[errors] Remove DirectCause

Author: at15

errors/cause.go

@@ -13,7 +13,7 @@ type causer interface {
 // If you want get direct cause, use DirectCause.
 // If error is nil, it will return nil. If error is not wrapped it will return the error itself.
 // error wrapped using https://github.com/pkg/errors also satisfies this interface and can be unwrapped as well.
-// TODO: might consider rename it to Unwrap since we are deprecating causer interface
+// Deprecated: Use Walk if you need root cause or Unwrap if you need direct cause.
 func Cause(err error) error {
 	if err == nil {
 		return nil
@@ -29,21 +29,4 @@ func Cause(err error) error {
 		}
 	}
 	return err
-}
-
-// DirectCause returns the direct cause of the error (if any).
-// It does NOT follow the cause chain all the way down, just the first one (if any),
-// If you want to get root cause, use Cause
-func DirectCause(err error) error {
-	if err == nil {
-		return nil
-	}
-	switch err.(type) {
-	case Wrapper:
-		return err.(Wrapper).Unwrap()
-	case causer:
-		return err.(causer).Cause()
-	default:
-		return err
-	}
-}
+}

errors/cause_test.go

@@ -21,18 +21,4 @@ func TestCause(t *testing.T) {
 
 	stderr := stderrors.New("std")
 	assert.Equal(t, stderr, errors.Cause(stderr))
-}
-
-func TestDirectCause(t *testing.T) {
-	assert.Nil(t, errors.DirectCause(nil))
-
-	errw := errors.Wrap(os.ErrClosed, "can't open closed file")
-	errww := errors.Wrap(errw, "wrap again")
-	assert.Equal(t, os.ErrClosed, errors.Cause(errww))
-	assert.Equal(t, os.ErrClosed, errors.Cause(errw))
-	assert.NotEqual(t, os.ErrClosed, errors.DirectCause(errww))
-	assert.Equal(t, "can't open closed file", errors.DirectCause(errww).(errors.Messenger).Message())
-
-	stderr := stderrors.New("std")
-	assert.Equal(t, stderr, errors.DirectCause(stderr))
-}
+}

errors/inspect.go

@@ -6,8 +6,8 @@ import (
 
 // inspect.go defines functions for inspecting wrapped error or error list
 
-// Unwrap returns the underlying error. If the error is not wrapped, it returns nil.
-// Its behavior is same as standard library.
+// Unwrap returns the first underlying error. If the error is not wrapped, it returns nil.
+// It does NOT follow the entire error chain. Its behavior is same as standard library.
 func Unwrap(err error) error {
 	if err == nil {
 		return nil