no error when using spread operator with object of incorrect type

[DetachHead]

TypeScript Version: 4.2.0-dev.20201126

Search Terms:
spread operator type safe
Code

type Foo = {bar: number}
let foo: Foo = {bar: 1}

foo.baz = 1 //Property 'baz' does not exist on type 'Foo'.
foo = {...foo, baz: 1 } //Type '{ baz: number; bar: number; }' is not assignable to type 'Foo'. Object literal may only specify known properties, and 'baz' does not exist in type 'Foo'.
foo = {...foo, ...{baz: 1} } // no error

Expected behavior:
error on the last line as property baz does not exist on type Foo
Actual behavior:
no error
Playground Link:
https://www.typescriptlang.org/play?ts=4.2.0-dev.20201126#code/C4TwDgpgBAYg9nKBeKBvARgQwE4C4oB2ArgLboTYC+AsAFAA2EwUAZgvvIihjvgIw1adNnAB0WAF7IofKAHo5ABWxxI2UFADkkzVAAmcCAGdCcZhAAeASyPM4BKKEhbOm0cITTUonyIA0UJL8UJTycgAq4NCaqIGYEvjEZBQA3HF4hKTk2GmUujamzJhGRlYA5gSY6IyOiE7RrqJQAPLoAFYQAMbM9FbAFJj0UCSYIFD29GNGkJ1WLGMA1gRwAO4OYCpqwFbGAZgEelo6+oYmy+bWtlBWDvUuCG4eXGg+ov5QrzwJMqGhCqZQCgqbBAA
Related Issues:

[MartinJohns]

Duplicate of #39998.

On a side-note: This is still type-safe. Extra-properties on objects are allowed. Excess property checks are more of a linter feature.

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.