Strange exception, with EXTREMELY SIMPLE toString() in a struct

[Radu via Digitalmars-d-learn]

On Monday, 7 December 2015 at 08:17:27 UTC, Enjoys Math wrote:
> Exception Message:
> First-chance exception: std.format.FormatException Unterminated 
> format specifier: "%" at 
> C:\D\dmd2\windows\bin\..\..\src\phobos\std\format.d(828)
>
> [CODE]
> module set;
> import std.conv;
>
> struct Set(T) {
> 	string toString() const {
> 		auto str = "{";
> 		return str;
> 	}
> }
>
> unittest {
> 	import std.stdio;
> 	auto A = Set!int();
> 	writeln(A);
> }
> [/CODE]

Are you running this in VisualD plugin? This is the only place I 
get that exception. Running it from the command line works as 
expected on 2.069.1 win32