babel-sync-me.js

// All credit goes to https://github.com/egoist/babel-plugin-sync
// Copied here to tweak further
const MAKE_ME_SYNC = '$MakeMeSync';

const shouldMakeSync = (comments) => {
  return (
    comments &&
    comments.find((comment) => {
      return comment.value.trim() === MAKE_ME_SYNC;
    })
  );
};

const markAsSynced = (node) => {
  node.leadingComments = node.leadingComments.map((c) => {
    if (c.value.trim() === MAKE_ME_SYNC) {
      c.value = ' __SYNCED__';
    }
    return c;
  });
};

const syncCallee = (callee) => {
  if (callee.type === 'MemberExpression') {
    callee.property.name += 'Sync';
  } else {
    callee.name += 'Sync';
  }
};

module.exports = function ({ types: t }) {
  return {
    name: 'sync',

    visitor: {
      ClassMethod(path) {
        if (path.node.async && shouldMakeSync(path.node.leadingComments)) {
          markAsSynced(path.node);
          const originalNode = t.cloneDeep(path.node);

          path.node.trailingComments = originalNode.trailingComments;
          originalNode.trailingComments = [];

          path.insertBefore(originalNode);

          path.node.async = false;
          path.node.key.name += 'Sync';

          path.traverse({
            AwaitExpression(path) {
              const { callee } = path.node.argument;
              syncCallee(callee);
              path.replaceWith(path.node.argument);
            },
            CallExpression(path) {
              if (path.parent.type === 'ReturnStatement' && shouldMakeSync(path.parent.trailingComments)) {
                syncCallee(path.node.callee);
              }
            },
          });
        }
      },
    },
  };
};