terraform: require the prefix match with a "." in Diff.Instances

terraform/diff.go

@@ -172,8 +172,10 @@ func (d *ModuleDiff) Empty() bool {
 func (d *ModuleDiff) Instances(id string) []*InstanceDiff {
 	var result []*InstanceDiff
 	for k, diff := range d.Resources {
-		if strings.HasPrefix(k, id) && !diff.Empty() {
-			result = append(result, diff)
+		if k == id || strings.HasPrefix(k, id+".") {
+			if !diff.Empty() {
+				result = append(result, diff)
+			}
 		}
 	}
 

terraform/diff_test.go

@@ -1,6 +1,7 @@
 package terraform
 
 import (
+	"reflect"
 	"strings"
 	"testing"
 )
@@ -268,6 +269,68 @@ func TestInstanceDiff_Empty(t *testing.T) {
 	}
 }
 
+func TestModuleDiff_Instances(t *testing.T) {
+	yesDiff := &InstanceDiff{Destroy: true}
+	noDiff := &InstanceDiff{Destroy: true, DestroyTainted: true}
+
+	cases := []struct {
+		Diff   *ModuleDiff
+		Id     string
+		Result []*InstanceDiff
+	}{
+		{
+			&ModuleDiff{
+				Resources: map[string]*InstanceDiff{
+					"foo": yesDiff,
+					"bar": noDiff,
+				},
+			},
+			"foo",
+			[]*InstanceDiff{
+				yesDiff,
+			},
+		},
+
+		{
+			&ModuleDiff{
+				Resources: map[string]*InstanceDiff{
+					"foo":   yesDiff,
+					"foo.0": yesDiff,
+					"bar":   noDiff,
+				},
+			},
+			"foo",
+			[]*InstanceDiff{
+				yesDiff,
+				yesDiff,
+			},
+		},
+
+		{
+			&ModuleDiff{
+				Resources: map[string]*InstanceDiff{
+					"foo":     yesDiff,
+					"foo.0":   yesDiff,
+					"foo_bar": noDiff,
+					"bar":     noDiff,
+				},
+			},
+			"foo",
+			[]*InstanceDiff{
+				yesDiff,
+				yesDiff,
+			},
+		},
+	}
+
+	for i, tc := range cases {
+		actual := tc.Diff.Instances(tc.Id)
+		if !reflect.DeepEqual(actual, tc.Result) {
+			t.Fatalf("%d: %#v", i, actual)
+		}
+	}
+}
+
 func TestInstanceDiff_RequiresNew(t *testing.T) {
 	rd := &InstanceDiff{
 		Attributes: map[string]*ResourceAttrDiff{