From 646c341b33c993f033c80234ec07bc7f86ec918d Mon Sep 17 00:00:00 2001
From: Craig Spence <craigspence0@gmail.com>
Date: Wed, 17 Feb 2021 03:11:01 +0100
Subject: [PATCH] =?UTF-8?q?fix(betterer=20=F0=9F=90=9B):=20make=20typescri?=
 =?UTF-8?q?pt=20properly=20optional?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .betterer.ts                           |  1 -
 README.md                              |  4 +--
 packages/betterer/package.json         |  3 ++
 packages/betterer/src/register.ts      | 39 +++++++++++++++++---------
 packages/betterer/src/runner/runner.ts |  2 +-
 yarn.lock                              |  2 +-
 6 files changed, 32 insertions(+), 19 deletions(-)

diff --git a/.betterer.ts b/.betterer.ts
index 07481f5be..783170551 100644
--- a/.betterer.ts
+++ b/.betterer.ts
@@ -1,4 +1,3 @@
-import { eslint } from '@betterer/eslint';
 import { regexp } from '@betterer/regexp';
 
 export default {
diff --git a/README.md b/README.md
index 00eb87b26..828c16135 100644
--- a/README.md
+++ b/README.md
@@ -17,13 +17,11 @@ npx @betterer/cli init
 To do it yourself, run the following from the root of your project:
 
 ```bash
-npm install @betterer/cli typescript --save-dev
+npm install @betterer/cli --save-dev
 ```
 
 You'll then need to make your own test file and test commands.
 
-_Note: Typescript is required to execute the `betterer` command. Your code does not have to be written in TS to use Betterer! Referencing it as a peer dependency helps to prevent unexpected behavior._
-
 ---
 
 ## Why?
diff --git a/packages/betterer/package.json b/packages/betterer/package.json
index 8ded78c99..818026f9f 100644
--- a/packages/betterer/package.json
+++ b/packages/betterer/package.json
@@ -44,6 +44,9 @@
     "ts-node": "^9.0.0",
     "tslib": "^2.0.3"
   },
+  "optionalDependencies": {
+    "typescript": ">=2.7"
+  },
   "devDependencies": {
     "@types/callsite": "^1.0.30",
     "@types/prettier": "^1.12.0"
diff --git a/packages/betterer/src/register.ts b/packages/betterer/src/register.ts
index 4e8ea35ef..b837fc130 100644
--- a/packages/betterer/src/register.ts
+++ b/packages/betterer/src/register.ts
@@ -1,4 +1,4 @@
-import { RegisterOptions, register } from 'ts-node';
+import type { RegisterOptions } from 'ts-node';
 
 import { BettererConfig } from './config';
 
@@ -9,7 +9,7 @@ export const TS_EXTENSION = '.ts';
 type Extensions = typeof require.extensions;
 
 let isRegistered = false;
-export function registerExtensions(config: BettererConfig): void {
+export async function registerExtensions(config: BettererConfig): Promise<void> {
   if (isRegistered) {
     return;
   }
@@ -23,17 +23,7 @@ export function registerExtensions(config: BettererConfig): void {
   const JS = EXTENSIONS[JS_EXTENSION];
 
   if (!EXTENSIONS[TS_EXTENSION]) {
-    // Use TS-Node register to allow `.betterer.ts` config files:
-    const tsRegisterOptions: RegisterOptions = {
-      transpileOnly: true,
-      compilerOptions: {
-        module: 'commonjs'
-      }
-    };
-    if (config.tsconfigPath) {
-      tsRegisterOptions.project = config.tsconfigPath;
-    }
-    register(tsRegisterOptions);
+    await registerTypeScript(config);
   }
 
   // Force `.betterer.results` files to be loaded as JS:
@@ -41,3 +31,26 @@ export function registerExtensions(config: BettererConfig): void {
     JS(m, filePath);
   };
 }
+
+async function registerTypeScript(config: BettererConfig): Promise<void> {
+  let tsNode: typeof import('ts-node');
+  try {
+    await import('typescript');
+    tsNode = await import('ts-node');
+  } catch {
+    // Environment doesn't have TypeScript available, move on!
+    return;
+  }
+
+  // Use TS-Node register to allow `.betterer.ts` config files:
+  const tsRegisterOptions: RegisterOptions = {
+    transpileOnly: true,
+    compilerOptions: {
+      module: 'commonjs'
+    }
+  };
+  if (config.tsconfigPath) {
+    tsRegisterOptions.project = config.tsconfigPath;
+  }
+  tsNode.register(tsRegisterOptions);
+}
diff --git a/packages/betterer/src/runner/runner.ts b/packages/betterer/src/runner/runner.ts
index 8f356d8b7..a13b13fbf 100644
--- a/packages/betterer/src/runner/runner.ts
+++ b/packages/betterer/src/runner/runner.ts
@@ -21,7 +21,7 @@ export class BettererRunnerΩ implements BettererRunner {
     let reporter = loadReporters([DEFAULT_REPORTER]);
     try {
       config = await createConfig(partialConfig);
-      registerExtensions(config);
+      await registerExtensions(config);
       if (config.silent) {
         reporter = loadReporters([]);
       }
diff --git a/yarn.lock b/yarn.lock
index db7185475..576a7193a 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -9280,7 +9280,7 @@ typedarray@^0.0.6:
   resolved "https://registry.npmjs.org/typedarray/-/typedarray-0.0.6.tgz#867ac74e3864187b1d3d47d996a78ec5c8830777"
   integrity sha1-hnrHTjhkGHsdPUfZlqeOxciDB3c=
 
-typescript@^4.1.3:
+typescript@>=2.7, typescript@^4.1.3:
   version "4.1.5"
   resolved "https://registry.npmjs.org/typescript/-/typescript-4.1.5.tgz#123a3b214aaff3be32926f0d8f1f6e704eb89a72"
   integrity sha512-6OSu9PTIzmn9TCDiovULTnET6BgXtDYL4Gg4szY+cGsc3JP1dQL8qvE8kShTRx1NIw4Q9IBHlwODjkjWEtMUyA==