rebuild the engine in Rust

Python was never the house language here: the mw-* desktop surface it came from is 39 bash scripts and was exactly one Python script, the one this was extracted from. What it cost was distribution, a widget dependency that needed pipx and a Python floor, and 24ms of interpreter startup before a line of the program ran. The port is verified rather than asserted. Both implementations were run over 199,446 day-records, 26 jurisdictions across 21 years, with every field of every record required to match; the JSON, the iCalendar and 480 renderings of the text output are identical too. examples/dump.rs is the harness. What the type system actually buys, which is less than the usual claim and more than nothing: - Level is an ordered enum, strictest first, so reads as 'a is stricter' and relaxed_to() is the one place a feast can lift a fast. No rule can get the direction backwards. - Date is a newtype over the Julian Day Number and JulianDate is a separate type, so a civil date and an ecclesiastical one cannot be mixed up. That confusion is the single most common way calendar code goes wrong. - Octets is a newtype in the iCalendar folder, because the bug it replaced counted characters against a limit RFC 5545 states in octets. - Movables is a struct, not a map, so a mistyped key is a compile error rather than a None at the far end of the program. Of the six defects an adversarial review found in the Python, exactly one had a shape a type system would have caught. The rest were logic, and the tests came with them. The menologion is compiled in with include_str!, so the binary answers on its own: 930KB, no runtime, 1.2ms to start against Python's 36ms.
2026-10-23 03:07:12 +00:00 · 2026-09-18 11:13:15 -04:00
parent 8247b51805
commit d115616eff
44 changed files with 3367 additions and 2287 deletions
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+//! Who keeps which calendar, and by whose rule.
+//!
+//! A jurisdiction is four independent choices, and conflating any two of them
+//! is how calendar code usually goes wrong:
+//!
+//! - **paschalion**: which table gives Pascha
+//! - **menologion**: which calendar the fixed feasts are read on
+//! - **rule**: which fasting discipline is kept
+//! - **menaia**: which supplementary commemorations to load, if any
+//!
+//! The pairings are not free. Almost every Orthodox Church keeps the Julian
+//! Paschalion; what divides them is the menologion. The "old calendar" churches
+//! read the fixed feasts on the Julian calendar too, the "new calendar"
+//! churches on the Revised Julian, which agrees with the Gregorian for every
+//! date until 2800. So a new-calendar church keeps the Nativity with the West
+//! and Pascha with the East, which is not a compromise but exactly what the
+//! 1923 congress decided.
+//!
+//! Only two bodies here use the Gregorian Paschalion: the Finnish Orthodox
+//! Church, alone among the Orthodox, and the Byzantine Catholic churches.
+
+use crate::calendars::Date;
+use crate::paschalion::Paschalion;
+
+/// Which calendar the *fixed* feasts are read on.
+#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+pub enum MenologionKind {
+    Julian,
+    /// Revised Julian, which agrees with the Gregorian for every date until 2800.
+    RevisedJulian,
+}
+
+#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+pub enum RuleKind {
+    Orthodox,
+    Ruthenian,
+}
+
+/// The short name people use for a paschalion/menologion combination.
+#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+pub enum Calendar {
+    Old,
+    New,
+    Western,
+}
+
+impl Calendar {
+    pub fn key(self) -> &'static str {
+        match self {
+            Calendar::Old => "old",
+            Calendar::New => "new",
+            Calendar::Western => "western",
+        }
+    }
+}
+
+#[derive(Clone, Copy, Debug)]
+pub struct Jurisdiction {
+    pub key: &'static str,
+    pub name: &'static str,
+    pub paschalion: Paschalion,
+    pub menologion: MenologionKind,
+    pub rule: RuleKind,
+    /// Supplementary commemoration sets to overlay, fetched not shipped.
+    pub menaia: &'static [&'static str],
+    pub note: &'static str,
+}
+
+impl Jurisdiction {
+    pub fn calendar(&self) -> Calendar {
+        match (self.paschalion, self.menologion) {
+            (Paschalion::Gregorian, MenologionKind::RevisedJulian) => Calendar::Western,
+            (_, MenologionKind::Julian) => Calendar::Old,
+            _ => Calendar::New,
+        }
+    }
+
+    /// The ecclesiastical (year, month, day) a civil date is reckoned as.
