From 7982e0e6806db640220c5a879ab7c73d3907001a Mon Sep 17 00:00:00 2001
From: "Gang Zhao (Hermes)" <zhaogang@meta.com>
Date: Mon, 24 Jun 2024 11:11:50 -0700
Subject: [PATCH] Remove old daylightSavingTA() (#1245)

Summary: Pull Request resolved: https://github.com/facebook/hermes/pull/1245

Reviewed By: avp

Differential Revision: D52579225
---
 include/hermes/VM/JSLib/DateUtil.h   |  4 ---
 lib/VM/JSLib/DateUtil.cpp            | 44 ----------------------------
 unittests/VMRuntime/DateUtilTest.cpp |  8 +++++
 3 files changed, 8 insertions(+), 48 deletions(-)

diff --git a/include/hermes/VM/JSLib/DateUtil.h b/include/hermes/VM/JSLib/DateUtil.h
index a5f2125ba0a..0e2f884e4e3 100644
--- a/include/hermes/VM/JSLib/DateUtil.h
+++ b/include/hermes/VM/JSLib/DateUtil.h
@@ -112,10 +112,6 @@ double localTZA();
 //===----------------------------------------------------------------------===//
 // ES5.1 15.9.1.8
 
-/// Daylight saving time adjustment, in milliseconds, at time \p t.
-/// \param t timestamp in milliseconds.
-double daylightSavingTA(double t);
-
 namespace detail {
 // Exposed for test only
 int32_t equivalentTime(int64_t epochSecs);
diff --git a/lib/VM/JSLib/DateUtil.cpp b/lib/VM/JSLib/DateUtil.cpp
index bf5a9b3c40f..e8c42eebbe6 100644
--- a/lib/VM/JSLib/DateUtil.cpp
+++ b/lib/VM/JSLib/DateUtil.cpp
@@ -372,50 +372,6 @@ int32_t detail::equivalentTime(int64_t epochSecs) {
   return (eqYearAsEpochDays + dayOfYear) * SECONDS_PER_DAY + secsOfDay;
 }
 
-double daylightSavingTA(double t) {
-  // The spec says LocalTime should only take finite time value and return 0 in
-  // case conversion fails. Once we enforce the finite input at the caller site,
-  // we should remove the below check or replace it with an assertion. For now,
-  // let's return NaN instead if it's not finite value.
-  if (!std::isfinite(t)) {
-    return std::numeric_limits<double>::quiet_NaN();
-  }
-
-  // Convert t to seconds and get the actual time needed.
-  const double seconds = t / MS_PER_SECOND;
-  // If the number of seconds is higher or lower than a unix timestamp can
-  // support, clamp it. This is not correct in all cases, but returning NaN (for
-  // Invalid Date) breaks date construction entirely. Clamping only results in
-  // small errors in daylight savings time. This is only a problem in systems
-  // with a 32-bit time_t, like some Android systems.
-  time_t local = 0;
-  if (seconds > TIME_RANGE_SECS || seconds < -TIME_RANGE_SECS) {
-    // Return NaN if input is outside Time Range allowed in ES5.1
-    return std::numeric_limits<double>::quiet_NaN();
-  }
-  // This will truncate any fractional seconds, which is ok for daylight
-  // savings time calculations.
-  local = detail::equivalentTime(static_cast<int64_t>(seconds));
-
-  std::tm tm;
-#ifdef _WINDOWS
-  // The return value of localtime_s on Windows is an error code instead of
-  // a pointer to std::tm. For simplicity, we don't inspect the concrete error
-  // code and just return 0.
-  auto err = ::localtime_s(&tm, &local);
-  if (err) {
-    return 0;
-  }
-#else
-  std::tm *brokenTime = ::localtime_r(&local, &tm);
-  if (!brokenTime) {
-    // Local time is invalid.
-    return 0;
-  }
-#endif
-  return tm.tm_isdst ? MS_PER_HOUR : 0;
-}
-
 //===----------------------------------------------------------------------===//
 // ES5.1 15.9.1.9
 
diff --git a/unittests/VMRuntime/DateUtilTest.cpp b/unittests/VMRuntime/DateUtilTest.cpp
index e97eafb19f4..f664250e9ea 100644
--- a/unittests/VMRuntime/DateUtilTest.cpp
+++ b/unittests/VMRuntime/DateUtilTest.cpp
@@ -213,13 +213,21 @@ TEST(DateUtilTest, EquivalentTimeTest) {
 }
 
 TEST(DateUtilTest, DaylightSavingTATest) {
+  LocalTimeOffsetCache localTimeOffsetCache;
+  /// A wrapper that implements the deleted daylightSavingTA() function.
+  auto daylightSavingTA = [&localTimeOffsetCache](double timeMs) {
+    return localTimeOffsetCache.daylightSavingOffsetInMs(timeMs);
+  };
+
   setTimeZone("America/Los_Angeles");
+  localTimeOffsetCache.reset();
   EXPECT_EQ(MS_PER_HOUR, daylightSavingTA(1489530532000)); // Mar 14, 2017
   EXPECT_EQ(MS_PER_HOUR, daylightSavingTA(1019514530000)); // Apr 22, 2002
   EXPECT_EQ(0, daylightSavingTA(1487111330000)); // Feb 14, 2017
   EXPECT_EQ(0, daylightSavingTA(1017700130000)); // Apr 1, 2002
 
   setTimeZone("America/Chicago");
+  localTimeOffsetCache.reset();
   EXPECT_EQ(MS_PER_HOUR, daylightSavingTA(1489530532000)); // Mar 14, 2017
   EXPECT_EQ(MS_PER_HOUR, daylightSavingTA(1019514530000)); // Apr 22, 2002
   EXPECT_EQ(0, daylightSavingTA(1487111330000)); // Feb 14, 2017