Reland "if chains → switch expressions" (#148634)

I did a goof a while back:

![late initialization error](https://github.com/flutter/flutter/assets/10457200/47dc423f-0dd0-4869-9a11-59cb7d1ea46e)

Now that [the bug is fixed](flutter/flutter@e9d4035), I think we're good to re-implement the if-chains cleanup!

Related:

- flutter/flutter#147793
- flutter/flutter#148556
- flutter/flutter#148548

dev/benchmarks/macrobenchmarks/lib/src/picture_cache.dart

@@ -209,13 +209,11 @@ class ListItem extends StatelessWidget {
   }
 
   String _convertCountToStr(int count) {
-    if (count < 10000) {
-      return count.toString();
-    } else if (count < 100000) {
-      return '${(count / 10000).toStringAsPrecision(2)}w';
-    } else {
-      return '${(count / 10000).floor()}w';
-    }
+    return switch (count) {
+      < 10000  => count.toString(),
+      < 100000 => '${(count / 10000).toStringAsPrecision(2)}w',
+      _        => '${(count / 10000).floor()}w',
+    };
   }
 
   Widget _buildUserInfo() {

dev/benchmarks/macrobenchmarks/lib/src/web/bench_build_material_checkbox.dart

@@ -31,13 +31,11 @@ class BenchBuildMaterialCheckbox extends WidgetBuildRecorder {
   }
 
   Row _buildRow() {
-    if (_isChecked == null) {
-      _isChecked = true;
-    } else if (_isChecked!) {
-      _isChecked = false;
-    } else {
-      _isChecked = null;
-    }
+    _isChecked = switch (_isChecked) {
+      null  => true,
+      true  => false,
+      false => null,
+    };
 
     return Row(
       children: List<Widget>.generate(10, (int i) {

dev/conductor/core/lib/src/start.dart

@@ -255,16 +255,14 @@ class StartContext extends Context {
     if (atBranchPoint) {
       return ReleaseType.BETA_INITIAL;
     }
-
-    if (releaseChannel == 'stable') {
-      if (lastVersion.type == VersionType.stable) {
-        return ReleaseType.STABLE_HOTFIX;
-      } else {
-        return ReleaseType.STABLE_INITIAL;
-      }
+    if (releaseChannel != 'stable') {
+      return ReleaseType.BETA_HOTFIX;
     }
 
-    return ReleaseType.BETA_HOTFIX;
+    return switch (lastVersion.type) {
+      VersionType.stable => ReleaseType.STABLE_HOTFIX,
+      VersionType.development || VersionType.gitDescribe || VersionType.latest => ReleaseType.STABLE_INITIAL,
+    };
   }
 
   Future<void> run() async {

dev/integration_tests/flutter_gallery/lib/demo/material/backdrop_demo.dart

@@ -307,13 +307,11 @@ class _BackdropDemoState extends State<BackdropDemo> with SingleTickerProviderSt
     }
 
     final double flingVelocity = details.velocity.pixelsPerSecond.dy / _backdropHeight;
-    if (flingVelocity < 0.0) {
-      _controller.fling(velocity: math.max(2.0, -flingVelocity));
-    } else if (flingVelocity > 0.0) {
-      _controller.fling(velocity: math.min(-2.0, -flingVelocity));
-    } else {
-      _controller.fling(velocity: _controller.value < 0.5 ? -2.0 : 2.0);
-    }
+    _controller.fling(velocity: switch (flingVelocity) {
+      < 0.0 => math.max(2.0, -flingVelocity),
+      > 0.0 => math.min(-2.0, -flingVelocity),
+      _ => _controller.value < 0.5 ? -2.0 : 2.0,
+    });
   }
 
