Restore support for empty prefix in 'ResourceDiff.GetChangedKeysPrefix'.

helper/schema/resource_diff.go

@@ -254,13 +254,13 @@ func (d *ResourceDiff) clear(key string) error {
 	return nil
 }
 
-// GetChangedKeysPrefix helps to implement Resource.CustomizeDiff
-// where we need to act on all nested fields
-// without calling out each one separately
+// GetChangedKeysPrefix helps to implement Resource.CustomizeDiff where we need to act
+// on all nested fields without calling out each one separately.
+// An empty prefix is supported, returning all changed keys.
 func (d *ResourceDiff) GetChangedKeysPrefix(prefix string) []string {
 	keys := make([]string, 0)
 	for k := range d.diff.Attributes {
-		if k == prefix || childAddrOf(k, prefix) {
+		if k == prefix || childAddrOf(k, prefix) || prefix == "" {
 			keys = append(keys, k)
 		}
 	}

helper/schema/resource_diff_test.go

@@ -1237,6 +1237,36 @@ func TestGetChangedKeysPrefix(t *testing.T) {
 				"foo",
 			},
 		},
+		{
+			Name: "basic primitive diff with empty prefix",
+			Schema: map[string]*Schema{
+				"foo": {
+					Type:     TypeString,
+					Optional: true,
+					Computed: true,
+				},
+			},
+			State: &terraform.InstanceState{
+				Attributes: map[string]string{
+					"foo": "bar",
+				},
+			},
+			Config: testConfig(t, map[string]interface{}{
+				"foo": "baz",
+			}),
+			Diff: &terraform.InstanceDiff{
+				Attributes: map[string]*terraform.ResourceAttrDiff{
+					"foo": {
+						Old: "bar",
+						New: "baz",
+					},
+				},
+			},
+			Key: "",
+			ExpectedKeys: []string{
+				"foo",
+			},
+		},
 		{
 			Name: "nested field filtering",
 			Schema: map[string]*Schema{