config: nicer error if dir isn't a dir

config/loader.go

@@ -49,6 +49,16 @@ func LoadDir(root string) (*Config, error) {
 		return nil, err
 	}
 
+	fi, err := f.Stat()
+	if err != nil {
+		return nil, err
+	}
+	if !fi.IsDir() {
+		return nil, fmt.Errorf(
+			"configuration path must be a directory: %s",
+			root)
+	}
+
 	err = nil
 	for err != io.EOF {
 		var fis []os.FileInfo

config/loader_test.go

@@ -149,6 +149,13 @@ func TestLoadDir_basic(t *testing.T) {
 	}
 }
 
+func TestLoadDir_file(t *testing.T) {
+	_, err := LoadDir(filepath.Join(fixtureDir, "variables.tf"))
+	if err == nil {
+		t.Fatal("should error")
+	}
+}
+
 func TestLoadDir_noConfigs(t *testing.T) {
 	_, err := LoadDir(filepath.Join(fixtureDir, "dir-empty"))
 	if err == nil {