When we implemented Handle, nullptr_t was still a typedef to 0 on some platforms. Now that it is a real thing everywhere, we should be able to replace our NullPtr workaround with a constructor taking std::nullptr_t. The only remaining issue is that some platforms do not have a modern libstdc++, so do not have std::nullptr_t. Luckily we can get around that by using decltype(nullptr) instead. This patch appears to work locally; try run is below to check the other platforms: https://treeherder.mozilla.org/#/jobs?repo=try&revision=3b845f5801f5 The attached patch was generated with: $ find . -name "*.cpp" -o -name "*.h" -exec sed -i 's/JS::NullPtr()/nullptr/g' \{\} \; $ find . -name "*.cpp" -o -name "*.h" -exec sed -i 's/js::NullPtr()/nullptr/g' \{\} \; $ find . -name "*.cpp" -o -name "*.h" -exec sed -i 's/NullPtr()/nullptr/g' \{\} \; With a bit of hand tweaking afterwards to fix up Codegen.py and JS::GCCellPtr::NullPtr.

Whoops! Forgot that the null needs to be at the second level of indirection. Easy enough to solve. https://treeherder.mozilla.org/#/jobs?repo=try&revision=a53f9c3cec0b

Try run looks green. https://treeherder.mozilla.org/#/jobs?repo=try&revision=a53f9c3cec0b

Comment on attachment 8605513 [details] [diff] [review] use_nullptr_t_instead_of_NullPtr-v1.diff Review of attachment 8605513 [details] [diff] [review]: ----------------------------------------------------------------- ::: js/public/RootingAPI.h @@ +120,5 @@ > > template <typename T> > class PersistentRootedBase {}; > > +static void*const ConstNullValue = nullptr; static void* const ConstNullValue = nullptr; assuming this is still needed? @@ +407,3 @@ > static_assert(mozilla::IsPointer<T>::value, > + "nullptr_t overload not valid for non-pointer types"); > + ptr = reinterpret_cast<const T*>(&js::ConstNullValue); Wouldn't this be better with just a static nullptr declared right here? Or do we compare these pointers somehow?

InternalHandle's constructor also needed an &nullptr and I thought it would be simpler to share them. I mean, it would be weird for null handle != null handle, even if we never actually use the feature.