@typescript-bot run dt
@typescript-bot perf test this

Heya @ahejlsberg, I've started to run the perf test suite on this PR at c44f1a4. You can monitor the build here. It should now contribute to this PR's status checks.

Update: The results are in!

Heya @ahejlsberg, I've started to run the parallelized Definitely Typed test suite on this PR at c44f1a4. You can monitor the build here. It should now contribute to this PR's status checks.

@ahejlsberg
The results of the perf run you requested are in!

@typescript-bot pack this

Heya @amcasey, I've started to run the tarball bundle task on this PR at d6d9dd7. You can monitor the build here. It should now contribute to this PR's status checks.

Hey @amcasey, I've packed this into an installable tgz. You can install it for testing by referencing it in your package.json like so:

{
    "devDependencies": {
        "typescript": "https://typescript.visualstudio.com/cf7ac146-d525-443c-b23c-0d58337efebc/_apis/build/builds/63158/artifacts?artifactName=tgz&fileId=A987F38F6364514260C7A68F64FA1F26CC816EB374A422F9891F2C151AB1791A02&fileName=/typescript-3.8.0-insiders.20200204.tgz"
    }
}

and then running npm install.

There is also a playground for this build.

10-run average from the original machine shows a 7% improvement. Very nice!

This change fixes a failure in checking in @types/mongoose of the form:

interface E {
    stack: string;
}
declare var y: E | undefined
declare var x: E;
var x = y; // error expected here, but none given
x.stack

It's very surprising to me that we didn't give an error here before. Note that we did give an error for number | undefined.

Maybe it's because we weren't strictly checking duplicate declaration sites before. Normal code like var x: E | undefined = y gives the error before this change.