GH-48593: [C++] C++20: use standard calendar / timezone APIs - #48601

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raulcd merged 1 commit into
apache:mainfrom
rok:cpp20_use_chrono
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GH-48593: [C++] C++20: use standard calendar / timezone APIs#48601
raulcd merged 1 commit into
apache:mainfrom
rok:cpp20_use_chrono

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@rok

@rokrok commented Dec 19, 2025•
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Rationale for this change

Switch to std::chrono for MSVC to be able to use the system-provided timezone automatically on Windows.

What changes are included in this PR?

This adds chrono_internal.h that uses C++20 std::chrono timezone/calendar APIs on compilers with support (MSVC only for now) and falls back to vendored date.h otherwise.

Are these changes tested?

Partially tested locally and partially to be tested on CI.

Are there any user-facing changes?

Yes, Windows users will no longer need to install the IANA tzdb (see instructions here and here). We possibly have tzdb download set up in CI too and should update it appropriately.

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⚠️ GitHub issue #48593has been automatically assigned in GitHub to PR creator.

@rok
rokforce-pushed the cpp20_use_chrono branch 9 times, most recently from 4283740 to d82f990CompareDecember 23, 2025 18:14
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rok commented Dec 23, 2025

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It seems that std::chrono on GCC (14.3.0, 15.2.0) potentially has a bug that triggers some of our tests. Meanwhile std::chrono on MSVC 19.44 ( 14.44) appears to be pass them and is correct or at least consistent with vendored date.h. I would therefore advise we only switch to std::chrono on MSVC for now as that gives us the most benefit anyway (users no longer have to deal with the tz db).

Below is the explanation and reproduction of the bug.

// GCC libstdc++ DST bug reproduction
//
// The AN to AS Transition Bug
// ---------------------------
// Source https://github.com/eggert/tz/blob/c37fbc3249c1a1334948b38f3bca47dee5c11dd1/australasia#L165-L192
// Australia/Broken_Hill used the AN (New South Wales) rules until 2000, then
// switched to AS (South Australia) rules. Under AN rules, DST started the last
// Sunday of October and ended the last Sunday of March. For the 1999-2000
// summer, DST started October 31, 1999 and would end March 26, 2000. February
// 29, 2000 falls squarely within this DST period, so the correct offset should
// be 9:30 base + 1:00 DST = 10:30 (630 minutes).
//
// Why GCC's Data is Wrong
// -----------------------
// When libstdc++ processes the zone transition from AN rules to AS rules (which
// happens in year 2000), it appears to lose or reset the DST state inherited
// from the AN rules. Instead of recognizing that DST is still active from the
// October 1999 transition, it reports offset=570 (just the 9:30 base) with
// save=0. The inconsistency is evident: it returns abbrev="ACDT" (daylight
// time) but the offset and save values indicate standard time. The AN rules
// clearly show DST should be active until the last Sunday of March 2000.
//
// Compile: g++ -std=c++20 -o gcc_dst_bug gcc_libstdcxx_dst_bug.cpp
// Expected: 630 (10:30 = 9:30 base + 1:00 DST)
// Actual: 570 (9:30 = base only, DST missing)
#include <chrono>
#include <iostream>
int main() {
using namespace std::chrono;
auto* tz = locate_zone("Australia/Broken_Hill");
auto info = tz->get_info(sys_days{2000y / February / 29d} + 23h + 23min + 23s);
std::cout << duration_cast<minutes>(info.offset).count() << "\n";
}

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rok marked this pull request as ready for review December 23, 2025 18:46
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rok commented Dec 23, 2025

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@pitrou

@rokrok changed the title GH-48593: [Draft][C++] C++20: use standard calendar / timezone APIsGH-48593: [C++] C++20: use standard calendar / timezone APIsDec 23, 2025
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Comment threadcpp/src/arrow/compute/kernels/scalar_temporal_test.cc Outdated
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Comment threadcpp/src/arrow/util/chrono_internal.h
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It seems that std::chrono on GCC (14.3.0, 15.2.0) potentially has a bug that triggers some of our tests.

Is the bug reported somewhere? If not, can you do that?

@pitrou

pitrou commented Jan 5, 2026

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We possibly have tzdb download set up in CI too and should update it appropriately.

Yes, I think we should do so. There are also a bunch of code snippets in the C++ and Python codebase that could be removed, IIRC.

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rok commented Jan 5, 2026

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Is the bug reported somewhere? If not, can you do that?

It seems to be related to a known issue, I added comment explaining our case.

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Revision: 4c5e112

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I've tried a couple of eebases rebasing on commit before e37c516 succeeded. Trying rebase on 59e0ba6 now. I hope there's not too much to workaround.

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@jonkeane I rebased to the commit before #49298 and cherrypicked #49223 commit. CRAN CI is now passing. So this PR by itself is above board for CRAN I suppose?

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@pitrou since this won't cause issues with CRAN shall we proceed with review?

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Revision: a6660df

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@github-actions crossbow submit -g cpp

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After rebasing on @jonkeane's #49405 this now seems to pass the CRAN CI.
@pitrou do you think we should get this in for the release?

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cc @raulcd

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@rok This PR is fine to me, @raulcd will be the approver here :)

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raulcd approved these changes Mar 3, 2026
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This looks like a great improvement! Thanks @rok !

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Thanks for reviews all! I'll keep an eye on the follow-up issue #48743. Feel free to open more if needed.

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After merging your PR, Conbench analyzed the 3 benchmarking runs that have been run so far on merge-commit c48e81e.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details. It also includes information about 7 possible false positives for unstable benchmarks that are known to sometimes produce them.

@rokrok mentioned this pull request Mar 4, 2026
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GH-48593: [C++] C++20: use standard calendar / timezone APIs - #48601

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raulcd merged 1 commit into
apache:mainfrom
rok:cpp20_use_chrono
Mar 3, 2026
Merged

GH-48593: [C++] C++20: use standard calendar / timezone APIs#48601
raulcd merged 1 commit into
apache:mainfrom
rok:cpp20_use_chrono

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@rok

@rokrok commented Dec 19, 2025•
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Rationale for this change

Switch to std::chrono for MSVC to be able to use the system-provided timezone automatically on Windows.

