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//! Utility functions.
pub use time_core::util::{days_in_year, is_leap_year, weeks_in_year};
use crate::Month;
/// Whether to adjust the date, and in which direction. Useful when implementing arithmetic.
pub(crate) enum DateAdjustment {
/// The previous day should be used.
Previous,
/// The next day should be used.
Next,
/// The date should be used as-is.
None,
}
/// Get the number of days in the month of a given year.
///
/// ```rust
/// # use time::{Month, util};
/// assert_eq!(util::days_in_year_month(2020, Month::February), 29);
/// ```
pub const fn days_in_year_month(year: i32, month: Month) -> u8 {
use Month::*;
match month {
January | March | May | July | August | October | December => 31,
April | June | September | November => 30,
February if is_leap_year(year) => 29,
February => 28,
}
}
#[cfg(feature = "local-offset")]
/// Utility functions relating to the local UTC offset.
pub mod local_offset {
use core::sync::atomic::{AtomicBool, Ordering};
/// Whether obtaining the local UTC offset is required to be sound.
static LOCAL_OFFSET_IS_SOUND: AtomicBool = AtomicBool::new(true);
/// The soundness of obtaining the local UTC offset.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Soundness {
/// Obtaining the local UTC offset is required to be sound. Undefined behavior will never
/// occur. This is the default.
Sound,
/// Obtaining the local UTC offset is allowed to invoke undefined behavior. **Setting this
/// value is strongly discouraged.** To do so, you must comply with the safety requirements
/// of [`time::local_offset::set_soundness`](set_soundness).
Unsound,
}
/// Set whether obtaining the local UTC offset is allowed to invoke undefined behavior. **Use of
/// this function is heavily discouraged.**
///
/// # Safety
///
/// If this method is called with [`Soundness::Sound`], the call is always sound. If this method
/// is called with [`Soundness::Unsound`], the following conditions apply.
///
/// - If the operating system provides a thread-safe environment, the call is sound.
/// - If the process is single-threaded, the call is sound.
/// - If the process is multi-threaded, no other thread may mutate the environment in any way at
/// the same time a call to a method that obtains the local UTC offset. This includes adding,
/// removing, or modifying an environment variable.
///
/// The first two conditions are automatically checked by `time`, such that you do not need to
/// declare your code unsound. Currently, the only known operating systems that does _not_
/// provide a thread-safe environment are some Unix-like OS's. All other operating systems
/// should succeed when attempting to obtain the local UTC offset.
///
/// Note that you must not only verify this safety condition for your code, but for **all** code
/// that will be included in the final binary. Notably, it applies to both direct and transitive
/// dependencies and to both Rust and non-Rust code. **For this reason it is not possible to
/// soundly pass [`Soundness::Unsound`] to this method if you are writing a library that may
/// used by others.**
///
/// If using this method is absolutely necessary, it is recommended to keep the time between
/// setting the soundness to [`Soundness::Unsound`] and setting it back to [`Soundness::Sound`]
/// as short as possible.
///
/// The following methods currently obtain the local UTC offset:
///
/// - [`OffsetDateTime::now_local`](crate::OffsetDateTime::now_local)
/// - [`UtcOffset::local_offset_at`](crate::UtcOffset::local_offset_at)
/// - [`UtcOffset::current_local_offset`](crate::UtcOffset::current_local_offset)
pub unsafe fn set_soundness(soundness: Soundness) {
LOCAL_OFFSET_IS_SOUND.store(soundness == Soundness::Sound, Ordering::Release);
}
/// Obtains the soundness of obtaining the local UTC offset. If it is [`Soundness::Unsound`],
/// it is allowed to invoke undefined behavior when obtaining the local UTC offset.
pub fn get_soundness() -> Soundness {
match LOCAL_OFFSET_IS_SOUND.load(Ordering::Acquire) {
false => Soundness::Unsound,
true => Soundness::Sound,
}
}
}