Typescript: try-finally block can cause 'used before assigned` error

[petebacondarwin]

TypeScript Version: 3.3.1 - 3.4.0-dev.20190201 (inclusive)
This is not a problem in 3.3.0-rc

Search Terms:
used before being assigned, try finally

Code

let x: number;
x = Math.random();
let a: number;
try {
    if (x) {
        a = 1;
    } else {
        a = 2;
    }
} finally {
    console.log(x);
}

console.log(a); // <- error here

Expected behavior:

No error.

Actual behavior:

[ts] Variable 'a' is used before being assigned. [2454]
let a: number

Workaround:
You can avoid the error by apply the ! operator to the let statement:

let x !: number;

Playground Link:

Here is the playground link.

But this does not show the problem because the playground currently uses TS 3.2.x

Related Issues:

This looks similar to https://github.com/Microsoft/TypeScript/issues/12205. But that issue has not re-appeared and this issue only occurs if there is an if-else block in the try-finally block.

[j-oliveras]

PR #29466 solved this but it seems that the change are lost.

The only versions that it works are 3.3.0-dev.20190118 and the 3.3.0-rc.

Starting 3.3.0-dev.20190119 the PR changes are lost. I only test 3.3.0-dev.20190119, 3.3.0-dev.20190123 (made hours after the 3.3.0-rc), 3.3.0-dev.20190125, 3.4.0-dev.20190129 and 3.4.0-dev.20190201.

// CC @weswigham

[DanielRosenwasser]

@weswigham can you port this into release-3.3?

[DanielRosenwasser]

This should be available in TypeScript 3.3.3333.

[AviVahl]

I thought the 3333 was a typo. :roll_eyes:
New version number is inconsistent with how this project versioned its past stable releases.
Why not simply 3.3.4?

[xaviergonz]

I think that's too late since 3.3.3333 > 3.3.4 by (3333 - 4) = 3329 patch versions :/

[tommck]

yeah.. really strange version number.. Would be good to hear a reason for it

[Gerst20051]

Is there a funny reason for the patch version to be 3333 instead of 4? @DanielRosenwasser @weswigham

[DanielRosenwasser]

It was simply for the repeating 3s. Sorry for any confusion, though otherwise we don't expect that it'll adversely affect anything else.

[tommck]

it's pretty weird that we can't have 3.3.4 now :) next version will be 3.3.3334 if it's a patch :)