Implementing switch expressions [refactoring flutter/lib/src/] (#143496)

This PR is the 8�ʰ step in the journey to solve issue #136139 and make the entire Flutter repo more readable.

(previous pull requests: #139048, #139882, #141591, #142279, #142634, #142793, #143293)

I did a pass through all of `packages/flutter/lib/src/` and found a whole bunch of `switch` statements to improve: most of them were really simple, but many involved some thorough refactoring.

This pull request is just the complicated stuff. � I'll make comments to describe the changes, and then in the future there will be another PR (and it'll be much easier to review than this one).

Author: nate-thegrate

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

@@ -1013,36 +1013,27 @@ class CupertinoDynamicColor extends Color with Diagnosticable {
   /// brightness, normal contrast, [CupertinoUserInterfaceLevelData.base]
   /// elevation level).
   CupertinoDynamicColor resolveFrom(BuildContext context) {
-    Brightness brightness = Brightness.light;
-    if (_isPlatformBrightnessDependent) {
-      brightness = CupertinoTheme.maybeBrightnessOf(context) ?? Brightness.light;
-    }
-    bool isHighContrastEnabled = false;
-    if (_isHighContrastDependent) {
-      isHighContrastEnabled = MediaQuery.maybeHighContrastOf(context) ?? false;
-    }
+    final Brightness brightness = _isPlatformBrightnessDependent
+      ? CupertinoTheme.maybeBrightnessOf(context) ?? Brightness.light
+      : Brightness.light;
 
     final CupertinoUserInterfaceLevelData level = _isInterfaceElevationDependent
       ? CupertinoUserInterfaceLevel.maybeOf(context) ?? CupertinoUserInterfaceLevelData.base
       : CupertinoUserInterfaceLevelData.base;
 
-    final Color resolved;
-    switch (brightness) {
-      case Brightness.light:
-        switch (level) {
-          case CupertinoUserInterfaceLevelData.base:
-            resolved = isHighContrastEnabled ? highContrastColor : color;
-          case CupertinoUserInterfaceLevelData.elevated:
-            resolved = isHighContrastEnabled ? highContrastElevatedColor : elevatedColor;
-        }
-      case Brightness.dark:
-        switch (level) {
-          case CupertinoUserInterfaceLevelData.base:
-            resolved = isHighContrastEnabled ? darkHighContrastColor : darkColor;
-          case CupertinoUserInterfaceLevelData.elevated:
-            resolved = isHighContrastEnabled ? darkHighContrastElevatedColor : darkElevatedColor;
-        }
-    }
+    final bool highContrast = _isHighContrastDependent
+      && (MediaQuery.maybeHighContrastOf(context) ?? false);
+
+    final Color resolved = switch ((brightness, level, highContrast)) {
+      (Brightness.light, CupertinoUserInterfaceLevelData.base,     false) => color,
+      (Brightness.light, CupertinoUserInterfaceLevelData.base,     true)  => highContrastColor,
+      (Brightness.light, CupertinoUserInterfaceLevelData.elevated, false) => elevatedColor,
+      (Brightness.light, CupertinoUserInterfaceLevelData.elevated, true)  => highContrastElevatedColor,
+      (Brightness.dark,  CupertinoUserInterfaceLevelData.base,     false) => darkColor,
+      (Brightness.dark,  CupertinoUserInterfaceLevelData.base,     true)  => darkHighContrastColor,
+      (Brightness.dark,  CupertinoUserInterfaceLevelData.elevated, false) => darkElevatedColor,
+      (Brightness.dark,  CupertinoUserInterfaceLevelData.elevated, true)  => darkHighContrastElevatedColor,
+    };
 
     Element? debugContext;
     assert(() {

packages/flutter/lib/src/material/chip.dart

@@ -1925,10 +1925,11 @@ class _RenderChip extends RenderBox with SlottedContainerRenderObjectMixin<_Chip
       assert(sizes.content >= boxSize.height);
       switch (textDirection!) {
         case TextDirection.rtl:
-          return Offset(x - boxSize.width, (sizes.content - boxSize.height + sizes.densityAdjustment.dy) / 2.0);
+          x -= boxSize.width;
         case TextDirection.ltr:
-          return Offset(x, (sizes.content - boxSize.height + sizes.densityAdjustment.dy) / 2.0);
+          break;
       }
+      return Offset(x, (sizes.content - boxSize.height + sizes.densityAdjustment.dy) / 2.0);
     }
 
