TypeScript non-null assertion operator not stripped off with deep optional chaining

[maxdavidson]

Bug Report

• I would like to work on a fix!

I noticed a really strange regression in in @babel/core 7.12.7. When used with optional chaining, the TypeScript postfix "!" operator (non-null assertion) sometimes won't get stripped off, resulting in a syntax error.

Input:

const a = 1;
const b = () => a?.b?.c!.d

Output with @babel/core@7.12.3:

const a = 1;

const b = () => {
  var _a$b;

  return a === null || a === void 0 ? void 0 : (_a$b = a.b) === null || _a$b === void 0 ? void 0 : _a$b.c.d;
};

Output with @babel/core@7.12.7:

const a = 1;

const b = () => {
  var _a$b;

  return a === null || a === void 0 ? void 0 : (_a$b = a.b) === null || _a$b === void 0 ? void 0 : _a$b.c!.d;
};

Notice the _a$b.c!.d at the end

Plugins used:

• @babel/preset-typescript@7.12.7
• @babel/plugin-proposal-optional-chaining@7.12.7 (via preset-env)

[babel-bot]

Hey @maxdavidson! We really appreciate you taking the time to report an issue. The collaborators on this project attempt to help as many people as possible, but we're a limited number of volunteers, so it's possible this won't be addressed swiftly.

If you need any help, or just have general Babel or JavaScript questions, we have a vibrant Slack community that typically always has someone willing to help. You can sign-up here for an invite."

[JLHwung]

Another minimal test case:

a => a?.b!?.c

This is likely a regression introduced at #12302.

[nicolo-ribaudo]

Fixed in 7.12.9