Refactoring with Codemods to Automate API Adjustments

Clear a Stale Function Toggle

Let’s begin with a easy but sensible instance to display the
energy of codemods. Think about you’re utilizing a feature
toggle in your
codebase to manage the discharge of unfinished or experimental options.
As soon as the function is stay in manufacturing and dealing as anticipated, the subsequent
logical step is to scrub up the toggle and any associated logic.

As an example, take into account the next code:

const knowledge = featureToggle('feature-new-product-list') ? { title: 'Product' } : undefined;

As soon as the function is absolutely launched and now not wants a toggle, this
could be simplified to:

const knowledge = { title: 'Product' };

The duty entails discovering all situations of featureToggle within the
codebase, checking whether or not the toggle refers to
feature-new-product-list, and eradicating the conditional logic surrounding
it. On the similar time, different function toggles (like
feature-search-result-refinement, which can nonetheless be in improvement)
ought to stay untouched. The codemod must perceive the construction
of the code to use adjustments selectively.

Understanding the AST

Earlier than we dive into writing the codemod, let’s break down how this
particular code snippet seems to be in an AST. You should use instruments like AST
Explorer to visualise how supply code and AST
are mapped. It’s useful to know the node sorts you are interacting
with earlier than making use of any adjustments.

The picture beneath exhibits the syntax tree when it comes to ECMAScript syntax. It
accommodates nodes like Identifier (for variables), StringLiteral (for the
toggle title), and extra summary nodes like CallExpression and
ConditionalExpression.

Determine 2: The Summary Syntax Tree illustration of the function toggle verify

On this AST illustration, the variable knowledge is assigned utilizing a
ConditionalExpression. The check a part of the expression calls
featureToggle('feature-new-product-list'). If the check returns true,
the consequent department assigns { title: 'Product' } to knowledge. If
false, the alternate department assigns undefined.

For a activity with clear enter and output, I want writing checks first,
then implementing the codemod. I begin by defining a unfavourable case to
guarantee we don’t unintentionally change issues we wish to go away untouched,
adopted by an actual case that performs the precise conversion. I start with
a easy state of affairs, implement it, then add a variation (like checking if
featureToggle is named inside an if assertion), implement that case, and
guarantee all checks go.

This method aligns properly with Test-Driven Development (TDD), even
if you happen to don’t follow TDD recurrently. Understanding precisely what the
transformation’s inputs and outputs are earlier than coding improves security and
effectivity, particularly when tweaking codemods.

With jscodeshift, you may write checks to confirm how the codemod
behaves:

const rework = require("../remove-feature-new-product-list");

defineInlineTest(
  rework,
  {},
  `
  const knowledge = featureToggle('feature-new-product-list') ? { title: 'Product' } : undefined;
  `,
  `
  const knowledge = { title: 'Product' };
  `,
  "delete the toggle feature-new-product-list in conditional operator"
);

The defineInlineTest perform from jscodeshift lets you outline
the enter, anticipated output, and a string describing the check’s intent.
Now, operating the check with a traditional jest command will fail as a result of the
codemod isn’t written but.

The corresponding unfavourable case would make sure the code stays unchanged
for different function toggles:

defineInlineTest(
  rework,
  {},
  `
  const knowledge = featureToggle('feature-search-result-refinement') ? { title: 'Product' } : undefined;
  `,
  `
  const knowledge = featureToggle('feature-search-result-refinement') ? { title: 'Product' } : undefined;
  `,
  "don't change different function toggles"
);

Writing the Codemod

Let’s begin by defining a easy rework perform. Create a file
referred to as rework.js with the next code construction:

module.exports = perform(fileInfo, api, choices) {
  const j = api.jscodeshift;
  const root = j(fileInfo.supply);

  // manipulate the tree nodes right here

  return root.toSource();
};

This perform reads the file right into a tree and makes use of jscodeshift’s API to
question, modify, and replace the nodes. Lastly, it converts the AST again to
supply code with .toSource().

Now we are able to begin implementing the rework steps:

1. Discover all situations of featureToggle.
2. Confirm that the argument handed is 'feature-new-product-list'.
3. Change your entire conditional expression with the consequent half,
   successfully eradicating the toggle.

