What version of Go are you using (go version)?

go version go1.7 darwin/amd64

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/almcpherson/gopath"
GORACE=""
GOROOT="/Users/almcpherson/go1.7"
GOTOOLDIR="/Users/almcpherson/go1.7/pkg/tool/darwin_amd64"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/jv/2c5lqc993lgdnm85hggybmw43959v8/T/go-build941373586=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"

What did you do?

Running benchmarks to see why
func stateEndTop(s *scanner, c byte) int

is making calls to

func (s *scanner) error(c byte, context string) int

on valid json.

package mapping

import (
	"encoding/json"
	"testing"
)

func BenchmarkLittleJSON(b *testing.B) {
	little := []byte(`{ "hello": "world", "x": {"n": 1, "m":2}, "world": ["1","2","3"], "what": "heh?"}`)
	for i := 0; i < b.N; i++ {
		var result struct {
			Hello string `json:"hello"`
			World []string `json:"world"`
		}
		if err := json.Unmarshal(little, &result); err != nil {
			b.Error(err)
		}
	}
}

https://play.golang.org/p/Fsvp3vGwXO

go test -bench "BenchmarkLittleJSON" -cpuprofile c.out
go tool pprof -peek error test.test c.out

What did you expect to see?

no calls to error

What did you see instead?

calls to error

1.18s of 1.18s total ( 100%)
----------------------------------------------------------+-------------
flat flat% sum% cum cum% calls calls% + context
----------------------------------------------------------+-------------
0.21s 100% | encoding/json.stateEndTop
0 0% 0% 0.21s 17.80% | encoding/json.(*scanner).error
0.11s 52.38% | runtime.concatstring4
0.07s 33.33% | encoding/json.quoteChar
0.03s 14.29% | runtime.newobject
----------------------------------------------------------+-------------