fix: incorrect timezone correction for DST dates, fixes #604

.github/workflows/check.yml

@@ -20,7 +20,9 @@ jobs:
       - name: Test
         run: |
           npm run lint
-          npm run test
+          TZ=Etc/GMT npm run test
+          TZ=Asia/Shanghai npm run test
+          TZ=America/New_York npm run test
       - name: Coverage
         uses: coverallsapp/[email protected]
         with:

src/util/liquid-date.ts

@@ -14,6 +14,6 @@ export interface LiquidDate {
   getMonth(): number;
   getFullYear(): number;
   getTimezoneOffset(): number;
-  toLocaleTimeString(locale?: string, init?: any): string;
-  toLocaleDateString(locale?: string, init?: any): string;
+  toLocaleTimeString(): string;
+  toLocaleDateString(): string;
 }

src/util/timezone-date.spec.ts

@@ -24,6 +24,12 @@ describe('TimezoneDate', () => {
     const date = new TimezoneDate('2021-12-07T00:00:00.001+08:00', -480)
     expect(date.getDay()).toBe(2)
   })
+  it('should support .toLocaleString()', () => {
+    const date = new TimezoneDate('2021-10-06T00:00:00.001+00:00', -480)
+    expect(date.toLocaleString('en-US')).toMatch(/8:00:00\sAM$/)
+    expect(date.toLocaleString('en-US', { timeZone: 'America/New_York' })).toMatch(/8:00:00\sPM$/)
+    expect(() => date.toLocaleString()).not.toThrow()
+  })
   it('should support .toLocaleTimeString()', () => {
     const date = new TimezoneDate('2021-10-06T00:00:00.001+00:00', -480)
     expect(date.toLocaleTimeString('en-US')).toMatch(/^8:00:00\sAM$/)

src/util/timezone-date.ts

@@ -2,7 +2,6 @@ import { LiquidDate } from './liquid-date'
 
 // one minute in milliseconds
 const OneMinute = 60000
-const hostTimezoneOffset = new Date().getTimezoneOffset()
 const ISO8601_TIMEZONE_PATTERN = /([zZ]|([+-])(\d{2}):(\d{2}))$/
 
 /**
@@ -22,7 +21,7 @@ export class TimezoneDate implements LiquidDate {
       : new Date(init)
     this.timezoneOffset = timezoneOffset
 
-    const diff = (hostTimezoneOffset - this.timezoneOffset) * OneMinute
+    const diff = (this.date.getTimezoneOffset() - this.timezoneOffset) * OneMinute
     const time = this.date.getTime() + diff
     this.displayDate = new Date(time)
   }
@@ -56,22 +55,16 @@ export class TimezoneDate implements LiquidDate {
     return this.displayDate.getFullYear()
   }
   toLocaleString (locale?: string, init?: any) {
-    if (locale === undefined) {
-      return this.displayDate.toLocaleString(locale)
+    if (init?.timeZone) {
+      return this.date.toLocaleString(locale, init)
     }
-    return this.date.toLocaleString(locale, init)
+    return this.displayDate.toLocaleString(locale, init)
   }
-  toLocaleTimeString (locale?: string, init?: any) {
-    if (locale === undefined) {
-      return this.displayDate.toLocaleTimeString(locale)
-    }
-    return this.date.toLocaleTimeString(locale, init)
+  toLocaleTimeString (locale?: string) {
+    return this.displayDate.toLocaleTimeString(locale)
   }
-  toLocaleDateString (locale?: string, init?: any) {
-    if (locale === undefined) {
-      return this.displayDate.toLocaleDateString(locale)
-    }
-    return this.date.toLocaleDateString(locale, init)
+  toLocaleDateString (locale?: string) {
+    return this.displayDate.toLocaleDateString(locale)
   }
   getTimezoneOffset () {
     return this.timezoneOffset!

test/e2e/issues.spec.ts

@@ -406,4 +406,24 @@ describe('Issues', function () {
     const html = await engine.parseAndRender(template)
     expect(html).toContain('true')
   })
+  it('#604 date filter appears to add DST correction to UTC dates', () => {
+    const engine = new Liquid({
+      timezoneOffset: 'Etc/GMT'
+    })
+
+    const html = engine.parseAndRenderSync(
+      '{{ "2023-04-05T12:00:00Z" | date: "%Y-%m-%dT%H:%M:%S%z", "Etc/GMT" }}' +
+      '{{ "2023-01-05T12:00:00Z" | date: "%Y-%m-%dT%H:%M:%S%z", 0 }}' +
+      '{{ "2023-01-05T12:00:00Z" | date: "%Y-%m-%dT%H:%M:%S%z", "Etc/GMT" }}' +
+      '{{ "2023-01-05T12:00:00Z" | date: "%Y-%m-%dT%H:%M:%S%z" }}' +
+      '{{ "2023-01-05T12:00:00+0000" | date: "%Y-%m-%dT%H:%M:%S%z", 0 }}'
+    )
+    const expected =
+      '2023-04-05T12:00:00+0000' +
+      '2023-01-05T12:00:00+0000' +
+      '2023-01-05T12:00:00+0000' +
+      '2023-01-05T12:00:00+0000' +
+      '2023-01-05T12:00:00+0000'
+    expect(html).toEqual(expected)
+  })
 })