terraform: refresh ignores variables with no values [GH-478]

terraform/context.go

@@ -1611,19 +1611,25 @@ func (c *walkContext) computeResourceVariable(
 	// Get the relevant module
 	module := c.Context.state.ModuleByPath(c.Path)
 
-	r, ok := module.Resources[id]
+	var r *ResourceState
-	if !ok {
+	if module != nil {
-		if v.Multi && v.Index == 0 {
+		var ok bool
+		r, ok = module.Resources[id]
+		if !ok && v.Multi && v.Index == 0 {
 			r, ok = module.Resources[v.ResourceId()]
 		}
 		if !ok {
-			return "", fmt.Errorf(
+			r = nil
-				"Resource '%s' not found for variable '%s'",
-				id,
-				v.FullKey())
 		}
 	}
 
+	if r == nil {
+		return "", fmt.Errorf(
+			"Resource '%s' not found for variable '%s'",
+			id,
+			v.FullKey())
+	}
+
 	if r.Primary == nil {
 		goto MISSING
 	}

terraform/context_test.go

@@ -4110,6 +4110,22 @@ func TestContextRefresh_modules(t *testing.T) {
 	}
 }
 
+func TestContextRefresh_moduleInputComputedOutput(t *testing.T) {
+	m := testModule(t, "refresh-module-input-computed-output")
+	p := testProvider("aws")
+	p.DiffFn = testDiffFn
+	ctx := testContext(t, &ContextOpts{
+		Module: m,
+		Providers: map[string]ResourceProviderFactory{
+			"aws": testProviderFuncFixed(p),
+		},
+	})
+
+	if _, err := ctx.Refresh(); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+}
+
 // GH-70
 func TestContextRefresh_noState(t *testing.T) {
 	p := testProvider("aws")

terraform/test-fixtures/refresh-module-input-computed-output/child/main.tf

@@ -0,0 +1,9 @@
+variable "input" {}
+
+resource "aws_instance" "foo" {
+    foo = "${var.input}"
+}
+
+output "foo" {
+    value = "${aws_instance.foo.foo}"
+}

terraform/test-fixtures/refresh-module-input-computed-output/main.tf

@@ -0,0 +1,8 @@
+module "child" {
+    input = "${aws_instance.bar.foo}"
+    source = "./child"
+}
+
+resource "aws_instance" "bar" {
+    compute = "foo"
+}