     // These are the offsets to the upper left corners of the boxes (including
@@ -2036,20 +2037,11 @@ class _RenderChip extends RenderBox with SlottedContainerRenderObjectMixin<_Chip
     if (enableAnimation.isCompleted) {
       return Colors.white;
     }
-    final ColorTween enableTween;
-    switch (theme.brightness) {
-      case Brightness.light:
-        enableTween = ColorTween(
-          begin: Colors.white.withAlpha(_kDisabledAlpha),
-          end: Colors.white,
-        );
-      case Brightness.dark:
-        enableTween = ColorTween(
-          begin: Colors.black.withAlpha(_kDisabledAlpha),
-          end: Colors.black,
-        );
-    }
-    return enableTween.evaluate(enableAnimation)!;
+    final Color color = switch (theme.brightness) {
+      Brightness.light => Colors.white,
+      Brightness.dark  => Colors.black,
+    };
+    return ColorTween(begin: color.withAlpha(_kDisabledAlpha), end: color).evaluate(enableAnimation)!;
   }
 
   void _paintCheck(Canvas canvas, Offset origin, double size) {

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

@@ -482,26 +482,20 @@ class _DatePickerDialogState extends State<DatePickerDialog> with RestorationMix
 
   Size _dialogSize(BuildContext context) {
     final bool useMaterial3 = Theme.of(context).useMaterial3;
+    final bool isCalendar = switch (_entryMode.value) {
+      DatePickerEntryMode.calendar || DatePickerEntryMode.calendarOnly => true,
+      DatePickerEntryMode.input || DatePickerEntryMode.inputOnly => false,
+    };
     final Orientation orientation = MediaQuery.orientationOf(context);
 
-    switch (_entryMode.value) {
-      case DatePickerEntryMode.calendar:
-      case DatePickerEntryMode.calendarOnly:
-        switch (orientation) {
-          case Orientation.portrait:
-            return useMaterial3 ? _calendarPortraitDialogSizeM3 : _calendarPortraitDialogSizeM2;
-          case Orientation.landscape:
-            return _calendarLandscapeDialogSize;
-        }
-      case DatePickerEntryMode.input:
-      case DatePickerEntryMode.inputOnly:
-        switch (orientation) {
-          case Orientation.portrait:
-            return useMaterial3 ? _inputPortraitDialogSizeM3 : _inputPortraitDialogSizeM2;
-          case Orientation.landscape:
-            return _inputLandscapeDialogSize;
-        }
-    }
+    return switch ((isCalendar, orientation)) {
+      (true,  Orientation.portrait) when useMaterial3 => _calendarPortraitDialogSizeM3,
+      (false, Orientation.portrait) when useMaterial3 => _inputPortraitDialogSizeM3,
+      (true,  Orientation.portrait)  => _calendarPortraitDialogSizeM2,
+      (false, Orientation.portrait)  => _inputPortraitDialogSizeM2,
+      (true,  Orientation.landscape) => _calendarLandscapeDialogSize,
+      (false, Orientation.landscape) => _inputLandscapeDialogSize,
+    };
   }
 
   static const Map<ShortcutActivator, Intent> _formShortcutMap = <ShortcutActivator, Intent>{

packages/flutter/lib/src/material/drawer.dart

@@ -662,8 +662,6 @@ class DrawerControllerState extends State<DrawerController> with SingleTickerPro
   }
 
   Widget _buildDrawer(BuildContext context) {
-    final bool drawerIsStart = widget.alignment == DrawerAlignment.start;
-    final TextDirection textDirection = Directionality.of(context);
     final bool isDesktop;
     switch (Theme.of(context).platform) {
       case TargetPlatform.android:
@@ -676,18 +674,13 @@ class DrawerControllerState extends State<DrawerController> with SingleTickerPro
         isDesktop = true;
     }
 
-    double? dragAreaWidth = widget.edgeDragWidth;
-    if (widget.edgeDragWidth == null) {
-      final EdgeInsets padding = MediaQuery.paddingOf(context);
-      switch (textDirection) {
-        case TextDirection.ltr:
-          dragAreaWidth = _kEdgeDragWidth +
-            (drawerIsStart ? padding.left : padding.right);
-        case TextDirection.rtl:
-          dragAreaWidth = _kEdgeDragWidth +
-            (drawerIsStart ? padding.right : padding.left);
-      }
-    }
+    final double dragAreaWidth = widget.edgeDragWidth
+      ?? _kEdgeDragWidth + switch ((widget.alignment, Directionality.of(context))) {
+        (DrawerAlignment.start, TextDirection.ltr) => MediaQuery.paddingOf(context).left,
+        (DrawerAlignment.start, TextDirection.rtl) => MediaQuery.paddingOf(context).right,
+        (DrawerAlignment.end,   TextDirection.rtl) => MediaQuery.paddingOf(context).left,
+        (DrawerAlignment.end,   TextDirection.ltr) => MediaQuery.paddingOf(context).right,
+      };
 
     if (_controller.status == AnimationStatus.dismissed) {
       if (widget.enableOpenDragGesture && !isDesktop) {

packages/flutter/lib/src/material/list_tile.dart

@@ -1377,55 +1377,27 @@ class _RenderListTile extends RenderBox with SlottedContainerRenderObjectMixin<_
       }
     }
 
