Friday, March 22, 2019

Automated rename refactoring in N4JS IDE

Refactoring is probably one of the most important tools for us, software developers since we constantly need to change the structure of the code to improve the code quality or to prepare the code for new features etc. The most used refactoring operation is arguably rename refactoring. Find and replace could be used for renaming but the risk of renaming unrelated names is pretty high.

N4JS IDE provides a powerful way of automatically renaming a definition and all its references with a comparable user experience as rename refactoring of Eclipse Java Development Tool (JDT).  The slogan is: I want to rename this thing, do it for me however you like but please in a safe manner so that I can move on! This will exactly be your experience with rename refactoring in N4JS IDE.

Simple rename example

Let's have look at a simple example to see how rename refactoring works in N4JS IDE in action. Assume that we have an N4JS file with the following content.

When the cursor is at A of the constructor new A()and we press Cmd + Shift + R to rename A to B, the rename refactoring suggests that it would rename A to B at 3 different locations. After entering the new name B and pressing enter, the class A and all its usages are renamed to B, fully automatically :-)

Name conflicts detection 

Renaming an element may cause name conflicts. The rename refactoring in N4JS IDE provides comprehensive checks for detecting name conflicts. If the new name would cause name conflicts, the rename refactoring is disallowed.

In the example above,  renaming class A to class C would cause a name conflict because in the script scope the name C already exists. The rename refactoring provided by N4JS IDE can recognize this conflict and shows an error message.

In a large code base, these checks are a true life saver. Imagine having to manually verify these kinds of name conflicts across hundred of files.

Additionally, N4JS IDE's rename refactoring is capable of recognizing name conflicts when renaming

  • members of classifier
  • formal parameters of a function or method
  • field of a structural type
  • enum literal
  • local variable, constant
  • global variable, constant
  • etc.

Rename composed members

N4JS language supports composed elements. Renaming a composed element is somewhat special.

In this example, is a composed member because ab is of the intersection type A & B which is composed of both A and B. Renaming would rename all the definitions that contribute to the creation of as well as all references of these definitions.

Preview of changes

When you start rename refactoring operation, you have the possibility to see the preview of changes before actually executing the operation.

Note that the preview shows the changes in each file in a very recognizable manner.

Undo changes

After the rename refactoring, if you feel regret and would like to undo the operation, simply press Cmd + Z. The undo will undo all the changes in affected files previously done by the rename refactoring.

Current limitations

As the time of this writing, the rename refactoring in N4JS IDE still has several limitations:
  • Renaming alias is not supported
  • Checking name conflicts do not take into account shadowing

By Minh Quang Tran