microbundle/src/lib/babel-custom.js

import { createConfigItem } from '@babel/core';
import babelPlugin from 'rollup-plugin-babel';
import merge from 'lodash.merge';
import transformFastRest from './transform-fast-rest';
import { isTruthy } from '../utils';

const ESMODULES_TARGET = {
	esmodules: true,
};

const mergeConfigItems = (type, ...configItemsToMerge) => {
	const mergedItems = [];

	configItemsToMerge.forEach(configItemToMerge => {
		configItemToMerge.forEach(item => {
			const itemToMergeWithIndex = mergedItems.findIndex(
				mergedItem =>
					(mergedItem.name || mergedItem.file.resolved) ===
					(item.name || item.file.resolved),
			);

			if (itemToMergeWithIndex === -1) {
				mergedItems.push(item);
				return;
			}

			mergedItems[itemToMergeWithIndex] = createConfigItem(
				[
					mergedItems[itemToMergeWithIndex].file.resolved,
					merge(mergedItems[itemToMergeWithIndex].options, item.options),
				],
				{
					type,
				},
			);
		});
	});

	return mergedItems;
};

const createConfigItems = (type, items) => {
	return items.map(item => {
		let { name, value, ...options } = item;
		value = value || [require.resolve(name), options];
		return createConfigItem(value, { type });
	});
};

const presetEnvRegex = RegExp(/@babel\/(preset-)?env/);

export default () => {
	return babelPlugin.custom(babelCore => {
		return {
			// Passed the plugin options.
			options({ custom: customOptions, ...pluginOptions }) {
				return {
					// Pull out any custom options that the plugin might have.
					customOptions,

					// Pass the options back with the two custom options removed.
					pluginOptions,
				};
			},

			config(config, { customOptions }) {
				const targets = customOptions.targets;
				const isNodeTarget = targets && targets.node != null;

				const defaultPlugins = createConfigItems(
					'plugin',
					[
						{
							name: '@babel/plugin-transform-react-jsx',
							pragma: customOptions.pragma || 'h',
							pragmaFrag: customOptions.pragmaFrag || 'Fragment',
						},
						!customOptions.typescript && {
							name: '@babel/plugin-transform-flow-strip-types',
						},
						isTruthy(customOptions.defines) && {
							name: 'babel-plugin-transform-replace-expressions',
							replace: customOptions.defines,
						},
						!customOptions.modern && {
							name: 'babel-plugin-transform-async-to-promises',
							inlineHelpers: true,
							externalHelpers: false,
							minify: true,
						},
						!customOptions.modern &&
							!isNodeTarget && {
								value: [
									transformFastRest,
									{
										// Use inline [].slice.call(arguments)
										helper: false,
										literal: true,
									},
									'transform-fast-rest',
								],
							},
						{
							name: '@babel/plugin-proposal-class-properties',
							loose: true,
						},
						!customOptions.modern && {
							name: '@babel/plugin-transform-regenerator',
							async: false,
						},
						{
							name: 'babel-plugin-macros',
						},
					].filter(Boolean),
				);

				const babelOptions = config.options || {};

				const envIdx = (babelOptions.presets || []).findIndex(preset =>
					presetEnvRegex.test(preset.file.request),
				);

				const environmentPreset = customOptions.modern
					? '@babel/preset-modules'
					: '@babel/preset-env';

				if (envIdx !== -1) {
					const preset = babelOptions.presets[envIdx];
					babelOptions.presets[envIdx] = createConfigItem(
						[
							environmentPreset,
							Object.assign(
								merge(
									{
										loose: true,
										useBuiltIns: false,
										targets: customOptions.targets,
									},
									preset.options,
									{
										modules: false,
										exclude: merge(
											['transform-async-to-generator', 'transform-regenerator'],
											(preset.options && preset.options.exclude) || [],
										),
									},
								),
								customOptions.modern ? { targets: ESMODULES_TARGET } : {},
							),
						],
						{
							type: `preset`,
						},
					);
				} else {
					babelOptions.presets = createConfigItems('preset', [
						{
							name: environmentPreset,
							targets: customOptions.modern
								? ESMODULES_TARGET
								: customOptions.targets,
							modules: false,
							loose: true,
							useBuiltIns: false,
							exclude: [
								'transform-async-to-generator',
								'transform-regenerator',
							],
						},
					]);
				}

				// Merge babelrc & our plugins together
				babelOptions.plugins = mergeConfigItems(
					'plugin',
					defaultPlugins,
					babelOptions.plugins || [],
				);

				babelOptions.generatorOpts = {
					minified: customOptions.compress,
					compact: customOptions.compress,
					shouldPrintComment: comment => /[@#]__PURE__/.test(comment),
				};

				return babelOptions;
			},
		};
	});
};