Implement WithError(err) in exported, fixed doco.

entry.go

@@ -8,7 +8,7 @@ import (
 	"time"
 )
 
-// Defines the key when adding error using WithError.
+// Defines the key when adding errors using WithError.
 var ErrorKey = "error"
 
 // An entry is the final or intermediate Logrus logging entry. It contains all
@@ -56,7 +56,7 @@ func (entry *Entry) String() (string, error) {
 	return reader.String(), err
 }
 
-// Add an error as single field (with key "error") to the Entry.
+// Add an error as single field (using the key defined in ErrorKey) to the Entry.
 func (entry *Entry) WithError(err error) *Entry {
 	return entry.WithField(ErrorKey, err)
 }

entry_test.go

@@ -10,16 +10,25 @@ import (
 
 func TestEntryWithError(t *testing.T) {
 
+	assert := assert.New(t)
+
+	defer func() {
+		ErrorKey = "error"
+	}()
+
 	err := fmt.Errorf("kaboom at layer %d", 4711)
 
+	assert.Equal(err, WithError(err).Data["error"])
+
 	logger := New()
 	logger.Out = &bytes.Buffer{}
 	entry := NewEntry(logger)
 
-	assert.Equal(t, err, entry.WithError(err).Data["error"])
+	assert.Equal(err, entry.WithError(err).Data["error"])
 
 	ErrorKey = "err"
-	assert.Equal(t, err, entry.WithError(err).Data["err"])
+
+	assert.Equal(err, entry.WithError(err).Data["err"])
 
 }
 

exported.go

@@ -48,6 +48,11 @@ func AddHook(hook Hook) {
 	std.Hooks.Add(hook)
 }
 
+// WithError creates an entry from the standard logger and adds an error to it, using the value defined in ErrorKey as key.
+func WithError(err error) *Entry {
+	return std.WithField(ErrorKey, err)
+}
+
 // WithField creates an entry from the standard logger and adds a field to
 // it. If you want multiple fields, use `WithFields`.
 //