nx/packages/rollup/src/plugins/package-json/update-package-json.ts

import { basename, join, parse } from 'path';
import { writeJsonFile } from 'nx/src/utils/fileutils';
import { writeFileSync } from 'fs';
import { PackageJson } from 'nx/src/utils/package-json';
import { stripIndents, workspaceRoot } from '@nx/devkit';

export function updatePackageJson(
  options: {
    outputPath: string;
    main: string;
    format: string[];
    generateExportsField?: boolean;
    skipTypeField?: boolean;
    outputFileName?: string;
    additionalEntryPoints?: string[];
  },
  packageJson: PackageJson
) {
  const hasEsmFormat = options.format.includes('esm');
  const hasCjsFormat = options.format.includes('cjs');

  if (options.generateExportsField) {
    packageJson.exports =
      typeof packageJson.exports === 'string' ? {} : { ...packageJson.exports };
    packageJson.exports['./package.json'] = './package.json';
  }

  if (hasEsmFormat) {
    const esmExports = getExports({
      ...options,
      fileExt: '.esm.js',
    });

    packageJson.module = esmExports['.'];

    if (!hasCjsFormat) {
      if (!options.skipTypeField) packageJson.type = 'module';
      packageJson.main ??= esmExports['.'];
    }

    if (options.generateExportsField) {
      for (const [exportEntry, filePath] of Object.entries(esmExports)) {
        packageJson.exports[exportEntry] =
          // If CJS format is used, make sure `import` (from Node) points to same instance of the package.
          // Otherwise, packages that are required to be singletons (like React, RxJS, etc.) will break.
          // Reserve `module` entry for bundlers to accommodate tree-shaking.
          {
            [hasCjsFormat ? 'module' : 'import']: filePath,
            types: filePath.replace(/\.js$/, '.d.ts'),
          };
      }
    }
  }

  if (hasCjsFormat) {
    const cjsExports = getExports({
      ...options,
      fileExt: '.cjs.js',
    });

    packageJson.main = cjsExports['.'];

    if (!hasEsmFormat && !options.skipTypeField) {
      packageJson.type = 'commonjs';
    }

    if (options.generateExportsField) {
      for (const [exportEntry, filePath] of Object.entries(cjsExports)) {
        if (hasEsmFormat) {
          // If ESM format used, make sure `import` (from Node) points to a wrapped
          // version of CJS file to ensure the package remains a singleton.
          // TODO(jack): This can be made into a rollup plugin to re-use in Vite.
          const relativeFile = parse(filePath).base;
          const fauxEsmFilePath = filePath.replace(/\.cjs\.js$/, '.cjs.mjs');
          packageJson.exports[exportEntry]['import'] ??= fauxEsmFilePath;
          packageJson.exports[exportEntry]['default'] ??= filePath;
          // Set `types` field only if it's not already set as the preferred ESM Format.
          packageJson.exports[exportEntry]['types'] ??= filePath.replace(
            /\.js$/,
            '.d.ts'
          );
          // Re-export from relative CJS file, and Node will synthetically export it as ESM.
          // Make sure both ESM and CJS point to same instance of the package because libs like React, RxJS, etc. requires it.
          // Also need a special .cjs.default.js file that re-exports the `default` from CJS, or else
          // default import in Node will not work.
          writeFileSync(
            join(
              workspaceRoot,
              options.outputPath,
              filePath.replace(/\.cjs\.js$/, '.cjs.default.js')
            ),
            `exports._default = require('./${parse(filePath).base}').default;`
          );
          writeFileSync(
            join(workspaceRoot, options.outputPath, fauxEsmFilePath),
            // Re-export from relative CJS file, and Node will synthetically export it as ESM.
            stripIndents`
            export * from './${relativeFile}';
            export { _default as default } from './${relativeFile.replace(
              /\.cjs\.js$/,
              '.cjs.default.js'
            )}';
            `
          );
        } else {
          packageJson.exports[exportEntry] = filePath;
        }
      }
    }
  }

  if (packageJson.module) {
    packageJson.types ??= packageJson.module.replace(/\.js$/, '.d.ts');
  } else {
    packageJson.types ??= packageJson.main.replace(/\.js$/, '.d.ts');
  }

  writeJsonFile(
    join(workspaceRoot, options.outputPath, 'package.json'),
    packageJson
  );
}

interface Exports {
  [name: string]: string;
}

function getExports(options: {
  main?: string;
  fileExt: string;
  outputFileName?: string;
  additionalEntryPoints?: string[];
}): Exports {
  const exports: Exports = {};

  // Users may provide custom input option and skip the main field.
  if (options.main) {
    const mainFile = options.outputFileName
      ? options.outputFileName.replace(/\.[tj]s$/, '')
      : basename(options.main).replace(/\.[tj]s$/, '');
    exports['.'] = './' + mainFile + options.fileExt;
  }

  if (options.additionalEntryPoints) {
    for (const file of options.additionalEntryPoints) {
      const { name: fileName } = parse(file);
      exports['./' + fileName] = './' + fileName + options.fileExt;
    }
  }

  return exports;
}