babel-check-duplicated-nodes/lib/index.js

Babel helper module for babel transforms authors to check the AST against duplicated nodes.

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.default = checkDuplicatedNodes;

// https://github.com/babel/babel/blob/d383659ca6adec54b6054f77cdaa16da88e8a171/packages/babel-helper-transform-fixture-test-runner/src/index.js#L128
function checkDuplicatedNodes(babel, ast) {
  const nodes = new WeakSet();
  const parents = new WeakMap();

  const setParent = (child, parent) => {
    if (typeof child === "object" && child !== null) {
      let p = parents.get(child);

      if (!p) {
        p = [];
        parents.set(child, p);
      }

      p.unshift(parent);
    }
  };

  const registerChildren = node => {
    for (const key in node) {
      if (Array.isArray(node[key])) {
        node[key].forEach(child => setParent(child, node));
      } else {
        setParent(node[key], node);
      }
    }
  };

  const hidePrivateProperties = (key, val) => {
    // Hides properties like _shadowedFunctionLiteral,
    // which makes the AST circular
    if (key[0] === "_") return "[Private]";
    return val;
  };

  babel.types.traverseFast(ast, node => {
    registerChildren(node);

    if (nodes.has(node)) {
      throw new Error("Do not reuse nodes. Use `t.cloneNode` (or `t.clone`/`t.cloneDeep` if using babel@6) to copy them.\n" + JSON.stringify(node, hidePrivateProperties, 2) + "\nParent:\n" + JSON.stringify(parents.get(node), hidePrivateProperties, 2));
    }

    nodes.add(node);
  });
}