Is needed a test with an index type? Like:

interfaceBar{[id:string]:string;}declareconsta:Bardeletea["a"];deletea.b;

Is needed a test with an index type? Like:

Good point.

@typescript-bot pack this.

Hey, How are you?@typescript-bot

@typescript-bot pack this.

Heya@Kingwl, I've started to run the tarball bundle task on this PR at6e4b381. You can monitor the buildhere.

Hey@Kingwl, I've packed this intoan installable tgz. You can install it for testing by referencing it in yourpackage.json like so:

{    "devDependencies": {        "typescript": "https://typescript.visualstudio.com/cf7ac146-d525-443c-b23c-0d58337efebc/_apis/build/builds/71131/artifacts?artifactName=tgz&fileId=48169EB321B4086E6AE66D6A286AB7E7D6AA2CCF9BF40D7869FAD1ED36C17C9602&fileName=/typescript-3.9.0-insiders.20200413.tgz"    }}

and then runningnpm install.

There is also a playgroundfor this build.

This is a breaking change that was added in post beta with no test run on it. I think we should have had more due diligence before pulling it in. I think we should back it out and add it in for 4.0.

What's the reasoning behind excludingnull from this list?

the operand must now be any, unknown, never, or be optional (in that it contains undefined in the type)

Becausedelete doesn't leave behind anull.

Seeing a possible bug for the following case -even though TS recognizes thatkey in delete p[key] can be either 'foo' or 'bar', it does not error.

interface Props {    foo: string;    bar: string;}const p: Props = {    foo: 'hello',    bar: 'world'}const keys = ['foo', 'bar'] as const;keys.forEach(key => delete p[key]) // Should error since foo and bar are required props

Playground Link