vendor/resenje.org/singleflight/withoutcancel.go

//go:build !go1.21

// Copyright (c) 2009 The Go Authors. All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//    * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//    * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//    * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
// Source: https://cs.opensource.google/go/go/+/refs/tags/go1.21.1:src/context/context.go
// The only modifications to the original source were:
// - renaming WithoutCancel to withoutCancel
// - replacing the usage of internal reflectlite with reflect
// - replacing the usage of private value function with Value method call
package singleflight

import (
	"context"
	"reflect"
	"time"
)

// withoutCancel returns a copy of parent that is not canceled when parent is canceled.
// The returned context returns no Deadline or Err, and its Done channel is nil.
// Calling [Cause] on the returned context returns nil.
func withoutCancel(parent context.Context) context.Context {
	if parent == nil {
		panic("cannot create context from nil parent")
	}
	return withoutCancelCtx{parent}
}

type withoutCancelCtx struct {
	c context.Context
}

func (withoutCancelCtx) Deadline() (deadline time.Time, ok bool) {
	return
}

func (withoutCancelCtx) Done() <-chan struct{} {
	return nil
}

func (withoutCancelCtx) Err() error {
	return nil
}

func (c withoutCancelCtx) Value(key any) any {
	return c.c.Value(key)
}

func (c withoutCancelCtx) String() string {
	return contextName(c.c) + ".WithoutCancel"
}

type stringer interface {
	String() string
}

func contextName(c context.Context) string {
	if s, ok := c.(stringer); ok {
		return s.String()
	}
	return reflect.TypeOf(c).String()
}