First of all, amazing work on the 10.1 release. Lots of great stuff.

Thank you for filing! Check list:

• Is it a bug? Usage questions should often be asked in the forum instead.
• Concise, focused, friendly issue title & description.
• A minimal, reproducible example.
• OS and browser versions, if relevant.
• Is it already fixed in master?

the following compiles:

@@jsxConfig({ version: 3 }) let func = (~callback: (. string, bool, bool) => unit=(. _, _, _) => (), ()) => (); func(~callback=(. str, a, b) => (), ()) module Foo = { @react.component let make = ( ~callback: (. string, bool, bool) => unit=(. _, _, _) => (), ) => { React.null } } module Bar = { @react.component let make = () => <Foo callback={(. _, _, _) => ()} /> }

But changing to @@jsxConfig({ version: 4 }) gives the following error:

[E] Line 10, column 46: This has type: (. 'a, 'b, 'c) => unit Somewhere wanted: (string, bool, bool) => unit 

example