Make eligible functions const.

src/format/locales.rs

@@ -1,33 +1,33 @@
 use pure_rust_locales::{locale_match, Locale};
 
-pub(crate) fn short_months(locale: Locale) -> &'static [&'static str] {
+pub(crate) const fn short_months(locale: Locale) -> &'static [&'static str] {
     locale_match!(locale => LC_TIME::ABMON)
 }
 
-pub(crate) fn long_months(locale: Locale) -> &'static [&'static str] {
+pub(crate) const fn long_months(locale: Locale) -> &'static [&'static str] {
     locale_match!(locale => LC_TIME::MON)
 }
 
-pub(crate) fn short_weekdays(locale: Locale) -> &'static [&'static str] {
+pub(crate) const fn short_weekdays(locale: Locale) -> &'static [&'static str] {
     locale_match!(locale => LC_TIME::ABDAY)
 }
 
-pub(crate) fn long_weekdays(locale: Locale) -> &'static [&'static str] {
+pub(crate) const fn long_weekdays(locale: Locale) -> &'static [&'static str] {
     locale_match!(locale => LC_TIME::DAY)
 }
 
-pub(crate) fn am_pm(locale: Locale) -> &'static [&'static str] {
+pub(crate) const fn am_pm(locale: Locale) -> &'static [&'static str] {
     locale_match!(locale => LC_TIME::AM_PM)
 }
 
-pub(crate) fn d_fmt(locale: Locale) -> &'static str {
+pub(crate) const fn d_fmt(locale: Locale) -> &'static str {
     locale_match!(locale => LC_TIME::D_FMT)
 }
 
-pub(crate) fn d_t_fmt(locale: Locale) -> &'static str {
+pub(crate) const fn d_t_fmt(locale: Locale) -> &'static str {
     locale_match!(locale => LC_TIME::D_T_FMT)
 }
 
-pub(crate) fn t_fmt(locale: Locale) -> &'static str {
+pub(crate) const fn t_fmt(locale: Locale) -> &'static str {
     locale_match!(locale => LC_TIME::T_FMT)
 }

src/format/scan.rs

@@ -254,7 +254,7 @@ fn timezone_offset_internal<F>(
 where
     F: FnMut(&str) -> ParseResult<&str>,
 {
-    fn digits(s: &str) -> ParseResult<(u8, u8)> {
+    const fn digits(s: &str) -> ParseResult<(u8, u8)> {
         let b = s.as_bytes();
         if b.len() < 2 {
             Err(TOO_SHORT)

src/month.rs

@@ -66,7 +66,7 @@ impl Month {
     /// `m.succ()`: | `February` | `March`    | `...` | `January`
     #[inline]
     #[must_use]
-    pub fn succ(&self) -> Month {
+    pub const fn succ(&self) -> Month {
         match *self {
             Month::January => Month::February,
             Month::February => Month::March,
@@ -90,7 +90,7 @@ impl Month {
     /// `m.pred()`: | `December` | `January`  | `...` | `November`
     #[inline]
     #[must_use]
-    pub fn pred(&self) -> Month {
+    pub const fn pred(&self) -> Month {
         match *self {
             Month::January => Month::December,
             Month::February => Month::January,
@@ -114,7 +114,7 @@ impl Month {
     /// `m.number_from_month()`: | 1         | 2          | `...` | 12
     #[inline]
     #[must_use]
-    pub fn number_from_month(&self) -> u32 {
+    pub const fn number_from_month(&self) -> u32 {
         match *self {
             Month::January => 1,
             Month::February => 2,
@@ -139,7 +139,7 @@ impl Month {
     /// assert_eq!(Month::January.name(), "January")
     /// ```
     #[must_use]
-    pub fn name(&self) -> &'static str {
+    pub const fn name(&self) -> &'static str {
         match *self {
             Month::January => "January",
             Month::February => "February",

src/naive/internals.rs

@@ -301,7 +301,7 @@ impl Of {
     }
 
     #[inline]
-    pub(super) fn with_ordinal(&self, ordinal: u32) -> Option<Of> {
+    pub(super) const fn with_ordinal(&self, ordinal: u32) -> Option<Of> {
         if ordinal > 366 {
             return None;
         }
@@ -405,7 +405,7 @@ impl Mdf {
     }
 
