add IHermes::resetTimezoneCache()

Summary:
`IHermes::resetTimezoneCache()` must be called by the integrator when a
timezone change has been detected.

Reviewed By: dannysu

Differential Revision: D75544519

Pulled By: tmikov

fbshipit-source-id: 3b698d2768eb7e226963f95018cd1d0758d9012d

Author: troZee

API/hermes/hermes.cpp

@@ -28,6 +28,7 @@
 #include "hermes/VM/JSArray.h"
 #include "hermes/VM/JSArrayBuffer.h"
 #include "hermes/VM/JSLib.h"
+#include "hermes/VM/JSLib/JSLibStorage.h"
 #include "hermes/VM/JSLib/RuntimeJSONUtils.h"
 #include "hermes/VM/NativeState.h"
 #include "hermes/VM/Operations.h"
@@ -1070,6 +1071,7 @@ class HermesRuntimeImpl final : public HermesRuntime,
 
   /// Concrete declarations of HermesRuntime methods.
   void sampledTraceToStreamInDevToolsFormat(std::ostream &stream) override;
+  void resetTimezoneCache() override;
   sampling_profiler::Profile dumpSampledTraceToProfile() override;
   void loadSegment(
       std::unique_ptr<const jsi::Buffer> buffer,
@@ -1285,6 +1287,10 @@ class BufferAdapter final : public ::hermes::Buffer {
 };
 } // namespace
 
+void HermesRuntimeImpl::resetTimezoneCache() {
+  runtime_.getJSLibStorage()->localTimeOffsetCache.reset();
+}
+
 void HermesRuntimeImpl::loadSegment(
     std::unique_ptr<const jsi::Buffer> buffer,
     const jsi::Value &context) {

API/hermes/hermes.h

@@ -122,11 +122,16 @@ class HERMES_EXPORT HermesRuntime : public jsi::Runtime {
   /// be used by third parties.
   virtual sampling_profiler::Profile dumpSampledTraceToProfile() = 0;
 
-  // The base class declares most of the interesting methods.  This
-  // just declares new methods which are specific to HermesRuntime.
-  // The actual implementations of the pure virtual methods are
-  // provided by a class internal to the .cpp file, which is created
-  // by the factory.
+  /// Resets the timezone offset cache used by Hermes for performance
+  /// optimization. Hermes maintains a cached timezone offset to accelerate date
+  /// and time calculations. However, this cache does not automatically detect
+  /// changes to the system timezone. When the system timezone changes, the
+  /// integration layer (e.g., React Native) must call this method to invalidate
+  /// the cache and ensure correct time calculations.
+  ///
+  /// \note Call this method immediately after detecting any timezone change in
+  /// the integrator.
+  virtual void resetTimezoneCache() = 0;
 
   /// Load a new segment into the Runtime.
   /// The \param context must be a valid RequireContext retrieved from JS

unittests/API/APITest.cpp

@@ -98,6 +98,12 @@ TEST_P(HermesRuntimeTest, StrictHostFunctionBindTest) {
                   .getBool());
 }
 
+TEST_P(HermesRuntimeTest, ResetTimezoneCache) {
+  if (auto *hrt = castInterface<IHermes>(rt.get())) {
+    EXPECT_NO_THROW({ hrt->resetTimezoneCache(); });
+  }
+}
+
 TEST_P(HermesRuntimeTest, DescriptionTest) {
   // Minimally, if the description doesn't include "Hermes", something
   // is wrong.