+    pub fn fixed_of_civil(&self, date: Date) -> (i32, u32, u32) {
+        match self.menologion {
+            MenologionKind::Julian => {
+                let j = date.to_julian();
+                (j.year, j.month, j.day)
+            }
+            MenologionKind::RevisedJulian => date.ymd(),
+        }
+    }
+
+    /// The civil date of an ecclesiastical date in a given church year.
+    pub fn civil_of_fixed(&self, year: i32, month: u32, day: u32) -> Date {
+        match self.menologion {
+            MenologionKind::Julian => {
+                crate::calendars::JulianDate { year, month, day }.to_civil()
+            }
+            MenologionKind::RevisedJulian => Date::from_ymd(year, month, day)
+                .unwrap_or_else(|| Date::from_ymd(year, month, 28).expect("28th exists")),
+        }
+    }
+}
+
+use MenologionKind::{Julian as JulMen, RevisedJulian as RevJul};
+use Paschalion::{Gregorian as GregP, Julian as JulP};
+use RuleKind::{Orthodox as Orth, Ruthenian as Ruth};
+
+const NO_MENAIA: &[&str] = &[];
+const RUTHENIAN_MENAIA: &[&str] = &["ruthenian"];
+
+/// A reckoning without naming a church. `new` is the default.
+pub const CALENDARS: &[Jurisdiction] = &[
+    Jurisdiction { key: "old", name: "Old Calendar", paschalion: JulP, menologion: JulMen, rule: Orth, menaia: NO_MENAIA,
+        note: "Julian throughout, the reckoning of Moscow, Serbia, Georgia, Jerusalem and the Holy Mountain." },
+    Jurisdiction { key: "new", name: "New Calendar", paschalion: JulP, menologion: RevJul, rule: Orth, menaia: NO_MENAIA,
+        note: "Revised Julian fixed feasts with the Julian Paschalion: Constantinople, Greece, Antioch, Romania, Bulgaria, the OCA." },
+    Jurisdiction { key: "western", name: "Gregorian", paschalion: GregP, menologion: RevJul, rule: Orth, menaia: NO_MENAIA,
+        note: "Gregorian throughout, Pascha included. Kept by the Finnish Orthodox Church and by most Byzantine Catholics." },
+];
+
+pub const JURISDICTIONS: &[Jurisdiction] = &[
+    // old calendar
+    Jurisdiction { key: "moscow", name: "Russian Orthodox Church", paschalion: JulP, menologion: JulMen, rule: Orth, menaia: NO_MENAIA, note: "" },
+    Jurisdiction { key: "rocor", name: "Russian Orthodox Church Outside Russia", paschalion: JulP, menologion: JulMen, rule: Orth, menaia: NO_MENAIA, note: "" },
+    Jurisdiction { key: "serbian", name: "Serbian Orthodox Church", paschalion: JulP, menologion: JulMen, rule: Orth, menaia: NO_MENAIA, note: "" },
+    Jurisdiction { key: "georgian", name: "Georgian Orthodox Church", paschalion: JulP, menologion: JulMen, rule: Orth, menaia: NO_MENAIA, note: "" },
+    Jurisdiction { key: "jerusalem", name: "Patriarchate of Jerusalem", paschalion: JulP, menologion: JulMen, rule: Orth, menaia: NO_MENAIA, note: "" },
+    Jurisdiction { key: "athos", name: "The Holy Mountain", paschalion: JulP, menologion: JulMen, rule: Orth, menaia: NO_MENAIA,
+        note: "Athonite practice is stricter than the printed Typikon at many points." },
+    Jurisdiction { key: "polish", name: "Polish Orthodox Church", paschalion: JulP, menologion: JulMen, rule: Orth, menaia: NO_MENAIA,
+        note: "Returned to the Julian menologion in 2014 after decades on the Revised Julian; some parishes kept the new calendar." },
+    Jurisdiction { key: "macedonian", name: "Macedonian Orthodox Church", paschalion: JulP, menologion: JulMen, rule: Orth, menaia: NO_MENAIA, note: "" },
+
+    // new calendar