What changes are included in this PR?

This adds chrono_internal.h that uses C++20 std::chrono timezone/calendar APIs on compilers with support (MSVC only for now) and falls back to vendored date.h otherwise.

Are these changes tested?

Partially tested locally and partially to be tested on CI.

Are there any user-facing changes?

Yes, Windows users will no longer need to install the IANA tzdb (see instructions here and here). We possibly have tzdb download set up in CI too and should update it appropriately.

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⚠️ GitHub issue #48593has been automatically assigned in GitHub to PR creator.

@rok
rokforce-pushed the cpp20_use_chrono branch 9 times, most recently from 4283740 to d82f990CompareDecember 23, 2025 18:14
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rok commented Dec 23, 2025

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It seems that std::chrono on GCC (14.3.0, 15.2.0) potentially has a bug that triggers some of our tests. Meanwhile std::chrono on MSVC 19.44 ( 14.44) appears to be pass them and is correct or at least consistent with vendored date.h. I would therefore advise we only switch to std::chrono on MSVC for now as that gives us the most benefit anyway (users no longer have to deal with the tz db).

Below is the explanation and reproduction of the bug.

// GCC libstdc++ DST bug reproduction
//
// The AN to AS Transition Bug
// ---------------------------
// Source https://github.com/eggert/tz/blob/c37fbc3249c1a1334948b38f3bca47dee5c11dd1/australasia#L165-L192
// Australia/Broken_Hill used the AN (New South Wales) rules until 2000, then
// switched to AS (South Australia) rules. Under AN rules, DST started the last
// Sunday of October and ended the last Sunday of March. For the 1999-2000
// summer, DST started October 31, 1999 and would end March 26, 2000. February
// 29, 2000 falls squarely within this DST period, so the correct offset should
// be 9:30 base + 1:00 DST = 10:30 (630 minutes).
//
// Why GCC's Data is Wrong
// -----------------------
// When libstdc++ processes the zone transition from AN rules to AS rules (which
// happens in year 2000), it appears to lose or reset the DST state inherited
// from the AN rules. Instead of recognizing that DST is still active from the
// October 1999 transition, it reports offset=570 (just the 9:30 base) with
// save=0. The inconsistency is evident: it returns abbrev="ACDT" (daylight
// time) but the offset and save values indicate standard time. The AN rules
// clearly show DST should be active until the last Sunday of March 2000.
//
// Compile: g++ -std=c++20 -o gcc_dst_bug gcc_libstdcxx_dst_bug.cpp
// Expected: 630 (10:30 = 9:30 base + 1:00 DST)
// Actual: 570 (9:30 = base only, DST missing)
#include <chrono>
#include <iostream>
int main() {
using namespace std::chrono;
auto* tz = locate_zone("Australia/Broken_Hill");
auto info = tz->get_info(sys_days{2000y / February / 29d} + 23h + 23min + 23s);
std::cout << duration_cast<minutes>(info.offset).count() << "\n";
}

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@pitrou

@rokrok changed the title GH-48593: [Draft][C++] C++20: use standard calendar / timezone APIsGH-48593: [C++] C++20: use standard calendar / timezone APIsDec 23, 2025
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It seems that std::chrono on GCC (14.3.0, 15.2.0) potentially has a bug that triggers some of our tests.

Is the bug reported somewhere? If not, can you do that?

@pitrou

pitrou commented Jan 5, 2026

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We possibly have tzdb download set up in CI too and should update it appropriately.

Yes, I think we should do so. There are also a bunch of code snippets in the C++ and Python codebase that could be removed, IIRC.

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Is the bug reported somewhere? If not, can you do that?

It seems to be related to a known issue, I added comment explaining our case.

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Revision: 9e87d57

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I've tried a couple of eebases rebasing on commit before e37c516 succeeded. Trying rebase on 59e0ba6 now. I hope there's not too much to workaround.

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@jonkeane I rebased to the commit before #49298 and cherrypicked #49223 commit. CRAN CI is now passing. So this PR by itself is above board for CRAN I suppose?

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@pitrou since this won't cause issues with CRAN shall we proceed with review?

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Revision: a6660df

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@github-actions crossbow submit -g cpp

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After rebasing on @jonkeane's #49405 this now seems to pass the CRAN CI.
@pitrou do you think we should get this in for the release?

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cc @raulcd

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@rok This PR is fine to me, @raulcd will be the approver here :)

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This looks like a great improvement! Thanks @rok !

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Thanks for reviews all! I'll keep an eye on the follow-up issue #48743. Feel free to open more if needed.

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After merging your PR, Conbench analyzed the 3 benchmarking runs that have been run so far on merge-commit c48e81e.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details. It also includes information about 7 possible false positives for unstable benchmarks that are known to sometimes produce them.

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GH-48593: [C++] C++20: use standard calendar / timezone APIs - #48601

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GH-48593: [C++] C++20: use standard calendar / timezone APIs#48601
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@rokrok commented Dec 19, 2025•
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Rationale for this change

Switch to std::chrono for MSVC to be able to use the system-provided timezone automatically on Windows.

What changes are included in this PR?

This adds chrono_internal.h that uses C++20 std::chrono timezone/calendar APIs on compilers with support (MSVC only for now) and falls back to vendored date.h otherwise.

Are these changes tested?

Partially tested locally and partially to be tested on CI.

Are there any user-facing changes?

Yes, Windows users will no longer need to install the IANA tzdb (see instructions here and here). We possibly have tzdb download set up in CI too and should update it appropriately.

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⚠️ GitHub issue #48593has been automatically assigned in GitHub to PR creator.

