feat(CupertinoDatePicker): add a two points time seperator column (flutter#163417)

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This pull request adds a flag attribute to cupertino date picker to
show/hide the two points seperator ":" between minutes and hours, this
feature add more customization to the cupertino date picker widget.
This new flag is by default set to false and it's an optional flag, the
default cupertino date picker behavior stays the same.

**CupertinoDatePIcker before:**
<img
src="https://github.com/user-attachments/assets/94f6722d-b466-4272-b90f-6ac3b358ba6d"
width="200"/> <img
src="https://github.com/user-attachments/assets/125386fd-2b7d-4988-a54e-8893a7f5907b"
width="200"/>

**CupertinoDatePicker After**
<img
src="https://github.com/user-attachments/assets/b5a703d9-6c43-410d-819f-f864e9dde159"
width="200"/> <img
src="https://github.com/user-attachments/assets/26e828dd-81c4-456f-b8c7-7c116d691060"
width="200"/>

*List which issues are fixed by this PR. You must list at least one
issue. An issue is not required if the PR fixes something trivial like a
typo.*
Here's the issue in question for more details about the proposal and the
use cases:
[Issue#163416](flutter#163416)

*If you had to change anything in the [flutter/tests] repo, include a
link to the migration guide as per the [breaking change policy].*

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Author: koukibadr

packages/flutter/lib/src/cupertino/date_picker.dart

@@ -207,6 +207,8 @@ enum _PickerColumnType {
   minute,
   // AM/PM column in time and dateAndTime mode.
   dayPeriod,
+  // Time separator column in time and dateAndTime mode.
+  timeSeparator,
 }
 
 /// A date picker widget in iOS style.
@@ -303,6 +305,7 @@ class CupertinoDatePicker extends StatefulWidget {
     this.dateOrder,
     this.backgroundColor,
     this.showDayOfWeek = false,
+    this.showTimeSeparator = false,
     this.itemExtent = _kItemExtent,
     this.selectionOverlayBuilder,
   }) : initialDateTime = initialDateTime ?? DateTime.now(),
@@ -353,6 +356,12 @@ class CupertinoDatePicker extends StatefulWidget {
        assert(
          (initialDateTime ?? DateTime.now()).minute % minuteInterval == 0,
          'initial minute is not divisible by minute interval',
+       ),
+       assert(
+         !showTimeSeparator ||
+             mode == CupertinoDatePickerMode.dateAndTime ||
+             mode == CupertinoDatePickerMode.time,
+         'showTimeSeparator is only supported in time or dateAndTime modes',
        );
 
   /// The mode of the date picker as one of [CupertinoDatePickerMode]. Defaults
@@ -435,6 +444,16 @@ class CupertinoDatePicker extends StatefulWidget {
   /// Defaults to false.
   final bool showDayOfWeek;
 
+  /// Whether to show the time separator between hour and minute in the time
+  /// [CupertinoDatePickerMode.time] and datetime [CupertinoDatePickerMode.dateAndTime]
+  /// picker modes.
+  ///
+  /// Throws an error if set to true in [CupertinoDatePickerMode.date]
+  /// and [CupertinoDatePickerMode.monthYear] mode.
+  ///
+  /// Defaults to false.
+  final bool showTimeSeparator;
+
   /// {@macro flutter.cupertino.picker.itemExtent}
   ///
   /// Defaults to a value that matches the default iOS date picker wheel.
@@ -549,6 +568,8 @@ class CupertinoDatePicker extends StatefulWidget {
         }
       case _PickerColumnType.year:
         longTexts.add(localizations.datePickerYear(2018));
+      case _PickerColumnType.timeSeparator:
+        longTexts.add(':');
     }
 
     assert(
@@ -1045,6 +1066,29 @@ class _CupertinoDatePickerDateTimeState extends State<CupertinoDatePicker> {
     );
   }
 
