AK+Kernel+Userland: Don't allow AK::{Byte,}String and Vector::append() in the kernel

[spholz]

Kernel code should use KString instead of AK::{Byte,}String. Enforce this by making it a compile-time error to include <AK/String.h> or <AK/ByteString.h>.

Additional, make it not as easy to forget to handle OOMs by only allowing Vector::try_append() in the kernel.
(Not all Vector::append() overloads were guarded behind a #ifndef KERNEL before)

[spholz]

I'm not really sure if this is the right solution. Maybe we should instead not allow split_view() in the kernel at all. Directly using for_each_split_view() should be enough for most use cases in the kernel, otherwise we could maybe add try_split_view().

[nico]

Can always think about that in a follow-up 🙂

[nico]

(a bit surprising match() isn't allowed; I'm guessing it internally allocates)

[Hendiadyoin1]

Would be nice if we could make this a decorator or the like,
which seems to be feasible with an

#ifdef KERNEL
#define NOKERNEL [[error("Implicit allocation is disallowed in the Kernel")]]
#else
#define NOKERNEL
#endif

decorator

diagnose_if may also work, less if-def

[spholz]

Would be nice if we could make this a decorator or the like

Yeah the current #ifdef zoo isn't nice and I thought of maybe reorganizing some of these functions to only have one big #ifndef KERNEL block of functions that aren't allowed in the kernel.

which seems to be feasible with an

#ifdef KERNEL
#define NOKERNEL [[error("Implicit allocation is disallowed in the Kernel")]]
#else
#define NOKERNEL
#endif

decorator

diagnose_if may also work, less if-def

For some things I may want to include an additional message with what to use instead like:

#ifndef KERNEL
Vector(const&) = delete("use .clone() instead");
#endif

With that NOKERNEL approach we would need an overload with a message, but macros don't support overloading, so we would need a second version of that macro.

[spholz]

I think I'm going to keep using #ifndef KERNEL for now, as that is what we currently use in other places as well. If you want to change that, feel free to do so in another PR!