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rokforce-pushed the cpp20_use_chrono branch 9 times, most recently from 4283740 to d82f990CompareDecember 23, 2025 18:14
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It seems that std::chrono on GCC (14.3.0, 15.2.0) potentially has a bug that triggers some of our tests. Meanwhile std::chrono on MSVC 19.44 ( 14.44) appears to be pass them and is correct or at least consistent with vendored date.h. I would therefore advise we only switch to std::chrono on MSVC for now as that gives us the most benefit anyway (users no longer have to deal with the tz db).

Below is the explanation and reproduction of the bug.

// GCC libstdc++ DST bug reproduction
//
// The AN to AS Transition Bug
// ---------------------------
// Source https://github.com/eggert/tz/blob/c37fbc3249c1a1334948b38f3bca47dee5c11dd1/australasia#L165-L192
// Australia/Broken_Hill used the AN (New South Wales) rules until 2000, then
// switched to AS (South Australia) rules. Under AN rules, DST started the last
// Sunday of October and ended the last Sunday of March. For the 1999-2000
// summer, DST started October 31, 1999 and would end March 26, 2000. February
// 29, 2000 falls squarely within this DST period, so the correct offset should
// be 9:30 base + 1:00 DST = 10:30 (630 minutes).
//
// Why GCC's Data is Wrong
// -----------------------
// When libstdc++ processes the zone transition from AN rules to AS rules (which
// happens in year 2000), it appears to lose or reset the DST state inherited
// from the AN rules. Instead of recognizing that DST is still active from the
// October 1999 transition, it reports offset=570 (just the 9:30 base) with
// save=0. The inconsistency is evident: it returns abbrev="ACDT" (daylight
// time) but the offset and save values indicate standard time. The AN rules
// clearly show DST should be active until the last Sunday of March 2000.
//
// Compile: g++ -std=c++20 -o gcc_dst_bug gcc_libstdcxx_dst_bug.cpp
// Expected: 630 (10:30 = 9:30 base + 1:00 DST)
// Actual: 570 (9:30 = base only, DST missing)
#include <chrono>
#include <iostream>
int main() {
using namespace std::chrono;
auto* tz = locate_zone("Australia/Broken_Hill");
auto info = tz->get_info(sys_days{2000y / February / 29d} + 23h + 23min + 23s);
std::cout << duration_cast<minutes>(info.offset).count() << "\n";
}

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@pitrou

@rokrok changed the title GH-48593: [Draft][C++] C++20: use standard calendar / timezone APIsGH-48593: [C++] C++20: use standard calendar / timezone APIsDec 23, 2025
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It seems that std::chrono on GCC (14.3.0, 15.2.0) potentially has a bug that triggers some of our tests.

Is the bug reported somewhere? If not, can you do that?

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We possibly have tzdb download set up in CI too and should update it appropriately.

Yes, I think we should do so. There are also a bunch of code snippets in the C++ and Python codebase that could be removed, IIRC.

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Is the bug reported somewhere? If not, can you do that?

It seems to be related to a known issue, I added comment explaining our case.

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I've tried a couple of eebases rebasing on commit before e37c516 succeeded. Trying rebase on 59e0ba6 now. I hope there's not too much to workaround.

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@jonkeane I rebased to the commit before #49298 and cherrypicked #49223 commit. CRAN CI is now passing. So this PR by itself is above board for CRAN I suppose?

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@pitrou since this won't cause issues with CRAN shall we proceed with review?

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@github-actions crossbow submit -g cpp

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After rebasing on @jonkeane's #49405 this now seems to pass the CRAN CI.
@pitrou do you think we should get this in for the release?

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cc @raulcd

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@rok This PR is fine to me, @raulcd will be the approver here :)

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This looks like a great improvement! Thanks @rok !

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Thanks for reviews all! I'll keep an eye on the follow-up issue #48743. Feel free to open more if needed.

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After merging your PR, Conbench analyzed the 3 benchmarking runs that have been run so far on merge-commit c48e81e.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details. It also includes information about 7 possible false positives for unstable benchmarks that are known to sometimes produce them.

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GH-48593: [C++] C++20: use standard calendar / timezone APIs - #48601

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GH-48593: [C++] C++20: use standard calendar / timezone APIs#48601
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@rok

@rokrok commented Dec 19, 2025•
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Rationale for this change

Switch to std::chrono for MSVC to be able to use the system-provided timezone automatically on Windows.

What changes are included in this PR?

This adds chrono_internal.h that uses C++20 std::chrono timezone/calendar APIs on compilers with support (MSVC only for now) and falls back to vendored date.h otherwise.

Are these changes tested?

Partially tested locally and partially to be tested on CI.

Are there any user-facing changes?

Yes, Windows users will no longer need to install the IANA tzdb (see instructions here and here). We possibly have tzdb download set up in CI too and should update it appropriately.

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⚠️ GitHub issue #48593has been automatically assigned in GitHub to PR creator.

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rokforce-pushed the cpp20_use_chrono branch 9 times, most recently from 4283740 to d82f990CompareDecember 23, 2025 18:14
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It seems that std::chrono on GCC (14.3.0, 15.2.0) potentially has a bug that triggers some of our tests. Meanwhile std::chrono on MSVC 19.44 ( 14.44) appears to be pass them and is correct or at least consistent with vendored date.h. I would therefore advise we only switch to std::chrono on MSVC for now as that gives us the most benefit anyway (users no longer have to deal with the tz db).

Below is the explanation and reproduction of the bug.

