Fix CreateVectorOfNativeStructs for non-std vector types (cpp_vec_type + native_type)

When a field combines cpp_vec_type (e.g. eastl::vector) with native_type on a
struct, the generated Pack method now uses the pointer+size overload of
CreateVectorOfNativeStructs instead of the std::vector overload, which only
accepts std::vector. Adds a dedicated test covering the combined attribute case.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CMakeLists.txt

@@ -241,6 +241,8 @@ set(FlatBuffers_Tests_SRCS
   tests/native_type_test_impl.h
   tests/native_type_test_impl.cpp
   tests/cpp_vec_type_test_impl.h
+  tests/cpp_vec_type_native_type_test_impl.h
+  tests/cpp_vec_type_native_type_test_impl.cpp
   tests/alignment_test.h
   tests/alignment_test.cpp
   tests/64bit/offset64_test.h
@@ -556,6 +558,7 @@ if(FLATBUFFERS_BUILD_TESTS)
   compile_schema_for_test(tests/native_inline_table_test.fbs "${FLATC_OPT_COMP}")
   compile_schema_for_test(tests/native_type_test.fbs "${FLATC_OPT_COMP}")
   compile_schema_for_test(tests/cpp_vec_type_test.fbs "${FLATC_OPT_COMP}")
+  compile_schema_for_test(tests/cpp_vec_type_native_type_test.fbs "${FLATC_OPT_COMP}")
   compile_schema_for_test(tests/key_field/key_field_sample.fbs "${FLATC_OPT_COMP}")
   compile_schema_for_test(tests/64bit/test_64bit.fbs "${FLATC_OPT_COMP};--bfbs-gen-embed")
   compile_schema_for_test(tests/64bit/evolution/v1.fbs "${FLATC_OPT_COMP}")

src/idl_gen_cpp.cpp

@@ -3833,7 +3833,6 @@ class CppGenerator : public BaseGenerator {
                 code += "_fbb.CreateVectorOfNativeStructs<";
                 code += WrapInNameSpace(*vector_type.struct_def) + ", " +
                         native_type->constant + ">";
-                code += "(" + value;
                 // Field-level native_type_pack_name takes priority over
                 // struct-level
                 auto field_pack_name =
@@ -3842,6 +3841,14 @@ class CppGenerator : public BaseGenerator {
                     field_pack_name
                         ? field_pack_name
                         : struct_attrs.Lookup("native_type_pack_name");
+                // Non-std vectors (e.g. eastl::vector) don't match the
+                // std::vector overload, so use the pointer+size overload.
+                const bool is_std_vec = NativeVector(&field) == "std::vector";
+                if (is_std_vec) {
+                  code += "(" + value;
+                } else {
+                  code += "(" + value + ".data(), " + value + ".size()";
+                }
                 if (pack_name) {
                   code += ", ::flatbuffers::Pack" + pack_name->constant;
                 }

tests/cpp_vec_type_native_type_test.fbs

@@ -0,0 +1,15 @@
+native_include "cpp_vec_type_native_type_test_impl.h";
+
+namespace CppVecNativeTypeTest;
+
+struct Vec3 (native_type: "CppVecNativeTypeTest::Native::Vec3") {
+  x: float;
+  y: float;
+  z: float;
+}
+
+table Container {
+  points: [Vec3] (cpp_vec_type: "CppVecNativeTypeTest::CustomVec");
+}
+
+root_type Container;

tests/cpp_vec_type_native_type_test_impl.cpp

@@ -0,0 +1,15 @@
+#include "cpp_vec_type_native_type_test_impl.h"
+
+#include "cpp_vec_type_native_type_test_generated.h"
+
+namespace flatbuffers {
+CppVecNativeTypeTest::Vec3 Pack(
+    const CppVecNativeTypeTest::Native::Vec3& obj) {
+  return CppVecNativeTypeTest::Vec3(obj.x, obj.y, obj.z);
+}
+
+const CppVecNativeTypeTest::Native::Vec3 UnPack(
+    const CppVecNativeTypeTest::Vec3& obj) {
+  return CppVecNativeTypeTest::Native::Vec3(obj.x(), obj.y(), obj.z());
+}
+}  // namespace flatbuffers

