Excess property check not working with certain intersections

[ahejlsberg]

🕗 Version & Regression Information

This is the behavior in every version I tried.

⏯ Playground Link

Playground link with relevant code

💻 Code

let x1: { data: { a: string } } = { data: { a: "hello", b: true }};  // Excess property error
let x2: { data: { a: string } } & { x?: string } = { data: { a: "hello", b: true }};  // Excess property error
let x3: { [key: string]: { a: string } } = { data: { a: "hello", b: true }};  // Excess property error
let x4: { [key: string]: { a: string } } & { x?: string } = { data: { a: "hello", b: true }};  // No error!

🙁 Actual behavior

No excess property error on the last line of example.

🙂 Expected behavior

Excess property errors on all lines of example.

[ahejlsberg]

This issue was uncovered by #49503. With #49503 there is now an excess property error issued in one of the tests of the waterline Definitely Typed package. That error should have been there all along (and the test even seems to indicate so in a comment).