Prevalify

0-prevalify.js

const path = require('path');
const { createMacro } = require("babel-plugin-macros");
const objectToAST = require("babel-plugin-preval/src/object-to-ast"); // https://github.com/kentcdodds/babel-plugin-preval/blob/b6eeba02ee93d425cc673ffc23dc62375d0416e5/src/object-to-ast.js

export default fn =>
  createMacro(({ references, state, babel }) => {
    references.default.forEach(referencePath => {
      if (referencePath.parentPath.type === "CallExpression") {
        const __filename = state.file.opts.filename;
        const __dirname = path.dirname(__filename);
        const callExpressionPath = referencePath.parentPath;
        const args = callExpressionPath
          .get("arguments")
          .map(arg => arg.evaluate().value);
        const value = fn.apply({ __filename, __dirname }, args);
        referencePath.parentPath.replaceWith(objectToAST(value));
      } else {
        const source = referencePath
          .findParent(babel.types.isExpression)
          .getSource();
        throw new Error(
          `This is not supported: \`${source}\`. Please use a function call`
        );
      }
    });
  });

1-macro.js

const fs = require('fs');
const path = require('path');
const prevalify = require('prevalify');

const readFile = (filepath) => {
  const resolvedPath = path.resolve(this.__dirname || process.cwd(), filepath);
  return fs.readFileSync(resolvedPath, { encoding: 'utf-8' });
};

export default prevalify(readFile);

2-usage.js

const readFile = require('read-file/macro');
const fileContents = readFile('./README.md');