Add an `_unchecked_lifetime` version of the Cpp interop wrap fns.

This is useful/necessary when the caller wants to tie the View to a lifetime other than a stack frame, including 'static.

The documentation is clarified that the preexisting one should be preferred in most situations, and only use the new one where tying the View lifetime to a stack frame isn't suitable.

PiperOrigin-RevId: 666396427

rust/codegen_traits.rs

@@ -150,15 +150,41 @@ pub(crate) mod interop {
         /// must not be deleted.
         fn __unstable_as_raw_message(&self) -> *const c_void;
 
-        /// Wraps the provided pointer as a MessageView. This takes a ref
-        /// of a pointer so that a stack variable's lifetime can be used
-        /// to help make the borrow checker safer.
+        /// Wraps the provided pointer as a MessageView.
+        ///
+        /// This takes a ref of a pointer so that a stack variable's lifetime
+        /// can be used for a safe lifetime; under most cases this is
+        /// the correct lifetime and this should be used as:
+        /// ```
+        /// fn called_from_cpp(msg: *const c_void) {
+        ///   // `msg` is known live for the current stack frame, so view's
+        ///   // lifetime is also tied to the current stack frame here:
+        ///   let view = unsafe { __unstable_wrap_raw_message(&msg); }
+        ///   do_something_with_view(view);
+        /// }
+        /// ```
         ///
         /// # Safety
         ///   - The underlying message must be for the same type as `Self`
         ///   - The underlying message must be alive for 'msg and not mutated
         ///     while the wrapper is live.
         unsafe fn __unstable_wrap_raw_message(raw: &'msg *const c_void) -> Self;
+
+        /// Wraps the provided pointer as a MessageView.
+        ///
+        /// Unlike `__unstable_wrap_raw_message` this has no constraints
+        /// on lifetime: the caller has a free choice for the lifetime.
+        ///
+        /// As this is much easier to get the lifetime wrong than
+        /// `__unstable_wrap_raw_message`, prefer using that wherever
+        /// your lifetime can be tied to a stack lifetime, and only use this one
+        /// if its not possible (e.g. with a 'static lifetime).
+        ///
+        /// # Safety
+        ///   - The underlying message must be for the same type as `Self`
+        ///   - The underlying message must be alive for the caller-chosen 'msg
+        ///     and not mutated while the wrapper is live.
+        unsafe fn __unstable_wrap_raw_message_unchecked_lifetime(raw: *const c_void) -> Self;
     }
 
     /// Traits related to message mut interop. Note that these trait fns
@@ -176,11 +202,39 @@ pub(crate) mod interop {
 
         /// Wraps the provided C++ pointer as a MessageMut.
         ///
+        /// This takes a ref of a pointer so that a stack variable's lifetime
+        /// can be used for a safe lifetime; under most cases this is
+        /// the correct lifetime and this should be used as:
+        /// ```
+        /// fn called_from_cpp(msg: *mut c_void) {
+        ///   // `msg` is known live for the current stack frame, so mut's
+        ///   // lifetime is also tied to the current stack frame here:
+        ///   let m = unsafe { __unstable_wrap_raw_message_mut(&mut msg); }
+        ///   do_something_with_mut(m);
+        /// }
+        ///
         /// # Safety
         ///   - The underlying message must be for the same type as `Self`
         ///   - The underlying message must be alive for 'msg and not read or
         ///     mutated while the wrapper is live.
         #[cfg(cpp_kernel)]
         unsafe fn __unstable_wrap_raw_message_mut(raw: &'msg mut *mut c_void) -> Self;
+
+        /// Wraps the provided pointer as a MessageMut.
+        ///
+        /// Unlike `__unstable_wrap_raw_message_mut` this has no constraints
+        /// on lifetime: the caller has a free choice for the lifetime.
+        ///
+        /// As this is much easier to get the lifetime wrong than
+        /// `__unstable_wrap_raw_message_mut`, prefer using that wherever
+        /// the lifetime can be tied to a stack lifetime, and only use this one
+        /// if its not possible (e.g. with a 'static lifetime).
+        ///
+        /// # Safety
+        ///   - The underlying message must be for the same type as `Self`
+        ///   - The underlying message must be alive for the caller-chosen 'msg
+        ///     and not mutated while the wrapper is live.
+        #[cfg(cpp_kernel)]
+        unsafe fn __unstable_wrap_raw_message_mut_unchecked_lifetime(raw: *mut c_void) -> Self;
     }
 }

