Weird template error in Phobos (after editing) that I can't quite get. Compiler bug?

[Atila Neves via Digitalmars-d-learn]

On Wednesday, 22 March 2017 at 14:06:56 UTC, Atila Neves wrote:
> isInputRange looks like this:
>
> template isInputRange(R)
> {
>     enum bool isInputRange = is(typeof(
>     (inout int = 0)
>     {
>         R r = R.init;     // can define a range object
>         if (r.empty) {}   // can test for empty
>         r.popFront;       // can invoke popFront()
>         auto h = r.front; // can get the front of the range
>     }));
> }
>
> [...]

Got the same error when I changed it to:

enum isInputRange(R) = is(typeof({...}));

Which might explain why it's still inside an explicit template 
declaration. Or not, this whole thing is weird to me.

Atila