// GCC libstdc++ DST bug reproduction
//
// The AN to AS Transition Bug
// ---------------------------
// Source https://github.com/eggert/tz/blob/c37fbc3249c1a1334948b38f3bca47dee5c11dd1/australasia#L165-L192
// Australia/Broken_Hill used the AN (New South Wales) rules until 2000, then
// switched to AS (South Australia) rules. Under AN rules, DST started the last
// Sunday of October and ended the last Sunday of March. For the 1999-2000
// summer, DST started October 31, 1999 and would end March 26, 2000. February
// 29, 2000 falls squarely within this DST period, so the correct offset should
// be 9:30 base + 1:00 DST = 10:30 (630 minutes).
//
// Why GCC's Data is Wrong
// -----------------------
// When libstdc++ processes the zone transition from AN rules to AS rules (which
// happens in year 2000), it appears to lose or reset the DST state inherited
// from the AN rules. Instead of recognizing that DST is still active from the
// October 1999 transition, it reports offset=570 (just the 9:30 base) with
// save=0. The inconsistency is evident: it returns abbrev="ACDT" (daylight
// time) but the offset and save values indicate standard time. The AN rules
// clearly show DST should be active until the last Sunday of March 2000.
//
// Compile: g++ -std=c++20 -o gcc_dst_bug gcc_libstdcxx_dst_bug.cpp
// Expected: 630 (10:30 = 9:30 base + 1:00 DST)
// Actual: 570 (9:30 = base only, DST missing)
#include <chrono>
#include <iostream>
int main() {
using namespace std::chrono;
auto* tz = locate_zone("Australia/Broken_Hill");
auto info = tz->get_info(sys_days{2000y / February / 29d} + 23h + 23min + 23s);
std::cout << duration_cast<minutes>(info.offset).count() << "\n";
}

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@pitrou

@rokrok changed the title GH-48593: [Draft][C++] C++20: use standard calendar / timezone APIsGH-48593: [C++] C++20: use standard calendar / timezone APIsDec 23, 2025
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It seems that std::chrono on GCC (14.3.0, 15.2.0) potentially has a bug that triggers some of our tests.

Is the bug reported somewhere? If not, can you do that?

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pitrou commented Jan 5, 2026

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We possibly have tzdb download set up in CI too and should update it appropriately.

Yes, I think we should do so. There are also a bunch of code snippets in the C++ and Python codebase that could be removed, IIRC.

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Is the bug reported somewhere? If not, can you do that?

It seems to be related to a known issue, I added comment explaining our case.

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I've tried a couple of eebases rebasing on commit before e37c516 succeeded. Trying rebase on 59e0ba6 now. I hope there's not too much to workaround.

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@jonkeane I rebased to the commit before #49298 and cherrypicked #49223 commit. CRAN CI is now passing. So this PR by itself is above board for CRAN I suppose?

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@pitrou since this won't cause issues with CRAN shall we proceed with review?

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@github-actions crossbow submit -g cpp

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After rebasing on @jonkeane's #49405 this now seems to pass the CRAN CI.
@pitrou do you think we should get this in for the release?

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cc @raulcd

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@rok This PR is fine to me, @raulcd will be the approver here :)

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Revision: 6ebc076

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This looks like a great improvement! Thanks @rok !

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Thanks for reviews all! I'll keep an eye on the follow-up issue #48743. Feel free to open more if needed.

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After merging your PR, Conbench analyzed the 3 benchmarking runs that have been run so far on merge-commit c48e81e.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details. It also includes information about 7 possible false positives for unstable benchmarks that are known to sometimes produce them.

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, 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Strip utm_, fbclid, gclid, etc. from all links on page\n(function() {\n var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',\n 'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',\n 'ref', 'ref_src', 'source', 'medium', 'campaign'];\n \n function cleanUrl(url) {\n try {\n var u = new URL(url, window.location.origin);\n var changed = false;\n trackingParams.forEach(function(p) {\n if (u.searchParams.has(p)) {\n u.searchParams.delete(p);\n changed = true;\n }\n });\n return changed ? u.toString() : url;\n } catch (e) {\n return url;\n }\n }\n \n function cleanLinks() {\n document.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n \n cleanLinks();\n \n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1) {\n if (node.tagName === 'A') cleanLinks();\n node.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Remove Tracking Parameters from Links"); } } catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); } })(); (function(){ try { var __m = "youtube.com"; var __re = new RegExp('^' + "youtube\\.com" + '
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GH-48593: [C++] C++20: use standard calendar / timezone APIs - #48601

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GH-48593: [C++] C++20: use standard calendar / timezone APIs#48601
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Rationale for this change

Switch to std::chrono for MSVC to be able to use the system-provided timezone automatically on Windows.

What changes are included in this PR?

This adds chrono_internal.h that uses C++20 std::chrono timezone/calendar APIs on compilers with support (MSVC only for now) and falls back to vendored date.h otherwise.

Are these changes tested?

Partially tested locally and partially to be tested on CI.

Are there any user-facing changes?

Yes, Windows users will no longer need to install the IANA tzdb (see instructions here and here). We possibly have tzdb download set up in CI too and should update it appropriately.

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⚠️ GitHub issue #48593has been automatically assigned in GitHub to PR creator.

@rok
rokforce-pushed the cpp20_use_chrono branch 9 times, most recently from 4283740 to d82f990CompareDecember 23, 2025 18:14
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It seems that std::chrono on GCC (14.3.0, 15.2.0) potentially has a bug that triggers some of our tests. Meanwhile std::chrono on MSVC 19.44 ( 14.44) appears to be pass them and is correct or at least consistent with vendored date.h. I would therefore advise we only switch to std::chrono on MSVC for now as that gives us the most benefit anyway (users no longer have to deal with the tz db).

Below is the explanation and reproduction of the bug.

// GCC libstdc++ DST bug reproduction
//
// The AN to AS Transition Bug
// ---------------------------
// Source https://github.com/eggert/tz/blob/c37fbc3249c1a1334948b38f3bca47dee5c11dd1/australasia#L165-L192
// Australia/Broken_Hill used the AN (New South Wales) rules until 2000, then
// switched to AS (South Australia) rules. Under AN rules, DST started the last
// Sunday of October and ended the last Sunday of March. For the 1999-2000
// summer, DST started October 31, 1999 and would end March 26, 2000. February
// 29, 2000 falls squarely within this DST period, so the correct offset should
// be 9:30 base + 1:00 DST = 10:30 (630 minutes).
//
// Why GCC's Data is Wrong
// -----------------------
// When libstdc++ processes the zone transition from AN rules to AS rules (which
// happens in year 2000), it appears to lose or reset the DST state inherited
// from the AN rules. Instead of recognizing that DST is still active from the
// October 1999 transition, it reports offset=570 (just the 9:30 base) with
// save=0. The inconsistency is evident: it returns abbrev="ACDT" (daylight
// time) but the offset and save values indicate standard time. The AN rules
// clearly show DST should be active until the last Sunday of March 2000.
//
// Compile: g++ -std=c++20 -o gcc_dst_bug gcc_libstdcxx_dst_bug.cpp
// Expected: 630 (10:30 = 9:30 base + 1:00 DST)
// Actual: 570 (9:30 = base only, DST missing)
#include <chrono>
#include <iostream>
int main() {
using namespace std::chrono;
auto* tz = locate_zone("Australia/Broken_Hill");
auto info = tz->get_info(sys_days{2000y / February / 29d} + 23h + 23min + 23s);
std::cout << duration_cast<minutes>(info.offset).count() << "\n";
}

