1 files changed, 114 insertions, 0 deletions
diff --git a/vendor/time/src/sys/local_offset_at/windows.rs b/vendor/time/src/sys/local_offset_at/windows.rs
new file mode 100644
index 000000000..fed01bf3a
--- /dev/null
+++ b/vendor/time/src/sys/local_offset_at/windows.rs
@@ -0,0 +1,114 @@
+//! Get the system's UTC offset on Windows.
+
+use core::mem::MaybeUninit;
+
+use crate::{OffsetDateTime, UtcOffset};
+
+// ffi: WINAPI FILETIME struct
+#[repr(C)]
+#[allow(non_snake_case, clippy::missing_docs_in_private_items)]
+struct FileTime {
+    dwLowDateTime: u32,
+    dwHighDateTime: u32,
+}
+
+// ffi: WINAPI SYSTEMTIME struct
+#[repr(C)]
+#[allow(non_snake_case, clippy::missing_docs_in_private_items)]
+struct SystemTime {
+    wYear: u16,
+    wMonth: u16,
+    wDayOfWeek: u16,
+    wDay: u16,
+    wHour: u16,
+    wMinute: u16,
+    wSecond: u16,
+    wMilliseconds: u16,
+}
+
+#[link(name = "kernel32")]
+extern "system" {
+    // https://docs.microsoft.com/en-us/windows/win32/api/timezoneapi/nf-timezoneapi-systemtimetofiletime
+    fn SystemTimeToFileTime(lpSystemTime: *const SystemTime, lpFileTime: *mut FileTime) -> i32;
+
+    // https://docs.microsoft.com/en-us/windows/win32/api/timezoneapi/nf-timezoneapi-systemtimetotzspecificlocaltime
+    fn SystemTimeToTzSpecificLocalTime(
+        lpTimeZoneInformation: *const core::ffi::c_void, // We only pass `nullptr` here
+        lpUniversalTime: *const SystemTime,
+        lpLocalTime: *mut SystemTime,
+    ) -> i32;
+}
+
+/// Convert a `SYSTEMTIME` to a `FILETIME`. Returns `None` if any error occurred.
+fn systemtime_to_filetime(systime: &SystemTime) -> Option<FileTime> {
+    let mut ft = MaybeUninit::uninit();
+
+    // Safety: `SystemTimeToFileTime` is thread-safe.
+    if 0 == unsafe { SystemTimeToFileTime(systime, ft.as_mut_ptr()) } {
+        // failed
+        None
+    } else {
+        // Safety: The call succeeded.
+        Some(unsafe { ft.assume_init() })
+    }
+}
+
+/// Convert a `FILETIME` to an `i64`, representing a number of seconds.
+fn filetime_to_secs(filetime: &FileTime) -> i64 {
+    /// FILETIME represents 100-nanosecond intervals
+    const FT_TO_SECS: i64 = 10_000_000;
+    ((filetime.dwHighDateTime as i64) << 32 | filetime.dwLowDateTime as i64) / FT_TO_SECS
+}
+
+/// Convert an [`OffsetDateTime`] to a `SYSTEMTIME`.
+fn offset_to_systemtime(datetime: OffsetDateTime) -> SystemTime {
+    let (_, month, day_of_month) = datetime.to_offset(UtcOffset::UTC).date().to_calendar_date();
+    SystemTime {
+        wYear: datetime.year() as _,
+        wMonth: month as _,
+        wDay: day_of_month as _,
+        wDayOfWeek: 0, // ignored
+        wHour: datetime.hour() as _,
+        wMinute: datetime.minute() as _,
+        wSecond: datetime.second() as _,
+        wMilliseconds: datetime.millisecond(),
+    }
+}
+
+/// Obtain the system's UTC offset.
+pub(super) fn local_offset_at(datetime: OffsetDateTime) -> Option<UtcOffset> {
+    // This function falls back to UTC if any system call fails.
+    let systime_utc = offset_to_systemtime(datetime.to_offset(UtcOffset::UTC));
+
+    // Safety: `local_time` is only read if it is properly initialized, and
+    // `SystemTimeToTzSpecificLocalTime` is thread-safe.
+    let systime_local = unsafe {
+        let mut local_time = MaybeUninit::uninit();
+
+        if 0 == SystemTimeToTzSpecificLocalTime(
+            core::ptr::null(), // use system's current timezone
+            &systime_utc,
+            local_time.as_mut_ptr(),
+        ) {
+            // call failed
+            return None;
+        } else {
+            local_time.assume_init()
+        }
+    };
+
+    // Convert SYSTEMTIMEs to FILETIMEs so we can perform arithmetic on them.
+    let ft_system = systemtime_to_filetime(&systime_utc)?;
+    let ft_local = systemtime_to_filetime(&systime_local)?;
+
+    let diff_secs: i32 = (filetime_to_secs(&ft_local) - filetime_to_secs(&ft_system))
+        .try_into()
+        .ok()?;
+
+    UtcOffset::from_hms(
+        (diff_secs / 3_600) as _,
+        ((diff_secs / 60) % 60) as _,
+        (diff_secs % 60) as _,
+    )
+    .ok()
+}