Unexpected line break after marshal

[kopwei]

When I want to marshal a map value into a yaml text file, i found that Mashal() function generates an unexpected line break in the mashalled bytes array.
Here is the example code:

package main

import (
    "fmt"
    "gopkg.in/yaml.v2"
)

func main() {
    m := make(map[string][]string)
    var values []string
    values = append(values, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa bbb")
    m["key"] = values
    converted_str, _ := yaml.Marshal(&m)
    fmt.Printf("%v\n", converted_str)
    fmt.Printf("%s\n", converted_str)
}

Output:
$ go run test.go 
[107 101 121 58 10 45 32 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 97 10 32 32 98 98 98 10]
key:
- aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
  bbb

There is an extra line break generated before "bbb". If I reduce the number of character 'a', Marshal() function works as expected and no extra line break.

Go version: 1.10
Platform: MacOS 10.13.3 and Ubuntu 16.04.4

[kopwei]

Found the cause, there is a "emitter.best_width" value in source code and it is set to 80 and will generate line break if the space character's index is larger than that.