Circular inference failure (regression)

[falsandtru]

TypeScript Version: 2.5.0-dev.20170613

Code

I tried to make a simple repro but it failed. I had to add the annotation as follows. The previous code was working until 2.4.0-dev.20170606.

falsandtru/pjax-api@f5dbc6d

-  .extract(parser => (html: string) => Just(parser(html)));
+  .extract(parser => (html: string): Maybe<Document> => Just(parser(html)));

Expected behavior:

no error

Actual behavior:

TypeScript error: src/lib/html.ts(9,22): Error TS7024: Function implicitly has return type 'any' because it does not have a return type annotation and is referenced directly or indirectly in one of its return expressions.

[ahejlsberg]

I'm quite certain this relates to #16072 and #16305. Since we now make inferences from the return types of generic functions we will at times more eagerly resolve return statements and return expressions of lambdas. That appears to be what is happening here and I'm not sure there's much we can do about it.

[falsandtru]

Hm, okay thanks!