rust/test/cpp/interop/main.rs

@@ -35,6 +35,8 @@ extern "C" {
 
     fn NewWithExtension() -> *mut c_void;
     fn GetBytesExtension(msg: *const c_void) -> PtrAndLen;
+
+    fn GetConstStaticTestAllTypes() -> *const c_void;
 }
 
 #[gtest]
@@ -138,3 +140,14 @@ fn smuggle_extension() {
         unsafe { GetBytesExtension(msg2.as_mut().__unstable_as_raw_message_mut()).as_ref() };
     assert_eq!(bytes, b"smuggled");
 }
+
+#[gtest]
+fn view_of_const_static() {
+    let view: TestAllTypesView<'static> = unsafe {
+        TestAllTypesView::__unstable_wrap_raw_message_unchecked_lifetime(
+            GetConstStaticTestAllTypes(),
+        )
+    };
+    assert_eq!(view.optional_int64(), 0);
+    assert_eq!(view.default_int32(), 41);
+}

rust/test/cpp/interop/test_utils.cc

@@ -59,3 +59,8 @@ extern "C" int32_t TakeOwnershipAndGetOptionalInt32(
   delete msg;
   return i;
 }
+
+extern "C" const void* GetConstStaticTestAllTypes() {
+  static const auto* msg = new protobuf_unittest::TestAllTypes;
+  return msg;
+}

src/google/protobuf/compiler/rust/message.cc

@@ -1339,6 +1339,14 @@ void GenerateRs(Context& ctx, const Descriptor& msg) {
                 $pbr$::RawMessage::new(*msg as *mut _).unwrap())
           }
         }
+        unsafe fn __unstable_wrap_raw_message_mut_unchecked_lifetime(
+            msg: *mut std::ffi::c_void) -> Self {
+          Self {
+            inner: $pbr$::MutatorMessageRef::wrap_raw(
+                $pbi$::Private,
+                $pbr$::RawMessage::new(msg as *mut _).unwrap())
+          }
+        }
         fn __unstable_as_raw_message_mut(&mut self) -> *mut std::ffi::c_void {
           self.raw_msg().as_ptr() as *mut _
         }
@@ -1349,6 +1357,10 @@ void GenerateRs(Context& ctx, const Descriptor& msg) {
           msg: &'a *const std::ffi::c_void) -> Self {
           Self::new($pbi$::Private, $pbr$::RawMessage::new(*msg as *mut _).unwrap())
         }
+        unsafe fn __unstable_wrap_raw_message_unchecked_lifetime(
+          msg: *const std::ffi::c_void) -> Self {
+          Self::new($pbi$::Private, $pbr$::RawMessage::new(msg as *mut _).unwrap())
+        }
         fn __unstable_as_raw_message(&self) -> *const std::ffi::c_void {
           self.msg.as_ptr() as *const _
         }
@@ -1365,6 +1377,10 @@ void GenerateRs(Context& ctx, const Descriptor& msg) {
           msg: &'a *const std::ffi::c_void) -> Self {
           Self::new($pbi$::Private, $pbr$::RawMessage::new(*msg as *mut _).unwrap())
         }
+        unsafe fn __unstable_wrap_raw_message_unchecked_lifetime(
+          msg: *const std::ffi::c_void) -> Self {
+          Self::new($pbi$::Private, $pbr$::RawMessage::new(msg as *mut _).unwrap())
+        }
         fn __unstable_as_raw_message(&self) -> *const std::ffi::c_void {
           self.msg.as_ptr() as *const _
         }