let_unit_value giving suggestion that fails to compile if implemented

[mhlakhani]

In 1.23, FromIterator<()> for () was stabilized. I tried to write some new code to use this feature. As a simplified example I have the code in this playground:

https://play.rust-lang.org/?gist=3d3f6bde3183c079b072006ecf26b389&version=stable

Clippy will report the error on line 5. However if I remove the annotation and change it to this:

https://play.rust-lang.org/?gist=286a63d7f9e930265093ad211b5ddfc1&version=stable

I now get a compile error because the compiler doesn't know the return type.

Should clippy not warn in this case?

PS: This seemed different enough from #1502 that I filed a separate issue, feel free to merge.

[oli-obk]

Yea this is a dupe of #1502

commenting further there