Initial commit

vendor/github.com/cockroachdb/errors/errbase/unwrap.go

@@ -0,0 +1,71 @@
+// Copyright 2019 The Cockroach Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+// implied. See the License for the specific language governing
+// permissions and limitations under the License.
+
+package errbase
+
+// Sadly the go 2/1.13 design for errors has promoted the name
+// `Unwrap()` for the method that accesses the cause, whilst the
+// ecosystem has already chosen `Cause()`. In order to unwrap
+// reliably, we must thus support both.
+//
+// See: https://github.com/golang/go/issues/31778
+
+// UnwrapOnce accesses the direct cause of the error if any, otherwise
+// returns nil.
+//
+// It supports both errors implementing causer (`Cause()` method, from
+// github.com/pkg/errors) and `Wrapper` (`Unwrap()` method, from the
+// Go 2 error proposal).
+//
+// UnwrapOnce treats multi-errors (those implementing the
+// `Unwrap() []error` interface as leaf-nodes since they cannot
+// reasonably be iterated through to a single cause. These errors
+// are typically constructed as a result of `fmt.Errorf` which results
+// in a `wrapErrors` instance that contains an interpolated error
+// string along with a list of causes.
+//
+// The go stdlib does not define output on `Unwrap()` for a multi-cause
+// error, so we default to nil here.
+func UnwrapOnce(err error) (cause error) {
+	switch e := err.(type) {
+	case interface{ Cause() error }:
+		return e.Cause()
+	case interface{ Unwrap() error }:
+		return e.Unwrap()
+	}
+	return nil
+}
+
+// UnwrapAll accesses the root cause object of the error.
+// If the error has no cause (leaf error), it is returned directly.
+// UnwrapAll treats multi-errors as leaf nodes.
+func UnwrapAll(err error) error {
+	for {
+		if cause := UnwrapOnce(err); cause != nil {
+			err = cause
+			continue
+		}
+		break
+	}
+	return err
+}
+
+// UnwrapMulti access the slice of causes that an error contains, if it is a
+// multi-error.
+func UnwrapMulti(err error) []error {
+	if me, ok := err.(interface{ Unwrap() []error }); ok {
+		return me.Unwrap()
+	}
+	return nil
+}