JJJ  SSSSS  333333    GGGG  EEEEEEE NN   NN 
    JJJ SS         3333  GG  GG EE      NNN  NN 
    JJJ  SSSSS    3333  GG      EEEEE   NN N NN 
JJ  JJJ      SS     333 GG   GG EE      NN  NNN 
 JJJJJ   SSSSS  333333   GGGGGG EEEEEEE NN   NN 
                                                

Author: mee Contact: meeteshmehta@cse.iitb.ac.in

This project generates boilerplate code to restrict types of values that can be contained in the AST

This project was developed to generate boilerplate code for Iridium's Three Address Code pass. It was originally intended to be name 3JS, but as class names cant start with 3 we named it JS3.

Setup

This project requires nodeJS and npm.

npm i

Usage

Lets say we want to restrict the language such that the Program body can only contain ImportDeclaration statements.

1. Nodes that we want to restrict types are described in languageRestriction.json.

{
  "@babelImports": [ "ImportDeclaration" ],
  "Program": {
    "body": "Array< ImportDeclaration >"
  }
  
}

2. Get the babel AST Type information file and name it orig.ts (Usually it exists in node_modules/@babel/types/lib/index.d.ts). The one we are using is from version @babel/core -> ^7.25.2.

3. Run this command to generate the outputs.

node --import=tsx main.ts

4. This will generate three files as output, JS3Constructors.ts, JS3Handlers.ts, JS3Types.ts.

The output

The file JS3Types.ts contains interfaces and types aliases on the restricted nodes.

export type JS3Program_body = Array< ImportDeclaration >;

export interface JS3Program extends Program {
  body: JS3Program_body;
}

The file JS3Handlers.ts contains visitor functions for the modified nodes with boilerplate code.

type OtherProps = any;

function handleProgram(node: Program, ...otherProps: OtherProps) {
  // 4 fallthrough props, 1 restricted props
  let orig_body = node.body; // Handling prop body
  let fin_body : JS3Program_body; // Handling prop body
  if (Array.isArray ( orig_body )) { 
    for (const _arrProp of orig_body) {
      if(isBlockStatement (_arrProp)) {
        console.error("TODO // unhandled Program->[body]->BlockStatement");
      } else if(isBreakStatement (_arrProp)) {
        console.error("TODO // unhandled Program->[body]->BreakStatement");
      } // ... All the constructors
    }
  }

  // let result: JS3Program = generateJS3Program(fin_body, node);
} 

The file JS3Constructors.ts contains constructors to generate the new nodes.

export function generateBaseNodeFrom(from: Node): Node {
  const { start, end, loc, range, extra } = from;
  const result = { start, end, loc, range, extra } as Node
  return result
}

export function generateJS3Program(_body : JS3Program_body, from: Program) : JS3Program {
  let to: JS3Program = generateBaseNodeFrom(from) as JS3Program;
  to.type = from.type;
  to.directives = from.directives;
  to.sourceType = from.sourceType;
  to.interpreter = from.interpreter;
  to.body = _body;
  return to;
}