RangeError: Maximum call stack size exceeded

[benjamin-hg]

While playing around with generic type constraints, I came across a bug in the typescriptServices.js used on the ts playground:

TypeScript Version: 1.8.2 (66d9c92bd3d6127ed3142876bc1a446bbd8395de)

Code

function cast<TSparse extends TFull|TSparse, TFull extends TFull & TSparse>
(input:TSparse):TFull{
    return input; 
} 

Expected behavior:
A (meaningful) compile error or compiled code or both

Actual behavior:
RangeError: "Maximum call stack size exceeded" and no compile result in TS Playground with this code.

[benjamin-hg]

I know it's an exotic kind of type constraint usage and I'm not very surprised it didn't work. I just reported it because the compiler probably is not supposed to crash.

[benjamin-hg]

BTW: what I was trying to do:

Problem:
I have an interface Item that has a lot of non-optional properties. In some unit tests, I need to create objects of that interface, but do not need all these properties.

I want to be able to define a "sparse" item with only some of the otherwise mandatory properties present.

My approach:
I created an interface SparseItem that has the same properties, but all are optional. I use it for the variable that holds my test dummy.

When I want to pass it to methods that expect an object of interface Item, I have to do a kind of cast.

var item = <Item><any>sparseItem;

would have done the job, but not very safely. So I thought I could wirte a cast function that would do a better job. Usage like this:

var item:Item = cast<SparseItem, Item>(sparseItem);

My goal:

• When a property of Item is removed or renamed, but not on SparseItem and it is still used, I get an error.
• (Optional) When a property is added to Item, but not on SparseItem, I get an error.

[mhegazy]

This should be flagged as an error by the compiler. a type parameter can not depend on itself, this is not supported.
I think what you are looking for is something like a type operator that gives you an all optional version of a type. this is tracked by #7004

[benjamin-hg]

@mhegazy yes, exactly -- thanks for pointing me to #7004

[sandersn]

Fixed in 3.8