terraform: handle module dependencies with a diff

terraform/graph.go

@@ -601,6 +601,23 @@ func graphAddDiff(g *depgraph.Graph, d *ModuleDiff) error {
 				num--
 				i--
 
+			case *GraphNodeModule:
+				// We invert any module dependencies so we're destroyed
+				// first, before any modules are applied.
+				newDep := &depgraph.Dependency{
+					Name:   n.Name,
+					Source: dep.Target,
+					Target: n,
+				}
+				dep.Target.Deps = append(dep.Target.Deps, newDep)
+
+				// Drop the dependency. We may have created
+				// an inverse depedency if the dependent resource
+				// is also being deleted, but this dependence is
+				// no longer required.
+				deps[i], deps[num-1] = deps[num-1], nil
+				num--
+				i--
 			case *GraphNodeResourceProvider:
 				// Keep these around, but fix up the source to be ourselves
 				// rather than the old node.
@@ -608,7 +625,7 @@ func graphAddDiff(g *depgraph.Graph, d *ModuleDiff) error {
 				newDep.Source = n
 				deps[i] = &newDep
 			default:
-				panic(fmt.Errorf("Unhandled depedency type: %#v", dep.Meta))
+				panic(fmt.Errorf("Unhandled depedency type: %#v", dep.Target.Meta))
 			}
 		}
 		n.Deps = deps[:num]

terraform/graph_test.go

@@ -624,6 +624,68 @@ func TestGraphAddDiff_destroy_counts(t *testing.T) {
 	}
 }
 
+func TestGraphAddDiff_module(t *testing.T) {
+	m := testModule(t, "graph-diff-module")
+	diff := &Diff{
+		Modules: []*ModuleDiff{
+			&ModuleDiff{
+				Path: rootModulePath,
+				Resources: map[string]*InstanceDiff{
+					"aws_instance.foo": &InstanceDiff{
+						Destroy: true,
+					},
+				},
+			},
+		},
+	}
+
+	g, err := Graph(&GraphOpts{Module: m, Diff: diff})
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	actual := strings.TrimSpace(g.String())
+	expected := strings.TrimSpace(testTerraformGraphDiffModuleStr)
+	if actual != expected {
+		t.Fatalf("bad:\n\n%s", actual)
+	}
+}
+
+func TestGraphAddDiff_moduleDestroy(t *testing.T) {
+	m := testModule(t, "graph-diff-module")
+	diff := &Diff{
+		Modules: []*ModuleDiff{
+			&ModuleDiff{
+				Path: rootModulePath,
+				Resources: map[string]*InstanceDiff{
+					"aws_instance.foo": &InstanceDiff{
+						Destroy: true,
+					},
+				},
+			},
+			&ModuleDiff{
+				Path: []string{"root", "child"},
+				Resources: map[string]*InstanceDiff{
+					"aws_instance.foo": &InstanceDiff{
+						Destroy: true,
+					},
+				},
+			},
+		},
+	}
+
+	g, err := Graph(&GraphOpts{Module: m, Diff: diff})
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	actual := strings.TrimSpace(g.String())
+	expected := strings.TrimSpace(testTerraformGraphDiffModuleStr)
+	if actual != expected {
+		t.Fatalf("bad:\n\n%s", actual)
+	}
+}
+
 func TestGraphEncodeDependencies(t *testing.T) {
 	m := testModule(t, "graph-basic")
 	state := &State{
@@ -873,6 +935,19 @@ root
   root -> aws_load_balancer.weblb
 `
 
+const testTerraformGraphDiffModuleStr = `
+root: root
+aws_instance.foo
+  aws_instance.foo -> aws_instance.foo (destroy)
+  aws_instance.foo -> module.child
+aws_instance.foo (destroy)
+module.child
+  module.child -> aws_instance.foo (destroy)
+root
+  root -> aws_instance.foo
+  root -> module.child
+`
+
 const testTerraformGraphModulesStr = `
 root: root
 aws_instance.web

terraform/test-fixtures/graph-diff-module/child/main.tf

@@ -0,0 +1,5 @@
+resource "aws_instance" "foo" {}
+
+output "bar" {
+    value = "baz"
+}

terraform/test-fixtures/graph-diff-module/main.tf

@@ -0,0 +1,7 @@
+module "child" {
+    source = "./child"
+}
+
+resource "aws_instance" "foo" {
+    value = "${module.child.bar}"
+}