From e4c59d4de8b418ff3121f1f4116b3b94063be0e9 Mon Sep 17 00:00:00 2001
From: jackylee-ch <qcsd2011@gmail.com>
Date: Mon, 18 May 2026 16:52:42 +0800
Subject: [PATCH] [Velox] Fix Arrow vendored datetime build failure on macOS
 C++20 libc++
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Arrow 15.0.0 ships a vendored copy of Howard Hinnant's date library. On
macOS with `-std=c++20`, libc++'s `std::chrono` exposes its own
`operator<<` for `sys_time` and related clock types that collides with
`date::operator<<` pulled in via `using namespace date;` /
`using date::operator<<;` in `vendored/datetime/tz.cpp` and
`vendored/datetime/tz_private.h`. The resulting ambiguous overload
resolution fails the Arrow CPP build:

  cpp/src/arrow/vendored/datetime/tz.cpp: error: use of overloaded
  operator '<<' is ambiguous (with operand types 'std::ostream' and
  'const date::sys_seconds')

Linux libstdc++ does not expose the conflicting `chrono::operator<<` so
the build is unaffected there.

Add `ep/build-velox/src/fix_vendored_datetime_operator.patch` that
replaces the ADL-driven `os << timepoint` call sites with an explicit
qualified call `date::operator<<(os, timepoint)` so the vendored
overload is selected unambiguously regardless of what `std::chrono`
provides. Apply the patch from `dev/build-arrow.sh::prepare_arrow_build`
right after the existing Arrow patches (`modify_arrow.patch`,
`modify_arrow_dataset_scan_option.patch`, `cmake-compatibility.patch`,
`support_ibm_power.patch`).

Two callsites are touched:
- tz.cpp:2734 in `operator<<(std::ostream&, const leap_second&)` —
  drops the `using namespace date;` and calls
  `date::operator<<(os, x.date_)`.
- tz_private.h:291 in `operator<<(std::ostream&, const transition&)` —
  drops `using date::operator<<;` and calls
  `date::operator<<(os, t.timepoint)`.

Verification:
- macOS 14 arm64 with Apple Clang 17, `-std=c++20`: Arrow CPP build
  reaches successful link of `libarrow.a` and the JNI cdata/dataset
  shared libraries; before the patch the build aborted at the first
  TU including `tz_private.h`.
- Linux x86_64 build is unaffected because the patched code paths only
  fail on libc++. Local Ubuntu 22.04 build verified clean.
---
 dev/build-arrow.sh                            |  3 ++
 .../src/fix_vendored_datetime_operator.patch  | 37 +++++++++++++++++++
 2 files changed, 40 insertions(+)
 create mode 100644 ep/build-velox/src/fix_vendored_datetime_operator.patch

diff --git a/dev/build-arrow.sh b/dev/build-arrow.sh
index 54c6faaf331..8bb2a19b3fe 100755
--- a/dev/build-arrow.sh
+++ b/dev/build-arrow.sh
@@ -34,6 +34,9 @@ function prepare_arrow_build() {
   patch -p1 < $CURRENT_DIR/../ep/build-velox/src/modify_arrow_dataset_scan_option.patch
   patch -p1 < $CURRENT_DIR/../ep/build-velox/src/cmake-compatibility.patch
   patch -p1 < $CURRENT_DIR/../ep/build-velox/src/support_ibm_power.patch
+  # Fix C++20 operator<< ambiguity in Arrow's vendored Howard Hinnant date
+  # library on macOS libc++ (sys_time overload conflicts with date::operator<<).
+  patch -p1 < $CURRENT_DIR/../ep/build-velox/src/fix_vendored_datetime_operator.patch
   popd
 }
 
diff --git a/ep/build-velox/src/fix_vendored_datetime_operator.patch b/ep/build-velox/src/fix_vendored_datetime_operator.patch
new file mode 100644
index 00000000000..3843a9ee68b
--- /dev/null
+++ b/ep/build-velox/src/fix_vendored_datetime_operator.patch
@@ -0,0 +1,37 @@
+Fix C++20 operator<< ambiguity in Arrow's vendored Howard Hinnant date library.
+
+On macOS libc++ with -std=c++20, std::chrono's own operator<< for sys_time
+overloads conflict with the vendored `date::operator<<` pulled in via
+`using date::operator<<` / `using namespace date`, producing an ambiguous
+overload resolution error when streaming sys_seconds/sys_time values.
+
+Replace the ADL-driven `<<` call sites with an explicit qualified call
+`date::operator<<(os, timepoint)` so the vendored overload is selected
+unambiguously regardless of what std::chrono provides.
+
+diff --git a/cpp/src/arrow/vendored/datetime/tz.cpp b/cpp/src/arrow/vendored/datetime/tz.cpp
+--- a/cpp/src/arrow/vendored/datetime/tz.cpp
++++ b/cpp/src/arrow/vendored/datetime/tz.cpp
+@@ -2734,8 +2734,7 @@
+ std::ostream&
+ operator<<(std::ostream& os, const leap_second& x)
+ {
+-    using namespace date;
+-    return os << x.date_ << "  +";
++    return date::operator<<(os, x.date_) << "  +";
+ }
+
+ #if USE_OS_TZDB
+diff --git a/cpp/src/arrow/vendored/datetime/tz_private.h b/cpp/src/arrow/vendored/datetime/tz_private.h
+--- a/cpp/src/arrow/vendored/datetime/tz_private.h
++++ b/cpp/src/arrow/vendored/datetime/tz_private.h
+@@ -291,8 +291,7 @@
+     std::ostream&
+     operator<<(std::ostream& os, const transition& t)
+     {
+-        using date::operator<<;
+-        os << t.timepoint << "Z ";
++        date::operator<<(os, t.timepoint) << "Z ";
+         if (t.info->offset >= std::chrono::seconds{0})
+             os << '+';
+         os << make_time(t.info->offset);