-    final double leadingY;
-    final double trailingY;
-
-    switch (titleAlignment) {
-      case ListTileTitleAlignment.threeLine: {
-        if (isThreeLine) {
-          leadingY = _minVerticalPadding;
-          trailingY = _minVerticalPadding;
-        } else {
-          leadingY = (tileHeight - leadingSize.height) / 2.0;
-          trailingY = (tileHeight - trailingSize.height) / 2.0;
-        }
-        break;
-      }
-      case ListTileTitleAlignment.titleHeight: {
-        // This attempts to implement the redlines for the vertical position of the
-        // leading and trailing icons on the spec page:
-        //   https://m2.material.io/components/lists#specs
-        // The interpretation for these redlines is as follows:
-        //  - For large tiles (> 72dp), both leading and trailing controls should be
-        //    a fixed distance from top. As per guidelines this is set to 16dp.
-        //  - For smaller tiles, trailing should always be centered. Leading can be
-        //    centered or closer to the top. It should never be further than 16dp
-        //    to the top.
-        if (tileHeight > 72.0) {
-          leadingY = 16.0;
-          trailingY = 16.0;
-        } else {
-          leadingY = math.min((tileHeight - leadingSize.height) / 2.0, 16.0);
-          trailingY = (tileHeight - trailingSize.height) / 2.0;
-        }
-        break;
-      }
-      case ListTileTitleAlignment.top: {
-        leadingY = _minVerticalPadding;
-        trailingY = _minVerticalPadding;
-        break;
-      }
-      case ListTileTitleAlignment.center: {
-        leadingY = (tileHeight - leadingSize.height) / 2.0;
-        trailingY = (tileHeight - trailingSize.height) / 2.0;
-        break;
-      }
-      case ListTileTitleAlignment.bottom: {
-        leadingY = tileHeight - leadingSize.height - _minVerticalPadding;
-        trailingY = tileHeight - trailingSize.height - _minVerticalPadding;
-        break;
-      }
-    }
+    final double leadingDiff = tileHeight - leadingSize.height;
+    final double trailingDiff = tileHeight - trailingSize.height;
+
+    final (double leadingY, double trailingY) = switch (titleAlignment) {
+      ListTileTitleAlignment.threeLine when isThreeLine => (_minVerticalPadding, _minVerticalPadding),
+      ListTileTitleAlignment.threeLine => (leadingDiff / 2.0, trailingDiff / 2.0),
+      // This attempts to implement the redlines for the vertical position of the
+      // leading and trailing icons on the spec page:
+      //   https://m2.material.io/components/lists#specs
+      //
+      // For large tiles (> 72dp), both leading and trailing controls should be
+      // a fixed distance from top. As per guidelines this is set to 16dp.
+      ListTileTitleAlignment.titleHeight when tileHeight > 72.0 => (16.0, 16.0),
+      // For smaller tiles, trailing should always be centered. Leading can be
+      // centered or closer to the top. It should never be further than 16dp
+      // to the top.
+      ListTileTitleAlignment.titleHeight => (math.min(leadingDiff / 2.0, 16.0), trailingDiff / 2.0),
+      ListTileTitleAlignment.top => (_minVerticalPadding, _minVerticalPadding),
+      ListTileTitleAlignment.center => (leadingDiff / 2.0, trailingDiff / 2.0),
+      ListTileTitleAlignment.bottom => (leadingDiff - _minVerticalPadding, trailingDiff - _minVerticalPadding),
+    };
 
     switch (textDirection) {
       case TextDirection.rtl: {

packages/flutter/lib/src/rendering/sliver.dart

@@ -1729,22 +1729,11 @@ abstract class RenderSliver extends RenderObject {
 /// Mixin for [RenderSliver] subclasses that provides some utility functions.
 mixin RenderSliverHelpers implements RenderSliver {
   bool _getRightWayUp(SliverConstraints constraints) {
-    bool rightWayUp;
-    switch (constraints.axisDirection) {
-      case AxisDirection.up:
-      case AxisDirection.left:
-        rightWayUp = false;
-      case AxisDirection.down:
-      case AxisDirection.right:
-        rightWayUp = true;
-    }
-    switch (constraints.growthDirection) {
-      case GrowthDirection.forward:
-        break;
-      case GrowthDirection.reverse:
-        rightWayUp = !rightWayUp;
-    }
-    return rightWayUp;
+    final bool reversed = axisDirectionIsReversed(constraints.axisDirection);
+    return switch (constraints.growthDirection) {
+      GrowthDirection.forward => !reversed,
+      GrowthDirection.reverse => reversed,
+    };
   }
 
