helper/schema: computed values should not be Get-able

helper/schema/resource_data.go

@@ -273,7 +273,7 @@ func (d *ResourceData) getPrimitive(
 
 	if d.diff != nil && source >= getSourceDiff {
 		attrD, ok := d.diff.Attributes[k]
-		if ok {
+		if ok && !attrD.NewComputed {
 			result = attrD.New
 			resultSet = true
 		}

helper/schema/resource_data_test.go

@@ -15,6 +15,33 @@ func TestResourceDataGet(t *testing.T) {
 		Key    string
 		Value  interface{}
 	}{
+		{
+			Schema: map[string]*Schema{
+				"availability_zone": &Schema{
+					Type:     TypeString,
+					Optional: true,
+					Computed: true,
+					ForceNew: true,
+				},
+			},
+
+			State: nil,
+
+			Diff: &terraform.ResourceDiff{
+				Attributes: map[string]*terraform.ResourceAttrDiff{
+					"availability_zone": &terraform.ResourceAttrDiff{
+						Old:         "",
+						New:         "",
+						NewComputed: true,
+					},
+				},
+			},
+
+			Key: "availability_zone",
+
+			Value: nil,
+		},
+
 		{
 			Schema: map[string]*Schema{
 				"availability_zone": &Schema{