handle variables recursively, add some examples

example-files/config/variables.tf

@@ -0,0 +1,32 @@
+variable "instance_type" {
+  default = "t2.micro"
+}
+
+variable "ami" {
+  default = "ami-f2d3638a"
+}
+
+variable "project" {
+  default = "demo"
+}
+
+resource "aws_instance" "first" {
+  ami = "${var.ami}"
+  instance_type = "${var.instance_type}"
+  tags = {
+    project = "${var.project}"
+  }
+}
+
+variable "instance_type_2" {
+  default = "c4.large"
+}
+
+resource "aws_instance" "second" {
+  ami = "${var.ami}"
+  instance_type = "${var.instance_type_2}"
+  tags = {
+    project = "${var.project}"
+  }
+}
+

example-files/rules/variables.tf

@@ -0,0 +1,24 @@
+version: 1
+description: Rules for Terraform configuration files
+type: Terraform
+files:
+  - "*.tf"
+rules:
+
+  - id: INSTANCE_TYPE
+    message: Instance type should be t2.micro or m3.medium
+    resource: aws_instance
+    assertions:
+      - key: instance_type
+        op: in
+        value: t2.micro,m3.medium
+    severity: WARNING
+
+  - id: PROJECT_TAG
+    message: Check project tag
+    resource: aws_instance
+    assertions:
+      - key: "tags[].project|[0]"
+        op: eq
+        value: demo
+    severity: WARNING

linter/terraform.go

@@ -147,15 +147,40 @@ func (l TerraformResourceLoader) Load(filename string) ([]assertion.Resource, er
 	return resources, nil
 }
 
-func replaceVariables(templateResource map[string]interface{}, variables map[string]interface{}) map[string]interface{} {
+func replaceVariables(templateResource interface{}, variables map[string]interface{}) interface{} {
+	switch v := templateResource.(type) {
+	case map[string]interface{}:
+		return replaceVariablesInMap(v, variables)
+	default:
+		assertion.Debugf("replaceVariables cannot process type %T\n", v)
+		return templateResource
+	}
+}
+
+func replaceVariablesInMap(templateResource map[string]interface{}, variables map[string]interface{}) interface{} {
 	for key, value := range templateResource {
-		if s, ok := value.(string); ok { // FIXME is not a string, need to recurse
-			templateResource[key] = resolveValue(s, variables)
+		switch v := value.(type) {
+		case string:
+			templateResource[key] = resolveValue(v, variables)
+		case map[string]interface{}:
+			templateResource[key] = replaceVariablesInMap(v, variables)
+		case []interface{}:
+			templateResource[key] = replaceVariablesInList(v, variables)
+		default:
+			assertion.Debugf("replaceVariablesInMap cannot process type %T\n", v)
 		}
 	}
 	return templateResource
 }
 
+func replaceVariablesInList(list []interface{}, variables map[string]interface{}) []interface{} {
+	result := []interface{}{}
+	for _, e := range list {
+		result = append(result, replaceVariables(e, variables))
+	}
+	return result
+}
+
 func resolveValue(s string, variables map[string]interface{}) string {
 	pattern := "[$][{]var[.](?P<name>.*)[}]"
 	re, _ := regexp.Compile(pattern)