   // Stacks a BackdropPanel, which displays the selected category, on top

dev/integration_tests/flutter_gallery/lib/demo/material/list_demo.dart

@@ -184,21 +184,18 @@ class _ListDemoState extends State<ListDemo> {
   }
 
   Widget buildListTile(BuildContext context, String item) {
-    Widget? secondary;
-    if (_itemType == _MaterialListType.twoLine) {
-      secondary = const Text('Additional item information.');
-    } else if (_itemType == _MaterialListType.threeLine) {
-      secondary = const Text(
-        'Even more additional list item information appears on line three.',
-      );
-    }
+    final String? subtitle = switch (_itemType) {
+      _MaterialListType.oneLine || _MaterialListType.oneLineWithAvatar || null => null,
+      _MaterialListType.twoLine   => 'Additional item information.',
+      _MaterialListType.threeLine => 'Even more additional list item information appears on line three.',
+    };
     return MergeSemantics(
       child: ListTile(
         isThreeLine: _itemType == _MaterialListType.threeLine,
         dense: _dense,
         leading: _showAvatars != null ? ExcludeSemantics(child: CircleAvatar(child: Text(item))) : null,
         title: Text('This item represents $item.'),
-        subtitle: secondary,
+        subtitle: subtitle != null ? Text(subtitle) : null,
         trailing: _showIcons != null ? Icon(Icons.info, color: Theme.of(context).disabledColor) : null,
       ),
     );

dev/integration_tests/flutter_gallery/lib/gallery/backdrop.dart

@@ -246,13 +246,11 @@ class _BackdropState extends State<Backdrop> with SingleTickerProviderStateMixin
     }
 
     final double flingVelocity = details.velocity.pixelsPerSecond.dy / _backdropHeight;
-    if (flingVelocity < 0.0) {
-      _controller!.fling(velocity: math.max(2.0, -flingVelocity));
-    } else if (flingVelocity > 0.0) {
-      _controller!.fling(velocity: math.min(-2.0, -flingVelocity));
-    } else {
-      _controller!.fling(velocity: _controller!.value < 0.5 ? -2.0 : 2.0);
-    }
+    _controller!.fling(velocity: switch (flingVelocity) {
+      < 0.0 => math.max(2.0, -flingVelocity),
+      > 0.0 => math.min(-2.0, -flingVelocity),
+      _ => _controller!.value < 0.5 ? -2.0 : 2.0,
+    });
   }
 
   void _toggleFrontLayer() {

dev/integration_tests/flutter_gallery/lib/gallery/syntax_highlighter.dart

@@ -337,22 +337,14 @@ class _HighlightSpan {
   }
 
   TextStyle? textStyle(SyntaxHighlighterStyle? style) {
-    if (type == _HighlightType.number) {
-      return style!.numberStyle;
-    } else if (type == _HighlightType.comment) {
-      return style!.commentStyle;
-    } else if (type == _HighlightType.keyword) {
-      return style!.keywordStyle;
-    } else if (type == _HighlightType.string) {
-      return style!.stringStyle;
-    } else if (type == _HighlightType.punctuation) {
-      return style!.punctuationStyle;
-    } else if (type == _HighlightType.klass) {
-      return style!.classStyle;
-    } else if (type == _HighlightType.constant) {
-      return style!.constantStyle;
-    } else {
-      return style!.baseStyle;
-    }
+    return switch (type) {
+      _HighlightType.number      => style!.numberStyle,
+      _HighlightType.comment     => style!.commentStyle,
+      _HighlightType.keyword     => style!.keywordStyle,
+      _HighlightType.string      => style!.stringStyle,
+      _HighlightType.punctuation => style!.punctuationStyle,
+      _HighlightType.klass       => style!.classStyle,
+      _HighlightType.constant    => style!.constantStyle,
+    };
   }
 }

dev/integration_tests/new_gallery/lib/demos/material/cards_demo.dart

@@ -416,20 +416,15 @@ class _CardsDemoState extends State<CardsDemo> with RestorationMixin {
             for (final TravelDestination destination in destinations(context))
               Container(
                 margin: const EdgeInsets.only(bottom: 8),
-                child: (destination.cardType == CardType.standard)
-                    ? TravelDestinationItem(destination: destination)
-                    : destination.cardType == CardType.tappable
-                        ? TappableTravelDestinationItem(
-                            destination: destination)
-                        : SelectableTravelDestinationItem(
-                            destination: destination,
-                            isSelected: _isSelected.value,
-                            onSelected: () {
-                              setState(() {
-                                _isSelected.value = !_isSelected.value;
-                              });
-                            },
-                          ),
+                child: switch (destination.cardType) {
+                  CardType.standard => TravelDestinationItem(destination: destination),
+                  CardType.tappable => TappableTravelDestinationItem(destination: destination),
+                  CardType.selectable => SelectableTravelDestinationItem(
+                    destination: destination,
+                    isSelected: _isSelected.value,
+                    onSelected: () => setState(() { _isSelected.value = !_isSelected.value; }),
+                  ),
+                },
               ),
           ],
         ),

