@codemod-utils/ast

@codemod-utils/ast

Utilities for handling abstract syntax tree

What is it?

@codemod-utils/ast wraps the methods from ember-template-recast and recast, libraries that help you parse and transform *.hbs and *.{js,ts} files.

The wrappers help you read and write files of different types in the same way. This way, you can focus on learning the builders and visit methods, the building blocks for transforming code (library-dependent).

Outline for transforming *.hbs files

import { ASTHandlebars as AST } from '@codemod-utils/ast';

function transformCode(file) {
  const traverse = AST.traverse();

  const ast = traverse(file, {
    /* Use AST.builders to transform the tree */
  });

  return AST.print(ast);
}

Outline for transforming *.{js,ts} files

import { ASTJavaScript as AST } from '@codemod-utils/ast';

function transformCode(file, isTypeScript) {
  const traverse = AST.traverse(isTypeScript);

  const ast = traverse(file, {
    /* Use AST.builders to transform the tree */
  });

  return AST.print(ast);
}

API

ASTHandlebars

• Builders
• Visit methods

ASTJavaScript

• Builders
• Visit methods

How to test your code

Currently, ember-template-recast and recast lack documentation and tutorials. This is unfortunate, given the large amount of builders and visit methods that they provide to help you transform code.

I recommend using AST Explorer to test a small piece of code and familiarize with the API. The error messages from TypeScript, which you can find in your browser's console, can sometimes help. AST Workshop provides a good starting point for Handlebars.

If you intend to publish your codemod, I recommend using @codemod-utils/tests (create and test file fixtures) to check the output and prevent regressions.

AST Explorer for Handlebars

Select the following options to create a 4-tab window:

• Language: Handlebars
• Parser: ember-template-recast
• Transform: ember-template-recast

Copy-paste the visit methods from your file to AST explorer, then rename AST.builders to b.

Example

/* Your file */
import { ASTHandlebars as AST } from '@codemod-utils/ast';

function transformCode(file) {
  const traverse = AST.traverse();

  const ast = traverse(file, {
    AttrNode(node) {
      if (node.name !== 'local-class') {
        return;
      }

      node.name = 'class';

      const attributeValue = node.value.chars.trim();

      node.value = AST.builders.mustache(
        AST.builders.path(`this.styles.${attributeValue}`),
      );
    },
  });

  return AST.print(ast);
}

/* AST Explorer */
module.exports = function(env) {
  const b = env.syntax.builders;

  return {
    AttrNode(node) {
      if (node.name !== 'local-class') {
        return;
      }

      node.name = 'class';

      const attributeValue = node.value.chars.trim();

      node.value = b.mustache(
        b.path(`this.styles.${attributeValue}`),
      );
    },
  };
};

AST Explorer for TypeScript

Select the following options to create a 4-tab window:

• Language: JavaScript
• Parser: recast
• Transform: recast

Copy-paste the visit methods from your file to AST explorer, then rename AST.builders to b.

Example

/* Your file */
import { ASTJavaScript as AST } from '@codemod-utils/ast';

export function transformCode(file) {
  const traverse = AST.traverse(true);

  const ast = traverse(file, {
    visitClassDeclaration(path) {
      const { body } = path.node.body;

      const nodesToAdd = [
        AST.builders.classProperty(
          AST.builders.identifier('styles'),
          AST.builders.identifier('styles'),
        ),
      ];

      body.unshift(...nodesToAdd);

      return false;
    },
  });

  return AST.print(ast);
}

/* AST Explorer */
export default function transformer(code, { recast, parsers }) {
  const ast = recast.parse(code, { parser: parsers.typescript });
  const b = recast.types.builders;

  recast.visit(ast, {
    visitClassDeclaration(path) {
      const { body } = path.node.body;

      const nodesToAdd = [
        b.classProperty(
          b.identifier('styles'),
          b.identifier('styles')
        )
      ];

      body.unshift(...nodesToAdd);

      return false;
    }
  });

  return recast.print(ast).code;
}

Compatibility

• Node.js v16 or above

Contributing

See the Contributing guide for details.

License

This project is licensed under the MIT License.