terraform: module w/ computed output works

terraform/context.go

@@ -473,8 +473,8 @@ func (c *walkContext) Walk() error {
 	if m == nil {
 		return nil
 	}
-	config := m.Config()
-	if len(config.Outputs) == 0 {
+	conf := m.Config()
+	if len(conf.Outputs) == 0 {
 		return nil
 	}
 
@@ -490,11 +490,18 @@ func (c *walkContext) Walk() error {
 	}
 
 	outputs := make(map[string]string)
-	for _, o := range config.Outputs {
+	for _, o := range conf.Outputs {
 		if err := c.computeVars(o.RawConfig); err != nil {
 			return err
 		}
 		vraw := o.RawConfig.Config()["value"]
+		if vraw == nil {
+			// This likely means that the result of the output is
+			// a computed variable.
+			if o.RawConfig.Raw["value"] != nil {
+				vraw = config.UnknownVariableValue
+			}
+		}
 		if vraw != nil {
 			outputs[o.Name] = vraw.(string)
 		}

terraform/context_test.go

@@ -1513,6 +1513,29 @@ func TestContextPlan_moduleVar(t *testing.T) {
 	}
 }
 
+func TestContextPlan_moduleVarComputed(t *testing.T) {
+	m := testModule(t, "plan-module-var-computed")
+	p := testProvider("aws")
+	p.DiffFn = testDiffFn
+	ctx := testContext(t, &ContextOpts{
+		Module: m,
+		Providers: map[string]ResourceProviderFactory{
+			"aws": testProviderFuncFixed(p),
+		},
+	})
+
+	plan, err := ctx.Plan(nil)
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	actual := strings.TrimSpace(plan.String())
+	expected := strings.TrimSpace(testTerraformPlanModuleVarComputedStr)
+	if actual != expected {
+		t.Fatalf("bad:\n%s", actual)
+	}
+}
+
 func TestContextPlan_nil(t *testing.T) {
 	m := testModule(t, "plan-nil")
 	p := testProvider("aws")

terraform/terraform_test.go

@@ -545,6 +545,23 @@ STATE:
 <no state>
 `
 
+const testTerraformPlanModuleVarComputedStr = `
+DIFF:
+
+CREATE: aws_instance.bar
+  foo:  "" => "<computed>"
+  type: "" => "aws_instance"
+
+module.child:
+  CREATE: aws_instance.foo
+    foo:  "" => "<computed>"
+    type: "" => "aws_instance"
+
+STATE:
+
+<no state>
+`
+
 const testTerraformPlanOrphanStr = `
 DIFF:
 

terraform/test-fixtures/plan-module-var-computed/child/main.tf

@@ -0,0 +1,7 @@
+resource "aws_instance" "foo" {
+    compute = "foo"
+}
+
+output "num" {
+    value = "${aws_instance.foo.foo}"
+}

terraform/test-fixtures/plan-module-var-computed/main.tf

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