Start testing against Rust edition 2024

This change also makes all the necessary fixes to get us compatible with
edition 2024.

I set things up so that we test edition 2024 with Bazel but keep Cargo on
edition 2021. This seems like a nice way to go since it allows us to get full
test coverage of both editions without us having to increment our minimum
supported Rust version.

PiperOrigin-RevId: 816241556

MODULE.bazel

@@ -179,9 +179,13 @@ register_toolchains(
 )
 
 rust = use_extension("@rules_rust//rust:extensions.bzl", "rust", dev_dependency = True)
+
+# As of October 2025, our minimum supported Rust version is 1.79. However, we
+# use 1.85.0 here so that we can get some test coverage with edition 2024.
+# Cargo and our Bazel WORKSPACE build are both still on edition 2021.
 rust.toolchain(
-    edition = "2021",
-    versions = ["1.79.0"],
+    edition = "2024",
+    versions = ["1.85.0"],
 )
 
 crate = use_extension("@rules_rust//crate_universe:extension.bzl", "crate", dev_dependency = True)

rust/bazel/aspects.bzl

@@ -262,7 +262,7 @@ def _compile_rust(ctx, attr, src, extra_srcs, deps, runtime):
             aliases = {runtime: "protobuf"},
             output = lib,
             metadata = rmeta,
-            edition = "2021",
+            edition = "2024",
             is_test = False,
             rustc_env = {},
             compile_data = depset([]),

rust/cpp.rs

@@ -103,7 +103,7 @@ pub struct InnerProtoString {
     owned_ptr: CppStdString,
 }
 
-extern "C" {
+unsafe extern "C" {
     pub fn proto2_rust_Message_delete(m: RawMessage);
     pub fn proto2_rust_Message_clear(m: RawMessage);
     pub fn proto2_rust_Message_parse(m: RawMessage, input: PtrAndLen) -> bool;
@@ -149,7 +149,7 @@ impl From<&[u8]> for InnerProtoString {
     }
 }
 
-extern "C" {
+unsafe extern "C" {
     fn proto2_rust_cpp_new_string(src: PtrAndLen) -> CppStdString;
     fn proto2_rust_cpp_delete_string(src: CppStdString);
     fn proto2_rust_cpp_string_to_view(src: CppStdString) -> PtrAndLen;
@@ -324,7 +324,7 @@ impl From<RustStringRawParts> for String {
     }
 }
 
-extern "C" {
+unsafe extern "C" {
     fn proto2_rust_utf8_debug_string(raw: RawMessage) -> RustStringRawParts;
 }
 
@@ -335,7 +335,7 @@ pub fn debug_string(raw: RawMessage, f: &mut fmt::Formatter<'_>) -> fmt::Result
     write!(f, "{dbg_str}")
 }
 
-extern "C" {
+unsafe extern "C" {
     /// # Safety
     /// - `raw1` and `raw2` legally dereferenceable MessageLite* pointers.
     #[link_name = "proto2_rust_messagelite_equals"]
@@ -662,7 +662,7 @@ macro_rules! impl_repeated_primitives {
         $reserve_thunk:ident $(,)?
     ]),* $(,)?) => {
         $(
-            extern "C" {
+            unsafe extern "C" {
                 fn $new_thunk() -> RawRepeatedField;
                 fn $free_thunk(f: RawRepeatedField);
                 fn $add_thunk(f: RawRepeatedField, v: <$t as CppTypeConversions>::InsertElemType);
@@ -747,7 +747,7 @@ macro_rules! impl_repeated_primitives {
 
 impl_repeated_primitives!(i32, u32, i64, u64, f32, f64, bool, ProtoString, ProtoBytes);
 
-extern "C" {
+unsafe extern "C" {
     pub fn proto2_rust_RepeatedField_Message_new() -> RawRepeatedField;
     pub fn proto2_rust_RepeatedField_Message_free(field: RawRepeatedField);
     pub fn proto2_rust_RepeatedField_Message_size(field: RawRepeatedField) -> usize;
@@ -1354,7 +1354,7 @@ macro_rules! impl_map_primitives {
         $remove_thunk:ident,
     ]),* $(,)?) => {
         $(
-            extern "C" {
+            unsafe extern "C" {
                 pub fn $insert_thunk(
                     m: RawMap,
                     key: $cpp_type,
@@ -1397,7 +1397,7 @@ impl_map_primitives!(
     ProtoString, PtrAndLen;
 );
 
-extern "C" {
+unsafe extern "C" {
     fn proto2_rust_thunk_UntypedMapIterator_increment(iter: &mut UntypedMapIterator);
 
     pub fn proto2_rust_map_new(key_prototype: MapValue, value_prototype: MapValue) -> RawMap;

rust/cpp_kernel/rust_alloc_for_cpp_api.rs

@@ -7,8 +7,8 @@
 
 use std::alloc::{alloc, Layout};
 
-#[no_mangle]
-extern "C" fn proto2_rust_alloc(size: usize, align: usize) -> *mut u8 {
+#[unsafe(no_mangle)]
+unsafe extern "C" fn proto2_rust_alloc(size: usize, align: usize) -> *mut u8 {
     if size == 0 {
         // A 0-sized layout is legal but the global allocator isn't required to support
         // it so return a dangling pointer instead.