     #[inline]
-    pub(super) fn with_month(&self, month: u32) -> Option<Mdf> {
+    pub(super) const fn with_month(&self, month: u32) -> Option<Mdf> {
         if month > 12 {
             return None;
         }
@@ -421,7 +421,7 @@ impl Mdf {
     }
 
     #[inline]
-    pub(super) fn with_day(&self, day: u32) -> Option<Mdf> {
+    pub(super) const fn with_day(&self, day: u32) -> Option<Mdf> {
         if day > 31 {
             return None;
         }

src/naive/time/mod.rs

@@ -241,7 +241,7 @@ impl NaiveTime {
     /// ```
     #[inline]
     #[must_use]
-    pub fn from_hms_opt(hour: u32, min: u32, sec: u32) -> Option<NaiveTime> {
+    pub const fn from_hms_opt(hour: u32, min: u32, sec: u32) -> Option<NaiveTime> {
         NaiveTime::from_hms_nano_opt(hour, min, sec, 0)
     }
 
@@ -366,7 +366,7 @@ impl NaiveTime {
     /// ```
     #[inline]
     #[must_use]
-    pub fn from_hms_nano_opt(hour: u32, min: u32, sec: u32, nano: u32) -> Option<NaiveTime> {
+    pub const fn from_hms_nano_opt(hour: u32, min: u32, sec: u32, nano: u32) -> Option<NaiveTime> {
         if hour >= 24 || min >= 60 || sec >= 60 || nano >= 2_000_000_000 {
             return None;
         }
@@ -409,7 +409,7 @@ impl NaiveTime {
     /// ```
     #[inline]
     #[must_use]
-    pub fn from_num_seconds_from_midnight_opt(secs: u32, nano: u32) -> Option<NaiveTime> {
+    pub const fn from_num_seconds_from_midnight_opt(secs: u32, nano: u32) -> Option<NaiveTime> {
         if secs >= 86_400 || nano >= 2_000_000_000 {
             return None;
         }

src/offset/fixed.rs

@@ -55,7 +55,7 @@ impl FixedOffset {
     /// assert_eq!(&datetime.to_rfc3339(), "2016-11-08T00:00:00+05:00")
     /// ```
     #[must_use]
-    pub fn east_opt(secs: i32) -> Option<FixedOffset> {
+    pub const fn east_opt(secs: i32) -> Option<FixedOffset> {
         if -86_400 < secs && secs < 86_400 {
             Some(FixedOffset { local_minus_utc: secs })
         } else {
@@ -89,7 +89,7 @@ impl FixedOffset {
     /// assert_eq!(&datetime.to_rfc3339(), "2016-11-08T00:00:00-05:00")
     /// ```
     #[must_use]
-    pub fn west_opt(secs: i32) -> Option<FixedOffset> {
+    pub const fn west_opt(secs: i32) -> Option<FixedOffset> {
         if -86_400 < secs && secs < 86_400 {
             Some(FixedOffset { local_minus_utc: -secs })
         } else {

src/offset/local/tz_info/parser.rs

@@ -237,7 +237,7 @@ impl<'a> Cursor<'a> {
     }
 
     /// Returns `true` if data is remaining
-    pub(crate) fn is_empty(&self) -> bool {
+    pub(crate) const fn is_empty(&self) -> bool {
         self.remaining.is_empty()
     }
 

src/offset/local/tz_info/rule.rs

@@ -127,7 +127,7 @@ pub(super) struct AlternateTime {
 
 impl AlternateTime {
     /// Construct a transition rule representing alternate local time types
-    fn new(
+    const fn new(
         std: LocalTimeType,
         dst: LocalTimeType,
         dst_start: RuleDay,
@@ -504,7 +504,7 @@ impl RuleDay {
     }
 