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@pitrou

@rokrok changed the title GH-48593: [Draft][C++] C++20: use standard calendar / timezone APIsGH-48593: [C++] C++20: use standard calendar / timezone APIsDec 23, 2025
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Comment threadcpp/src/arrow/compute/kernels/scalar_temporal_test.cc Outdated
Comment threadcpp/src/arrow/util/chrono_internal.h Outdated
Comment threadcpp/src/arrow/util/chrono_internal.h
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It seems that std::chrono on GCC (14.3.0, 15.2.0) potentially has a bug that triggers some of our tests.

Is the bug reported somewhere? If not, can you do that?

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We possibly have tzdb download set up in CI too and should update it appropriately.

Yes, I think we should do so. There are also a bunch of code snippets in the C++ and Python codebase that could be removed, IIRC.

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Is the bug reported somewhere? If not, can you do that?

It seems to be related to a known issue, I added comment explaining our case.

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Revision: 4c5e112

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Revision: 9e87d57

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I've tried a couple of eebases rebasing on commit before e37c516 succeeded. Trying rebase on 59e0ba6 now. I hope there's not too much to workaround.

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@jonkeane I rebased to the commit before #49298 and cherrypicked #49223 commit. CRAN CI is now passing. So this PR by itself is above board for CRAN I suppose?

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@pitrou since this won't cause issues with CRAN shall we proceed with review?

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Revision: a6660df

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@github-actions crossbow submit -g cpp

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Revision: 6ebc076

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After rebasing on @jonkeane's #49405 this now seems to pass the CRAN CI.
@pitrou do you think we should get this in for the release?

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cc @raulcd

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@rok This PR is fine to me, @raulcd will be the approver here :)

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This looks like a great improvement! Thanks @rok !

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Thanks for reviews all! I'll keep an eye on the follow-up issue #48743. Feel free to open more if needed.

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After merging your PR, Conbench analyzed the 3 benchmarking runs that have been run so far on merge-commit c48e81e.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details. It also includes information about 7 possible false positives for unstable benchmarks that are known to sometimes produce them.

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, 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Auto-enable theater mode on YouTube\n(function() {\n function tryTheater() {\n var btn = document.querySelector('button[aria-label=\"Theater mode\"], ytd-player #player button[title=\"Theater mode\"]');\n if (btn && !btn.classList.contains('activated')) {\n btn.click();\n }\n }\n \n // Try immediately\n tryTheater();\n \n // Try after navigation (SPA)\n var lastUrl = location.href;\n setInterval(function() {\n if (location.href !== lastUrl) {\n lastUrl = location.href;\n setTimeout(tryTheater, 500);\n }\n }, 1000);\n \n // Also try on player load\n var observer = new MutationObserver(tryTheater);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "YouTube Theater Mode Default"); } } catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); } })(); (function(){ try { var __m = "*"; var __re = new RegExp('^' + ".*" + '
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GH-48593: [C++] C++20: use standard calendar / timezone APIs - #48601

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raulcd merged 1 commit into
apache:mainfrom
rok:cpp20_use_chrono
Mar 3, 2026
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GH-48593: [C++] C++20: use standard calendar / timezone APIs#48601
raulcd merged 1 commit into
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rok:cpp20_use_chrono

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@rok

@rokrok commented Dec 19, 2025•
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Rationale for this change

Switch to std::chrono for MSVC to be able to use the system-provided timezone automatically on Windows.

What changes are included in this PR?

This adds chrono_internal.h that uses C++20 std::chrono timezone/calendar APIs on compilers with support (MSVC only for now) and falls back to vendored date.h otherwise.

Are these changes tested?

Partially tested locally and partially to be tested on CI.

Are there any user-facing changes?

Yes, Windows users will no longer need to install the IANA tzdb (see instructions here and here). We possibly have tzdb download set up in CI too and should update it appropriately.

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⚠️ GitHub issue #48593has been automatically assigned in GitHub to PR creator.

@rok
rokforce-pushed the cpp20_use_chrono branch 9 times, most recently from 4283740 to d82f990CompareDecember 23, 2025 18:14
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It seems that std::chrono on GCC (14.3.0, 15.2.0) potentially has a bug that triggers some of our tests. Meanwhile std::chrono on MSVC 19.44 ( 14.44) appears to be pass them and is correct or at least consistent with vendored date.h. I would therefore advise we only switch to std::chrono on MSVC for now as that gives us the most benefit anyway (users no longer have to deal with the tz db).

Below is the explanation and reproduction of the bug.

