Daniel Bertalan 9feb1ce39f LibJS+LibWeb: Apply the Rule of Zero to {Nonnull,}GCPtr<T> ...

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

2023-08-07 22:20:03 -04:00

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