   /// Utility function for [hitTestChildren] for use when the children are

packages/flutter/lib/src/rendering/sliver_group.dart

@@ -37,14 +37,11 @@ class RenderSliverCrossAxisGroup extends RenderSliver with ContainerRenderObject
 
   @override
   double childCrossAxisPosition(RenderSliver child) {
-    switch (constraints.axisDirection) {
-      case AxisDirection.up:
-      case AxisDirection.down:
-        return (child.parentData! as SliverPhysicalParentData).paintOffset.dx;
-      case AxisDirection.left:
-      case AxisDirection.right:
-        return (child.parentData! as SliverPhysicalParentData).paintOffset.dy;
-    }
+    final Offset paintOffset = (child.parentData! as SliverPhysicalParentData).paintOffset;
+    return switch (constraints.axis) {
+      Axis.vertical   => paintOffset.dx,
+      Axis.horizontal => paintOffset.dy,
+    };
   }
 
   @override

packages/flutter/lib/src/rendering/viewport.dart

@@ -925,22 +925,13 @@ abstract class RenderViewportBase<ParentDataClass extends ContainerParentDataMix
     assert(child is RenderSliver);
     final RenderSliver sliver = child as RenderSliver;
 
-    final double targetMainAxisExtent;
     // The scroll offset of `rect` within `child`.
-    switch (applyGrowthDirectionToAxisDirection(axisDirection, growthDirection)) {
-      case AxisDirection.up:
-        leadingScrollOffset += pivotExtent - rectLocal.bottom;
-        targetMainAxisExtent = rectLocal.height;
-      case AxisDirection.right:
-        leadingScrollOffset += rectLocal.left;
-        targetMainAxisExtent = rectLocal.width;
-      case AxisDirection.down:
-        leadingScrollOffset += rectLocal.top;
-        targetMainAxisExtent = rectLocal.height;
-      case AxisDirection.left:
-        leadingScrollOffset += pivotExtent - rectLocal.right;
-        targetMainAxisExtent = rectLocal.width;
-    }
+    leadingScrollOffset += switch (applyGrowthDirectionToAxisDirection(axisDirection, growthDirection)) {
+      AxisDirection.up    => pivotExtent - rectLocal.bottom,
+      AxisDirection.left  => pivotExtent - rectLocal.right,
+      AxisDirection.right => rectLocal.left,
+      AxisDirection.down  => rectLocal.top,
+    };
 
     // So far leadingScrollOffset is the scroll offset of `rect` in the `child`
     // sliver's sliver coordinate system. The sign of this value indicates
@@ -973,35 +964,26 @@ abstract class RenderViewportBase<ParentDataClass extends ContainerParentDataMix
         // If child's growth direction is reverse, when viewport.offset is
         // `leadingScrollOffset`, it is positioned just outside of the leading
         // edge of the viewport.
-        switch (axis) {
-          case Axis.vertical:
-            leadingScrollOffset -= targetRect.height;
-          case Axis.horizontal:
-            leadingScrollOffset -= targetRect.width;
-        }
+        leadingScrollOffset -= switch (axis) {
+          Axis.vertical   => targetRect.height,
+          Axis.horizontal => targetRect.width,
+        };
     }
 
-    final double mainAxisExtent;
-    switch (axis) {
-      case Axis.horizontal:
-        mainAxisExtent = size.width - extentOfPinnedSlivers;
-      case Axis.vertical:
-        mainAxisExtent = size.height - extentOfPinnedSlivers;
-    }
+    final double mainAxisExtentDifference = switch (axis) {
+      Axis.horizontal => size.width - extentOfPinnedSlivers - rectLocal.width,
+      Axis.vertical => size.height - extentOfPinnedSlivers - rectLocal.height,
+    };
 
-    final double targetOffset = leadingScrollOffset - (mainAxisExtent - targetMainAxisExtent) * alignment;
+    final double targetOffset = leadingScrollOffset - mainAxisExtentDifference * alignment;
     final double offsetDifference = offset.pixels - targetOffset;
 
-    switch (axisDirection) {
-      case AxisDirection.down:
-        targetRect = targetRect.translate(0.0, offsetDifference);
-      case AxisDirection.right:
-        targetRect = targetRect.translate(offsetDifference, 0.0);
-      case AxisDirection.up:
-        targetRect = targetRect.translate(0.0, -offsetDifference);
-      case AxisDirection.left:
-        targetRect = targetRect.translate(-offsetDifference, 0.0);
-    }
+    targetRect = switch (axisDirection) {
+      AxisDirection.up    => targetRect.translate(0.0, -offsetDifference),
+      AxisDirection.down  => targetRect.translate(0.0,  offsetDifference),
+      AxisDirection.left  => targetRect.translate(-offsetDifference, 0.0),
+      AxisDirection.right => targetRect.translate( offsetDifference, 0.0),
+    };
 
     return RevealedOffset(offset: targetOffset, rect: targetRect);
   }