terraform: add output orphan transformer

terraform/graph_config_node.go

@@ -137,6 +137,10 @@ func (n *GraphNodeConfigOutput) ConfigType() GraphNodeConfigType {
 	return GraphNodeConfigTypeOutput
 }
 
+func (n *GraphNodeConfigOutput) OutputName() string {
+	return n.Output.Name
+}
+
 func (n *GraphNodeConfigOutput) DependableName() []string {
 	return []string{n.Name()}
 }

terraform/graph_config_node_test.go

@@ -41,6 +41,13 @@ func TestGraphNodeConfigModuleExpand(t *testing.T) {
 	}
 }
 
+func TestGraphNodeConfigOutput_impl(t *testing.T) {
+	var _ dag.Vertex = new(GraphNodeConfigOutput)
+	var _ dag.NamedVertex = new(GraphNodeConfigOutput)
+	var _ graphNodeConfig = new(GraphNodeConfigOutput)
+	var _ GraphNodeOutput = new(GraphNodeConfigOutput)
+}
+
 func TestGraphNodeConfigProvider_impl(t *testing.T) {
 	var _ dag.Vertex = new(GraphNodeConfigProvider)
 	var _ dag.NamedVertex = new(GraphNodeConfigProvider)

terraform/test-fixtures/transform-orphan-output-basic/main.tf

@@ -0,0 +1 @@
+output "foo" { value = "bar" }

terraform/transform_output.go

@@ -0,0 +1,59 @@
+package terraform
+
+import (
+	"fmt"
+)
+
+// GraphNodeOutput is an interface that nodes that are outputs must
+// implement. The OutputName returned is the name of the output key
+// that they manage.
+type GraphNodeOutput interface {
+	OutputName() string
+}
+
+// AddOutputOrphanTransformer is a transformer that adds output orphans
+// to the graph. Output orphans are outputs that are no longer in the
+// configuration and therefore need to be removed from the state.
+type AddOutputOrphanTransformer struct {
+	State *State
+}
+
+func (t *AddOutputOrphanTransformer) Transform(g *Graph) error {
+	// Get the state for this module. If we have no state, we have no orphans
+	state := t.State.ModuleByPath(g.Path)
+	if state == nil {
+		return nil
+	}
+
+	// Create the set of outputs we do have in the graph
+	found := make(map[string]struct{})
+	for _, v := range g.Vertices() {
+		on, ok := v.(GraphNodeOutput)
+		if !ok {
+			continue
+		}
+
+		found[on.OutputName()] = struct{}{}
+	}
+
+	// Go over all the outputs. If we don't have a graph node for it,
+	// create it. It doesn't need to depend on anything, since its just
+	// setting it empty.
+	for k, _ := range state.Outputs {
+		if _, ok := found[k]; ok {
+			continue
+		}
+
+		g.Add(&graphNodeOrphanOutput{OutputName: k})
+	}
+
+	return nil
+}
+
+type graphNodeOrphanOutput struct {
+	OutputName string
+}
+
+func (n *graphNodeOrphanOutput) Name() string {
+	return fmt.Sprintf("output.%s (orphan)", n.OutputName)
+}

terraform/transform_output_test.go

@@ -0,0 +1,45 @@
+package terraform
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestAddOutputOrphanTransformer(t *testing.T) {
+	mod := testModule(t, "transform-orphan-output-basic")
+	state := &State{
+		Modules: []*ModuleState{
+			&ModuleState{
+				Path: RootModulePath,
+				Outputs: map[string]string{
+					"foo": "bar",
+					"bar": "baz",
+				},
+			},
+		},
+	}
+
+	g := Graph{Path: RootModulePath}
+	{
+		tf := &ConfigTransformer{Module: mod}
+		if err := tf.Transform(&g); err != nil {
+			t.Fatalf("err: %s", err)
+		}
+	}
+
+	transform := &AddOutputOrphanTransformer{State: state}
+	if err := transform.Transform(&g); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	actual := strings.TrimSpace(g.String())
+	expected := strings.TrimSpace(testTransformOrphanOutputBasicStr)
+	if actual != expected {
+		t.Fatalf("bad:\n\n%s", actual)
+	}
+}
+
+const testTransformOrphanOutputBasicStr = `
+output.bar (orphan)
+output.foo
+`