[Issue 17420] std.format.formatObject doesn't work with @safe toString specialization

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=17420

--- Comment #3 from Nick Treleaven <nick at geany.org> ---
Sorry, yes (didn't have the source code to hand).

> If the toString overload is marked with any of these, hasToString!(YourType) == 0

class N
{
    @nogc void toString(scope void delegate(const(char)[])@nogc sink);
}

hasToString!(N, char) is 2. I think the problem is:

class E : Throwable
{
    override void toString(scope void delegate(const(char[]))@nogc sink) const;
}

Error: function E.toString does not override any function, did you mean to
override 'object.Throwable.toString'?

First, note that Throwable.toString takes a delegate with a const(char[])
parameter, not const(char)[], this is confusing and should be fixed.

Next, if you remove @nogc from sink above it compiles. Shouldn't dmd allow
overriding a method that takes a non- at nogc delegate with one that takes a @nogc
delegate?

--