utils/BabelCacheBuster.mjs

/*
 * Copyright (C) 2025 Apple Inc. All rights reserved.
 * Copyright 2025 Google LLC
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
 * THE POSSIBILITY OF SUCH DAMAGE.
 */

// Babel plugin that adds CACHE_BUST_COMMENT to every function body.
const CACHE_BUST_COMMENT = "ThouShaltNotCache";

export default function({ types: t }) {
  return {
    visitor: {
      Function(path) {
        const bodyPath = path.get("body");
        // Handle arrow functions: () => "value"
        // Convert them to block statements: () => { return "value"; }
        if (!bodyPath.isBlockStatement()) {
          const newBody = t.blockStatement([t.returnStatement(bodyPath.node)]);
          path.set("body", newBody);
        }

        // Handle empty function bodies: function foo() {}
        // Add an empty statement so we have a first node to attach the comment to.
        if (path.get("body.body").length === 0) {
          path.get("body").pushContainer("body", t.emptyStatement());
        }

        const firstNode = path.node.body.body[0];
        t.addComment(firstNode, "leading", CACHE_BUST_COMMENT);
      },
    },
  };
};