config: parse depends_on for outputs

config/config.go

@@ -154,6 +154,7 @@ type Variable struct {
 type Output struct {
 	Name      string
 	Sensitive bool
+	DependsOn []string
 	RawConfig *RawConfig
 }
 

config/config_string.go

@@ -100,6 +100,13 @@ func outputsStr(os []*Output) string {
 
 		result += fmt.Sprintf("%s\n", n)
 
+		if len(o.DependsOn) > 0 {
+			result += fmt.Sprintf("  dependsOn\n")
+			for _, d := range o.DependsOn {
+				result += fmt.Sprintf("    %s\n", d)
+			}
+		}
+
 		if len(o.RawConfig.Variables) > 0 {
 			result += fmt.Sprintf("  vars\n")
 			for _, rawV := range o.RawConfig.Variables {

config/loader_hcl.go

@@ -292,11 +292,21 @@ func loadOutputsHcl(list *ast.ObjectList) ([]*Output, error) {
 	for _, item := range list.Items {
 		n := item.Keys[0].Token.Value().(string)
 
+		var listVal *ast.ObjectList
+		if ot, ok := item.Val.(*ast.ObjectType); ok {
+			listVal = ot.List
+		} else {
+			return nil, fmt.Errorf("output '%s': should be an object", n)
+		}
+
 		var config map[string]interface{}
 		if err := hcl.DecodeObject(&config, item.Val); err != nil {
 			return nil, err
 		}
 
+		// Delete special keys
+		delete(config, "depends_on")
+
 		rawConfig, err := NewRawConfig(config)
 		if err != nil {
 			return nil, fmt.Errorf(
@@ -305,9 +315,22 @@ func loadOutputsHcl(list *ast.ObjectList) ([]*Output, error) {
 				err)
 		}
 
+		// If we have depends fields, then add those in
+		var dependsOn []string
+		if o := listVal.Filter("depends_on"); len(o.Items) > 0 {
+			err := hcl.DecodeObject(&dependsOn, o.Items[0].Val)
+			if err != nil {
+				return nil, fmt.Errorf(
+					"Error reading depends_on for output %q: %s",
+					n,
+					err)
+			}
+		}
+
 		result = append(result, &Output{
 			Name:      n,
 			RawConfig: rawConfig,
+			DependsOn: dependsOn,
 		})
 	}
 

config/loader_test.go

@@ -286,6 +286,26 @@ func TestLoadFileBasic_modules(t *testing.T) {
 	}
 }
 
+func TestLoadFile_outputDependsOn(t *testing.T) {
+	c, err := LoadFile(filepath.Join(fixtureDir, "output-depends-on.tf"))
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	if c == nil {
+		t.Fatal("config should not be nil")
+	}
+
+	if c.Dir != "" {
+		t.Fatalf("bad: %#v", c.Dir)
+	}
+
+	actual := outputsStr(c.Outputs)
+	if actual != strings.TrimSpace(outputDependsOnStr) {
+		t.Fatalf("bad:\n%s", actual)
+	}
+}
+
 func TestLoadJSONBasic(t *testing.T) {
 	raw, err := ioutil.ReadFile(filepath.Join(fixtureDir, "basic.tf.json"))
 	if err != nil {
@@ -1092,6 +1112,12 @@ aws_instance.web (x1)
     user: var.foo
 `
 
+const outputDependsOnStr = `
+value
+  dependsOn
+    foo
+`
+
 const variablesVariablesStr = `
 bar
   <>

config/test-fixtures/output-depends-on.tf

@@ -0,0 +1,4 @@
+output "value" {
+    value = "foo"
+    depends_on = ["foo"]
+}