config: validate that only proper variables can be in the count

config/config.go

@@ -255,6 +255,26 @@ func (c *Config) Validate() error {
 
 	// Validate resources
 	for n, r := range resources {
+		// Verify count variables
+		for _, v := range r.RawCount.Variables {
+			switch v.(type) {
+			case *ModuleVariable:
+				errs = append(errs, fmt.Errorf(
+					"%s: resource count can't reference module variable: %s",
+					n,
+					v.FullKey()))
+			case *ResourceVariable:
+				errs = append(errs, fmt.Errorf(
+					"%s: resource count can't reference resource variable: %s",
+					n,
+					v.FullKey()))
+			case *UserVariable:
+				// Good
+			default:
+				panic("Unknown type in count var: " + n)
+			}
+		}
+
 		for _, d := range r.DependsOn {
 			if _, ok := resources[d]; !ok {
 				errs = append(errs, fmt.Errorf(

config/config_test.go

@@ -53,6 +53,27 @@ func TestConfigValidate_badDependsOn(t *testing.T) {
 	}
 }
 
+func TestConfigValidate_countModuleVar(t *testing.T) {
+	c := testConfig(t, "validate-count-module-var")
+	if err := c.Validate(); err == nil {
+		t.Fatal("should not be valid")
+	}
+}
+
+func TestConfigValidate_countResourceVar(t *testing.T) {
+	c := testConfig(t, "validate-count-resource-var")
+	if err := c.Validate(); err == nil {
+		t.Fatal("should not be valid")
+	}
+}
+
+func TestConfigValidate_countUserVar(t *testing.T) {
+	c := testConfig(t, "validate-count-user-var")
+	if err := c.Validate(); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+}
+
 func TestConfigValidate_dupModule(t *testing.T) {
 	c := testConfig(t, "validate-dup-module")
 	if err := c.Validate(); err == nil {

config/test-fixtures/validate-count-module-var/main.tf

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

config/test-fixtures/validate-count-resource-var/main.tf

@@ -0,0 +1,5 @@
+resource "aws_instance" "foo" {}
+
+resource "aws_instance" "web" {
+    count = "${aws_instance.foo.bar}"
+}

config/test-fixtures/validate-count-user-var/main.tf

@@ -0,0 +1,5 @@
+variable "foo" {}
+
+resource "aws_instance" "web" {
+    count = "${var.foo}"
+}