terraform: StateAdd edge case test for multi-count to single index

terraform/state_add.go

@@ -160,6 +160,14 @@ func stateAddFunc_Resource_Resource(s *State, fromAddr, addr *ResourceAddress, r
 			return fmt.Errorf("resource move with no value to: %s", addr)
 		}
 
+		// If there is an index, this is an error since we can't assign
+		// a set of resources to a single index
+		if addr.Index >= 0 {
+			return fmt.Errorf(
+				"multiple resources can't be moved to a single index: "+
+					"%s => %s", fromAddr, addr)
+		}
+
 		// Add each with a specific index
 		for i, rs := range list {
 			addrCopy := addr.Copy()

terraform/state_add_test.go

@@ -416,6 +416,30 @@ func TestStateAdd(t *testing.T) {
 			},
 		},
 
+		"ResourceState with count unspecified => Resource Addr (new with count)": {
+			true,
+			"aws_instance.bar",
+			"aws_instance.foo[0]",
+			[]*ResourceState{
+				&ResourceState{
+					Type: "test_instance",
+					Primary: &InstanceState{
+						ID: "foo",
+					},
+				},
+
+				&ResourceState{
+					Type: "test_instance",
+					Primary: &InstanceState{
+						ID: "bar",
+					},
+				},
+			},
+
+			&State{},
+			nil,
+		},
+
 		"ResourceState => Resource Addr (existing)": {
 			true,
 			"aws_instance.bar",