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Recursive Mapped Conditional Type inferring top-level children to any #25860
Description
TypeScript Version: 3.1.0-dev.20180721
Search Terms: any recursive mapped conditional inference
Code
interface MyNumbers {
cool: {
mysteriouslySo: number;
comfortablySo: number;
};
scary: {
ominouslySo: number;
};
}
type MapLeaves<OldShape, NewLeaf> = OldShape extends {}
? { [k in keyof OldShape]: MapLeaves<OldShape[k], NewLeaf> }
: NewLeaf;
// This is inferring as { cool: any, scary: any }, not what I expected!
type MyStrings = MapLeaves<MyNumbers, string>;Expected behavior:
I'm not sure if I'm misusing recursive mapped conditional types here, but I expected MyStrings to be
interface MyNumbers {
cool: {
mysteriouslySo: string;
comfortablySo: string;
};
scary: {
ominouslySo: string;
};
}Actual behavior:
It's inferred as
{ cool: any, scary: any }Playground Link:
Link
Activity
ahejlsberg commentedon Jul 22, 2018
Duplicate of #23897. The types are actually computed correctly, but our type display logic doesn't currently descend into recursive mapped types because they could potentially be infinite.
Here,
ShouldBeStringis indeed of typestring. By the way, note that I had to change{}toobjectin your conditional type. The{}type is actually a supertype of every type butnullorundefined, whereasobjectis a supertype of only objects (and not primitive types).osdiab commentedon Jul 22, 2018
Ah, interesting. Sounds like displaying it with some kind of ellipsis or placeholder type would be more ideal. I'll post to that issue.
typescript-bot commentedon Aug 1, 2018
Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.