Module variables not being interpolated

Variables weren't being interpolated during the Input phase, causing a
syntax error on the interpolation string. Adding `walkInput` to the
EvalTree operations prevents skipping the interpolation step.

terraform/context_input_test.go

@@ -569,3 +569,26 @@ func TestContext2Input_varPartiallyComputed(t *testing.T) {
 		t.Fatalf("err: %s", err)
 	}
 }
+
+// Module variables weren't being interpolated during the Input walk.
+// https://github.com/hashicorp/terraform/issues/5322
+func TestContext2Input_interpolateVar(t *testing.T) {
+	input := new(MockUIInput)
+
+	m := testModule(t, "input-interpolate-var")
+	p := testProvider("null")
+	p.ApplyFn = testApplyFn
+	p.DiffFn = testDiffFn
+
+	ctx := testContext2(t, &ContextOpts{
+		Module: m,
+		Providers: map[string]ResourceProviderFactory{
+			"template": testProviderFuncFixed(p),
+		},
+		UIInput: input,
+	})
+
+	if err := ctx.Input(InputModeStd); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+}

terraform/eval_context_builtin.go

@@ -291,6 +291,7 @@ func (ctx *BuiltinEvalContext) Interpolate(
 			Path:     ctx.Path(),
 			Resource: r,
 		}
+
 		vs, err := ctx.Interpolater.Values(scope, cfg.Variables)
 		if err != nil {
 			return nil, err

terraform/eval_interpolate.go

@@ -1,8 +1,6 @@
 package terraform
 
-import (
+import "github.com/hashicorp/terraform/config"
-	"github.com/hashicorp/terraform/config"
-)
 
 // EvalInterpolate is an EvalNode implementation that takes a raw
 // configuration and interpolates it.

terraform/graph_config_node_output.go

@@ -44,7 +44,7 @@ func (n *GraphNodeConfigOutput) DependentOn() []string {
 // GraphNodeEvalable impl.
 func (n *GraphNodeConfigOutput) EvalTree() EvalNode {
 	return &EvalOpFilter{
-		Ops: []walkOperation{walkRefresh, walkPlan, walkApply, walkDestroy},
+		Ops: []walkOperation{walkRefresh, walkPlan, walkApply, walkDestroy, walkInput},
 		Node: &EvalSequence{
 			Nodes: []EvalNode{
 				&EvalWriteOutput{

terraform/interpolate.go

@@ -129,6 +129,7 @@ func (i *Interpolater) valueModuleVar(
 	n string,
 	v *config.ModuleVariable,
 	result map[string]ast.Variable) error {
+
 	// If we're computing all dynamic fields, then module vars count
 	// and we mark it as computed.
 	if i.Operation == walkValidate {

terraform/test-fixtures/input-interpolate-var/child/main.tf

@@ -0,0 +1,5 @@
+variable "list" { }
+resource "template_file" "temp" {
+  count     = "${length(split(",", var.list))}"
+  template  = "foo"
+}

terraform/test-fixtures/input-interpolate-var/main.tf

@@ -0,0 +1,7 @@
+module "source" {
+  source = "./source"
+}
+module "child" {
+  source  = "./child"
+  list = "${module.source.list}"
+}

terraform/test-fixtures/input-interpolate-var/source/main.tf

@@ -0,0 +1 @@
+output "list" { value = "foo,bar,baz" }