bind: Maintain backwards compatibility for map[string]interface{} bin…

…ding (#2656)

* bind: Maintain backwards compatibility for map[string]interface{} binding

* bind to single string for map[string]interface{}{}

bind.go

@@ -159,6 +159,10 @@ func (b *DefaultBinder) bindData(destination interface{}, data map[string][]stri
 		for k, v := range data {
 			if isElemString {
 				val.SetMapIndex(reflect.ValueOf(k), reflect.ValueOf(v[0]))
+			} else if isElemInterface {
+				// To maintain backward compatibility, we always bind to the first string value
+				// and not the slice of strings when dealing with map[string]interface{}{}
+				val.SetMapIndex(reflect.ValueOf(k), reflect.ValueOf(v[0]))
 			} else {
 				val.SetMapIndex(reflect.ValueOf(k), reflect.ValueOf(v))
 			}

bind_test.go

@@ -497,8 +497,8 @@ func TestDefaultBinder_bindDataToMap(t *testing.T) {
 		assert.NoError(t, new(DefaultBinder).bindData(&dest, exampleData, "param"))
 		assert.Equal(t,
 			map[string]interface{}{
-				"multiple": []string{"1", "2"},
-				"single":   []string{"3"},
+				"multiple": "1",
+				"single":   "3",
 			},
 			dest,
 		)
@@ -509,8 +509,8 @@ func TestDefaultBinder_bindDataToMap(t *testing.T) {
 		assert.NoError(t, new(DefaultBinder).bindData(&dest, exampleData, "param"))
 		assert.Equal(t,
 			map[string]interface{}{
-				"multiple": []string{"1", "2"},
-				"single":   []string{"3"},
+				"multiple": "1",
+				"single":   "3",
 			},
 			dest,
 		)