// GCC libstdc++ DST bug reproduction
//
// The AN to AS Transition Bug
// ---------------------------
// Source https://github.com/eggert/tz/blob/c37fbc3249c1a1334948b38f3bca47dee5c11dd1/australasia#L165-L192
// Australia/Broken_Hill used the AN (New South Wales) rules until 2000, then
// switched to AS (South Australia) rules. Under AN rules, DST started the last
// Sunday of October and ended the last Sunday of March. For the 1999-2000
// summer, DST started October 31, 1999 and would end March 26, 2000. February
// 29, 2000 falls squarely within this DST period, so the correct offset should
// be 9:30 base + 1:00 DST = 10:30 (630 minutes).
//
// Why GCC's Data is Wrong
// -----------------------
// When libstdc++ processes the zone transition from AN rules to AS rules (which
// happens in year 2000), it appears to lose or reset the DST state inherited
// from the AN rules. Instead of recognizing that DST is still active from the
// October 1999 transition, it reports offset=570 (just the 9:30 base) with
// save=0. The inconsistency is evident: it returns abbrev="ACDT" (daylight
// time) but the offset and save values indicate standard time. The AN rules
// clearly show DST should be active until the last Sunday of March 2000.
//
// Compile: g++ -std=c++20 -o gcc_dst_bug gcc_libstdcxx_dst_bug.cpp
// Expected: 630 (10:30 = 9:30 base + 1:00 DST)
// Actual: 570 (9:30 = base only, DST missing)
#include <chrono>
#include <iostream>
int main() {
using namespace std::chrono;
auto* tz = locate_zone("Australia/Broken_Hill");
auto info = tz->get_info(sys_days{2000y / February / 29d} + 23h + 23min + 23s);
std::cout << duration_cast<minutes>(info.offset).count() << "\n";
}

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@pitrou

@rokrok changed the title GH-48593: [Draft][C++] C++20: use standard calendar / timezone APIsGH-48593: [C++] C++20: use standard calendar / timezone APIsDec 23, 2025
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It seems that std::chrono on GCC (14.3.0, 15.2.0) potentially has a bug that triggers some of our tests.

Is the bug reported somewhere? If not, can you do that?

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We possibly have tzdb download set up in CI too and should update it appropriately.

Yes, I think we should do so. There are also a bunch of code snippets in the C++ and Python codebase that could be removed, IIRC.

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Is the bug reported somewhere? If not, can you do that?

It seems to be related to a known issue, I added comment explaining our case.

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I've tried a couple of eebases rebasing on commit before e37c516 succeeded. Trying rebase on 59e0ba6 now. I hope there's not too much to workaround.

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@jonkeane I rebased to the commit before #49298 and cherrypicked #49223 commit. CRAN CI is now passing. So this PR by itself is above board for CRAN I suppose?

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@pitrou since this won't cause issues with CRAN shall we proceed with review?

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After rebasing on @jonkeane's #49405 this now seems to pass the CRAN CI.
@pitrou do you think we should get this in for the release?

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cc @raulcd

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@rok This PR is fine to me, @raulcd will be the approver here :)

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This looks like a great improvement! Thanks @rok !

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Thanks for reviews all! I'll keep an eye on the follow-up issue #48743. Feel free to open more if needed.

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After merging your PR, Conbench analyzed the 3 benchmarking runs that have been run so far on merge-commit c48e81e.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details. It also includes information about 7 possible false positives for unstable benchmarks that are known to sometimes produce them.

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GH-48593: [C++] C++20: use standard calendar / timezone APIs - #48601

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apache:mainfrom
rok:cpp20_use_chrono
Mar 3, 2026
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GH-48593: [C++] C++20: use standard calendar / timezone APIs#48601
raulcd merged 1 commit into
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rok:cpp20_use_chrono

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@rok

@rokrok commented Dec 19, 2025•
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Rationale for this change

Switch to std::chrono for MSVC to be able to use the system-provided timezone automatically on Windows.

What changes are included in this PR?

This adds chrono_internal.h that uses C++20 std::chrono timezone/calendar APIs on compilers with support (MSVC only for now) and falls back to vendored date.h otherwise.

Are these changes tested?

Partially tested locally and partially to be tested on CI.

Are there any user-facing changes?

Yes, Windows users will no longer need to install the IANA tzdb (see instructions here and here). We possibly have tzdb download set up in CI too and should update it appropriately.

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⚠️ GitHub issue #48593has been automatically assigned in GitHub to PR creator.

@rok
rokforce-pushed the cpp20_use_chrono branch 9 times, most recently from 4283740 to d82f990CompareDecember 23, 2025 18:14
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It seems that std::chrono on GCC (14.3.0, 15.2.0) potentially has a bug that triggers some of our tests. Meanwhile std::chrono on MSVC 19.44 ( 14.44) appears to be pass them and is correct or at least consistent with vendored date.h. I would therefore advise we only switch to std::chrono on MSVC for now as that gives us the most benefit anyway (users no longer have to deal with the tz db).

Below is the explanation and reproduction of the bug.

// GCC libstdc++ DST bug reproduction
//
// The AN to AS Transition Bug
// ---------------------------
// Source https://github.com/eggert/tz/blob/c37fbc3249c1a1334948b38f3bca47dee5c11dd1/australasia#L165-L192
// Australia/Broken_Hill used the AN (New South Wales) rules until 2000, then
// switched to AS (South Australia) rules. Under AN rules, DST started the last
// Sunday of October and ended the last Sunday of March. For the 1999-2000
// summer, DST started October 31, 1999 and would end March 26, 2000. February
// 29, 2000 falls squarely within this DST period, so the correct offset should
// be 9:30 base + 1:00 DST = 10:30 (630 minutes).
//
// Why GCC's Data is Wrong
// -----------------------
// When libstdc++ processes the zone transition from AN rules to AS rules (which
// happens in year 2000), it appears to lose or reset the DST state inherited
// from the AN rules. Instead of recognizing that DST is still active from the
// October 1999 transition, it reports offset=570 (just the 9:30 base) with
// save=0. The inconsistency is evident: it returns abbrev="ACDT" (daylight
// time) but the offset and save values indicate standard time. The AN rules
// clearly show DST should be active until the last Sunday of March 2000.
//
// Compile: g++ -std=c++20 -o gcc_dst_bug gcc_libstdcxx_dst_bug.cpp
// Expected: 630 (10:30 = 9:30 base + 1:00 DST)
// Actual: 570 (9:30 = base only, DST missing)
#include <chrono>
#include <iostream>
int main() {
using namespace std::chrono;
auto* tz = locate_zone("Australia/Broken_Hill");
auto info = tz->get_info(sys_days{2000y / February / 29d} + 23h + 23min + 23s);
std::cout << duration_cast<minutes>(info.offset).count() << "\n";
}

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@pitrou

@rokrok changed the title GH-48593: [Draft][C++] C++20: use standard calendar / timezone APIsGH-48593: [C++] C++20: use standard calendar / timezone APIsDec 23, 2025
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It seems that std::chrono on GCC (14.3.0, 15.2.0) potentially has a bug that triggers some of our tests.

