[golangBuild] Add better error logging to isMainPackage (#5308)

Co-authored-by: Ashly Mathew <ashly.mathew@sap.com>
Co-authored-by: Googlom <36107508+Googlom@users.noreply.github.com>

cmd/golangBuild.go

@@ -570,7 +570,7 @@ func isMainPackage(utils golangBuildUtils, pkg string) (bool, error) {
 	utils.Stderr(outBuffer)
 	err := utils.RunExecutable("go", "list", "-f", "{{ .Name }}", pkg)
 	if err != nil {
-		return false, err
+		return false, fmt.Errorf("%w: %s", err, outBuffer.String())
 	}
 
 	if outBuffer.String() != "main" {

cmd/golangBuild_test.go

@@ -4,6 +4,7 @@
 package cmd
 
 import (
+	"errors"
 	"fmt"
 	"io"
 	"net/http"
@@ -871,6 +872,19 @@ func TestRunGolangBuildPerArchitecture(t *testing.T) {
 	})
 }
 
+func TestIsMainPackageError(t *testing.T) {
+	utils := newGolangBuildTestsUtils()
+	utils.ShouldFailOnCommand = map[string]error{
+		"go list -f {{ .Name }} package/foo": errors.New("some error"),
+	}
+	utils.StdoutReturn = map[string]string{
+		"go list -f {{ .Name }} package/foo": "some specific error log",
+	}
+	ok, err := isMainPackage(utils, "package/foo")
+	assert.False(t, ok)
+	assert.EqualError(t, err, "some error: some specific error log")
+}
+
 func TestPrepareGolangEnvironment(t *testing.T) {
 	modTestFile := `
 module private.example.com/m