core: fixing a small logic bug in diffList

helper/schema/schema.go

@@ -459,9 +459,10 @@ func (m schemaMap) diffList(
  o, n, _, computedList := d.diffChange(k)
  nSet := n != nil
 
- // If we have an old value, but no new value set but we're computed,
- // then nothing has changed.
- if o != nil && n == nil && schema.Computed {
+ // If we have an old value and no new value is set or will be
+ // computed once all variables can be interpolated and we're
+ // computed, then nothing has changed.
+ if o != nil && n == nil && !computedList && schema.Computed {
  return nil
  }
 

helper/schema/schema_test.go

@@ -1466,6 +1466,57 @@ func TestSchemaMap_Diff(t *testing.T) {
 
  Err: false,
  },
+
+ {
+ Schema: map[string]*Schema{
+ "internal": &Schema{
+ Type: TypeBool,
+ Required: true,
+ },
+
+ "instances": &Schema{
+ Type: TypeSet,
+ Elem: &Schema{Type: TypeString},
+ Optional: true,
+ Computed: true,
+ Set: func(v interface{}) int {
+ return len(v)
+ },
+ },
+ },
+
+ State: &terraform.InstanceState{
+ Attributes: map[string]string{
+ "internal": "false",
+ "instances.#": "0",
+ },
+ },
+
+ Config: map[string]interface{}{
+ "internal": true,
+ "instances": []interface{}{"${var.foo}"},
+ },
+
+ ConfigVariables: map[string]string{
+ "var.foo": config.UnknownVariableValue,
+ },
+
+ Diff: &terraform.InstanceDiff{
+ Attributes: map[string]*terraform.ResourceAttrDiff{
+ "internal": &terraform.ResourceAttrDiff{
+ Old: "0",
+ New: "1",
+ },
+
+ "instances.#": &terraform.ResourceAttrDiff{
+ Old: "0",
+ NewComputed: true,
+ },
+ },
+ },
+
+ Err: false,
+ },
  }
 
  for i, tc := range cases {