go/test/fixedbugs/issue7921.go

// +build !gcflags_noopt
// errorcheck -0 -m

// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package foo

import "bytes"

// In order to get desired results, we need a combination of
// both escape analysis and inlining.

func bufferNotEscape() string {
	// b itself does not escape, only its buf field will be
	// copied during String() call, but object "handle" itself
	// can be stack-allocated.
	var b bytes.Buffer
	b.WriteString("123") // ERROR "b does not escape"
	b.Write([]byte{'4'}) // ERROR "b does not escape" "\[\]byte literal does not escape"
	return b.String()    // ERROR "b does not escape" "inlining call" "string\(bytes\.b\.buf\[bytes.b.off:\]\) escapes to heap"
}

func bufferNoEscape2(xs []string) int { // ERROR "xs does not escape"
	b := bytes.NewBuffer(make([]byte, 0, 64)) // ERROR "inlining call" "make\(\[\]byte, 0, 64\) does not escape" "&bytes.Buffer literal does not escape"
	for _, x := range xs {
		b.WriteString(x)
	}
	return b.Len() // ERROR "inlining call"
}

func bufferNoEscape3(xs []string) string { // ERROR "xs does not escape"
	b := bytes.NewBuffer(make([]byte, 0, 64)) // ERROR "inlining call" "make\(\[\]byte, 0, 64\) does not escape" "&bytes.Buffer literal does not escape"
	for _, x := range xs {
		b.WriteString(x)
		b.WriteByte(',')
	}
	return b.String() // ERROR "inlining call" "string\(bytes.b.buf\[bytes\.b\.off:\]\) escapes to heap"
}

func bufferNoEscape4() []byte {
	var b bytes.Buffer
	b.Grow(64)       // ERROR "b does not escape"
	useBuffer(&b)    // ERROR "&b does not escape"
	return b.Bytes() // ERROR "inlining call" "b does not escape"
}

func bufferNoEscape5() { // ERROR "can inline bufferNoEscape5"
	b := bytes.NewBuffer(make([]byte, 0, 128)) // ERROR "inlining call" "make\(\[\]byte, 0, 128\) does not escape" "&bytes.Buffer literal does not escape"
	useBuffer(b)
}

//go:noinline
func useBuffer(b *bytes.Buffer) { // ERROR "b does not escape"
	b.WriteString("1234")
}