Now, we return original content in case of error

ordering/main.go

@@ -186,11 +186,24 @@ func GetTypeComments(d *ast.GenDecl) []string {
 func ReorderSource(filename, formatCommand string, reorderStructs bool, src interface{}) (string, error) {
 	methods, constructors, structs, err := Parse(filename, formatCommand, src)
 
+	// in all cases, we must return the original source code if an error occurs
+	// get the content of the file
+	var content []byte
+	if src == nil {
+		var err error
+		content, err = ioutil.ReadFile(filename)
+		if err != nil {
+			return "", err
+		}
+	} else {
+		content = src.([]byte)
+	}
+
 	if err != nil {
-		return "", err
+		return string(content), err
 	}
 	if len(structs) == 0 {
-		return "", errors.New("No structs found in " + filename + ", cannot reorder")
+		return string(content), errors.New("No structs found in " + filename + ", cannot reorder")
 	}
 
 	// sort methods by name
@@ -213,17 +226,6 @@ func ReorderSource(filename, formatCommand string, reorderStructs bool, src inte
 	if reorderStructs {
 		sort.Strings(structNames)
 	}
-	// get the content of the file
-	var content []byte
-	if src == nil {
-		var err error
-		content, err = ioutil.ReadFile(filename)
-		if err != nil {
-			return "", err
-		}
-	} else {
-		content = src.([]byte)
-	}
 
 	// Get the source code signature
 	sign := fmt.Sprintf("%x", sha256.Sum256(content))

ordering/main_test.go

@@ -120,3 +120,18 @@ func TestReorder(t *testing.T) {
 	}
 
 }
+
+func TestNoStruct(t *testing.T) {
+	const source = `package main
+    func main() {
+        fmt.Println("nothing")
+    }
+    `
+	content, err := ReorderSource(source, "gofmt", true, []byte(source))
+	if err == nil {
+		t.Error("Expected error")
+	}
+	if content != source {
+		t.Errorf("Expected:\n%s\nGot:\n%s\n", source, content)
+	}
+}