[errors] de-specialize Transient in favor of Tags.

common/errors/transient.go

-// Copyright 2015 The LUCI Authors. All rights reserved.
-// Use of this source code is governed under the Apache License, Version 2.0
-// that can be found in the LICENSE file.
-
-package errors
-
-// Transient is an Error implementation. It wraps an existing Error, marking
-// it as transient. This can be tested with IsTransient.
-type Transient interface {
-        error
-
-        // IsTransient returns true if this error type is transient.
-        IsTransient() bool
-}
-
-type transientWrapper struct {
-        error
-        finfo StackFrameInfo
-}
-
-var _ interface {
-        Transient
-        StackContexter
-} = transientWrapper{}
-
-func (t transientWrapper) IsTransient() bool {
-        return true
-}
-
-func (t transientWrapper) InnerError() error {
-        return t.error
-}
-
-func (t transientWrapper) StackContext() StackContext {
-        return StackContext{
-                FrameInfo:      t.finfo,
-                InternalReason: "errors.WrapTransient()",
-        }
-}
-
-// IsTransient tests if a given error or, if it is a container, any of its
-// contained errors is Transient.
-func IsTransient(err error) bool {
-        return Any(err, func(err error) bool {
-                if t, ok := err.(Transient); ok {
-                        return t.IsTransient()
-                }
-                return false
-        })
-}
-
-// WrapTransient wraps an existing error with in a Transient error.
-//
-// If the supplied error is already Transient, it will be returned. If the
-// supplied error is nil, nil wil be returned.
-//
-// If the supplied error is not Transient, the current stack frame will be
-// captured. This wrapping action will show up on the stack trace returned by
-// RenderStack.
-func WrapTransient(err error) error {
-        if err == nil || IsTransient(err) {
-                return err
-        }
-        return transientWrapper{err, StackFrameInfoForError(1, err)}
-}