Right here’s how we obtain this utilizing jscodeshift:

module.exports = perform (fileInfo, api, choices) {
  const j = api.jscodeshift;
  const root = j(fileInfo.supply);

  // Discover ConditionalExpression the place the check is featureToggle('feature-new-product-list')
  root
    .discover(j.ConditionalExpression, {
      check: {
        callee: { title: "featureToggle" },
        arguments: [{ value: "feature-new-product-list" }],
      },
    })
    .forEach((path) => {
      // Change the ConditionalExpression with the 'consequent'
      j(path).replaceWith(path.node.consequent);
    });

  return root.toSource();
};

The codemod above:

• Finds ConditionalExpression nodes the place the check calls
  featureToggle('feature-new-product-list').
• Replaces your entire conditional expression with the ensuing (i.e., {
title: 'Product' }), eradicating the toggle logic and leaving simplified code
  behind.

This instance demonstrates how straightforward it’s to create a helpful
transformation and apply it to a big codebase, considerably decreasing
guide effort.

You’ll want to put in writing extra check circumstances to deal with variations like
if-else statements, logical expressions (e.g.,
!featureToggle('feature-new-product-list')), and so forth to make the
codemod sturdy in real-world situations.

As soon as the codemod is prepared, you may check it out on a goal codebase,
such because the one you are engaged on. jscodeshift supplies a command-line
software that you should use to use the codemod and report the outcomes.

$ jscodeshift -t transform-name src/

After validating the outcomes, verify that each one purposeful checks nonetheless
go and that nothing breaks—even if you happen to’re introducing a breaking change.
As soon as happy, you may commit the adjustments and lift a pull request as
a part of your regular workflow.

Codemods Enhance Code High quality and Maintainability

Codemods aren’t simply helpful for managing breaking API adjustments—they will
considerably enhance code high quality and maintainability. As codebases
evolve, they usually accumulate technical debt, together with outdated function
toggles, deprecated strategies, or tightly coupled elements. Manually
refactoring these areas could be time-consuming and error-prone.

By automating refactoring duties, codemods assist maintain your codebase clear
and freed from legacy patterns. Repeatedly making use of codemods lets you
implement new coding requirements, take away unused code, and modernize your
codebase with out having to manually modify each file.

Refactoring an Avatar Element

Now, let’s take a look at a extra complicated instance. Suppose you’re working with
a design system that features an Avatar element tightly coupled with a
Tooltip. Each time a consumer passes a title prop into the Avatar, it
routinely wraps the avatar with a tooltip.

Determine 3: A avatar element with a tooltip

Right here’s the present Avatar implementation:

import { Tooltip } from "@design-system/tooltip";

const Avatar = ({ title, picture }: AvatarProps) => {
  if (title) {
    return (
      <Tooltip content material={title}>
        <CircleImage picture={picture} />
      </Tooltip>
    );
  }

  return <CircleImage picture={picture} />;
};

The aim is to decouple the Tooltip from the Avatar element,
giving builders extra flexibility. Builders ought to have the ability to determine
whether or not to wrap the Avatar in a Tooltip. Within the refactored model,
Avatar will merely render the picture, and customers can apply a Tooltip
manually if wanted.

Right here’s the refactored model of Avatar:

const Avatar = ({ picture }: AvatarProps) => {
  return <CircleImage picture={picture} />;
};

Now, customers can manually wrap the Avatar with a Tooltip as
wanted:

import { Tooltip } from "@design-system/tooltip";
import { Avatar } from "@design-system/avatar";

const UserProfile = () => {
  return (
    <Tooltip content material="Juntao Qiu">
      <Avatar picture="/juntao.qiu.avatar.png" />
    </Tooltip>
  );
};

The problem arises when there are tons of of Avatar usages unfold
throughout the codebase. Manually refactoring every occasion can be extremely
inefficient, so we are able to use a codemod to automate this course of.

Utilizing instruments like AST Explorer, we are able to
examine the element and see which nodes characterize the Avatar utilization
we’re focusing on. An Avatar element with each title and picture props
is parsed into an summary syntax tree as proven beneath:

Determine 4: AST of the Avatar element utilization

Writing the Codemod

Let’s break down the transformation into smaller duties:

• Discover Avatar utilization within the element tree.
• Examine if the title prop is current.
• If not, do nothing.
• If current:
• Create a Tooltip node.
• Add the title to the Tooltip.
• Take away the title from Avatar.
• Add Avatar as a toddler of the Tooltip.
• Change the unique Avatar node with the brand new Tooltip.

