Fix AssociatedMiniTable to be an unsafe trait with a safe fn, instead of having an unsafe fn.

`unsafe trait` means that the _implementation_ has constraints they need to meet for the behavior to be safe (which is the intent here, namely that it should always return the same value and always be a safe to deref value), unsafe on the fn means that the _caller_ of that fn has some constraints they need to meet for it to be safe (of which there are none in this case).

PiperOrigin-RevId: 668028628

rust/upb/associated_mini_table.rs

@@ -25,11 +25,12 @@ use super::upb_MiniTable;
 /// an extern "C" we cannot do that without the unstable `const_refs_to_static`.
 /// After that feature is stabilized (or if we move the MiniTable generation to
 /// .rs) this will be switched.
-pub trait AssociatedMiniTable {
-    /// SAFETY:
-    /// - The MiniTable pointer must be from Protobuf code generation and follow
-    ///   the corresponding invariants associated with upb's C API (the pointer
-    ///   should always have the same non-null value, the underlying pointee
-    ///   should never be modified and should have 'static lifetime).
-    unsafe fn mini_table() -> *const upb_MiniTable;
+///
+/// SAFETY:
+/// - The MiniTable pointer must be from Protobuf code generation and follow the
+///   corresponding invariants associated with upb's C API (the pointer should
+///   always have the same non-null value, the underlying pointee should never
+///   be modified and should have 'static lifetime).
+pub unsafe trait AssociatedMiniTable {
+    fn mini_table() -> *const upb_MiniTable;
 }

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

@@ -299,23 +299,23 @@ void IntoProxiedForMessage(Context& ctx, const Descriptor& msg) {
 void UpbGeneratedMessageTraitImpls(Context& ctx, const Descriptor& msg) {
   if (ctx.opts().kernel == Kernel::kUpb) {
     ctx.Emit({{"minitable", UpbMiniTableName(msg)}}, R"rs(
-      impl $pbr$::AssociatedMiniTable for $Msg$ {
+      unsafe impl $pbr$::AssociatedMiniTable for $Msg$ {
         #[inline(always)]
-        unsafe fn mini_table() -> *const $pbr$::upb_MiniTable {
+        fn mini_table() -> *const $pbr$::upb_MiniTable {
           $std$::ptr::addr_of!($minitable$)
         }
       }
 
-      impl $pbr$::AssociatedMiniTable for $Msg$View<'_> {
+      unsafe impl $pbr$::AssociatedMiniTable for $Msg$View<'_> {
         #[inline(always)]
-        unsafe fn mini_table() -> *const $pbr$::upb_MiniTable {
+        fn mini_table() -> *const $pbr$::upb_MiniTable {
           $std$::ptr::addr_of!($minitable$)
         }
       }
 
-      impl $pbr$::AssociatedMiniTable for $Msg$Mut<'_> {
+      unsafe impl $pbr$::AssociatedMiniTable for $Msg$Mut<'_> {
         #[inline(always)]
-        unsafe fn mini_table() -> *const $pbr$::upb_MiniTable {
+        fn mini_table() -> *const $pbr$::upb_MiniTable {
           $std$::ptr::addr_of!($minitable$)
         }
       }