From bd035b110830c24f40f509ac4eee9043d4f1bdeb Mon Sep 17 00:00:00 2001
From: "Stephan T. Lavavej" <stl@microsoft.com>
Date: Tue, 1 Feb 2022 15:32:49 -0800
Subject: [PATCH 1/3] C++20 compatibility: Qualify
 arrow_vendored::date::format().

---
 cpp/src/arrow/array/diff.cc | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/cpp/src/arrow/array/diff.cc b/cpp/src/arrow/array/diff.cc
index bcc065c69b4..c431f413709 100644
--- a/cpp/src/arrow/array/diff.cc
+++ b/cpp/src/arrow/array/diff.cc
@@ -639,7 +639,6 @@ class MakeFormatterImpl {
       auto fmt = fmt_str.c_str();
       auto unit = checked_cast<const T&>(*array.type()).unit();
       auto value = checked_cast<const NumericArray<T>&>(array).Value(index);
-      using arrow_vendored::date::format;
       using std::chrono::nanoseconds;
       using std::chrono::microseconds;
       using std::chrono::milliseconds;
@@ -649,32 +648,32 @@ class MakeFormatterImpl {
 
         switch (unit) {
           case TimeUnit::NANO:
-            *os << format(fmt, static_cast<nanoseconds>(value) + epoch);
+            *os << arrow_vendored::date::format(fmt, static_cast<nanoseconds>(value) + epoch);
             break;
           case TimeUnit::MICRO:
-            *os << format(fmt, static_cast<microseconds>(value) + epoch);
+            *os << arrow_vendored::date::format(fmt, static_cast<microseconds>(value) + epoch);
             break;
           case TimeUnit::MILLI:
-            *os << format(fmt, static_cast<milliseconds>(value) + epoch);
+            *os << arrow_vendored::date::format(fmt, static_cast<milliseconds>(value) + epoch);
             break;
           case TimeUnit::SECOND:
-            *os << format(fmt, static_cast<seconds>(value) + epoch);
+            *os << arrow_vendored::date::format(fmt, static_cast<seconds>(value) + epoch);
             break;
         }
         return;
       }
       switch (unit) {
         case TimeUnit::NANO:
-          *os << format(fmt, static_cast<nanoseconds>(value));
+          *os << arrow_vendored::date::format(fmt, static_cast<nanoseconds>(value));
           break;
         case TimeUnit::MICRO:
-          *os << format(fmt, static_cast<microseconds>(value));
+          *os << arrow_vendored::date::format(fmt, static_cast<microseconds>(value));
           break;
         case TimeUnit::MILLI:
-          *os << format(fmt, static_cast<milliseconds>(value));
+          *os << arrow_vendored::date::format(fmt, static_cast<milliseconds>(value));
           break;
         case TimeUnit::SECOND:
-          *os << format(fmt, static_cast<seconds>(value));
+          *os << arrow_vendored::date::format(fmt, static_cast<seconds>(value));
           break;
       }
     };

From bd49a6849c707c54e8b2427a06b29ec6463c3dbf Mon Sep 17 00:00:00 2001
From: "Stephan T. Lavavej" <stl@nuwen.net>
Date: Wed, 2 Feb 2022 02:43:38 -0800
Subject: [PATCH 2/3] Shorten lines with a namespace alias.

---
 cpp/src/arrow/array/diff.cc | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/cpp/src/arrow/array/diff.cc b/cpp/src/arrow/array/diff.cc
index c431f413709..ef66ef0678a 100644
--- a/cpp/src/arrow/array/diff.cc
+++ b/cpp/src/arrow/array/diff.cc
@@ -639,41 +639,42 @@ class MakeFormatterImpl {
       auto fmt = fmt_str.c_str();
       auto unit = checked_cast<const T&>(*array.type()).unit();
       auto value = checked_cast<const NumericArray<T>&>(array).Value(index);
+      namespace avd = arrow_vendored::date;
       using std::chrono::nanoseconds;
       using std::chrono::microseconds;
       using std::chrono::milliseconds;
       using std::chrono::seconds;
       if (AddEpoch) {
-        static arrow_vendored::date::sys_days epoch{arrow_vendored::date::jan / 1 / 1970};
+        static avd::sys_days epoch{avd::jan / 1 / 1970};
 
         switch (unit) {
           case TimeUnit::NANO:
-            *os << arrow_vendored::date::format(fmt, static_cast<nanoseconds>(value) + epoch);
+            *os << avd::format(fmt, static_cast<nanoseconds>(value) + epoch);
             break;
           case TimeUnit::MICRO:
-            *os << arrow_vendored::date::format(fmt, static_cast<microseconds>(value) + epoch);
+            *os << avd::format(fmt, static_cast<microseconds>(value) + epoch);
             break;
           case TimeUnit::MILLI:
-            *os << arrow_vendored::date::format(fmt, static_cast<milliseconds>(value) + epoch);
+            *os << avd::format(fmt, static_cast<milliseconds>(value) + epoch);
             break;
           case TimeUnit::SECOND:
-            *os << arrow_vendored::date::format(fmt, static_cast<seconds>(value) + epoch);
+            *os << avd::format(fmt, static_cast<seconds>(value) + epoch);
             break;
         }
         return;
       }
       switch (unit) {
         case TimeUnit::NANO:
-          *os << arrow_vendored::date::format(fmt, static_cast<nanoseconds>(value));
+          *os << avd::format(fmt, static_cast<nanoseconds>(value));
           break;
         case TimeUnit::MICRO:
-          *os << arrow_vendored::date::format(fmt, static_cast<microseconds>(value));
+          *os << avd::format(fmt, static_cast<microseconds>(value));
           break;
         case TimeUnit::MILLI:
-          *os << arrow_vendored::date::format(fmt, static_cast<milliseconds>(value));
+          *os << avd::format(fmt, static_cast<milliseconds>(value));
           break;
         case TimeUnit::SECOND:
-          *os << arrow_vendored::date::format(fmt, static_cast<seconds>(value));
+          *os << avd::format(fmt, static_cast<seconds>(value));
           break;
       }
     };

From e147dabdc57ce97f82d76500245384183dfc350e Mon Sep 17 00:00:00 2001
From: Antoine Pitrou <pitrou@free.fr>
Date: Wed, 2 Feb 2022 14:20:01 +0100
Subject: [PATCH 3/3] Add comment

---
 cpp/src/arrow/array/diff.cc | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/cpp/src/arrow/array/diff.cc b/cpp/src/arrow/array/diff.cc
index ef66ef0678a..16f4f9c7638 100644
--- a/cpp/src/arrow/array/diff.cc
+++ b/cpp/src/arrow/array/diff.cc
@@ -639,6 +639,8 @@ class MakeFormatterImpl {
       auto fmt = fmt_str.c_str();
       auto unit = checked_cast<const T&>(*array.type()).unit();
       auto value = checked_cast<const NumericArray<T>&>(array).Value(index);
+      // Using unqualified `format` directly would produce ambiguous
+      // lookup because of `std::format` (ARROW-15520).
       namespace avd = arrow_vendored::date;
       using std::chrono::nanoseconds;
       using std::chrono::microseconds;