Why can't an incomplete type be casted to void?

Question

Why does the following code give the following error?

Why does the type need to be complete in order to be casted to void?

struct Incomp         


        

Answer 1

I don't see anything prohibiting this, quoting N4140:

§5.4/4 The conversions performed by

[...]

— a static_cast (5.2.9),

[...]

can be performed using the cast notation of explicit type conversion.

§5.2.9/5 Otherwise, the static_cast shall perform one of the conversions listed below. No other conversion shall be performed explicitly using a static_cast.

§5.2.9/6 Any expression can be explicitly converted to type cv void, in which case it becomes a discarded-value expression (Clause 5). [...]

It's most likely a bug as tested on Rextester, an online VS2013 compiler, but compiles in rise4fun, Microsoft's online compiler which is bleeding edge.