C++23 P2448R2 [1] relaxed the requirements for constexpr destructors.
In C++23, Clang makes UniquePtr's destructor automatically constexpr.
Clang eagerly instantiates its body for the local UniquePtr<Encoder>
and UniquePtr<Decoder> variables in Encoding's inline factory methods.
Encoder and Decoder are only forward-declared at that point, so the
deleter's complete-type check fails.
To resolve this, move the NewDecoder() and NewDecoder factory methods
after the Encoding class definition so they have complete class
definitions for Encoder and Decoder.
[1] https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2448r2.html
MacOSX26.1.sdk/usr/include/c++/v1/__memory/unique_ptr.h:76:19: error: invalid application of 'sizeof' to an incomplete type 'mozilla::Encoder'
76 | static_assert(sizeof(_Tp) >= 0, "cannot delete an incomplete type");
| ^~~~~~~~~~~
MacOSX26.1.sdk/usr/include/c++/v1/__memory/unique_ptr.h:300:7: note: in instantiation of member function 'std::default_delete<mozilla::Encoder>::operator()' requested here
300 | __deleter_(__tmp);
| ^
MacOSX26.1.sdk/usr/include/c++/v1/__memory/unique_ptr.h:269:71: note: in instantiation of member function 'std::unique_ptr<mozilla::Encoder>::reset' requested here
269 | _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 ~unique_ptr() { reset(); }
| ^
obj-aarch64-apple-darwin25.0.0/dist/include/mozilla/Encoding.h:736:24: note: in instantiation of member function 'std::unique_ptr<mozilla::Encoder>::~unique_ptr' requested here
736 | UniquePtr<Encoder> encoder(encoding_new_encoder(this));
| ^
obj-aarch64-apple-darwin25.0.0/dist/include/mozilla/Encoding.h:28:7: note: forward declaration of 'mozilla::Encoder'
28 | class Encoder;
| ^
Differential Revision: https://phabricator.services.mozilla.com/D323890
Chris Peterson
78cb174eb3