tsc --init --target es2015 generates es6 tsconfig.json

Bug Report

When running tsc --init --target es2015, the generated target is es6.

{
  "compilerOptions": {
    /* Visit https://aka.ms/tsconfig.json to read more about this file */

    /* Basic Options */
    // "incremental": true,                         /* Enable incremental compilation */
    "target": "es6"                                 /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019', 'ES2020', or 'ESNEXT'. */
}

This is unfortunate as the generated file looks as if it was having an invalid option.

🔎 Search Terms

tsc init es2015 es6

🕗 Version & Regression Information

I'm using tsc 4.2.4, and replicated with tsc 4.4.0-dev.20210518

• I was unable to test this on prior versions because I don't think this is an actual regression. I found b871b5353c8a9ca6dedd6bc84706fd75ed86bae4, and I suspect that this is a left-over.

🙁 Actual behavior

{
  "compilerOptions": {
    "target": "es6"                                 /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019', 'ES2020', or 'ESNEXT'. */
}

🙂 Expected behavior

{
  "compilerOptions": {
    "target": "es2015"                                 /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019', 'ES2020', or 'ESNEXT'. */
}

まず、tsc --init 用の tsconfig.json を生成する実装と、--target の名前に使用されているマッピングを見つけます。es2015 を指定してコマンドを再現し、生成された target とその説明コメントに期待される綴りが使われていることを確認します。