Add helper function to generate stub TcParse tables with only a single handler.

Useful for test non-codegen types that have their own parsing logic.
Also forward the `ptr` through the post_loop_handler to allow it to fail.

PiperOrigin-RevId: 606714285

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

@@ -1947,7 +1947,8 @@ void MessageGenerator::GenerateClassDefinition(io::Printer* p) {
         [&] {
           if (!NeedsPostLoopHandler(descriptor_, options_)) return;
           p->Emit(R"cc(
-            static void PostLoopHandler(MessageLite* msg,
+            static const char* PostLoopHandler(MessageLite* msg,
+                                               const char* ptr,
                                                $pbi$::ParseContext* ctx);
           )cc");
         }},
@@ -2301,11 +2302,13 @@ void MessageGenerator::GenerateClassMethods(io::Printer* p) {
           [&] {
           }}},
         R"cc(
-          void $classname$::PostLoopHandler(MessageLite* msg,
+          const char* $classname$::PostLoopHandler(MessageLite* msg,
+                                                   const char* ptr,
                                                    ::_pbi::ParseContext* ctx) {
             $classname$* _this = static_cast<$classname$*>(msg);
             $annotate_deserialize$;
             $required$;
+            return ptr;
           }
         )cc");
   }

src/google/protobuf/generated_message_tctable_decl.h

@@ -285,7 +285,8 @@ struct alignas(uint64_t) TcParseTableBase {
   uint32_t aux_offset;
 
   const MessageLite* default_instance;
-  using PostLoopHandler = void (*)(MessageLite* msg, ParseContext* ctx);
+  using PostLoopHandler = const char* (*)(MessageLite* msg, const char* ptr,
+                                          ParseContext* ctx);
   PostLoopHandler post_loop_handler;
 
   // Handler for fields which are not handled by table dispatch.
@@ -541,6 +542,38 @@ static_assert(offsetof(TcParseTable<1>, fast_entries) ==
                   sizeof(TcParseTableBase),
               "Table entries must be laid out after TcParseTableBase.");
 
+template <typename T, const char* (*func)(T*, const char*, ParseContext*)>
+const char* StubParseImpl(PROTOBUF_TC_PARAM_DECL) {
+  return func(static_cast<T*>(msg), ptr, ctx);
+}
+
+template <typename T, const char* (*func)(T*, const char*, ParseContext*)>
+constexpr TcParseTable<0> CreateStubTcParseTable(
+    const MessageLite* default_instance,
+    TcParseTableBase::PostLoopHandler post_loop_handler = nullptr) {
+  return {
+      {
+          0,                  // has_bits_offset
+          0,                  // extension_offset
+          0,                  // max_field_number
+          0,                  // fast_idx_mask
+          0,                  // lookup_table_offset
+          0,                  // skipmap32
+          0,                  // field_entries_offset
+          0,                  // num_field_entries
+          0,                  // num_aux_entries
+          0,                  // aux_offset
+          default_instance,   //
+          post_loop_handler,  //
+          nullptr,            // fallback
+#ifdef PROTOBUF_PREFETCH_PARSE_TABLE
+          nullptr,  // to_prefetch
+#endif              // PROTOBUF_PREFETCH_PARSE_TABLE
+      },
+      {{{StubParseImpl<T, func>, {}}}},
+  };
+}
+
 }  // namespace internal
 }  // namespace protobuf
 }  // namespace google

src/google/protobuf/generated_message_tctable_lite.cc

@@ -97,7 +97,7 @@ inline PROTOBUF_ALWAYS_INLINE const char* TcParser::ParseLoopInlined(
   }
   table -= 1;
   if (ABSL_PREDICT_FALSE(table->has_post_loop_handler)) {
-    table->post_loop_handler(msg, ctx);
+    return table->post_loop_handler(msg, ptr, ctx);
   }
   return ptr;
 }