Fix bug with bson.Document.Set

Fixes a bug with bson.Document.Set where documents that are not in
lexicographical order would have elements incorrectly replaced.

GODRIVER-339

Change-Id: I37f1415ba10196121229b117f44b1eeb97e0a200

Author: skriptble

bson/document.go

@@ -256,7 +256,7 @@ func (d *Document) Set(elem *Element) *Document {
 	key := elem.Key() + "\x00"
 	i := sort.Search(len(d.index), func(i int) bool { return bytes.Compare(d.keyFromIndex(i), []byte(key)) >= 0 })
 	if i < len(d.index) && bytes.Compare(d.keyFromIndex(i), []byte(key)) == 0 {
-		d.elems[i] = elem
+		d.elems[d.index[i]] = elem
 		return d
 	}
 

bson/document_test.go

@@ -314,6 +314,12 @@ func TestDocument(t *testing.T) {
 				EC.Null("x"),
 				(&Document{}).Append(EC.Null("w"), EC.Null("y"), EC.Null("z"), EC.Null("x")),
 			},
+			{
+				"update-element-not-lexicographically-sorted",
+				NewDocument(EC.Int32("b", 1), EC.Int32("a", 2), EC.Int32("d", 3), EC.Int32("c", 4)),
+				EC.Int32("d", 5),
+				NewDocument(EC.Int32("b", 1), EC.Int32("a", 2), EC.Int32("d", 5), EC.Int32("c", 4)),
+			},
 		}
 
 		for _, tc := range testCases {