To start, we’ll discover all situations of Avatar (I’ll omit a few of the
checks, however you must write comparability checks first).

defineInlineTest(
    { default: rework, parser: "tsx" },
    {},
    `
    <Avatar title="Juntao Qiu" picture="/juntao.qiu.avatar.png" />
    `,
    `
    <Tooltip content material="Juntao Qiu">
      <Avatar picture="/juntao.qiu.avatar.png" />
    </Tooltip>
    `,
    "wrap avatar with tooltip when title is supplied"
  );

Much like the featureToggle instance, we are able to use root.discover with
search standards to find all Avatar nodes:

root
  .discover(j.JSXElement, {
    openingElement: { title: { title: "Avatar" } },
  })
  .forEach((path) => {
    // now we are able to deal with every Avatar occasion
  });

Subsequent, we verify if the title prop is current:

root
  .discover(j.JSXElement, {
    openingElement: { title: { title: "Avatar" } },
  })
  .forEach((path) => {
    const avatarNode = path.node;

    const nameAttr = avatarNode.openingElement.attributes.discover(
      (attr) => attr.title.title === "title"
    );

    if (nameAttr) {
      const tooltipElement = createTooltipElement(
        nameAttr.worth.worth,
        avatarNode
      );
      j(path).replaceWith(tooltipElement);
    }
  });

For the createTooltipElement perform, we use the
jscodeshift API to create a brand new JSX node, with the title
prop utilized to the Tooltip and the Avatar
element as a toddler. Lastly, we name replaceWith to
substitute the present path.

Right here’s a preview of the way it seems to be in
Hypermod, the place the codemod is written on
the left. The highest half on the fitting is the unique code, and the underside
half is the reworked outcome:

Determine 5: Run checks inside hypermod earlier than apply it to your codebase

This codemod searches for all situations of Avatar. If a
title prop is discovered, it removes the title prop
from Avatar, wraps the Avatar inside a
Tooltip, and passes the title prop to the
Tooltip.

By now, I hope it’s clear that codemods are extremely helpful and
that the workflow is intuitive, particularly for large-scale adjustments the place
guide updates can be an enormous burden. Nevertheless, that is not the entire
image. Within the subsequent part, I’ll make clear a few of the challenges
and the way we are able to deal with these less-than-ideal elements.

Leveraging Supply Graphs and Check-Pushed Codemods

To deal with these complexities, codemods must be used alongside different
strategies. As an example, a couple of years in the past, I participated in a design
system elements rewrite mission at Atlassian. We addressed this concern by
first looking the supply graph, which contained nearly all of inner
element utilization. This allowed us to know how elements have been used,
whether or not they have been imported below totally different names, or whether or not sure
public props have been often used. After this search section, we wrote our
check circumstances upfront, guaranteeing we coated nearly all of use circumstances, and
then developed the codemod.

In conditions the place we could not confidently automate the improve, we
inserted feedback or “TODOs” on the name websites. This allowed the
builders operating the script to deal with particular circumstances manually. Normally,
there have been solely a handful of such situations, so this method nonetheless proved
helpful for upgrading variations.

Using Current Code Standardization Instruments

As you may see, there are many edge circumstances to deal with, particularly in
codebases past your management—comparable to exterior dependencies. This
complexity signifies that utilizing codemods requires cautious supervision and a
assessment of the outcomes.

Nevertheless, in case your codebase has standardization instruments in place, comparable to a
linter that enforces a specific coding fashion, you may leverage these
instruments to cut back edge circumstances. By imposing a constant construction, instruments
like linters assist slim down the variations in code, making the
transformation simpler and minimizing sudden points.

As an example, you possibly can use linting guidelines to limit sure patterns,
comparable to avoiding nested conditional (ternary) operators or imposing named
exports over default exports. These guidelines assist streamline the codebase,
making codemods extra predictable and efficient.

Moreover, breaking down complicated transformations into smaller, extra
manageable ones lets you deal with particular person points extra exactly. As
we’ll quickly see, composing smaller codemods could make dealing with complicated
adjustments extra possible.

