Add regression test for invalid inline string code generation.

A bug was found during code review that didn't trigger any test failure
The fast TDP entry did not have the index in the aux_idx field.

PiperOrigin-RevId: 511570831

src/google/protobuf/generated_message_tctable_impl.h

@@ -271,7 +271,7 @@ inline void AlignFail(std::integral_constant<size_t, 1>,
 class PROTOBUF_EXPORT TcParser final {
  public:
   template <typename T>
-  static constexpr const TcParseTableBase* GetTable() {
+  static constexpr auto GetTable() -> decltype(&T::_table_.header) {
     return &T::_table_.header;
   }
 

src/google/protobuf/message_unittest.inc

@@ -62,11 +62,12 @@
 #include "google/protobuf/arena.h"
 #include "google/protobuf/descriptor.h"
 #include "google/protobuf/generated_message_reflection.h"
-#include "google/protobuf/message.h"
+#include "google/protobuf/generated_message_tctable_impl.h"
 #include "google/protobuf/io/coded_stream.h"
 #include "google/protobuf/io/io_win32.h"
 #include "google/protobuf/io/zero_copy_stream.h"
 #include "google/protobuf/io/zero_copy_stream_impl.h"
+#include "google/protobuf/message.h"
 #include "google/protobuf/test_util2.h"
 
 
@@ -1684,6 +1685,60 @@ class TestInputStream final : public io::ZeroCopyInputStream {
   size_t break_pos_;
 };
 
+template <typename T>
+static const internal::TcParseTableBase* GetTableIfAvailable(...) {
+  return nullptr;
+}
+
+template <typename T>
+static const internal::TcParseTableBase* GetTableIfAvailable(
+    decltype(internal::TcParser::GetTable<T>())) {
+  return internal::TcParser::GetTable<T>();
+}
+
+TEST(MESSAGE_TEST_NAME, TestRegressionInlinedStringAuxIdxMismatchOnFastParser) {
+  using Proto = UNITTEST::InlinedStringIdxRegressionProto;
+
+  auto* table = GetTableIfAvailable<Proto>(nullptr);
+  // Only test when TDP is on, and we have these fields inlined.
+  if (table != nullptr &&
+      table->fast_entry(1)->target() == internal::TcParser::FastSiS1) {
+    // optional string str1 = 1;
+    EXPECT_EQ(table->fast_entry(1)->bits.aux_idx(), 1);
+    // optional InlinedStringIdxRegressionProto sub = 2;
+    EXPECT_EQ(table->fast_entry(2)->bits.aux_idx(), 2);
+    // optional string str2 = 3;
+    // The aux_idx points to the inlined_string_idx and not the actual aux_idx.
+    EXPECT_EQ(table->fast_entry(3)->bits.aux_idx(), 2);
+    // optional string str3 = 4;
+    // The aux_idx points to the inlined_string_idx and not the actual aux_idx.
+    EXPECT_EQ(table->fast_entry(0)->bits.aux_idx(), 3);
+  }
+
+  std::string encoded;
+  {
+    Proto proto;
+    // We use strings longer than SSO.
+    proto.set_str1(std::string(100, 'a'));
+    proto.set_str2(std::string(100, 'a'));
+    proto.set_str3(std::string(100, 'a'));
+    encoded = proto.SerializeAsString();
+  }
+  Arena arena;
+  auto* proto = Arena::CreateMessage<Proto>(&arena);
+  // We don't alter donation here, so it works even if the idx are bad.
+  ASSERT_TRUE(proto->ParseFromString(encoded));
+  // Now we alter donation bits. str2's bit (#2) will be off, but its aux_idx
+  // (#3) will point to a donated string.
+  proto = Arena::CreateMessage<Proto>(&arena);
+  proto->mutable_str1();
+  proto->mutable_str2();
+  proto->mutable_str3();
+  // With the bug, this breaks the cleanup list, causing UB on arena
+  // destruction.
+  ASSERT_TRUE(proto->ParseFromString(encoded));
+}
+
 TEST(MESSAGE_TEST_NAME, TestRepeatedStringParsers) {
   google::protobuf::Arena arena;
 

src/google/protobuf/unittest.proto

@@ -1549,7 +1549,7 @@ message EnumParseTester {
 
   // An arbitrary field we can append to to break the runs of repeated fields.
   optional int32 other_field = 99;
-};
+}
 
 // This message contains different kind of bool fields to exercise the different
 // parsers in table-drived.
@@ -1566,7 +1566,7 @@ message BoolParseTester {
 
   // An arbitrary field we can append to to break the runs of repeated fields.
   optional int32 other_field = 99;
-};
+}
 
 message Int32ParseTester {
   optional int32 optional_int32_lowfield = 1;
@@ -1581,7 +1581,7 @@ message Int32ParseTester {
 
   // An arbitrary field we can append to to break the runs of repeated fields.
   optional int32 other_field = 99;
-};
+}
 
 message Int64ParseTester {
   optional int64 optional_int64_lowfield = 1;
@@ -1596,7 +1596,19 @@ message Int64ParseTester {
 
   // An arbitrary field we can append to to break the runs of repeated fields.
   optional int32 other_field = 99;
-};
+}
+
+message InlinedStringIdxRegressionProto {
+  // We mix data to make sure aux ids and inlined string idx do not match.
+  // aux_idx == inlined_string_idx == 1
+  optional string str1 = 1;
+  // aux_idx == 2
+  optional InlinedStringIdxRegressionProto sub = 2;
+  // aux_idx == 3, inlined_string_idx == 2
+  optional string str2 = 3;
+  // aux_idx == 4, inlined_string_idx == 3
+  optional bytes str3 = 4;
+}
 
 message StringParseTester {
   optional string optional_string_lowfield = 1;
@@ -1605,7 +1617,7 @@ message StringParseTester {
   repeated string repeated_string_lowfield = 2;
   repeated string repeated_string_midfield = 1002;
   repeated string repeated_string_hifield = 1000002;
-};
+}
 
 message BadFieldNames{
   optional int32 OptionalInt32 = 1;