     /// Construct a transition rule day represented by a zero-based Julian day in `[0, 365]`, taking occasional Feb 29 into account
-    fn julian_0(julian_day_0: u16) -> Result<Self, Error> {
+    const fn julian_0(julian_day_0: u16) -> Result<Self, Error> {
         if julian_day_0 > 365 {
             return Err(Error::TransitionRule("invalid rule day julian day"));
         }
@@ -737,7 +737,7 @@ const DAY_IN_MONTHS_LEAP_YEAR_FROM_MARCH: [i64; 12] =
 /// * `year`: Year
 /// * `month`: Month in `[1, 12]`
 /// * `month_day`: Day of the month in `[1, 31]`
-pub(crate) fn days_since_unix_epoch(year: i32, month: usize, month_day: i64) -> i64 {
+pub(crate) const fn days_since_unix_epoch(year: i32, month: usize, month_day: i64) -> i64 {
     let is_leap_year = is_leap_year(year);
 
     let year = year as i64;
@@ -768,7 +768,7 @@ pub(crate) fn days_since_unix_epoch(year: i32, month: usize, month_day: i64) ->
 }
 
 /// Check if a year is a leap year
-pub(crate) fn is_leap_year(year: i32) -> bool {
+pub(crate) const fn is_leap_year(year: i32) -> bool {
     year % 400 == 0 || (year % 4 == 0 && year % 100 != 0)
 }
 

src/offset/local/tz_info/timezone.rs

@@ -374,7 +374,7 @@ impl<'a> TimeZoneRef<'a> {
     }
 
     /// Convert Unix time to Unix leap time, from the list of leap seconds in a time zone
-    fn unix_time_to_unix_leap_time(&self, unix_time: i64) -> Result<i64, Error> {
+    const fn unix_time_to_unix_leap_time(&self, unix_time: i64) -> Result<i64, Error> {
         let mut unix_leap_time = unix_time;
 
         let mut i = 0;
@@ -563,7 +563,7 @@ impl LocalTimeType {
     }
 
     /// Construct a local time type with the specified UTC offset in seconds
-    pub(super) fn with_offset(ut_offset: i32) -> Result<Self, Error> {
+    pub(super) const fn with_offset(ut_offset: i32) -> Result<Self, Error> {
         if ut_offset == i32::min_value() {
             return Err(Error::LocalTimeType("invalid UTC offset"));
         }
@@ -608,7 +608,7 @@ fn find_tz_file(path: impl AsRef<Path>) -> Result<File, Error> {
 }
 
 #[inline]
-fn saturating_abs(v: i32) -> i32 {
+const fn saturating_abs(v: i32) -> i32 {
     if v.is_positive() {
         v
     } else if v == i32::min_value() {

src/round.rs

@@ -75,7 +75,7 @@ where
 }
 
 // Return the maximum span in nanoseconds for the target number of digits.
-fn span_for_digits(digits: u16) -> u32 {
+const fn span_for_digits(digits: u16) -> u32 {
     // fast lookup form of: 10^(9-min(9,digits))
     match digits {
         0 => 1_000_000_000,

src/weekday.rs

@@ -57,7 +57,7 @@ impl Weekday {
     /// `w.succ()`: | `Tue` | `Wed` | `Thu` | `Fri` | `Sat` | `Sun` | `Mon`
     #[inline]
     #[must_use]
-    pub fn succ(&self) -> Weekday {
+    pub const fn succ(&self) -> Weekday {
         match *self {
             Weekday::Mon => Weekday::Tue,
             Weekday::Tue => Weekday::Wed,
@@ -76,7 +76,7 @@ impl Weekday {
     /// `w.pred()`: | `Sun` | `Mon` | `Tue` | `Wed` | `Thu` | `Fri` | `Sat`
     #[inline]
     #[must_use]
-    pub fn pred(&self) -> Weekday {
+    pub const fn pred(&self) -> Weekday {
         match *self {
             Weekday::Mon => Weekday::Sun,
             Weekday::Tue => Weekday::Mon,