tests/cpp_vec_type_native_type_test_impl.h

@@ -0,0 +1,34 @@
+#ifndef CPP_VEC_TYPE_NATIVE_TYPE_TEST_IMPL_H
+#define CPP_VEC_TYPE_NATIVE_TYPE_TEST_IMPL_H
+
+#include <vector>
+
+namespace CppVecNativeTypeTest {
+
+namespace Native {
+struct Vec3 {
+  float x, y, z;
+  Vec3() : x(0), y(0), z(0) {}
+  Vec3(float x_, float y_, float z_) : x(x_), y(y_), z(z_) {}
+  bool operator==(const Vec3& o) const {
+    return x == o.x && y == o.y && z == o.z;
+  }
+};
+}  // namespace Native
+
+template <typename T>
+struct CustomVec : public std::vector<T> {
+  using std::vector<T>::vector;
+};
+
+struct Vec3;  // flatbuffers-generated struct
+
+}  // namespace CppVecNativeTypeTest
+
+namespace flatbuffers {
+CppVecNativeTypeTest::Vec3 Pack(const CppVecNativeTypeTest::Native::Vec3& obj);
+const CppVecNativeTypeTest::Native::Vec3 UnPack(
+    const CppVecNativeTypeTest::Vec3& obj);
+}  // namespace flatbuffers
+
+#endif  // CPP_VEC_TYPE_NATIVE_TYPE_TEST_IMPL_H

tests/test.cpp

@@ -65,6 +65,7 @@
 #include "monster_test_bfbs_generated.h"  // Generated using --bfbs-comments --bfbs-builtins --cpp --bfbs-gen-embed
 #include "cpp_vec_type_test_generated.h"
 #include "native_type_test_generated.h"
+#include "cpp_vec_type_native_type_test_generated.h"
 #include "test_assert.h"
 #include "util_test.h"
 #include "vector_table_naked_ptr_test.h"
@@ -1041,6 +1042,37 @@ void CppVecTypeTest() {
   TEST_ASSERT(*dst == *dst);
 }
 
+void CppVecTypeNativeTypeTest() {
+  // Verify that combining cpp_vec_type + native_type on a vector of structs
+  // produces the correct container type in the NativeTable.
+  static_assert(
+      std::is_same<
+          decltype(CppVecNativeTypeTest::ContainerT{}.points),
+          CppVecNativeTypeTest::CustomVec<
+              CppVecNativeTypeTest::Native::Vec3>>::value,
+      "points should be CustomVec<Native::Vec3>");
+
+  const int N = 3;
+  CppVecNativeTypeTest::ContainerT src;
+  for (int i = 0; i < N; ++i) {
+    src.points.push_back(
+        CppVecNativeTypeTest::Native::Vec3(1.0f * i, 2.0f * i, 3.0f * i));
+  }
+
+  flatbuffers::FlatBufferBuilder fbb;
+  fbb.Finish(CppVecNativeTypeTest::Container::Pack(fbb, &src));
+
+  auto dst =
+      CppVecNativeTypeTest::UnPackContainer(fbb.GetBufferPointer());
+
+  TEST_EQ(dst->points.size(), static_cast<size_t>(N));
+  for (int i = 0; i < N; ++i) {
+    TEST_EQ(dst->points[i].x, 1.0f * i);
+    TEST_EQ(dst->points[i].y, 2.0f * i);
+    TEST_EQ(dst->points[i].z, 3.0f * i);
+  }
+}
+
 // Guard against -Wunused-function on platforms without file tests.
 #ifndef FLATBUFFERS_NO_FILE_TESTS
 // VS10 does not support typed enums, exclude from tests
@@ -1877,6 +1909,7 @@ int FlatBufferTests(const std::string& tests_data_path) {
   FixedLengthArrayTest();
   NativeTypeTest();
   CppVecTypeTest();
+  CppVecTypeNativeTypeTest();
   OptionalScalarsTest();
   ParseFlexbuffersFromJsonWithNullTest();
   FlatbuffersSpanTest();