helper/schema: generate a full diff in destroy/create cycle

builtin/providers/aws/resource_aws_instance.go

@@ -91,6 +91,7 @@ func resourceAwsInstance() *schema.Resource {
 			"security_groups": &schema.Schema{
 				Type:     schema.TypeSet,
 				Optional: true,
+				Computed: true,
 				Elem:     &schema.Schema{Type: schema.TypeString},
 				Set: func(v interface{}) int {
 					return hashcode.String(v.(string))

helper/schema/resource.go

@@ -82,11 +82,8 @@ func (r *Resource) Apply(
 				return data.State(), err
 			}
 
-			// Reset the data to be empty
+			// Make sure the ID is gone.
-			data, err = schemaMap(r.Schema).Data(nil, d)
+			data.SetId("")
-			if err != nil {
-				return nil, err
-			}
 		}
 
 		// If we're only destroying, and not creating, then return
@@ -97,7 +94,7 @@ func (r *Resource) Apply(
 	}
 
 	err = nil
-	if s.ID == "" {
+	if data.Id() == "" {
 		// We're creating, it is a new resource.
 		err = r.Create(data, meta)
 	} else {

helper/schema/schema.go

@@ -177,6 +177,64 @@ func (m schemaMap) Diff(
 		}
 	}
 
+	// If the diff requires a new resource, then we recompute the diff
+	// so we have the complete new resource diff, and preserve the
+	// RequiresNew fields where necessary so the user knows exactly what
+	// caused that.
+	if result.RequiresNew() {
+		// Create the new diff
+		result2 := new(terraform.ResourceDiff)
+		result2.Attributes = make(map[string]*terraform.ResourceAttrDiff)
+
+		// Reset the data to not contain state
+		d.state = nil
+
+		// Perform the diff again
+		for k, schema := range m {
+			err := m.diff(k, schema, result2, d)
+			if err != nil {
+				return nil, err
+			}
+		}
+
+		// Force all the fields to not force a new since we know what we
+		// want to force new.
+		for k, attr := range result2.Attributes {
+			if attr == nil {
+				continue
+			}
+
+			if attr.RequiresNew {
+				attr.RequiresNew = false
+			}
+
+			if s != nil {
+				attr.Old = s.Attributes[k]
+			}
+		}
+
+		// Now copy in all the requires new diffs...
+		for k, attr := range result.Attributes {
+			if attr == nil {
+				continue
+			}
+
+			newAttr, ok := result2.Attributes[k]
+			if !ok {
+				newAttr = attr
+			}
+
+			if attr.RequiresNew {
+				newAttr.RequiresNew = true
+			}
+
+			result2.Attributes[k] = newAttr
+		}
+
+		// And set the diff!
+		result = result2
+	}
+
 	// Remove any nil diffs just to keep things clean
 	for k, v := range result.Attributes {
 		if v == nil {

helper/schema/schema_test.go

@@ -764,6 +764,104 @@ func TestSchemaMap_Diff(t *testing.T) {
 
 			Err: false,
 		},
+
+		/*
+		 * ForceNews
+		 */
+
+		{
+			Schema: map[string]*Schema{
+				"availability_zone": &Schema{
+					Type:     TypeString,
+					Optional: true,
+					ForceNew: true,
+				},
+
+				"address": &Schema{
+					Type:     TypeString,
+					Optional: true,
+					Computed: true,
+				},
+			},
+
+			State: &terraform.ResourceState{
+				Attributes: map[string]string{
+					"availability_zone": "bar",
+					"address":           "foo",
+				},
+			},
+
+			Config: map[string]interface{}{
+				"availability_zone": "foo",
+			},
+
+			Diff: &terraform.ResourceDiff{
+				Attributes: map[string]*terraform.ResourceAttrDiff{
+					"availability_zone": &terraform.ResourceAttrDiff{
+						Old:         "bar",
+						New:         "foo",
+						RequiresNew: true,
+					},
+
+					"address": &terraform.ResourceAttrDiff{
+						Old:         "foo",
+						New:         "",
+						NewComputed: true,
+					},
+				},
+			},
+
+			Err: false,
+		},
+
+		// Set
+		{
+			Schema: map[string]*Schema{
+				"availability_zone": &Schema{
+					Type:     TypeString,
+					Optional: true,
+					ForceNew: true,
+				},
+
+				"ports": &Schema{
+					Type:     TypeSet,
+					Optional: true,
+					Computed: true,
+					Elem:     &Schema{Type: TypeInt},
+					Set:      func(v interface{}) int { return v.(int) },
+				},
+			},
+
+			State: &terraform.ResourceState{
+				Attributes: map[string]string{
+					"availability_zone": "bar",
+					"ports.#":           "1",
+					"ports.0":           "80",
+				},
+			},
+
+			Config: map[string]interface{}{
+				"availability_zone": "foo",
+			},
+
+			Diff: &terraform.ResourceDiff{
+				Attributes: map[string]*terraform.ResourceAttrDiff{
+					"availability_zone": &terraform.ResourceAttrDiff{
+						Old:         "bar",
+						New:         "foo",
+						RequiresNew: true,
+					},
+
+					"ports.#": &terraform.ResourceAttrDiff{
+						Old:         "1",
+						New:         "",
+						NewComputed: true,
+					},
+				},
+			},
+
+			Err: false,
+		},
 	}
 
 	for i, tc := range cases {