config: error if unknown filetype

config/import_tree.go

@@ -2,6 +2,7 @@ package config
 
 import (
 	"fmt"
+	"path/filepath"
 )
 
 // configurable is an interface that must be implemented by any configuration
@@ -30,7 +31,17 @@ type fileLoaderFunc func(path string) (configurable, []string, error)
 // file. This function detects what kind of configuration file it is an
 // executes the proper fileLoaderFunc.
 func loadTree(root string) (*importTree, error) {
-	c, imps, err := loadFileLibucl(root)
+	var f fileLoaderFunc
+	switch filepath.Ext(root) {
+	case ".tf":
+		f = loadFileLibucl
+	default:
+		return nil, fmt.Errorf(
+			"%s: uknown configuration format. Use '.tf' or '.tf.rb' extension",
+			root)
+	}
+
+	c, imps, err := f(root)
 	if err != nil {
 		return nil, err
 	}

config/loader_test.go

@@ -7,6 +7,13 @@ import (
 	"testing"
 )
 
+func TestLoad_badType(t *testing.T) {
+	_, err := Load(filepath.Join(fixtureDir, "bad_type.tf.nope"))
+	if err == nil {
+		t.Fatal("should have error")
+	}
+}
+
 func TestLoadBasic(t *testing.T) {
 	c, err := Load(filepath.Join(fixtureDir, "basic.tf"))
 	if err != nil {

config/test-fixtures/bad_type.tf.nope

@@ -0,0 +1 @@
+variable "foo" {}