terraform: module variable transform must do children later (tested)

terraform/context_apply_test.go

@@ -3094,6 +3094,8 @@ func TestContext2Apply_destroyModuleWithAttrsReferencingResource(t *testing.T) {
 		if err != nil {
 			t.Fatalf("apply err: %s", err)
 		}
+
+		t.Logf("Step 1 state: %s", state)
 	}
 
 	h := new(HookRecordApplyOrder)

terraform/test-fixtures/transform-module-var-basic/child/main.tf

@@ -0,0 +1,3 @@
+variable "value" {}
+
+output "result" { value = "${var.value}" }

terraform/test-fixtures/transform-module-var-basic/main.tf

@@ -0,0 +1,4 @@
+module "child" {
+    source = "./child"
+    value = "foo"
+}

terraform/test-fixtures/transform-module-var-nested/child/child/main.tf

@@ -0,0 +1,3 @@
+variable "value" {}
+
+output "result" { value = "${var.value}" }

terraform/test-fixtures/transform-module-var-nested/child/main.tf

@@ -0,0 +1,6 @@
+variable "value" {}
+
+module "child" {
+    source = "./child"
+    value  = "${var.value}"
+}

terraform/test-fixtures/transform-module-var-nested/main.tf

@@ -0,0 +1,4 @@
+module "child" {
+    source = "./child"
+    value  = "foo"
+}

terraform/transform_module_variable.go

@@ -28,15 +28,32 @@ func (t *ModuleVariableTransformer) transform(g *Graph, parent, m *module.Tree)
 		return nil
 	}
 
-	// Transform all the children.
+	// If we have no parent, then don't do anything. This is because
+	// we need to be able to get the set value from the module declaration.
+	if err := t.transformSingle(g, parent, m); err != nil {
+		return nil
+	}
+
+	// Transform all the children. This has to be _after_ the above
+	// since children can reference parent variables but parents can't
+	// access children. Example:
+	//
+	//   module foo { value = "${var.foo}" }
+	//
+	// The "value" var in "foo" (a child) is accessing the "foo" bar
+	// in the parent (current module). However, there is no way for the
+	// current module to reference a variable in the child module.
 	for _, c := range m.Children() {
 		if err := t.transform(g, m, c); err != nil {
 			return err
 		}
 	}
 
-	// If we have no parent, then don't do anything. This is because
-	// we need to be able to get the set value from the module declaration.
+	return nil
+}
+
+func (t *ModuleVariableTransformer) transformSingle(g *Graph, parent, m *module.Tree) error {
+	// If we have no parent, we can't determine if the parent uses our variables
 	if parent == nil {
 		return nil
 	}
@@ -44,6 +61,7 @@ func (t *ModuleVariableTransformer) transform(g *Graph, parent, m *module.Tree)
 	// If we have no vars, we're done!
 	vars := m.Config().Variables
 	if len(vars) == 0 {
+		log.Printf("[TRACE] Module %#v has no variables, skipping.", m.Path())
 		return nil
 	}
 
@@ -56,7 +74,7 @@ func (t *ModuleVariableTransformer) transform(g *Graph, parent, m *module.Tree)
 		}
 	}
 	if mod == nil {
-		log.Printf("[INFO] Module %q not used, not adding variables", m.Name())
+		log.Printf("[INFO] Module %#v not used, not adding variables", m.Path())
 		return nil
 	}
 

terraform/transform_module_variable_test.go

@@ -0,0 +1,65 @@
+package terraform
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestModuleVariableTransformer(t *testing.T) {
+	g := Graph{Path: RootModulePath}
+	module := testModule(t, "transform-module-var-basic")
+
+	{
+		tf := &RootVariableTransformer{Module: module}
+		if err := tf.Transform(&g); err != nil {
+			t.Fatalf("err: %s", err)
+		}
+	}
+
+	{
+		tf := &ModuleVariableTransformer{Module: module}
+		if err := tf.Transform(&g); err != nil {
+			t.Fatalf("err: %s", err)
+		}
+	}
+
+	actual := strings.TrimSpace(g.String())
+	expected := strings.TrimSpace(testTransformModuleVarBasicStr)
+	if actual != expected {
+		t.Fatalf("bad:\n\n%s", actual)
+	}
+}
+
+func TestModuleVariableTransformer_nested(t *testing.T) {
+	g := Graph{Path: RootModulePath}
+	module := testModule(t, "transform-module-var-nested")
+
+	{
+		tf := &RootVariableTransformer{Module: module}
+		if err := tf.Transform(&g); err != nil {
+			t.Fatalf("err: %s", err)
+		}
+	}
+
+	{
+		tf := &ModuleVariableTransformer{Module: module}
+		if err := tf.Transform(&g); err != nil {
+			t.Fatalf("err: %s", err)
+		}
+	}
+
+	actual := strings.TrimSpace(g.String())
+	expected := strings.TrimSpace(testTransformModuleVarNestedStr)
+	if actual != expected {
+		t.Fatalf("bad:\n\n%s", actual)
+	}
+}
+
+const testTransformModuleVarBasicStr = `
+module.child.var.value
+`
+
+const testTransformModuleVarNestedStr = `
+module.child.module.child.var.value
+module.child.var.value
+`