fix(yaml): make MarshalYAML deterministic

This PR sorts the keys of a map[string]interface{} before marshaling to
YAML, similar to what the standard encoding/json does.

* fixes go-swagger/go-swagger#2850

Signed-off-by: Frederic BIDON <fredbi@yahoo.com>

yaml.go

@@ -19,6 +19,7 @@ import (
 	"fmt"
 	"path/filepath"
 	"reflect"
+	"sort"
 	"strconv"
 
 	"github.com/mailru/easyjson/jlexer"
@@ -286,7 +287,14 @@ func json2yaml(item interface{}) (*yaml.Node, error) {
 	case map[string]interface{}:
 		var n yaml.Node
 		n.Kind = yaml.MappingNode
-		for k, v := range val {
+		keys := make([]string, 0, len(val))
+		for k := range val {
+			keys = append(keys, k)
+		}
+		sort.Strings(keys)
+
+		for _, k := range keys {
+			v := val[k]
 			childNode, err := json2yaml(v)
 			if err != nil {
 				return nil, err

yaml_test.go

@@ -75,8 +75,30 @@ y: some value
 	assert.Equal(t, expected, string(ny.([]byte)))
 }
 
-func TestYAMLToJSON(t *testing.T) {
+func TestMarshalYAML(t *testing.T) {
+	t.Run("marshalYAML should be deterministic", func(t *testing.T) {
+		const (
+			jazon    = `{"1":"x","2":null,"3":{"a":1,"b":2,"c":3}}`
+			expected = `"1": x
+"2": null
+"3":
+    a: !!float 1
+    b: !!float 2
+    c: !!float 3
+`
+		)
+		const iterations = 10
+		for n := 0; n < iterations; n++ {
+			var data JSONMapSlice
+			require.NoError(t, json.Unmarshal([]byte(jazon), &data))
+			ny, err := data.MarshalYAML()
+			require.NoError(t, err)
+			assert.Equal(t, expected, string(ny.([]byte)))
+		}
+	})
+}
 
+func TestYAMLToJSON(t *testing.T) {
 	sd := `---
 1: the int key value
 name: a string value