Type intersections between {} and types with only optional members are not type-checked.

[JabX]

TypeScript Version:

• typescript@next (1.9.0-20160412)
• 1.8.9
• and probably all the way down to the initial type intersection release.

Code

let test: {} & {foo?} & {bar?};
test = 'hello'; // Valid.

Expected behavior:
Well I'd like to have an error for that!

I get autocompletion for foo and bar while typing test = {}, but it's not enforced.

My use case is when I use a type in functions or classes like T & {foo?} with T = {}.

[Arnavion]

Same as #7485 ?

[basarat]

Nothing special about intersection here. Any type with all optional members is considered compatible:

let test: {foo?:any;bar?:any;};
test = 'hello'; // Valid.

[DanielRosenwasser]

I think @Arnavion is correct (thanks a ton for digging that up!). Closing as a duplicate.