Disable logging by default

The log output is not of interest to the ordinary users, so it should only be enabled when one of the logging
configuration environment variables is set.

Author: per1234

configuration/configuration.go

@@ -56,12 +56,15 @@ func Initialize(flags *pflag.FlagSet, projectPaths []string) error {
 		}
 	}
 
+	logrus.SetOutput(defaultLogOutput)
+
 	if logFormatString, ok := os.LookupEnv("ARDUINO_CHECK_LOG_FORMAT"); ok {
 		logFormat, err := logFormatFromString(logFormatString)
 		if err != nil {
 			return fmt.Errorf("--log-format flag value %s not valid", logFormatString)
 		}
 		logrus.SetFormatter(logFormat)
+		logrus.SetOutput(os.Stderr) // Enable log output.
 	}
 
 	if logLevelString, ok := os.LookupEnv("ARDUINO_CHECK_LOG_LEVEL"); ok {
@@ -70,8 +73,7 @@ func Initialize(flags *pflag.FlagSet, projectPaths []string) error {
 			return fmt.Errorf("--log-level flag value %s not valid", logLevelString)
 		}
 		logrus.SetLevel(logLevel)
-	} else {
-		logrus.SetLevel(defaultLogLevel)
+		logrus.SetOutput(os.Stderr) // Enable log output.
 	}
 
 	superprojectTypeFilterString, _ := flags.GetString("project-type")

configuration/configuration_test.go

@@ -120,7 +120,6 @@ func TestInitializeLogFormat(t *testing.T) {
 
 func TestInitializeLogLevel(t *testing.T) {
 	require.Nil(t, Initialize(test.ConfigurationFlags(), projectPaths))
-	assert.Equal(t, defaultLogLevel, logrus.GetLevel(), "Default level")
 
 	os.Setenv("ARDUINO_CHECK_LOG_LEVEL", "foo")
 	assert.Error(t, Initialize(test.ConfigurationFlags(), projectPaths), "Invalid level")

configuration/defaults.go

@@ -18,9 +18,10 @@ package configuration
 // The default configuration settings.
 
 import (
+	"io/ioutil"
+
 	"github.com/arduino/arduino-check/configuration/checkmode"
 	"github.com/arduino/arduino-check/project/projecttype"
-	"github.com/sirupsen/logrus"
 )
 
 // Default check modes for each superproject type.
@@ -60,4 +61,4 @@ var defaultCheckModes = map[projecttype.Type]map[checkmode.Type]bool{
 	},
 }
 
-var defaultLogLevel = logrus.FatalLevel
+var defaultLogOutput = ioutil.Discard // Default to no log output.