+  // Builds the time separator column.
+  Widget _buildTimeSeparatorWidget(
+    double offAxisFraction,
+    TransitionBuilder itemPositioningBuilder,
+    Widget? selectionOverlay,
+  ) {
+    return ExcludeSemantics(
+      child: CupertinoPicker(
+        offAxisFraction: offAxisFraction,
+        itemExtent: widget.itemExtent,
+        useMagnifier: _kUseMagnifier,
+        magnification: _kMagnification,
+        backgroundColor: widget.backgroundColor,
+        squeeze: _kSqueeze,
+        onSelectedItemChanged: (int index) {},
+        selectionOverlay: selectionOverlay,
+        children: List<Widget>.generate(1, (int index) {
+          return itemPositioningBuilder(context, Text(':', style: _themeTextStyle(context)));
+        }),
+      ),
+    );
+  }
+
   // One or more pickers have just stopped scrolling.
   void _pickerDidStopScrolling() {
     // Call setState to update the greyed out date/hour/minute/meridiem.
@@ -1118,6 +1162,11 @@ class _CupertinoDatePickerDateTimeState extends State<CupertinoDatePicker> {
             ? <_ColumnBuilder>[_buildMinutePicker, _buildHourPicker]
             : <_ColumnBuilder>[_buildHourPicker, _buildMinutePicker];
 
+    // Adds time separator column if the picker is showing time separator.
+    if (widget.showTimeSeparator) {
+      columnWidths.insert(1, _getEstimatedColumnWidth(_PickerColumnType.timeSeparator));
+      pickerBuilders.insert(1, _buildTimeSeparatorWidget);
+    }
     // Adds am/pm column if the picker is not using 24h format.
     if (!widget.use24hFormat) {
       switch (localizations.datePickerDateTimeOrder) {

packages/flutter/test/cupertino/date_picker_test.dart

@@ -2488,6 +2488,87 @@ void main() {
     expect(widths.indexOf(largestWidth), equals(1));
   }, skip: isBrowser); // https://github.com/flutter/flutter/issues/39998
 
+  test('showTimeSeparator is only supported in time or dateAndTime mode', () async {
+    expect(
+      () => CupertinoDatePicker(
+        mode: CupertinoDatePickerMode.time,
+        onDateTimeChanged: (DateTime _) {},
+        showTimeSeparator: true,
+      ),
+      returnsNormally,
+    );
+
+    expect(
+      () => CupertinoDatePicker(onDateTimeChanged: (DateTime _) {}, showTimeSeparator: true),
+      returnsNormally,
+    );
+
+    expect(
+      () => CupertinoDatePicker(
+        mode: CupertinoDatePickerMode.date,
+        onDateTimeChanged: (DateTime _) {},
+        showTimeSeparator: true,
+      ),
+      throwsA(
+        isA<AssertionError>().having(
+          (AssertionError e) => e.message ?? 'Unknown error',
+          'message',
+          contains('showTimeSeparator is only supported in time or dateAndTime modes'),
+        ),
+      ),
+    );
+
+    expect(
+      () => CupertinoDatePicker(
+        mode: CupertinoDatePickerMode.monthYear,
+        onDateTimeChanged: (DateTime _) {},
+        showTimeSeparator: true,
+      ),
+      throwsA(
+        isA<AssertionError>().having(
+          (AssertionError e) => e.message ?? 'Unknown error',
+          'message',
+          contains('showTimeSeparator is only supported in time or dateAndTime modes'),
+        ),
+      ),
+    );
+  });
+
+  testWidgets('Time separator widget should be rendered when flag is set to true', (
+    WidgetTester tester,
+  ) async {
+    await tester.pumpWidget(
+      CupertinoApp(
+        home: Center(
+          child: CupertinoDatePicker(
+            mode: CupertinoDatePickerMode.time,
+            onDateTimeChanged: (DateTime dateTime) {},
+            showTimeSeparator: true,
+          ),
+        ),
+      ),
+    );
+
+    expect(find.text(':'), findsOneWidget);
+  });
+
+  testWidgets('Time separator widget should not be rendered when flag is set to false', (
+    WidgetTester tester,
+  ) async {
+    await tester.pumpWidget(
+      CupertinoApp(
+        home: Center(
+          child: CupertinoDatePicker(
+            mode: CupertinoDatePickerMode.time,
+            onDateTimeChanged: (DateTime _) {},
+          ),
+        ),
+      ),
+    );
+
+    expect(find.text(':'), findsNothing);
+  });
+
   // Regression test for https://github.com/flutter/flutter/issues/161773
   testWidgets('CupertinoDatePicker date value baseline alignment', (WidgetTester tester) async {
     await tester.pumpWidget(