terraform: don't process outputs when all we did was destroy

terraform/context.go

@@ -112,8 +112,11 @@ func (c *Context) Apply() (*State, error) {
 	// Walk
 	err = g.Walk(c.applyWalkFn())
 
+	// Prune the state so that we have as clean a state as possible
+	c.state.prune()
+
 	// If we have no errors, then calculate the outputs if we have any
-	if err == nil && len(c.config.Outputs) > 0 {
+	if err == nil && len(c.config.Outputs) > 0 && len(c.state.Resources) > 0 {
 		c.state.Outputs = make(map[string]string)
 		for _, o := range c.config.Outputs {
 			if err = c.computeVars(o.RawConfig); err != nil {

terraform/context_test.go

@@ -557,6 +557,46 @@ func TestContextApply_destroy(t *testing.T) {
 	}
 }
 
+func TestContextApply_destroyOutputs(t *testing.T) {
+	c := testConfig(t, "apply-destroy-outputs")
+	h := new(HookRecordApplyOrder)
+	p := testProvider("aws")
+	p.ApplyFn = testApplyFn
+	p.DiffFn = testDiffFn
+	ctx := testContext(t, &ContextOpts{
+		Config: c,
+		Hooks:  []Hook{h},
+		Providers: map[string]ResourceProviderFactory{
+			"aws": testProviderFuncFixed(p),
+		},
+	})
+
+	// First plan and apply a create operation
+	if _, err := ctx.Plan(nil); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	if _, err := ctx.Apply(); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	// Next, plan and apply a destroy operation
+	if _, err := ctx.Plan(&PlanOpts{Destroy: true}); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	h.Active = true
+
+	state, err := ctx.Apply()
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	if len(state.Resources) > 0 {
+		t.Fatalf("bad: %#v", state)
+	}
+}
+
 func TestContextApply_destroyOrphan(t *testing.T) {
 	c := testConfig(t, "apply-error")
 	p := testProvider("aws")

terraform/state.go

@@ -40,6 +40,16 @@ func (s *State) deepcopy() *State {
 	return result
 }
 
+// prune is a helper that removes any empty IDs from the state
+// and cleans it up in general.
+func (s *State) prune() {
+	for k, v := range s.Resources {
+		if v.ID == "" {
+			delete(s.Resources, k)
+		}
+	}
+}
+
 // Orphans returns a list of keys of resources that are in the State
 // but aren't present in the configuration itself. Hence, these keys
 // represent the state of resources that are orphans.

terraform/test-fixtures/apply-destroy-outputs/main.tf

@@ -0,0 +1,14 @@
+resource "aws_instance" "foo" {
+    id = "foo"
+    num = "2"
+}
+
+resource "aws_instance" "bar" {
+    id = "bar"
+    foo = "{aws_instance.foo.num}"
+    dep = "foo"
+}
+
+output "foo" {
+    value = "${aws_instance.foo.id}"
+}