Consider the following program:

package main

import (

const data = "short\nthisisverylonglong\n"

var in = bufio.NewScanner(strings.NewReader(data))

func next() []byte {
  return in.Bytes()

func main() {
  in.Buffer(make([]byte, 20), 20)
  s, t := string(next()), next()   // line 20
  fmt.Printf("%s\n", t)

What I expected at line 20:
1) call next()
2) convert it to string
3) call next()
4) assign to s and t

Expected output:


What was the actual compiled code:
1) call next()
2) call next()
3) convert first result to string
4) assign to s and t

Actual output:


0x008f 00143 (longscan.go:20)  PCDATA $0, $0
0x008f 00143 (longscan.go:20)  CALL   "".next(SB)
0x0094 00148 (longscan.go:20)  MOVQ   8(SP), AX
0x0099 00153 (longscan.go:20)  MOVQ   AX, ""..autotmp_21+88(SP)
0x009e 00158 (longscan.go:20)  MOVQ   16(SP), CX
0x00a3 00163 (longscan.go:20)  MOVQ   CX, ""..autotmp_22+80(SP)
0x00a8 00168 (longscan.go:20)  MOVQ   (SP), DX
0x00ac 00172 (longscan.go:20)  MOVQ   DX, ""..autotmp_23+104(SP)
0x00b1 00177 (longscan.go:20)  PCDATA $0, $1
0x00b1 00177 (longscan.go:20)  CALL   "".next(SB)
0x00b6 00182 (longscan.go:20)  MOVQ   16(SP), AX
0x00bb 00187 (longscan.go:20)  MOVQ   AX, "".t.cap+72(SP)
0x00c0 00192 (longscan.go:20)  MOVQ   8(SP), CX
0x00c5 00197 (longscan.go:20)  MOVQ   CX, "".t.len+64(SP)
0x00ca 00202 (longscan.go:20)  MOVQ   (SP), DX
0x00ce 00206 (longscan.go:20)  MOVQ   DX, "".t.ptr+96(SP)
0x00d3 00211 (longscan.go:20)  MOVQ   $0, (SP)
0x00db 00219 (longscan.go:20)  MOVQ   ""..autotmp_23+104(SP), BX
0x00e0 00224 (longscan.go:20)  MOVQ   BX, 8(SP)
0x00e5 00229 (longscan.go:20)  MOVQ   ""..autotmp_21+88(SP), BX
0x00ea 00234 (longscan.go:20)  MOVQ   BX, 16(SP)
0x00ef 00239 (longscan.go:20)  MOVQ   ""..autotmp_22+80(SP), BX
0x00f4 00244 (longscan.go:20)  MOVQ   BX, 24(SP)
0x00f9 00249 (longscan.go:20)  PCDATA $0, $2
0x00f9 00249 (longscan.go:20)  CALL   runtime.slicebytetostring(SB)
0x00fe 00254 (longscan.go:20)  MOVQ   32(SP), AX
0x0103 00259 (longscan.go:20)  MOVQ   40(SP), CX

In this case, second next() causes Scanner buffer clear, which invalidates 
result of first next() before making it to string.

I think is going to explain 
this situation, but I had hard time understanding.

Is current behavior consistent with language spec?

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