Pr/read project config only if it exists (#959)

* Read the project config only if it exists

This avoid trying reading the file and have the control flow based
on errors. Beside that it helps troubleshooting when we have some
logging (debug level only).

* formatting only

* Adjust log level

cmd/piper.go

@@ -8,6 +8,8 @@ import (
 	"strings"
 
 	"github.com/SAP/jenkins-library/pkg/config"
+	"github.com/SAP/jenkins-library/pkg/log"
+	"github.com/SAP/jenkins-library/pkg/piperutils"
 	"github.com/pkg/errors"
 	"github.com/spf13/cobra"
 )
@@ -78,9 +80,18 @@ func PrepareConfig(cmd *cobra.Command, metadata *config.StepData, stepName strin
 		stepConfig = config.GetStepConfigWithJSON(flagValues, GeneralConfig.StepConfigJSON, filters)
 	} else {
 		// use config & defaults
-
+		var customConfig io.ReadCloser
+		var err error
 		//accept that config file and defaults cannot be loaded since both are not mandatory here
-		customConfig, _ := openFile(GeneralConfig.CustomConfig)
+		if piperutils.FileExists(GeneralConfig.CustomConfig) {
+			if customConfig, err = openFile(GeneralConfig.CustomConfig); err != nil {
+				errors.Wrapf(err, "Cannot read '%s'", GeneralConfig.CustomConfig)
+			}
+		} else {
+			log.Entry().Infof("Project config file '%s' does not exist. No project configuration available.", GeneralConfig.CustomConfig)
+			customConfig = nil
+		}
+
 		var defaultConfig []io.ReadCloser
 		for _, f := range GeneralConfig.DefaultConfig {
 			//ToDo: support also https as source
@@ -88,7 +99,6 @@ func PrepareConfig(cmd *cobra.Command, metadata *config.StepData, stepName strin
 			defaultConfig = append(defaultConfig, fc)
 		}
 
-		var err error
 		stepConfig, err = myConfig.GetStepConfig(flagValues, GeneralConfig.ParametersJSON, customConfig, defaultConfig, filters, metadata.Spec.Inputs.Parameters, GeneralConfig.StageName, stepName)
 		if err != nil {
 			return errors.Wrap(err, "retrieving step configuration failed")

cmd/piper_test.go

@@ -13,8 +13,8 @@ import (
 )
 
 type execMockRunner struct {
-	dir   []string
-	calls []execCall
+	dir            []string
+	calls          []execCall
 	shouldFailWith error
 }
 
@@ -24,8 +24,8 @@ type execCall struct {
 }
 
 type shellMockRunner struct {
-	dir   string
-	calls []string
+	dir            string
+	calls          []string
 	shouldFailWith error
 }