terraform: dependsOn builds into the graph

terraform/graph.go

@@ -106,6 +106,9 @@ func Graph(opts *GraphOpts) (*depgraph.Graph, error) {
 	// and no dependencies.
 	graphAddConfigResources(g, opts.Config, opts.State)
 
+	// Add explicit dependsOn dependencies to the graph
+	graphAddExplicitDeps(g)
+
 	// Next, add the state orphans if we have any
 	if opts.State != nil {
 		graphAddOrphans(g, opts.Config, opts.State)
@@ -377,6 +380,48 @@ func graphAddDiff(g *depgraph.Graph, d *Diff) error {
 	return nil
 }
 
+// graphAddExplicitDeps adds the dependencies to the graph for the explicit
+// dependsOn configurations.
+func graphAddExplicitDeps(g *depgraph.Graph) {
+	depends := false
+
+	rs := make(map[string]*depgraph.Noun)
+	for _, n := range g.Nouns {
+		rn, ok := n.Meta.(*GraphNodeResource)
+		if !ok {
+			continue
+		}
+
+		rs[rn.Config.Id()] = n
+		if len(rn.Config.DependsOn) > 0 {
+			depends = true
+		}
+	}
+
+	// If we didn't have any dependsOn, just return
+	if !depends {
+		return
+	}
+
+	for _, n1 := range rs {
+		rn1 := n1.Meta.(*GraphNodeResource)
+		for _, d := range rn1.Config.DependsOn {
+			for _, n2 := range rs {
+				rn2 := n2.Meta.(*GraphNodeResource)
+				if rn2.Config.Id() != d {
+					continue
+				}
+
+				n1.Deps = append(n1.Deps, &depgraph.Dependency{
+					Name:   d,
+					Source: n1,
+					Target: n2,
+				})
+			}
+		}
+	}
+}
+
 // graphAddMissingResourceProviders adds GraphNodeResourceProvider nodes for
 // the resources that do not have an explicit resource provider specified
 // because no provider configuration was given.

terraform/graph_test.go

@@ -51,6 +51,21 @@ func TestGraph_cycle(t *testing.T) {
 	}
 }
 
+func TestGraph_dependsOn(t *testing.T) {
+	config := testConfig(t, "graph-depends-on")
+
+	g, err := Graph(&GraphOpts{Config: config})
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	actual := strings.TrimSpace(g.String())
+	expected := strings.TrimSpace(testTerraformGraphDependsStr)
+	if actual != expected {
+		t.Fatalf("bad:\n\n%s", actual)
+	}
+}
+
 func TestGraph_state(t *testing.T) {
 	config := testConfig(t, "graph-basic")
 	state := &State{
@@ -347,6 +362,16 @@ root
   root -> aws_load_balancer.weblb
 `
 
+const testTerraformGraphDependsStr = `
+root: root
+aws_instance.db
+  aws_instance.db -> aws_instance.web
+aws_instance.web
+root
+  root -> aws_instance.db
+  root -> aws_instance.web
+`
+
 const testTerraformGraphDiffStr = `
 root: root
 aws_instance.foo

terraform/test-fixtures/graph-depends-on/main.tf

@@ -0,0 +1,5 @@
+resource "aws_instance" "web" {}
+
+resource "aws_instance" "db" {
+	depends_on = ["aws_instance.web"]
+}