Optional chaining failing with `"target": "esnext"` in `tsconfig` -- Rollup doesn't understand this syntax yet

What happens and why it is wrong

https://github.com/brandon-leapyear/rollup-optional-chaining-repro

Copied from README:

yarn
yarn rollup -c

Uncomment the "target": "esnext" line in tsconfig.json to show the error:

index.ts: (3:57)
[!] Error: Unexpected token (Note that you need plugins to import files that are not JavaScript)
index.ts (3:57)
1: import React from 'react'
2: 
3: const a: { b?: string } = {}
                               ^
4: 
5: export default () => <span>{a?.b}</span>
Error: Unexpected token (Note that you need plugins to import files that are not JavaScript)
    at error (/Users/bchinn/Desktop/rollup-example/node_modules/rollup/dist/rollup.js:5351:30)
    at Module.error (/Users/bchinn/Desktop/rollup-example/node_modules/rollup/dist/rollup.js:9643:9)
    at tryParse (/Users/bchinn/Desktop/rollup-example/node_modules/rollup/dist/rollup.js:9552:16)
    at Module.setSource (/Users/bchinn/Desktop/rollup-example/node_modules/rollup/dist/rollup.js:9868:33)
    at /Users/bchinn/Desktop/rollup-example/node_modules/rollup/dist/rollup.js:12148:20
    at async Promise.all (index 0)
    at async Promise.all (index 0)
    at async Promise.all (index 0)

Seems to be a rollup-plugin-typescript2 bug because with "target": "esnext" uncommented, yarn tsc --noEmit still works (e.g. Typescript parses it fine).

Environment

Shouldn’t be relevant

Versions

• typescript: latest
• rollup: latest
• rollup-plugin-typescript2: latest

rollup.config.js

import typescript from 'rollup-plugin-typescript2'

export default {
  input: 'index.ts',
  output: [
    {
      file: 'dist/index.js',
      format: 'es',
    },
  ],
  plugins: [
    typescript({
      typescript: require('typescript'),
    })
  ],
}

tsconfig.json

{
  "compilerOptions": {
    "allowSyntheticDefaultImports": true,
    "jsx": "react",

    // Uncomment to break:
    // "target": "esnext",
  }
}

package.json

{
    "name": "rollup-optional-chaining-repro",
    "version": "0.0.1",
    "private": true,
    "devDependencies": {
        "rollup": "^1.27.0",
        "rollup-plugin-typescript2": "^0.25.2"
    },
    "dependencies": {
        "typescript": "^3.7.2"
    }
}

plugin output with verbosity 3

plugin-debug.txt

[ezolenko]

@dagda1 this is not a bug – this is typescript generating correct code (for esnext target) that rollup can’t quite consume. You can add babel plugin into the chain if you must have esnext.

[ezolenko]

Typescript transpiles a?.b to (_a = a) === null || _a === void 0 ? void 0 : _a.b when es2015 (default) is used.

It transpiles a?.b to a?.b when esnext is used. I guess this is a native JS feature in esnext,

The error you see is rollup failing to parse this. (not sure if they are supposed to support it or not).

You can verify by running tsc, getting it to emit index.js and then using js file as rollup input. You should get the same error.