github.com/urso/ecslog/backend/layout"
 
 	"github.com/elastic/beats/v7/x-pack/elastic-agent/pkg/agent/application/filters"
-	"github.com/elastic/beats/v7/x-pack/elastic-agent/pkg/agent/errors"
 	"github.com/elastic/beats/v7/x-pack/elastic-agent/pkg/agent/program"
 	"github.com/elastic/beats/v7/x-pack/elastic-agent/pkg/config"
 	"github.com/elastic/beats/v7/x-pack/elastic-agent/pkg/core/logger"
@@ -69,7 +68,7 @@ func (c *IntrospectOutputCmd) introspectOutputs() error {
 	if err != nil {
 		return err
 	} else if fleetConfig == nil {
-		return errors.New("no fleet config retrieved yet")
+		return fmt.Errorf("no fleet config retrieved yet")
 	}
 
 	return listOutputsFromMap(l, fleetConfig)
@@ -122,7 +121,7 @@ func (c *IntrospectOutputCmd) introspectOutput() error {
 	if err != nil {
 		return err
 	} else if fleetConfig == nil {
-		return errors.New("no fleet config retrieved yet")
+		return fmt.Errorf("no fleet config retrieved yet")
 	}
 
 	return printOutputFromMap(l, c.output, c.program, fleetConfig)
@@ -153,16 +152,16 @@ func printOutputFromConfig(log *logger.Logger, output, programName string, cfg *
 		}
 
 		if !programFound {
-			fmt.Printf("program '%s' is not recognized within output '%s', try running `elastic-agent introspect output` to find available outputs.\n",
+			return fmt.Errorf("program '%s' is not recognized within output '%s', try running `elastic-agent introspect output` to find available outputs",
 				programName,
 				output)
 		}
+
 		return nil
 	}
 
-	fmt.Printf("output '%s' is not recognized, try running `elastic-agent introspect output` to find available outputs.\n", output)
+	return fmt.Errorf("output '%s' is not recognized, try running `elastic-agent introspect output` to find available outputs", output)
 
-	return nil
 }
 
 func printOutputFromMap(log *logger.Logger, output, programName string, cfg map[string]interface{}) error {

x-pack/elastic-agent/pkg/agent/errors/error.go

@@ -27,6 +27,11 @@ type agentError struct {
 	meta    map[string]interface{}
 }
 
+// Unwrap returns nested error.
+func (e agentError) Unwrap() error {
+	return e.err
+}
+
 // Error returns a string consisting of a message and originating error.
 func (e agentError) Error() string {
 	if e.msg != "" {