Merge pull request #72 from vimeo/set_slice_mangler_nil_slice_propagate

transform: propagate nil slice in SetSliceMangler

ez/ez_test.go

@@ -166,7 +166,7 @@ func TestYAMLConfigEnvFlagWithValidatingConfigInitiallyValid(t *testing.T) {
 		Path: path,
 		Val1: 189,
 		Val2: "",
-		Set:  map[string]struct{}{},
+		Set:  map[string]struct{}(nil),
 	}
 	populatedConf := view.View()
 	assert.EqualValues(t, expectedConfig, *populatedConf)

transform/set_slice_mangler.go

@@ -28,7 +28,7 @@ func (*SetSliceMangler) Mangle(sf reflect.StructField) ([]reflect.StructField, e
 // Unmangle turns []T back into a map[T]struct{}.  Naturally, deduplication will
 // occur.
 func (*SetSliceMangler) Unmangle(sf reflect.StructField, vs []FieldValueTuple) (reflect.Value, error) {
-	if !(sf.Type.Kind() == reflect.Map && sf.Type.Elem() == emptyStructType) {
+	if sf.Type.Kind() != reflect.Map || sf.Type.Elem() != emptyStructType {
 		return vs[0].Value, nil
 	}
 
@@ -49,6 +49,11 @@ func (*SetSliceMangler) Unmangle(sf reflect.StructField, vs []FieldValueTuple) (
 		)
 	}
 
+	// If the slice is nil, return a nil map.
+	if slice.IsZero() {
+		return reflect.Zero(sf.Type), nil
+	}
+
 	// slice.Len() could be larger if there are duplicates, but it's likely
 	// a good place to start.
 	set := reflect.MakeMapWithSize(sf.Type, slice.Len())

transform/set_slice_mangler_test.go

@@ -55,6 +55,11 @@ func TestSetSliceManglerUnmangle(t *testing.T) {
 				"baz": {},
 			},
 		},
+		"nil": {
+			StructFieldType: reflect.TypeOf(map[int]struct{}{}),
+			SrcValue:        []int(nil),
+			ExpectedMap:     map[int]struct{}(nil),
+		},
 	}
 
 	for name, c := range cases {