Codemod Composition

Let’s revisit the function toggle elimination instance mentioned earlier. Within the code snippet
we’ve a toggle referred to as feature-convert-new should be eliminated:

import { featureToggle } from "./utils/featureToggle";

const convertOld = (enter: string) => {
  return enter.toLowerCase();
};

const convertNew = (enter: string) => {
  return enter.toUpperCase();
};

const outcome = featureToggle("feature-convert-new")
  ? convertNew("Good day, world")
  : convertOld("Good day, world");

console.log(outcome);

The codemod for take away a given toggle works effective, and after operating the codemod,
we wish the supply to appear like this:

const convertNew = (enter: string) => {
  return enter.toUpperCase();
};

const outcome = convertNew("Good day, world");

console.log(outcome);

Nevertheless, past eradicating the function toggle logic, there are further duties to
deal with:

• Take away the unused convertOld perform.
• Clear up the unused featureToggle import.

In fact, you possibly can write one massive codemod to deal with every thing in a
single go and check it collectively. Nevertheless, a extra maintainable method is
to deal with codemod logic like product code: break the duty into smaller,
unbiased items—similar to how you’d usually refactor manufacturing
code.

Breaking It Down

We will break the large transformation down into smaller codemods and
compose them. The benefit of this method is that every transformation
could be examined individually, protecting totally different circumstances with out interference.
Furthermore, it lets you reuse and compose them for various
functions.

As an example, you would possibly break it down like this:

• A change to take away a particular function toggle.
• One other transformation to scrub up unused imports.
• A change to take away unused perform declarations.

By composing these, you may create a pipeline of transformations:

import { removeFeatureToggle } from "./remove-feature-toggle";
import { removeUnusedImport } from "./remove-unused-import";
import { removeUnusedFunction } from "./remove-unused-function";

import { createTransformer } from "./utils";

const removeFeatureConvertNew = removeFeatureToggle("feature-convert-new");

const rework = createTransformer([
  removeFeatureConvertNew,
  removeUnusedImport,
  removeUnusedFunction,
]);

export default rework;

On this pipeline, the transformations work as follows:

1. Take away the feature-convert-new toggle.
2. Clear up the unused import assertion.
3. Take away the convertOld perform because it’s now not used.

Determine 6: Compose transforms into a brand new rework

You too can extract further codemods as wanted, combining them in
numerous orders relying on the specified final result.

Determine 7: Put totally different transforms right into a pipepline to type one other rework

The createTransformer Operate

The implementation of the createTransformer perform is comparatively
simple. It acts as a higher-order perform that takes an inventory of
smaller rework features, iterates by the checklist to use them to
the basis AST, and eventually converts the modified AST again into supply
code.

import { API, Assortment, FileInfo, JSCodeshift, Choices } from "jscodeshift";

sort TransformFunction = { (j: JSCodeshift, root: Assortment): void };

const createTransformer =
  (transforms: TransformFunction[]) =>
  (fileInfo: FileInfo, api: API, choices: Choices) => {
    const j = api.jscodeshift;
    const root = j(fileInfo.supply);

    transforms.forEach((rework) => rework(j, root));
    return root.toSource(choices.printOptions || { quote: "single" });
  };

export { createTransformer };

For instance, you possibly can have a rework perform that inlines
expressions assigning the function toggle name to a variable, so in later
transforms you don’t have to fret about these circumstances anymore:

const shouldEnableNewFeature = featureToggle('feature-convert-new');

if (!shouldEnableNewFeature && someOtherLogic) {
  //...
}

Turns into this:

if (!featureToggle('feature-convert-new') && someOtherLogic) {
  //...
}

Over time, you would possibly construct up a set of reusable, smaller
transforms, which may tremendously ease the method of dealing with difficult edge
circumstances. This method proved extremely efficient in our work refining design
system elements. As soon as we transformed one bundle—such because the button
element—we had a couple of reusable transforms outlined, like including feedback
at the beginning of features, eradicating deprecated props, or creating aliases
when a bundle is already imported above.

Every of those smaller transforms could be examined and used independently
or mixed for extra complicated transformations, which accelerates subsequent
conversions considerably. Consequently, our refinement work grew to become extra
environment friendly, and these generic codemods at the moment are relevant to different inner
and even exterior React codebases.

Since every rework is comparatively standalone, you may fine-tune them
with out affecting different transforms or the extra complicated, composed ones. For
occasion, you would possibly re-implement a rework to enhance efficiency—like
decreasing the variety of node-finding rounds—and with complete check
protection, you are able to do this confidently and safely.