From 3bbdfb932a3ea3796077819801d6031885bb512d Mon Sep 17 00:00:00 2001
From: Erdem Ersoy <erdemersoy256@gmail.com>
Date: Mon, 16 Mar 2026 02:36:47 +0300
Subject: [PATCH] [SYSSETUP] Fix DST setting checkbox (#8622)

- [SYSSETUP] Fix DST setting checkbox

Fix DST setting checkbox. The checkbox should be disabled and unchecked on timezones DST not applied, the checkbox should be enabled and checked on timezones DST applied. JIRA issue: CORE-20406
---
 dll/win32/syssetup/wizard.c | 78 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 76 insertions(+), 2 deletions(-)

diff --git a/dll/win32/syssetup/wizard.c b/dll/win32/syssetup/wizard.c
index 46c79016f0a..e0744c7fa36 100644
--- a/dll/win32/syssetup/wizard.c
+++ b/dll/win32/syssetup/wizard.c
@@ -1682,6 +1682,53 @@ DestroyTimeZoneList(PSETUPDATA SetupData)
 }
 
 
+static BOOL
+HasDaylightSavingTime(PTIMEZONE_ENTRY Entry)
+{
+    /* If StandardDate.wMonth and DaylightDate.wMonth are zero,
+     * the timezone does not observe daylight saving time */
+    return (Entry->TimezoneInfo.StandardDate.wMonth != 0 &&
+            Entry->TimezoneInfo.DaylightDate.wMonth != 0);
+}
+
+static PTIMEZONE_ENTRY
+GetSelectedTimeZoneEntry(PSETUPDATA SetupData, DWORD dwEntryIndex)
+{
+    PTIMEZONE_ENTRY Entry;
+
+    for (Entry = SetupData->TimeZoneListHead; Entry != NULL; Entry = Entry->Next)
+    {
+        if (Entry->Index == dwEntryIndex)
+            return Entry;
+    }
+
+    return NULL;
+}
+
+static PTIMEZONE_ENTRY
+GetTimeZoneEntryByIndex(PSETUPDATA SetupData, DWORD dwComboIndex)
+{
+    PTIMEZONE_ENTRY Entry;
+    DWORD i;
+
+    for (Entry = SetupData->TimeZoneListHead, i = 0; Entry != NULL && i < dwComboIndex; i++, Entry = Entry->Next);
+
+    return Entry;
+}
+
+static VOID
+UpdateAutoDaylightCheckbox(HWND hwndDlg, PTIMEZONE_ENTRY Entry)
+{
+    BOOL bHasDST = (Entry != NULL && HasDaylightSavingTime(Entry));
+
+    /* Enable or disable the checkbox based on DST support */
+    EnableWindow(GetDlgItem(hwndDlg, IDC_AUTODAYLIGHT), bHasDST);
+
+    /* Check the checkbox only if DST is supported, otherwise uncheck it */
+    SendDlgItemMessage(hwndDlg, IDC_AUTODAYLIGHT, BM_SETCHECK,
+                       (WPARAM)(bHasDST ? BST_CHECKED : BST_UNCHECKED), 0);
+}
+
 static VOID
 ShowTimeZoneList(HWND hwnd, PSETUPDATA SetupData, DWORD dwEntryIndex)
 {
@@ -1855,6 +1902,9 @@ DateTimePageDlgProc(HWND hwndDlg,
     {
         case WM_INITDIALOG:
         {
+            DWORD dwEntryIndex;
+            PTIMEZONE_ENTRY Entry;
+
             /* Save pointer to the global setup data */
             SetupData = (PSETUPDATA)((LPPROPSHEETPAGE)lParam)->lParam;
             SetWindowLongPtr(hwndDlg, GWLP_USERDATA, (DWORD_PTR)SetupData);
@@ -1866,17 +1916,31 @@ DateTimePageDlgProc(HWND hwndDlg,
                 ShowTimeZoneList(GetDlgItem(hwndDlg, IDC_TIMEZONELIST),
                                  SetupData, SetupData->TimeZoneIndex);
 
-                if (!SetupData->DisableAutoDaylightTimeSet)
+                Entry = GetSelectedTimeZoneEntry(SetupData, SetupData->TimeZoneIndex);
+                if (!SetupData->DisableAutoDaylightTimeSet && Entry != NULL && HasDaylightSavingTime(Entry))
                 {
                     SendDlgItemMessage(hwndDlg, IDC_AUTODAYLIGHT, BM_SETCHECK, (WPARAM)BST_CHECKED, 0);
+                    EnableWindow(GetDlgItem(hwndDlg, IDC_AUTODAYLIGHT), TRUE);
+                }
+                else
+                {
+                    SendDlgItemMessage(hwndDlg, IDC_AUTODAYLIGHT, BM_SETCHECK, (WPARAM)BST_UNCHECKED, 0);
+                    EnableWindow(GetDlgItem(hwndDlg, IDC_AUTODAYLIGHT), FALSE);
                 }
             }
             else
             {
+                /* Get the default time zone index from the registry */
+                dwEntryIndex = (DWORD)-1;
+                GetTimeZoneListIndex(&dwEntryIndex);
+
                 ShowTimeZoneList(GetDlgItem(hwndDlg, IDC_TIMEZONELIST),
                                  SetupData, -1);
 
-                SendDlgItemMessage(hwndDlg, IDC_AUTODAYLIGHT, BM_SETCHECK, (WPARAM)BST_CHECKED, 0);
+                /* Set the auto-daylight checkbox based on whether
+                 * the selected timezone observes DST */
+                Entry = GetSelectedTimeZoneEntry(SetupData, dwEntryIndex);
+                UpdateAutoDaylightCheckbox(hwndDlg, Entry);
             }
             break;
         }
@@ -1893,6 +1957,16 @@ DateTimePageDlgProc(HWND hwndDlg,
             break;
         }
 
+        case WM_COMMAND:
+            if (HIWORD(wParam) == CBN_SELCHANGE && LOWORD(wParam) == IDC_TIMEZONELIST)
+            {
+                /* User changed the timezone selection */
+                DWORD dwIndex = (DWORD)SendDlgItemMessage(hwndDlg, IDC_TIMEZONELIST, CB_GETCURSEL, 0, 0);
+                PTIMEZONE_ENTRY Entry = GetTimeZoneEntryByIndex(SetupData, dwIndex);
+                UpdateAutoDaylightCheckbox(hwndDlg, Entry);
+            }
+            break;
+
         case WM_NOTIFY:
             switch (((LPNMHDR)lParam)->code)
             {