+    Jurisdiction { key: "constantinople", name: "Ecumenical Patriarchate", paschalion: JulP, menologion: RevJul, rule: Orth, menaia: NO_MENAIA, note: "" },
+    Jurisdiction { key: "goarch", name: "Greek Orthodox Archdiocese of America", paschalion: JulP, menologion: RevJul, rule: Orth, menaia: NO_MENAIA, note: "" },
+    Jurisdiction { key: "greece", name: "Church of Greece", paschalion: JulP, menologion: RevJul, rule: Orth, menaia: NO_MENAIA, note: "" },
+    Jurisdiction { key: "antiochian", name: "Antiochian Orthodox Church", paschalion: JulP, menologion: RevJul, rule: Orth, menaia: NO_MENAIA, note: "" },
+    Jurisdiction { key: "oca", name: "Orthodox Church in America", paschalion: JulP, menologion: RevJul, rule: Orth, menaia: NO_MENAIA,
+        note: "Most parishes keep the new calendar; a minority, chiefly of Carpatho-Russian and Alaskan background, keep the old." },
+    Jurisdiction { key: "romanian", name: "Romanian Orthodox Church", paschalion: JulP, menologion: RevJul, rule: Orth, menaia: NO_MENAIA, note: "" },
+    Jurisdiction { key: "bulgarian", name: "Bulgarian Orthodox Church", paschalion: JulP, menologion: RevJul, rule: Orth, menaia: NO_MENAIA, note: "" },
+    Jurisdiction { key: "cyprus", name: "Church of Cyprus", paschalion: JulP, menologion: RevJul, rule: Orth, menaia: NO_MENAIA, note: "" },
+    Jurisdiction { key: "albanian", name: "Orthodox Church of Albania", paschalion: JulP, menologion: RevJul, rule: Orth, menaia: NO_MENAIA, note: "" },
+    Jurisdiction { key: "ukrainian", name: "Orthodox Church of Ukraine", paschalion: JulP, menologion: RevJul, rule: Orth, menaia: NO_MENAIA,
+        note: "Moved the fixed feasts to the Revised Julian calendar on 1 September 2023. The Julian Paschalion is retained." },
+
+    // gregorian throughout
+    Jurisdiction { key: "finnish", name: "Finnish Orthodox Church", paschalion: GregP, menologion: RevJul, rule: Orth, menaia: NO_MENAIA,
+        note: "The only Orthodox Church keeping the Gregorian Paschalion." },
+
+    // eastern catholic
+    Jurisdiction { key: "ruthenian", name: "Byzantine Catholic Metropolia of Pittsburgh", paschalion: GregP, menologion: RevJul, rule: Ruth, menaia: RUTHENIAN_MENAIA,
+        note: "Gregorian throughout. Fasting is reported under Ruthenian particular law, which binds far less than the Typikon prescribes." },
+    Jurisdiction { key: "ugcc", name: "Ukrainian Greek Catholic Church", paschalion: JulP, menologion: RevJul, rule: Ruth, menaia: RUTHENIAN_MENAIA,
+        note: "Moved the fixed feasts to the Revised Julian calendar on 1 September 2023, keeping the Julian Paschalion. Eparchies outside Ukraine vary; several keep the Gregorian Paschalion." },
+    Jurisdiction { key: "melkite", name: "Melkite Greek Catholic Church", paschalion: GregP, menologion: RevJul, rule: Ruth, menaia: NO_MENAIA,
+        note: "Practice is not uniform: parishes in the Middle East commonly keep the Julian Paschalion for the sake of the local Orthodox." },
+    Jurisdiction { key: "romanian-catholic", name: "Romanian Greek Catholic Church", paschalion: GregP, menologion: RevJul, rule: Ruth, menaia: NO_MENAIA, note: "" },
+];
+
+/// A jurisdiction key, a calendar name, or `None` for the default.
+pub fn resolve(name: Option<&str>) -> Result<&'static Jurisdiction, String> {
+    let Some(name) = name else {
+        return Ok(&CALENDARS[1]); // new
+    };
+    let key = name.trim().to_ascii_lowercase();
+    JURISDICTIONS
+        .iter()
+        .chain(CALENDARS.iter())
+        .find(|j| j.key == key)
+        .ok_or_else(|| name.to_string())
+}