dev/integration_tests/new_gallery/lib/demos/reference/two_pane_demo.dart

@@ -69,13 +69,10 @@ class TwoPaneDemoState extends State<TwoPaneDemo> with RestorationMixin {
         ),
         endPane: DetailsPane(
           selectedIndex: _currentIndex.value,
-          onClose: widget.type == TwoPaneDemoType.smallScreen
-              ? () {
-                  setState(() {
-                    _currentIndex.value = -1;
-                  });
-                }
-              : null,
+          onClose: switch (widget.type) {
+            TwoPaneDemoType.smallScreen => () => setState(() { _currentIndex.value = -1; }),
+            TwoPaneDemoType.foldable || TwoPaneDemoType.tablet => null,
+          },
         ),
       ),
     );
@@ -190,11 +187,11 @@ class SimulateScreen extends StatelessWidget {
         ),
         padding: const EdgeInsets.all(14),
         child: AspectRatio(
-          aspectRatio: type == TwoPaneDemoType.foldable
-              ? foldableAspectRatio
-              : type == TwoPaneDemoType.tablet
-                  ? tabletAspectRatio
-                  : singleScreenAspectRatio,
+          aspectRatio: switch (type) {
+            TwoPaneDemoType.foldable    => foldableAspectRatio,
+            TwoPaneDemoType.tablet      => tabletAspectRatio,
+            TwoPaneDemoType.smallScreen => singleScreenAspectRatio,
+          },
           child: LayoutBuilder(builder: (BuildContext context, BoxConstraints constraints) {
             final Size size = Size(constraints.maxWidth, constraints.maxHeight);
             final Size hingeSize = Size(size.width * hingeProportion, size.height);

dev/integration_tests/new_gallery/lib/pages/settings_icon/icon.dart

@@ -35,11 +35,11 @@ class _SettingsIconPainter extends CustomPainter {
   /// The icon is aligned to the bottom-start corner.
   void _computeCenterAndScaling(Size size) {
     _scaling = min(size.width / unitWidth, size.height / unitHeight);
-    _center = Directionality.of(context) == TextDirection.ltr
-        ? Offset(
-            unitWidth * _scaling / 2, size.height - unitHeight * _scaling / 2)
-        : Offset(size.width - unitWidth * _scaling / 2,
-            size.height - unitHeight * _scaling / 2);
+    final double dx = switch (Directionality.of(context)) {
+      TextDirection.rtl => size.width - unitWidth * _scaling / 2,
+      TextDirection.ltr => unitWidth * _scaling / 2,
+    };
+    _center = Offset(dx, size.height - unitHeight * _scaling / 2);
   }
 
   /// Transforms an offset in relative units into an offset in logical pixels.

dev/integration_tests/wide_gamut_test/integration_test/app_test.dart

@@ -103,21 +103,16 @@ bool _findBGR10Color(
   return foundDeepRed;
 }
 
-bool _findColor(List<Object?> result, List<double> color) {
+bool _findColor(List<dynamic> result, List<double> color) {
   expect(result, isNotNull);
   expect(result.length, 4);
-  final int width = (result[0] as int?)!;
-  final int height = (result[1] as int?)!;
-  final String format = (result[2] as String?)!;
-  if (format == 'MTLPixelFormatBGR10_XR') {
-    return _findBGR10Color((result[3] as Uint8List?)!, width, height, color);
-  } else if (format == 'MTLPixelFormatBGRA10_XR') {
-    return _findBGRA10Color((result[3] as Uint8List?)!, width, height, color);
-  } else if (format == 'MTLPixelFormatRGBA16Float') {
-    return _findRGBAF16Color((result[3] as Uint8List?)!, width, height, color);
-  } else {
-    fail('Unsupported pixel format: $format');
-  }
+  final [int width, int height, String format, Uint8List bytes] = result;
+  return switch (format) {
+    'MTLPixelFormatBGR10_XR'    => _findBGR10Color(bytes, width, height, color),
+    'MTLPixelFormatBGRA10_XR'   => _findBGRA10Color(bytes, width, height, color),
+    'MTLPixelFormatRGBA16Float' => _findRGBAF16Color(bytes, width, height, color),
+    _ => fail('Unsupported pixel format: $format'),
+  };
 }
 
 void main() {

dev/manual_tests/lib/density.dart

@@ -163,14 +163,12 @@ class _OptionsState extends State<Options> {
   double sliderValue = 0.0;
 
