Incorrect parse of parenthesized expression in second ternary operator operand

[ronnievdc]

TypeScript Version: 3.4.0-dev.20190328

Search Terms:
expression expected, Ternary operation, shorthand

Code

let a;
let b;
const c = true ? (a = 1, b = 2) : function () { return true; };

Expected behavior:

var a;
var b;
var c = true ? (a = 1, b = 2) : function () { return true; };

Actual behavior:

var a;
var b;
var c = true ? function (a, b) {
    if (a === void 0) { a = 1; }
    if (b === void 0) { b = 2; }
    return true;
} : ;

Playground Link:
https://www.typescriptlang.org/play/#src=let%20a%3B%0D%0Alet%20b%3B%0D%0Aconst%20c%20%3D%20true%20%3F%20(a%20%3D%201%2C%20b%20%3D%202)%20%3A%20function%20()%20%7B%20return%20true%3B%20%7D%3B

Related Issues:
#16241
#11582

[dragomirtitian]

A simpler repro is just to have () in the then of the ternary expression. This also causes weird parsing to occur:

 true ? (a): function () { return true; }

Transpiled as

true ? function (a) { return true; } : ;

[weswigham]

Looks like this stems from us parsing JSDoc function types function(), (or function(number, string) or function(number): number) outside of JSDoc. We should probably just disable that.

[andrewbranch]

Yep, that's exactly what's happening @weswigham. But disabling it outright prevents this quick fix from working:

Any suggestions? 🤔

[weswigham]

The quickfix is opportunistic in nature - we don't actually expect anyone to write let x: function(): void, since that's never been valid in anything. It's moreso for catching things like let x: string? (since postfix questionmark is a thing in flow/jsdoc but not TS)