nepdate 0.1.0-beta.1

Bikram Sambat (BS, the Nepali calendar) dates for Rust: conversion to and from the Gregorian calendar (AD), arithmetic, fiscal years, formatting in English or Nepali, and parsing. no_std, no dependencies by default, no heap allocation, no unsafe.

Tithi, public holidays and events are in the companion crate nepdate-patro, so this crate carries no patro data.

Status: 0.1.0-beta.1, the first public pre-release. The API may still change before 0.1.0.

Quick start

[dependencies]
nepdate = "=0.1.0-beta.1"

use nepdate::{Lang, LongDate, MonthOverflow, NepaliDate, Weekday};

// BS to AD.
let date = NepaliDate::new(2081, 4, 15)?;
let ad = date.to_gregorian();
assert_eq!((ad.year(), ad.month(), ad.day()), (2024, 7, 30));
assert_eq!(date.weekday(), Weekday::Tuesday);

// AD to BS.
assert_eq!(NepaliDate::from_gregorian(2024, 7, 30)?, date);

// Arithmetic never panics: out of range gives an error.
assert_eq!(date.checked_add_days(1000)?.to_string(), "2084/01/13");
assert_eq!(
    date.checked_add_months(13, MonthOverflow::Clamp)?.to_string(),
    "2082/05/15"
);

// Formatting and parsing.
assert_eq!(date.to_string(), "2081/04/15");
assert_eq!(
    date.long(LongDate::default(), Lang::En).to_string(),
    "Shrawan 15, 2081"
);
assert_eq!("2081/04/15".parse::<NepaliDate>()?, date);
assert_eq!(NepaliDate::parse_lenient("15 Shrawan 2081")?, date);
# Ok::<(), nepdate::Error>(())

Every formatter (short, long, format_pattern, Lang::digits, FiscalYear::label) has a write_to method that writes into any core::fmt::Write without allocating; to_string() needs std.

Two runnable examples are in the repository: convert (cargo run --example convert --features jiff -- 2081/04/15) and month_calendar (cargo run --example month_calendar -- 2081 4).

Supported range

BS 1901-01-01 to 2199-12-30 (AD 1844-04-11 to 2143-04-15). Every function returns Error::OutOfRange outside it. Month lengths for years beyond the officially published calendar are projections inherited from NepDate and may change in a later release (known data questions).

Features

Feature	Default	What it adds
`std`	yes	`std::error::Error` for `Error`, and `to_string()` through `Display`
`serde`	no	`Serialize` and `Deserialize` for `NepaliDate` as `"YYYY-MM-DD"`
`chrono`	no	`From<NepaliDate> for chrono::NaiveDate` and `TryFrom<chrono::NaiveDate>`
`jiff`	no	`From<NepaliDate> for jiff::civil::Date`, `TryFrom<jiff::civil::Date>`, `NepaliDate::today()` (the date in `Asia/Kathmandu`), `today_in(&TimeZone)` and `is_today()`. Turns on `std`

Without default features the crate builds for wasm32-unknown-unknown and other targets with no standard library.

Coming from C# NepDate

C#	Rust
`new NepaliDate(y, m, d)` (throws)	`NepaliDate::new(y, m, d)` returns `Result<NepaliDate, Error>` and is a `const fn`
`NepaliDate.Parse(s)` / `TryParse`	`s.parse::<NepaliDate>()` (strict) or `NepaliDate::parse_lenient(s)`
`date.EnglishDate`	`date.to_gregorian()`, or `chrono::NaiveDate::from(date)` with feature `chrono`
`DateTime.ToNepaliDate()`	`NepaliDate::from_gregorian(y, m, d)`, or `NepaliDate::try_from(naive_date)`
`AddDays(n)`	`checked_add_days(n)`
`AddMonths(n, awayFromMonthEnd)`	`checked_add_months(n, MonthOverflow::Clamp)` or `MonthOverflow::Overflow`
`MonthEndDay`	`month_length()`
`DayOfWeek`	`weekday()`
`ToString(format)`	`Display` (`YYYY/MM/DD`), `short(..)`, `long(..)` and `format_pattern(pattern, lang)`
`IsToday`	`is_today()` with feature `jiff`

The places where this crate deliberately behaves differently from C# NepDate are listed in PARITY.md.

Minimum supported Rust version

Rust 1.85 (edition 2024). Raising it is a minor version bump.

Data and license

The calendar data and conversion algorithm come from NepDate by Raju Prasai and contributors, used under the MIT License. Its notice ships in this crate as LICENSE-THIRD-PARTY. The shared data and the specification are maintained in sanamhub/nepdate.

This crate is MIT licensed (LICENSE). It is not affiliated with the Government of Nepal.

Topic	Where
What changed in each version	CHANGELOG.md
Speed against C# NepDate and other crates	benchmarks
Reporting a vulnerability	SECURITY.md
A wrong date, holiday or tithi	the hub's data error form
The other languages	sanamhub/nepdate