NonZero is not debugable in gdb (anonymous fields can't be accessed)

[Manishearth]

Servo recently switched to NonZero for its smart pointers. This means that our JS structs of the form

struct JSRef<T> {
ptr: *const T,
...
}

became

struct JSRef<T> {
ptr: NonZero<*const T>,
...
}

In the original system, print ref.ptr in gdb would nicely print a typed pointer (something like (struct foo::bar::Baz<Quux>)* 0x12345 IIRC). Now, it gives us simply {0x12345}, and there doesn't seem to be a way to get the inner data out. This is quite annoying since we use these pointers everywhere in the DOM.

The larger issue here I guess is that anonymous fields can't be accessed as an expression in gdb. Perhaps naming them .0, .1 explicitly would work?

cc @michaelwoerister @jdm

[michaelwoerister]

Maybe this could be solved by adding special support for NonZero in the pretty printers.

[michaelwoerister]

Tuple fields should now be accessible in the debugger via the names __0, __1, __2, etc. It's not as nice as .0, .1, etc, but it's the best that debuggers will let us do for the moment.

[Manishearth]

Thanks! 😄