From 09a2926bc8b8c60725748c3d3462e5b82fb34d63 Mon Sep 17 00:00:00 2001
From: Paul Dicker <pitdicker@gmail.com>
Date: Fri, 19 May 2023 15:42:42 +0200
Subject: [PATCH] Support encoding `-00:00` in `Parsed::offset`

---
 src/format/mod.rs    |  2 +-
 src/format/parsed.rs | 26 +++++++++++++++++++++-----
 2 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/src/format/mod.rs b/src/format/mod.rs
index 6b66ee49ae..147d929b71 100644
--- a/src/format/mod.rs
+++ b/src/format/mod.rs
@@ -57,7 +57,7 @@ use crate::{Month, ParseMonthError, ParseWeekdayError, Weekday};
 pub(crate) mod locales;
 
 pub use parse::{parse, parse_and_remainder};
-pub use parsed::Parsed;
+pub use parsed::{Parsed, NO_OFFSET_INFO};
 /// L10n locales.
 #[cfg(feature = "unstable-locales")]
 pub use pure_rust_locales::Locale;
diff --git a/src/format/parsed.rs b/src/format/parsed.rs
index 809a5ae782..740a9f1413 100644
--- a/src/format/parsed.rs
+++ b/src/format/parsed.rs
@@ -101,6 +101,9 @@ pub struct Parsed {
     pub timestamp: Option<i64>,
 
     /// Offset from the local time to UTC, in seconds.
+    ///
+    /// Use the constant [`NO_OFFSET_INFO`] to indicate there is an offset of `00:00`, but that its
+    /// relation to local time is unknown (`-00:00` in RFC 3339 and 2822).
     pub offset: Option<i32>,
 
     /// A dummy field to make this type not fully destructible (required for API stability).
@@ -108,6 +111,10 @@ pub struct Parsed {
     _dummy: (),
 }
 
+/// Constant to be used with [`Parsed::set_offset`] to indicate there is an offset of `00:00`, but
+/// that its relation to local time is unknown (`-00:00` in RFC 3339 and 2822).
+pub const NO_OFFSET_INFO: i32 = i32::MIN;
+
 /// Checks if `old` is either empty or has the same value as `new` (i.e. "consistent"),
 /// and if it is empty, set `old` to `new` as well.
 #[inline]
@@ -617,7 +624,12 @@ impl Parsed {
 
     /// Returns a parsed fixed time zone offset out of given fields.
     pub fn to_fixed_offset(&self) -> ParseResult<FixedOffset> {
-        self.offset.and_then(FixedOffset::east_opt).ok_or(OUT_OF_RANGE)
+        let offset = self.offset.ok_or(NOT_ENOUGH)?;
+        if offset == NO_OFFSET_INFO {
+            Ok(FixedOffset::OFFSET_UNKNOWN)
+        } else {
+            FixedOffset::east_opt(offset).ok_or(OUT_OF_RANGE)
+        }
     }
 
     /// Returns a parsed timezone-aware date and time out of given fields.
@@ -633,15 +645,19 @@ impl Parsed {
             (None, Some(_)) => 0, // UNIX timestamp may assume 0 offset
             (None, None) => return Err(NOT_ENOUGH),
         };
-        let datetime = self.to_naive_datetime_with_offset(offset)?;
-        let offset = FixedOffset::east_opt(offset).ok_or(OUT_OF_RANGE)?;
+        let (offset_i32, fixed_offset) = if offset == NO_OFFSET_INFO {
+            (0, FixedOffset::OFFSET_UNKNOWN)
+        } else {
+            (offset, FixedOffset::east_opt(offset).ok_or(OUT_OF_RANGE)?)
+        };
+        let datetime = self.to_naive_datetime_with_offset(offset_i32)?;
 
         // this is used to prevent an overflow when calling FixedOffset::from_local_datetime
         datetime
-            .checked_sub_signed(OldDuration::seconds(i64::from(offset.local_minus_utc())))
+            .checked_sub_signed(OldDuration::seconds(i64::from(offset_i32)))
             .ok_or(OUT_OF_RANGE)?;
 
-        match offset.from_local_datetime(&datetime) {
+        match fixed_offset.from_local_datetime(&datetime) {
             LocalResult::None => Err(IMPOSSIBLE),
             LocalResult::Single(t) => Ok(t),
             LocalResult::Ambiguous(..) => Err(NOT_ENOUGH),