GH-49991: [C++][FlightRPC] Fix unity build ordering issue

[spotaws]

Rationale for this change

Original error message:

/home/spot/git/sandbox/libarrow/libarrow-24.0.0-build/apache-arrow-24.0.0/cpp/src/arrow/flight/transport/grpc/grpc_client.cc: In member function ‘virtual arrow::Status
  arrow::flight::transport::grpc::{anonymous}::GrpcClientImpl::Init(const arrow::flight::FlightClientOptions&, const arrow::flight::Location&, const arrow::util::Uri&)’:
  /home/spot/git/sandbox/libarrow/libarrow-24.0.0-build/apache-arrow-24.0.0/cpp/src/arrow/flight/transport/grpc/grpc_client.cc:738:25: error: ‘FromAbslStatus’ was not declared in this scope; did you mean
  ‘FromGrpcStatus’?
    738 |           RETURN_NOT_OK(FromAbslStatus(certificate_provider->UpdateRoot(kDummyRootCert)));
        |                         ^~~~~~~~~~~~~~
  /home/spot/git/sandbox/libarrow/libarrow-24.0.0-build/apache-arrow-24.0.0/cpp/src/arrow/status.h:58:45: note: in definition of macro ‘ARROW_RETURN_NOT_OK’
     58 |     ::arrow::Status __s = ::arrow::ToStatus(status);           \
        |                                             ^~~~~~
  /home/spot/git/sandbox/libarrow/libarrow-24.0.0-build/apache-arrow-24.0.0/cpp/src/arrow/flight/transport/grpc/grpc_client.cc:738:11: note: in expansion of macro ‘RETURN_NOT_OK’
    738 |           RETURN_NOT_OK(FromAbslStatus(certificate_provider->UpdateRoot(kDummyRootCert)));
        |           ^~~~~~~~~~~~~
  In file included from /home/spot/git/sandbox/libarrow/libarrow-24.0.0-build/apache-arrow-24.0.0/cpp/redhat-linux-build/src/arrow/flight/CMakeFiles/arrow_flight_objlib.dir/Unity/unity_1_cxx.cxx:25:
  /home/spot/git/sandbox/libarrow/libarrow-24.0.0-build/apache-arrow-24.0.0/cpp/src/arrow/flight/transport/grpc/util_internal.cc: At global scope:
  /home/spot/git/sandbox/libarrow/libarrow-24.0.0-build/apache-arrow-24.0.0/cpp/src/arrow/flight/transport/grpc/util_internal.cc:335:8: warning: no previous declaration for ‘arrow::Status
  arrow::flight::transport::grpc::FromAbslStatus(const absl::lts_20260107::Status&)’ [-Wmissing-declarations]
    335 | Status FromAbslStatus(const ::absl::Status& absl_status) {
        |        ^~~~~~~~~~~~~~

In testing builds against latest grpc and protobuf, I found a Unity build (CMake UNITY_BUILD) ordering issue. The file server_tracing_middleware.cc is the first file in the Unity translation unit and includes util_internal.h without first including <grpcpp/grpcpp.h>. Since util_internal.h uses #pragma once, it's only processed once — at that point GRPC_CPP_VERSION_MAJOR is undefined, so the #if GRPC_CPP_VERSION_CHECK(1, 80, 0) guard evaluates to false and the FromAbslStatus declaration is skipped. When grpc_client.cc later tries to call FromAbslStatus, the declaration was never emitted.

What changes are included in this PR?

I added #include <grpcpp/version_info.h> at the top so the version macros are always available, moved the GRPC_CPP_VERSION_CHECK macro definition before the namespace block (with a safety check for the macros being defined), and added #include <absl/status/status.h> conditionally when gRPC >= 1.80.0

Are these changes tested?

Yes, I ran the full test suite with this change applied (and the build now succeeds).

100% tests passed, 0 tests failed out of 97

Label Time Summary:
arrow-compute-tests = 7.32 secproc (14 tests)
arrow-tests = 24.99 secproc (40 tests)
arrow_acero = 26.32 secproc (14 tests)
arrow_dataset = 27.48 secproc (14 tests)
arrow_flight = 2.00 secproc (2 tests)
filesystem = 0.86 secproc (2 tests)
parquet-tests = 11.88 secproc (13 tests)
unittest = 99.98 secproc (97 tests)

Total Test time (real) = 15.10 sec

Are there any user-facing changes?

No.

• GitHub Issue: [C++][FlightRPC] Fix Unity build ordering issue #49991

[github-actions]

Thanks for opening a pull request!

If this is not a minor PR. Could you open an issue for this pull request on GitHub? https://github.com/apache/arrow/issues/new/choose

Opening GitHub issues ahead of time contributes to the Openness of the Apache Arrow project.

Then could you also rename the pull request title in the following format?

GH-${GITHUB_ISSUE_ID}: [${COMPONENT}] ${SUMMARY}

or

MINOR: [${COMPONENT}] ${SUMMARY}

See also:

• Other pull requests
• Contribution Guidelines - Contributing Overview

[github-actions]

⚠️ GitHub issue #49991 has been automatically assigned in GitHub to PR creator.

[lidavidm]

Thanks for tracking this down - there's just a formatter error it seems

[kou]

Why do we need these checks?

It seems that grpcpp/version_info.h always provides them.

[spotaws]

I was being cautious and trying to future proof, but maybe it's overkill.

[kou]

If they are not needed, could you remove them to simplify our implementation?

[Copilot]

Pull request overview

Fixes a CMake UNITY_BUILD ordering problem in the Flight gRPC transport where util_internal.h could be processed before gRPC version macros were available, causing FromAbslStatus to not be declared (and later calls to fail to compile).

Changes:

• Include <grpcpp/version_info.h> in util_internal.h so GRPC_CPP_VERSION_* macros are available regardless of include order.
• Move/adjust GRPC_CPP_VERSION_CHECK macro definition so it is usable before the namespace block (with a fallback when version macros aren’t defined).
• Conditionally include <absl/status/status.h> when building against gRPC >= 1.80.0 so ::absl::Status is known for the conditional declaration.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.