config: validate dependsOn

config/config.go

@@ -155,6 +155,17 @@ func (c *Config) Validate() error {
 	}
 	dupped = nil
 
+	// Make sure all dependsOn are valid in resources
+	for n, r := range resources {
+		for _, d := range r.DependsOn {
+			if _, ok := resources[d]; !ok {
+				errs = append(errs, fmt.Errorf(
+					"%s: resource depends on non-existent resource '%s'",
+					n, d))
+			}
+		}
+	}
+
 	for source, vs := range vars {
 		for _, v := range vs {
 			rv, ok := v.(*ResourceVariable)

config/config_test.go

@@ -16,6 +16,13 @@ func TestConfigValidate(t *testing.T) {
 	}
 }
 
+func TestConfigValidate_badDependsOn(t *testing.T) {
+	c := testConfig(t, "validate-bad-depends-on")
+	if err := c.Validate(); err == nil {
+		t.Fatal("should not be valid")
+	}
+}
+
 func TestConfigValidate_badMultiResource(t *testing.T) {
 	c := testConfig(t, "validate-bad-multi-resource")
 	if err := c.Validate(); err == nil {

config/test-fixtures/validate-bad-depends-on/main.tf

@@ -0,0 +1,3 @@
+resource "aws_instance" "web" {
+    depends_on = ["aws_instance.db"]
+}

config/test-fixtures/validate-good/main.tf

@@ -32,4 +32,6 @@ resource aws_instance "web" {
         device_index = 0
         description = "Main network interface"
     }
+
+    depends_on = ["aws_security_group.firewall"]
 }