time/
util.rs

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1//! Utility functions, including updating time zone information.
2
3pub use time_core::util::{days_in_year, is_leap_year, weeks_in_year};
4
5use crate::Month;
6
7/// Whether to adjust the date, and in which direction. Useful when implementing arithmetic.
8pub(crate) enum DateAdjustment {
9    /// The previous day should be used.
10    Previous,
11    /// The next day should be used.
12    Next,
13    /// The date should be used as-is.
14    None,
15}
16
17/// Get the number of days in the month of a given year.
18///
19/// ```rust
20/// # use time::{Month, util};
21/// assert_eq!(util::days_in_month(Month::February, 2020), 29);
22/// ```
23pub const fn days_in_month(month: Month, year: i32) -> u8 {
24    month.length(year)
25}
26
27/// Get the number of days in the month of a given year.
28///
29/// ```rust
30/// # #![allow(deprecated)]
31/// # use time::{Month, util};
32/// assert_eq!(util::days_in_year_month(2020, Month::February), 29);
33/// ```
34#[deprecated(
35    since = "0.3.37",
36    note = "use `days_in_month` or `Month::length` instead"
37)]
38pub const fn days_in_year_month(year: i32, month: Month) -> u8 {
39    month.length(year)
40}
41
42/// Update time zone information from the system.
43///
44/// For a version of this function that is guaranteed to be sound, see [`refresh_tz`].
45///
46/// # Safety
47///
48/// This is a system call with specific requirements. The following is from POSIX's description of
49/// `tzset`:
50///
51/// > If a thread accesses `tzname`, `daylight`, or `timezone` directly while another thread is in a
52/// > call to `tzset()`, or to any function that is required or allowed to set timezone information
53/// > as if by calling `tzset()`, the behavior is undefined.
54///
55/// Effectively, this translates to the requirement that at least one of the following must be true:
56///
57/// - The operating system provides a thread-safe environment.
58/// - The process is single-threaded.
59/// - The process is multi-threaded **and** no other thread is mutating the environment in any way
60///   at the same time a call to a method that obtains the local UTC offset. This includes adding,
61///   removing, or modifying an environment variable.
62///
63/// ## Soundness is global
64///
65/// You must not only verify this safety conditions for your code, but for **all** code that will be
66/// included in the final binary. Notably, it applies to both direct and transitive dependencies and
67/// to both Rust and non-Rust code. **For this reason it is not possible for a library to soundly
68/// call this method.**
69///
70/// ## Forward compatibility
71///
72/// This currently only does anything on Unix-like systems. On other systems, it is a no-op. This
73/// may change in the future if necessary, expanding the safety requirements. It is expected that,
74/// at a minimum, calling this method when the process is single-threaded will remain sound.
75#[cfg(feature = "local-offset")]
76pub unsafe fn refresh_tz_unchecked() {
77    // Safety: The caller must uphold the safety requirements.
78    unsafe { crate::sys::refresh_tz_unchecked() };
79}
80
81/// Attempt to update time zone information from the system.
82///
83/// Returns `None` if the call is not known to be sound.
84#[cfg(feature = "local-offset")]
85pub fn refresh_tz() -> Option<()> {
86    crate::sys::refresh_tz()
87}
88
89#[doc(hidden)]
90#[cfg(feature = "local-offset")]
91#[allow(clippy::missing_const_for_fn)]
92#[deprecated(since = "0.3.37", note = "no longer needed; TZ is refreshed manually")]
93pub mod local_offset {
94    #[derive(Debug, Clone, Copy, PartialEq, Eq)]
95    pub enum Soundness {
96        Sound,
97        Unsound,
98    }
99
100    pub unsafe fn set_soundness(_: Soundness) {}
101
102    pub fn get_soundness() -> Soundness {
103        Soundness::Sound
104    }
105}
time/util.rs

time/
util.rs
