From d71e381091b3893148d3ac12406eacbc33f1debc Mon Sep 17 00:00:00 2001
From: Asifur Rahaman Meeru <asifur.rahaman@meeru.dev>
Date: Fri, 28 Aug 2026 09:47:17 +0600
Subject: [PATCH] fix(offset): correct ADT, AST, BST and GST to GNU's values

---
 src/items/offset.rs | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/src/items/offset.rs b/src/items/offset.rs
index 5ccdc10..a243d27 100644
--- a/src/items/offset.rs
+++ b/src/items/offset.rs
@@ -331,7 +331,7 @@ fn timezone_name_to_offset(input: &str) -> ModalResult<Offset> {
         "i" => Ok("+9"),
         "hst" => Ok("-10"),
         "h" => Ok("+8"),
-        "gst" => Ok("+4"),
+        "gst" => Ok("+10"),
         "gmt" => Ok("+0"),
         "g" => Ok("+7"),
         "f" => Ok("+6"),
@@ -350,15 +350,15 @@ fn timezone_name_to_offset(input: &str) -> ModalResult<Offset> {
         "cdt" => Ok("-5"),
         "cat" => Ok("+2"),
         "c" => Ok("+3"),
-        "bst" => Ok("+6"),
+        "bst" => Ok("+1"),
         "brt" => Ok("-3"),
         "brst" => Ok("-2"),
         "b" => Ok("+2"),
-        "ast" => Ok("-3"),
+        "ast" => Ok("-4"),
         "art" => Ok("-3"),
         "akst" => Ok("-9"),
         "akdt" => Ok("-8"),
-        "adt" => Ok("+4"),
+        "adt" => Ok("-3"),
         "a" => Ok("+1"),
         _ => Err(ErrMode::Backtrack(ContextError::new())),
     }?;
@@ -457,6 +457,14 @@ mod tests {
             ("mesz", off(false, 2, 0)),
             ("mest", off(false, 2, 0)),
             ("kst", off(false, 9, 0)),
+            // Each of these resolved to a different real meaning of the
+            // abbreviation than the one GNU date uses, e.g. BST as Bangladesh
+            // Standard Time rather than British Summer Time.
+            ("adt", off(true, 3, 0)),   // Atlantic Daylight, was +4
+            ("ast", off(true, 4, 0)),   // Atlantic Standard, was -3
+            ("bst", off(false, 1, 0)),  // British Summer, was +6
+            ("gst", off(false, 10, 0)), // Guam Standard, was +4
+            ("sst", off(true, 11, 0)),
             ("z123", off(false, 0, 0)), // space separator can be ignored if immediately followed by digits (GNU date behavior)
         ] {
             let mut s = input;