config: validate that count is an int

config/config.go

@@ -275,6 +275,18 @@ func (c *Config) Validate() error {
 			}
 		}
 
+		// Interpolate with a fixed number to verify that its a number
+		r.RawCount.interpolate(func(Interpolation) (string, error) {
+			return "5", nil
+		})
+		_, err := strconv.ParseInt(r.RawCount.Value().(string), 0, 0)
+		if err != nil {
+			errs = append(errs, fmt.Errorf(
+				"%s: resource count must be an integer",
+				n))
+		}
+		r.RawCount.init()
+
 		for _, d := range r.DependsOn {
 			if _, ok := resources[d]; !ok {
 				errs = append(errs, fmt.Errorf(

config/config_test.go

@@ -53,6 +53,13 @@ func TestConfigValidate_badDependsOn(t *testing.T) {
 	}
 }
 
+func TestConfigValidate_countInt(t *testing.T) {
+	c := testConfig(t, "validate-count-int")
+	if err := c.Validate(); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+}
+
 func TestConfigValidate_countModuleVar(t *testing.T) {
 	c := testConfig(t, "validate-count-module-var")
 	if err := c.Validate(); err == nil {
@@ -60,6 +67,13 @@ func TestConfigValidate_countModuleVar(t *testing.T) {
 	}
 }
 
+func TestConfigValidate_countNotInt(t *testing.T) {
+	c := testConfig(t, "validate-count-not-int")
+	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 {

config/raw_config.go

@@ -79,24 +79,9 @@ func (r *RawConfig) Config() map[string]interface{} {
 //
 // If a variable key is missing, this will panic.
 func (r *RawConfig) Interpolate(vs map[string]string) error {
-	config, err := copystructure.Copy(r.Raw)
+	return r.interpolate(func(i Interpolation) (string, error) {
-	if err != nil {
-		return err
-	}
-	r.config = config.(map[string]interface{})
-
-	fn := func(i Interpolation) (string, error) {
 		return i.Interpolate(vs)
-	}
+	})
-
-	w := &interpolationWalker{F: fn, Replace: true}
-	err = reflectwalk.Walk(r.config, w)
-	if err != nil {
-		return err
-	}
-
-	r.unknownKeys = w.unknownKeys
-	return nil
 }
 
 func (r *RawConfig) init() error {
@@ -126,6 +111,23 @@ func (r *RawConfig) init() error {
 	return nil
 }
 
+func (r *RawConfig) interpolate(fn interpolationWalkerFunc) error {
+	config, err := copystructure.Copy(r.Raw)
+	if err != nil {
+		return err
+	}
+	r.config = config.(map[string]interface{})
+
+	w := &interpolationWalker{F: fn, Replace: true}
+	err = reflectwalk.Walk(r.config, w)
+	if err != nil {
+		return err
+	}
+
+	r.unknownKeys = w.unknownKeys
+	return nil
+}
+
 func (r *RawConfig) merge(r2 *RawConfig) *RawConfig {
 	rawRaw, err := copystructure.Copy(r.Raw)
 	if err != nil {

config/test-fixtures/validate-count-int/main.tf

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

config/test-fixtures/validate-count-not-int/main.tf

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