a?.b.c() produces different result than a?.b!.c()

[alex-kinokon]

Bug Report

• I would like to work on a fix!

Input Code

• REPL or Repo link if applicable:

a?.b.c()
a?.b!.c()

Actual behavior

"use strict";

var _a, _a2;

(_a = a) === null || _a === void 0 ? void 0 : _a.b.c();
((_a2 = a) === null || _a2 === void 0 ? void 0 : _a2.b).c();

Expected behavior/code
The ! should have no effect on the produced code.

Problem: Suppose a is null, then the second line can be reduced to:

   ((_a2 = a) === null || _a2 === void 0 ? void 0 : _a2.b).c()
=> ((a2 = null) === null || _a2 === void 0 ? void 0 : _a2.b).c()
=> (null === null || _a2 === void 0 ? void 0 : _a2.b).c()
=> (true ? void 0 : _a2.b).c()
=> undefined.c()

Babel Configuration (babel.config.js, .babelrc, package.json#babel, cli command, .eslintrc)

• Filename: babel.config.js

{
  "presets": ["@babel/preset-typescript", "@babel/preset-stage-3"]
}

Environment

• Babel version(s): 7.7.7
• How you are using Babel: https://babeljs.io/repl

Possible Solution
¯\_(ツ)_/

Additional context/Screenshots
Add any other context about the problem here. If applicable, add screenshots to help explain.

[babel-bot]

Hey @proteriax! 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.

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[macabeus]

I'm working in a fix to this bug.

[macabeus]

PR opened: #10961

[nicolo-ribaudo]

EDIT: This is fixed in TS 3.9

This is correct. For reference, this is what the TypeScript compiler (verision 3.8) does: [TS Playground]

a?.b.c
a?.b!.c

a?.b.c()
a?.b!.c()

a === null || a === void 0 ? void 0 : a.b.c;
(a === null || a === void 0 ? void 0 : a.b).c;
a === null || a === void 0 ? void 0 : a.b.c();
(a === null || a === void 0 ? void 0 : a.b).c();

And this is Babel's output: [Babel repl]

(_a = a) === null || _a === void 0 ? void 0 : _a.b.c;
((_a2 = a) === null || _a2 === void 0 ? void 0 : _a2.b).c;
(_a3 = a) === null || _a3 === void 0 ? void 0 : _a3.b.c();
((_a4 = a) === null || _a4 === void 0 ? void 0 : _a4.b).c();

[alex-kinokon]

@nicolo-ribaudo There’s a bug filed at the TypeScript repo.