This invariant is enforced by the fact that `NonnullGCPtr` can only be
constructed from references.
This commit fixes an instance where we compared a pointer to null after
we have already dereferenced it.
The compiler-generated copy constructor and copy assignment operator
already do the right thing (which is to simply copy the underlying
pointer).
The [Itanium C++ ABI][1] treats any class with non-trivial copy/move
constructors and destructors as non-trivial for the purposes of calls --
even if they are functionally identical to the compiler-generated ones.
If a class is non-trivial, it cannot be passed or returned in registers,
only via an invisible reference, which is worse for codegen. This commit
makes `{Nonnull,}GCPtr` trivial.
As the compiler can be sure that capturing a `GCPtr` by value has no
side effects, a few `-Wunused-lambda-capture` warnings had to be
addressed in LibWeb.
GCC seems to have a bug that prevents `ExceptionOr<Variant<GCPtr<T>>>`
from being implicitly constructed from `GCPtr<T>` after this change. A
non-invasive workaround is to explicitly construct the inner Variant
type.
[1]: https://itanium-cxx-abi.github.io/cxx-abi/abi.html#non-trivial
Without this change, using {Nonnull,}GCPtr<T const> would complain that
there are multiple constructors which resolve to the same type (T& and
T const&). This removes that disambiguation and allows us to slowly fix
all of the constness issues surrounding GCPtrs. This change will not be
necessary in the future as we will be able to remove all of the const
qualifiers from the Ptr classes (they'll be in the template type
instead).
GCPtr can be null so it's not safe to assign it to a NonnullGCPtr unless
you know it to be non-null.
This exposed a number of wrong uses in LibWeb which had to be fixed as
part of this change.
Note that this still keeps the old behaviour of putting things in std by
default on serenity so the tools can be happy, but if USING_AK_GLOBALLY
is unset, AK behaves like a good citizen and doesn't try to put things
in the ::std namespace.
std::nothrow_t and its friends get to stay because I'm being told that
compilers assume things about them and I can't yeet them into a
different namespace...for now.
Even if the pointer value is const, the value they point to is not
necessarily const, so these functions should not add the qualifier.
This also removes the redundant non-const implementations of these
operators.
These are two new smart pointers that are really just raw pointers under
the hood. The initial benefit is all in the names, they allow us to
declare that we're pointing at something in the GC heap.
Later we may also find ways to add debugging logic or static analysis to
these types.
