From 5cf5392222681eed921a049a46fcf1a277347975 Mon Sep 17 00:00:00 2001
From: Roy Ivy III <rivy.dev@gmail.com>
Date: Thu, 7 Jan 2021 13:57:32 -0600
Subject: [PATCH] maint/build ~ add `rollup` for ESM generation

- TypeScript fails to correctly generate an ESM module with correct line endings
  - ref: <https://github.com/microsoft/TypeScript/issues/18442#issuecomment-749896695>
  - ref: <https://github.com/microsoft/TypeScript/issues/18442>
  - ref: <https://github.com/microsoft/TypeScript/issues/37582>
  - ref: <https://github.com/microsoft/TypeScript/pull/35148>
---
 .rollup.config.js | 19 +++++++++++++++++++
 package.json      |  3 +++
 2 files changed, 22 insertions(+)
 create mode 100644 .rollup.config.js

diff --git a/.rollup.config.js b/.rollup.config.js
new file mode 100644
index 0000000..9f28d17
--- /dev/null
+++ b/.rollup.config.js
@@ -0,0 +1,19 @@
+// ref: <https://devhints.io/rollup>
+// setup: `npm i rollup @rollup/plugin-typescript` or `npm i rollup rollup-plugin-typescript2` (for visible TS error output)
+
+// import typescript from '@rollup/plugin-typescript';
+import typescript from 'rollup-plugin-typescript2';
+
+export default [
+	// ES module build (replaces broken basic TypeScript compilation)
+	// * ref: <https://github.com/microsoft/TypeScript/issues/18442> , <https://github.com/alshdavid/rxjs/blob/main/rollup.config.js#L10>
+	// * ref: <https://github.com/microsoft/TypeScript/pull/35148>
+	// * ref: <https://github.com/microsoft/TypeScript/issues/37582>
+	{
+		preserveModules: true,
+		input: ['src/index.ts'],
+		external: ['path', 'os'],
+		output: [{ exports: 'auto', dir: 'build/esm', format: 'esm', entryFileNames: '[name].mjs' }],
+		plugins: [typescript({ tsconfig: './tsconfig/tsconfig.esm.json' })],
+	},
+];
diff --git a/package.json b/package.json
index ee53a05..05b3c76 100644
--- a/package.json
+++ b/package.json
@@ -57,6 +57,7 @@
 		"build:cjs": "tsc -p tsconfig/tsconfig.cjs.json",
 		"build:cjs/esm": "shx mkdir -p build/cjs && shx cp -r src/esm-wrapper build/cjs",
 		"## build:esm * [2020-12-22; rivy] TS compiles to ESMs are broken due to extension mishandling (use `rollup`)": "tsc -p tsconfig/tsconfig.esm.json",
+		"build:esm": "rollup -c .rollup.config.js",
 		"build:umd": "tsc -p tsconfig/tsconfig.umd.json",
 		"build:tests": "tsc -p tsconfig/tsconfig.tests.json",
 		"build:types": "tsc -p tsconfig/tsconfig.types.json && run-s --silent _:update:dist.types",
@@ -177,6 +178,8 @@
 		"remark-footnotes": "^3.0.0",
 		"remark-preset-lint-recommended": "^5.0.0",
 		"rimraf": "^3.0.2",
+		"rollup": "^2.36.1",
+		"rollup-plugin-typescript2": "^0.29.0",
 		"shx": "^0.3.3",
 		"ts-node": "^9.0.0",
 		"tsd": "^0.13.1",