rust/shared.rs

@@ -78,8 +78,8 @@ use utf8;
 
 // If the Upb and C++ kernels are both linked into the same binary, this symbol
 // will be defined twice and cause a link error.
-#[no_mangle]
-extern "C" fn __Disallow_Upb_And_Cpp_In_Same_Binary() {}
+#[unsafe(no_mangle)]
+unsafe extern "C" fn __Disallow_Upb_And_Cpp_In_Same_Binary() {}
 
 /// An error that happened during parsing.
 #[derive(Debug, Clone)]

rust/test/cpp/interop/main.rs

@@ -27,7 +27,7 @@ macro_rules! proto_assert_eq {
 
 // Helper functions invoking C++ Protobuf APIs directly in C++.
 // Defined in `test_utils.cc`.
-extern "C" {
+unsafe extern "C" {
     fn TakeOwnershipAndGetOptionalInt64(msg: *mut c_void) -> i64;
     fn DeserializeInteropTestMessage(data: *const u8, len: usize) -> *mut c_void;
     fn MutateInteropTestMessage(msg: *mut c_void);

rust/upb/sys/mem/arena.rs

@@ -17,7 +17,7 @@ pub const UPB_MALLOC_ALIGN: usize = 8;
 const _CHECK_UPB_MALLOC_ALIGN_AT_LEAST_POINTER_ALIGNED: () =
     assert!(UPB_MALLOC_ALIGN >= align_of::<*const ()>());
 
-extern "C" {
+unsafe extern "C" {
     // `Option<NonNull<T: Sized>>` is ABI-compatible with `*mut T`
     pub fn upb_Arena_New() -> Option<RawArena>;
     pub fn upb_Arena_Free(arena: RawArena);

rust/upb/sys/message/array.rs

@@ -19,7 +19,7 @@ use sys::opaque_pointee::opaque_pointee;
 opaque_pointee!(upb_Array);
 pub type RawArray = NonNull<upb_Array>;
 
-extern "C" {
+unsafe extern "C" {
     pub fn upb_Array_New(a: RawArena, r#type: CType) -> RawArray;
     pub fn upb_Array_Size(arr: RawArray) -> usize;
     pub fn upb_Array_Set(arr: RawArray, i: usize, val: upb_MessageValue);

rust/upb/sys/message/map.rs

@@ -30,7 +30,7 @@ pub enum MapInsertStatus {
 
 pub const UPB_MAP_BEGIN: usize = usize::MAX;
 
-extern "C" {
+unsafe extern "C" {
     pub fn upb_Map_New(arena: RawArena, key_type: CType, value_type: CType) -> RawMap;
     pub fn upb_Map_Size(map: RawMap) -> usize;
     pub fn upb_Map_Insert(

rust/upb/sys/message/message.rs

@@ -21,7 +21,7 @@ use sys::opaque_pointee::opaque_pointee;
 opaque_pointee!(upb_Message);
 pub type RawMessage = NonNull<upb_Message>;
 
-extern "C" {
+unsafe extern "C" {
     /// # Safety
     /// - `mini_table` and `arena` must be valid to deref
     pub fn upb_Message_New(mini_table: RawMiniTable, arena: RawArena) -> Option<RawMessage>;

rust/upb/sys/mini_table/mini_table.rs

@@ -51,7 +51,7 @@ pub type RawMiniTableField = NonNull<upb_MiniTableField>;
 // we are not currently using it.
 opaque_pointee!(upb_Status);
 
-extern "C" {
+unsafe extern "C" {
     /// Finds the field with the provided number, will return NULL if no such
     /// field is found.
     ///

rust/upb/sys/text/text.rs

@@ -12,7 +12,7 @@ mod sys {
 use sys::message::message::RawMessage;
 use sys::mini_table::mini_table::RawMiniTable;
 
-extern "C" {
+unsafe extern "C" {
     /// Returns the minimum needed length (excluding NULL) that `buf` has to be
     /// to hold the `msg`s debug string.
     ///

rust/upb/sys/wire/wire.rs

@@ -39,7 +39,7 @@ pub enum DecodeStatus {
 }
 // LINT.ThenChange()
 
-extern "C" {
+unsafe extern "C" {
     // SAFETY:
     // - `mini_table` is the one associated with `msg`
     // - `buf` and `buf_size` are legally writable.

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

@@ -320,7 +320,7 @@ void GenerateEnumDefinition(Context& ctx, const EnumDescriptor& desc,
         }
 
         unsafe fn repeated_free(_private: $pbi$::Private, f: &mut $pb$::Repeated<Self>) {
-          $pbr$::free_enum_repeated(f)
+          unsafe { $pbr$::free_enum_repeated(f) }
         }
 
         fn repeated_len(r: $pb$::View<$pb$::Repeated<Self>>) -> usize {

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

@@ -795,7 +795,7 @@ void GenerateRs(Context& ctx, const Descriptor& msg, const upb::DefPool& pool) {
              }},
         },
         R"rs(
-        extern "C" {
+        unsafe extern "C" {
           $message_externs$
           $accessor_externs$
           $oneof_externs$