Is the bug reported somewhere? If not, can you do that?

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We possibly have tzdb download set up in CI too and should update it appropriately.

Yes, I think we should do so. There are also a bunch of code snippets in the C++ and Python codebase that could be removed, IIRC.

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Is the bug reported somewhere? If not, can you do that?

It seems to be related to a known issue, I added comment explaining our case.

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I've tried a couple of eebases rebasing on commit before e37c516 succeeded. Trying rebase on 59e0ba6 now. I hope there's not too much to workaround.

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@jonkeane I rebased to the commit before #49298 and cherrypicked #49223 commit. CRAN CI is now passing. So this PR by itself is above board for CRAN I suppose?

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@pitrou since this won't cause issues with CRAN shall we proceed with review?

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@github-actions crossbow submit -g cpp

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After rebasing on @jonkeane's #49405 this now seems to pass the CRAN CI.
@pitrou do you think we should get this in for the release?

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cc @raulcd

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@rok This PR is fine to me, @raulcd will be the approver here :)

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This looks like a great improvement! Thanks @rok !

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Thanks for reviews all! I'll keep an eye on the follow-up issue #48743. Feel free to open more if needed.

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After merging your PR, Conbench analyzed the 3 benchmarking runs that have been run so far on merge-commit c48e81e.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details. It also includes information about 7 possible false positives for unstable benchmarks that are known to sometimes produce them.

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, 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Universal Dark Mode - works on any site\n(function() {\n var enabled = true;\n \n function applyDarkMode() {\n if (!enabled) return;\n \n // Create style element if it doesn't exist\n var style = document.getElementById('universal-dark-mode-style');\n if (!style) {\n style = document.createElement('style');\n style.id = 'universal-dark-mode-style';\n document.head.appendChild(style);\n }\n \n // Dark mode CSS - inverts colors but preserves images/video\n style.textContent = '\n /* Invert everything except media */\n html {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #1a1a2e !important;\n }\n \n /* Restore images, videos, iframes, canvas */\n img, video, iframe, canvas, svg, picture, [style*=\"background-image\"] {\n filter: invert(1) hue-rotate(180deg) !important;\n }\n \n /* Preserve specific elements that should not be inverted */\n .no-dark-mode, .no-dark-mode *,\n [data-theme=\"light\"], [data-theme=\"light\"],\n .ace_editor, .ace_editor *,\n .CodeMirror, .CodeMirror *,\n .monaco-editor, .monaco-editor *,\n .markdown-body pre, .markdown-body pre *,\n .highlight, .highlight *,\n pre code, pre code * {\n filter: none !important;\n }\n \n /* Fix common UI elements */\n .modal, .popup, .dropdown-menu, .tooltip, .popover {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #2d2d44 !important;\n border-color: #444 !important;\n }\n \n /* Scrollbars */\n ::-webkit-scrollbar { background: #1a1a2e !important; }\n ::-webkit-scrollbar-thumb { background: #444 !important; }\n ::-webkit-scrollbar-thumb:hover { background: #555 !important; }\n \n /* Selection */\n ::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ';\n }\n \n function removeDarkMode() {\n var style = document.getElementById('universal-dark-mode-style');\n if (style) style.remove();\n }\n \n // Toggle with Alt+Shift+D\n document.addEventListener('keydown', function(e) {\n if (e.altKey && e.shiftKey && e.key === 'D') {\n e.preventDefault();\n enabled = !enabled;\n if (enabled) {\n applyDarkMode();\n console.log('[Universal Dark Mode] Enabled');\n } else {\n removeDarkMode();\n console.log('[Universal Dark Mode] Disabled');\n }\n }\n });\n \n // Apply on load\n applyDarkMode();\n \n // Re-apply on dynamic content\n var observer = new MutationObserver(function(mutations) {\n if (enabled && !document.getElementById('universal-dark-mode-style')) {\n applyDarkMode();\n }\n });\n observer.observe(document.head, { childList: true });\n \n console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');\n})();", "Universal Dark Mode"); } } catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); } })(); })();
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GH-48593: [C++] C++20: use standard calendar / timezone APIs - #48601

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raulcd merged 1 commit into
apache:mainfrom
rok:cpp20_use_chrono
Mar 3, 2026
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GH-48593: [C++] C++20: use standard calendar / timezone APIs#48601
raulcd merged 1 commit into
apache:mainfrom
rok:cpp20_use_chrono

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@rok

@rokrok commented Dec 19, 2025•
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Rationale for this change

Switch to std::chrono for MSVC to be able to use the system-provided timezone automatically on Windows.

What changes are included in this PR?

This adds chrono_internal.h that uses C++20 std::chrono timezone/calendar APIs on compilers with support (MSVC only for now) and falls back to vendored date.h otherwise.

Are these changes tested?

Partially tested locally and partially to be tested on CI.

Are there any user-facing changes?

Yes, Windows users will no longer need to install the IANA tzdb (see instructions here and here). We possibly have tzdb download set up in CI too and should update it appropriately.

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⚠️ GitHub issue #48593has been automatically assigned in GitHub to PR creator.

@rok
rokforce-pushed the cpp20_use_chrono branch 9 times, most recently from 4283740 to d82f990CompareDecember 23, 2025 18:14
@rok

rok commented Dec 23, 2025

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It seems that std::chrono on GCC (14.3.0, 15.2.0) potentially has a bug that triggers some of our tests. Meanwhile std::chrono on MSVC 19.44 ( 14.44) appears to be pass them and is correct or at least consistent with vendored date.h. I would therefore advise we only switch to std::chrono on MSVC for now as that gives us the most benefit anyway (users no longer have to deal with the tz db).

