From 9cfa3a8cb16f70a9022381b092407dc7eecf07b3 Mon Sep 17 00:00:00 2001
From: Yoshiya Hinosawa <stibium121@gmail.com>
Date: Fri, 22 Sep 2023 10:32:06 +0100
Subject: [PATCH] fix(datetime): fix dayOfYear when the timezone has DST

---
 .github/workflows/ci.yml | 7 +++++++
 datetime/day_of_year.ts  | 3 ++-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 3b81b7f68048..de16f04ac67e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -33,6 +33,13 @@ jobs:
       - name: Run tests canary
         run: deno task test
 
+      - name: Run timezone-dependent tests
+        run: |
+          TZ=Australia/Sydney deno test datetime
+          TZ=Europe/London deno test datetime
+          TZ=America/Toronto deno test datetime
+        if: matrix.os == 'ubuntu-22.04'
+
       - name: Type check browser compatible modules
         shell: bash
         run: deno task test:browser
diff --git a/datetime/day_of_year.ts b/datetime/day_of_year.ts
index 8de69faf7785..4b1bb059f868 100644
--- a/datetime/day_of_year.ts
+++ b/datetime/day_of_year.ts
@@ -22,7 +22,8 @@ export function dayOfYear(date: Date): number {
   const yearStart = new Date(date);
 
   yearStart.setFullYear(date.getFullYear(), 0, 0);
-  const diff = date.getTime() - yearStart.getTime();
+  const diff = (date.getTime() - date.getTimezoneOffset() * 60 * 1000) -
+    (yearStart.getTime() - yearStart.getTimezoneOffset() * 60 * 1000);
 
   return Math.floor(diff / DAY);
 }