[TypeScript 3.7] add support for optional chaining

[patrik-piskay]

Environments:

• Prettier Version: 1.18.2
• Running Prettier via: CLI

Steps to reproduce:
I was able to reproduce in the playground when using the typescript parser, which I guess it's the parser that ends up being used by prettier in typescript files? In my case its happening for both .ts and .tsx file extensions.

https://prettier.io/playground/#N4Igxg9gdgLgprEAuEBDAdAIwPzrCAGhAgAcYBLaAZ2VFQCd6IB3ABQYRpVQDcJyAJoRCZ6qMAGs4MAMolx5KAHNkMegFc4RABYwAtgBsA6tvLwq8sHBmcz5HmYCeycFRpFFVOPRisxSvVRkADNUAy8iACsqAA8AITFJaRlUPTgAGUU4ELCIkGiYmUUlAzgARXUIeBzwrRB5ei96FxhHEjgqMHpyMmESbtgjQRhtZAAOAAYifogvIzESF36O7x5sogBHSvg-Ui40KgBaKDg4ATPhejgt8iu-VACgpFDaoi89clUNOqpi0oqqtlnrk6jBUJghgIRsgAExENSocgGYoAYQgekCLig0HWIHUXgAKuCuC8vABfMlAA

Expected behavior: does not throw "Expression expected" syntax error when using optional chaining in typescript files

Actual behavior: throw "Expression expected" syntax error when using optional chaining in typescript files

[sosukesuzuki]

Thanks for creating the issue. It is still in dev, we have not support it yet as mentioned in #6574.

[lppedd]

@sosukesuzuki but you mean dev for Prettier or for TypeScript?

[sosukesuzuki]

@lppedd I meant dev for TypeScript. But, I think we should prepare for TS 3.7 👍

[lppedd]

@sosukesuzuki thanks! Here we are already using TS 3.7 beta.

[alexander-akait]

I think we need update ts parser

[sosukesuzuki]

@evilebottnawi I think so too. But, I'm worried that we can't update typescript-estree that because of the version of Node that Prettier supports...

[0rvar]

Could we use the babel parser instead? It already has support for Typescript when using the typescript preset

[alexander-akait]

@0rvar #6400, should be shipped in 1.19

[lppedd]

@evilebottnawi so that means after merging that PR, potentially I could build Prettier and use the Babel parser with 3.7 (and thus keep formatting)?

[alexander-akait]

@lppedd should be, but we still need add tests to avoid regression

[lppedd]

@evilebottnawi sure. It would be only a temporary solution to keep using Prettier.

[fisker]

Can typescript v3.7.0-beta https://www.npmjs.com/package/typescript/v/3.7.0-beta help?
As I tested yesterday when I do #6519 , it's safe to update to v3.7.0-beta

[alexander-akait]

@fisker sometimes ts command do big changes on alpha or beta, better wait stable release

[fisker]

@evilebottnawi you're right, I'm going to test on 3.7.0-beta to prepare for 3.7 stable release