[C++][FlightRPC][ODBC] Clang 20 compiles failed on macOS 26

[HuaHuaY]

Describe the bug, including details regarding any error messages, version, and platform.

There are four kinds of compile errors.

1. Incorrect initialization way.

[build] cpp/src/arrow/flight/sql/odbc/odbc_impl/accessors/timestamp_array_accessor.cc:98:20: error: missing field 'tm_min' initializer [-Werror,-Wmissing-field-initializers]
[build]    98 |   tm timestamp = {0};
[build]       | 

2. Used deprecated standard library APIs std::wstring_convert and std::codecvt_utf8.

[build] In file included from cpp/src/arrow/flight/sql/odbc/odbc_impl/encoding.cc:18:
[build] In file included from cpp/src/arrow/flight/sql/odbc/odbc_impl/encoding.h:23:
[build] /nix/store/4b6hc41dl32baac3vwy7xa29xzz14rzp-libcxx-20.1.8-dev/include/c++/v1/locale:3226:1: error: 'wstring_convert<std::codecvt_utf8<char16_t>, char16_t>' is deprecated [-Werror,-Wdeprecated-declarations]
[build]  3226 | wstring_convert<_Codecvt, _Elem, _WideAlloc, _ByteAlloc>::to_bytes(const _Elem* __frm, const _Elem* __frm_end) {
[build]       | ^
[build] cpp/src/arrow/flight/sql/odbc/odbc_impl/encoding.h:111:32: note: in instantiation of member function 'std::wstring_convert<std::codecvt_utf8<char16_t>, char16_t>::to_bytes' requested here
[build]   111 |   auto byte_string = converter.to_bytes((CHAR_TYPE*)wcs_string,
[build]       |                                ^
[build] cpp/src/arrow/flight/sql/odbc/odbc_impl/encoding.h:126:14: note: in instantiation of function template specialization 'arrow::flight::sql::odbc::WcsToUtf8<char16_t>' requested here
[build]   126 |       return WcsToUtf8<char16_t>(wcs_string, length_in_code_units, result);
[build]       |              ^
[build] /nix/store/4b6hc41dl32baac3vwy7xa29xzz14rzp-libcxx-20.1.8-dev/include/c++/v1/locale:3083:28: note: 'wstring_convert<std::codecvt_utf8<char16_t>, char16_t>' has been explicitly marked deprecated here
[build]  3083 | class _LIBCPP_TEMPLATE_VIS _LIBCPP_DEPRECATED_IN_CXX17 wstring_convert {
[build]       |                            ^
[build] /nix/store/4b6hc41dl32baac3vwy7xa29xzz14rzp-libcxx-20.1.8-dev/include/c++/v1/__config:725:41: note: expanded from macro '_LIBCPP_DEPRECATED_IN_CXX17'
[build]   725 | #    define _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_DEPRECATED
[build]       |                                         ^
[build] /nix/store/4b6hc41dl32baac3vwy7xa29xzz14rzp-libcxx-20.1.8-dev/include/c++/v1/__config:698:49: note: expanded from macro '_LIBCPP_DEPRECATED'
[build]   698 | #      define _LIBCPP_DEPRECATED __attribute__((__deprecated__))
[build]       |

3. Implicit conversion loses integer precision.

[build] cpp/src/arrow/flight/sql/odbc/odbc_impl/odbc_descriptor.cc:489:49: error: implicit conversion loses integer precision: 'size_t' (aka 'unsigned long') to 'int' [-Werror,-Wshorten-64-to-32]
[build]   489 |     int16_t concise_type = rsmd->GetConciseType(one_based_index);
[build]       |

4. Unused private field.

[build] In file included from cpp/src/arrow/flight/sql/odbc/odbc_impl/flight_sql_connection.cc:18:
[build] cpp/src/arrow/flight/sql/odbc/odbc_impl/flight_sql_connection.h:50:15: error: private field 'odbc_version_' is not used [-Werror,-Wunused-private-field]
[build]    50 |   OdbcVersion odbc_version_;
[build]       |               ^
[build] 1 error generated.

Component(s)

C++, FlightRPC

[HuaHuaY]

The second error is not easy to fix. We have these code which use deprecated std::wstring_convert and std::codecvt_utf8. #46622 (issue GH-46576) tried to suppress compilation errors by adding ARROW_SUPPRESS_DEPRECATION_WARNING. But at least in my local environment, this error no longer occurs at the template definition, but rather where the template is actually instantiated.

// GH-46576: suppress unicode warnings
ARROW_SUPPRESS_DEPRECATION_WARNING
template <typename CHAR_TYPE>
inline void WcsToUtf8(const void* wcs_string, size_t length_in_code_units,
                      std::vector<uint8_t>* result) {
  thread_local std::wstring_convert<std::codecvt_utf8<CHAR_TYPE>, CHAR_TYPE> converter;
  auto byte_string = converter.to_bytes((CHAR_TYPE*)wcs_string,
                                        (CHAR_TYPE*)wcs_string + length_in_code_units);

  uint32_t length_in_bytes = static_cast<uint32_t>(byte_string.size());
  const uint8_t* data = (uint8_t*)byte_string.data();

  result->reserve(length_in_bytes);
  result->assign(data, data + length_in_bytes);
}
ARROW_UNSUPPRESS_DEPRECATION_WARNING

I think there are two ways to fix this:

1. Wrap the #include <codecvt> and #include <locale> statements in encoding.h with ARROW_SUPPRESS_DEPRECATION_WARNING. Additionally, any code that includes both encoding.h and <locale> must include encoding.h first. This is necessary because the deprecation warning must be suppressed the moment the compiler encounters <locale> within the compilation unit. This is inconvenient, as headers like <vector> also internally include <locale>; effectively, if a compilation unit depends—directly or transitively—on encoding.h, encoding.h must be manually included at the very top of the source file.
2. Replace this standard library API with the Boost boost::locale::conv::utf_to_utf.

@kou @alinaliBQ @lidavidm Please take a look. What do you think about this?

[HuaHuaY]

I lean towards Option 2 and have submitted a PR. If there are reasons why we cannot choose Option 2, I can adjust the PR's behavior accordingly.

[alinaliBQ]

Hi @HuaHuaY, thank you for submitting this issue and looking into it! I'll defer to David and kou on the use of Boost, but as far as I know, we're generally trying to avoid implementations from Boost where possible.

[lidavidm]

I don't know if we've really written down why we don't use Boost, but generally we prefer to avoid the dependency where possible.

We already vendor utfcpp. Is that sufficient?

[HuaHuaY]

We already vendor utfcpp. Is that sufficient?

I have replaced with utfcpp.

[kou]

+1 for utfcpp.

[lidavidm]

Issue resolved by pull request 50757
#50757