   String _densityToProfile(VisualDensity density) {
-    if (density == VisualDensity.standard) {
-      return 'standard';
-    } else if (density == VisualDensity.compact) {
-      return 'compact';
-    } else if (density == VisualDensity.comfortable) {
-      return 'comfortable';
-    }
-    return 'custom';
+    return switch (density) {
+      VisualDensity.standard    => 'standard',
+      VisualDensity.compact     => 'compact',
+      VisualDensity.comfortable => 'comfortable',
+      _ => 'custom',
+    };
   }
 
   VisualDensity _profileToDensity(String? profile) {

dev/manual_tests/lib/page_view.dart

@@ -70,9 +70,7 @@ class PageViewAppState extends State<PageViewApp> {
 
   void switchScrollDirection() {
     setState(() {
-      scrollDirection = (scrollDirection == Axis.vertical)
-        ? Axis.horizontal
-        : Axis.vertical;
+      scrollDirection = flipAxis(scrollDirection);
     });
   }
 
@@ -113,9 +111,7 @@ class PageViewAppState extends State<PageViewApp> {
   AppBar _buildAppBar() {
     return AppBar(
       title: const Text('PageView'),
-      actions: <Widget>[
-        Text(scrollDirection == Axis.horizontal ? 'horizontal' : 'vertical'),
-      ],
+      actions: <Widget>[Text(scrollDirection.name)],
     );
   }
 

dev/tools/gen_defaults/lib/template.dart

@@ -169,16 +169,13 @@ abstract class TokenTemplate {
   }
 
   String? _numToString(Object? value, [int? digits]) {
-    if (value == null) {
-      return null;
-    }
-    if (value is num) {
-      if (value == double.infinity) {
-        return 'double.infinity';
-      }
-      return digits == null ? value.toString() : value.toStringAsFixed(digits);
-    }
-    return getToken(value as String).toString();
+    return switch (value) {
+      null => null,
+      double.infinity => 'double.infinity',
+      num() when digits == null => value.toString(),
+      num() => value.toStringAsFixed(digits!),
+      _ => getToken(value as String).toString(),
+    };
   }
 
   /// Generate an elevation value for the given component token.

dev/tools/gen_keycodes/lib/utils.dart

@@ -205,18 +205,11 @@ Map<String, String> reverseMapOfListOfString(Map<String, List<String>> inMap, vo
 ///
 /// Will modify the input map.
 Map<String, dynamic> removeEmptyValues(Map<String, dynamic> map) {
-  return map..removeWhere((String key, dynamic value) {
-    if (value == null) {
-      return true;
-    }
-    if (value is Map<String, dynamic>) {
-      final Map<String, dynamic> regularizedMap = removeEmptyValues(value);
-      return regularizedMap.isEmpty;
-    }
-    if (value is Iterable<dynamic>) {
-      return value.isEmpty;
-    }
-    return false;
+  return map..removeWhere((String key, dynamic value) => switch (value) {
+    null => true,
+    Map<String, dynamic>() => removeEmptyValues(value).isEmpty,
+    Iterable<dynamic>() => value.isEmpty,
+    _ => false,
   });
 }
 

examples/api/lib/material/snack_bar/snack_bar.2.dart

@@ -123,13 +123,10 @@ class _SnackBarExampleState extends State<SnackBarExample> {
               const Text('Multi Line Text'),
               Switch(
                 value: _multiLine,
-                onChanged: _snackBarBehavior == SnackBarBehavior.fixed
-                    ? null
-                    : (bool value) {
-                        setState(() {
-                          _multiLine = !_multiLine;
-                        });
-                      },
+                onChanged: switch (_snackBarBehavior) {
+                  SnackBarBehavior.fixed || null => null,
+                  SnackBarBehavior.floating => (bool value) => setState(() { _multiLine = !_multiLine; }),
+                },
               ),
             ],
           ),
@@ -139,13 +136,10 @@ class _SnackBarExampleState extends State<SnackBarExample> {
               value: _sliderValue,
               divisions: 20,
               label: _sliderValue.toStringAsFixed(2),
-              onChanged: _snackBarBehavior == SnackBarBehavior.fixed
-                  ? null
-                  : (double value) {
-                      setState(() {
-                        _sliderValue = value;
-                      });
-                    },
+              onChanged: switch (_snackBarBehavior) {
+                SnackBarBehavior.fixed || null => null,
+                SnackBarBehavior.floating => (double value) => setState(() { _sliderValue = value; }),
+              },
             ),
           ]),
           const SizedBox(height: 16.0),