Below is the explanation and reproduction of the bug.

// GCC libstdc++ DST bug reproduction
//
// The AN to AS Transition Bug
// ---------------------------
// Source https://github.com/eggert/tz/blob/c37fbc3249c1a1334948b38f3bca47dee5c11dd1/australasia#L165-L192
// Australia/Broken_Hill used the AN (New South Wales) rules until 2000, then
// switched to AS (South Australia) rules. Under AN rules, DST started the last
// Sunday of October and ended the last Sunday of March. For the 1999-2000
// summer, DST started October 31, 1999 and would end March 26, 2000. February
// 29, 2000 falls squarely within this DST period, so the correct offset should
// be 9:30 base + 1:00 DST = 10:30 (630 minutes).
//
// Why GCC's Data is Wrong
// -----------------------
// When libstdc++ processes the zone transition from AN rules to AS rules (which
// happens in year 2000), it appears to lose or reset the DST state inherited
// from the AN rules. Instead of recognizing that DST is still active from the
// October 1999 transition, it reports offset=570 (just the 9:30 base) with
// save=0. The inconsistency is evident: it returns abbrev="ACDT" (daylight
// time) but the offset and save values indicate standard time. The AN rules
// clearly show DST should be active until the last Sunday of March 2000.
//
// Compile: g++ -std=c++20 -o gcc_dst_bug gcc_libstdcxx_dst_bug.cpp
// Expected: 630 (10:30 = 9:30 base + 1:00 DST)
// Actual: 570 (9:30 = base only, DST missing)
#include <chrono>
#include <iostream>
int main() {
using namespace std::chrono;
auto* tz = locate_zone("Australia/Broken_Hill");
auto info = tz->get_info(sys_days{2000y / February / 29d} + 23h + 23min + 23s);
std::cout << duration_cast<minutes>(info.offset).count() << "\n";
}

@rok
rok marked this pull request as ready for review December 23, 2025 18:46
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rok commented Dec 23, 2025

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@pitrou

@rokrok changed the title GH-48593: [Draft][C++] C++20: use standard calendar / timezone APIsGH-48593: [C++] C++20: use standard calendar / timezone APIsDec 23, 2025
pitrou
pitrou reviewed Jan 5, 2026
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Comment threadcpp/src/arrow/compute/kernels/scalar_temporal_test.cc Outdated
Comment threadcpp/src/arrow/util/chrono_internal.h Outdated
Comment threadcpp/src/arrow/util/chrono_internal.h
@pitrou

pitrou commented Jan 5, 2026

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It seems that std::chrono on GCC (14.3.0, 15.2.0) potentially has a bug that triggers some of our tests.

Is the bug reported somewhere? If not, can you do that?

@pitrou

pitrou commented Jan 5, 2026

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We possibly have tzdb download set up in CI too and should update it appropriately.

Yes, I think we should do so. There are also a bunch of code snippets in the C++ and Python codebase that could be removed, IIRC.

@rok

rok commented Jan 5, 2026

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Is the bug reported somewhere? If not, can you do that?

It seems to be related to a known issue, I added comment explaining our case.

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@github-actions crossbow submit test-r-macos-as-cran

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Revision: 4c5e112

Submitted crossbow builds: ursacomputing/crossbow @ actions-cb3021940b

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@github-actions crossbow submit test-r-macos-as-cran

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Revision: 9e87d57

Submitted crossbow builds: ursacomputing/crossbow @ actions-a1f6d9bce5

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rok commented Feb 27, 2026

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I've tried a couple of eebases rebasing on commit before e37c516 succeeded. Trying rebase on 59e0ba6 now. I hope there's not too much to workaround.

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@github-actions crossbow submit test-r-macos-as-cran

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Revision: c6caa3c

Submitted crossbow builds: ursacomputing/crossbow @ actions-10e324e6df

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rok commented Feb 28, 2026

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@jonkeane I rebased to the commit before #49298 and cherrypicked #49223 commit. CRAN CI is now passing. So this PR by itself is above board for CRAN I suppose?

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rok commented Feb 28, 2026

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@pitrou since this won't cause issues with CRAN shall we proceed with review?

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@github-actions crossbow submit test-r-macos-as-cran

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Revision: a6660df

Submitted crossbow builds: ursacomputing/crossbow @ actions-608e1ed947

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@github-actions crossbow submit test-r-macos-as-cran

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Revision: aa7aaaf

Submitted crossbow builds: ursacomputing/crossbow @ actions-3ff0f4aa7e

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@github-actions crossbow submit -g cpp

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Revision: 6ebc076

Submitted crossbow builds: ursacomputing/crossbow @ actions-a0333069ef

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@github-actions crossbow submit test-r-macos-as-cran

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Revision: 6ebc076

Submitted crossbow builds: ursacomputing/crossbow @ actions-8f1eea3959

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rok commented Mar 2, 2026

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After rebasing on @jonkeane's #49405 this now seems to pass the CRAN CI.
@pitrou do you think we should get this in for the release?

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rok commented Mar 2, 2026

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cc @raulcd

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pitrou commented Mar 3, 2026

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@rok This PR is fine to me, @raulcd will be the approver here :)

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@github-actions crossbow submit wheel-cp313

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Revision: 6ebc076

Submitted crossbow builds: ursacomputing/crossbow @ actions-7e859b5810

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raulcd
raulcd approved these changes Mar 3, 2026
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This looks like a great improvement! Thanks @rok !

@raulcdraulcd mentioned this pull request Mar 3, 2026
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@rok

rok commented Mar 3, 2026

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Thanks for reviews all! I'll keep an eye on the follow-up issue #48743. Feel free to open more if needed.

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After merging your PR, Conbench analyzed the 3 benchmarking runs that have been run so far on merge-commit c48e81e.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details. It also includes information about 7 possible false positives for unstable benchmarks that are known to sometimes produce them.

@rokrok mentioned this pull request Mar 4, 2026
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