Reprise: Dropdown Menu layout respects menu items intrinsic sizes (#42033)

* Reprise: Dropdown Menu layout respects menu items intrinsic sizes

* updated per review feedback

* updated per review feedback

packages/flutter/test/material/dropdown_test.dart

@@ -1683,4 +1683,171 @@ void main() {
     verifyPaintedShadow(customPaintTwo, 24);
     debugDisableShadows = true;
   });
+
+  testWidgets('Variable size and oversized menu items', (WidgetTester tester) async {
+    final List<double> itemHeights = <double>[30, 40, 50, 60];
+    double dropdownValue = itemHeights[0];
+
+    Widget buildFrame() {
+      return MaterialApp(
+        home: Scaffold(
+          body: Center(
+            child: StatefulBuilder(
+              builder: (BuildContext context, StateSetter setState) {
+                return DropdownButton<double>(
+                  onChanged: (double value) {
+                    setState(() { dropdownValue = value; });
+                  },
+                  value: dropdownValue,
+                  itemHeight: null,
+                  items: itemHeights.map<DropdownMenuItem<double>>((double value) {
+                    return DropdownMenuItem<double>(
+                      key: ValueKey<double>(value),
+                      value: value,
+                      child: Center(
+                        child: Container(
+                          width: 100,
+                          height: value,
+                          color: Colors.blue,
+                        ),
+                      ),
+                    );
+                  }).toList(),
+                );
+              },
+            ),
+          ),
+        ),
+      );
+    }
+
+    final Finder dropdownIcon = find.byType(Icon);
+    final Finder item30 = find.byKey(const ValueKey<double>(30));
+    final Finder item40 = find.byKey(const ValueKey<double>(40));
+    final Finder item50 = find.byKey(const ValueKey<double>(50));
+    final Finder item60 = find.byKey(const ValueKey<double>(60));
+
+    // Only the DropdownButton is visible. It contains the selected item
+    // and a dropdown arrow icon.
+    await tester.pumpWidget(buildFrame());
+    expect(dropdownIcon, findsOneWidget);
+    expect(item30, findsOneWidget);
+
+    // All menu items have a minimum height of 48. The centers of the
+    // dropdown icon and the selected menu item are vertically aligned
+    // and horizontally adjacent.
+    expect(tester.getSize(item30), const Size(100, 48));
+    expect(tester.getCenter(item30).dy, tester.getCenter(dropdownIcon).dy);
+    expect(tester.getTopRight(item30).dx, tester.getTopLeft(dropdownIcon).dx);
+
+    // Show the popup menu.
+    await tester.tap(item30);
+    await tester.pumpAndSettle();
+
+    // Each item appears twice, once in the menu and once
+    // in the dropdown button's IndexedStack.
+    expect(item30.evaluate().length, 2);
+    expect(item40.evaluate().length, 2);
+    expect(item50.evaluate().length, 2);
+    expect(item60.evaluate().length, 2);
+
+    // Verify that the items have the expected sizes. The width of the items
+    // that appear in the menu is padded by 16 on the left and right.
+    expect(tester.getSize(item30.first), const Size(100, 48));
+    expect(tester.getSize(item40.first), const Size(100, 48));
+    expect(tester.getSize(item50.first), const Size(100, 50));
+    expect(tester.getSize(item60.first), const Size(100, 60));
+    expect(tester.getSize(item30.last), const Size(132, 48));
+    expect(tester.getSize(item40.last), const Size(132, 48));
+    expect(tester.getSize(item50.last), const Size(132, 50));
+    expect(tester.getSize(item60.last), const Size(132, 60));
+
+    // The vertical center of the selectedItem (item30) should
+    // line up with its button counterpart.
+    expect(tester.getCenter(item30.first).dy, tester.getCenter(item30.last).dy);
+
+    // The menu items should be arranged in a column.
+    expect(tester.getBottomLeft(item30.last), tester.getTopLeft(item40.last));
+    expect(tester.getBottomLeft(item40.last), tester.getTopLeft(item50.last));
+    expect(tester.getBottomLeft(item50.last), tester.getTopLeft(item60.last));
+
+    // Dismiss the menu by selecting item40 and then show the menu again.
+    await tester.tap(item40.last);
+    await tester.pumpAndSettle();
+    expect(dropdownValue, 40);
+    await tester.tap(item40.first);
+    await tester.pumpAndSettle();
+
+    // The vertical center of the selectedItem (item40) should
+    // line up with its button counterpart.
+    expect(tester.getCenter(item40.first).dy, tester.getCenter(item40.last).dy);
+  });
+
+  testWidgets('DropdownButton hint is selected item', (WidgetTester tester) async {
+    const double hintPaddingOffset = 8;
+    const List<String> itemValues = <String>['item0', 'item1', 'item2', 'item3'];
+    String selectedItem = 'item0';
+
+    Widget buildFrame() {
+      return MaterialApp(
+        home: Scaffold(
+          body: ButtonTheme(
+            alignedDropdown: true,
+            child: DropdownButtonHideUnderline(
+              child: Center(
+                child: StatefulBuilder(
+                  builder: (BuildContext context, StateSetter setState) {
+                    // The pretzel below is from an actual app. The price
+                    // of limited configurability is keeping this working.
+                    return DropdownButton<String>(
+                      isExpanded: true,
+                      elevation: 2,
+                      value: null,
+                      hint: LayoutBuilder(
+                        builder: (BuildContext context, BoxConstraints constraints) {
+                          // Stack with a positioned widget is used to override the
+                          // hard coded 16px margin in the dropdown code, so that
+                          // this hint aligns "properly" with the menu.
+                          return Stack(
+                            alignment: Alignment.topCenter,
+                            overflow: Overflow.visible,
+                            children: <Widget>[
+                              PositionedDirectional(
+                                width: constraints.maxWidth + hintPaddingOffset,
+                                start: -hintPaddingOffset,
+                                top: 4.0,
+                                child: Text('-$selectedItem-'),
+                              ),
+                            ],
+                          );
+                        },
+                      ),
+                      onChanged: (String value) {
+                        setState(() { selectedItem = value; });
+                      },
+                      icon: Container(),
+                      items: itemValues.map<DropdownMenuItem<String>>((String value) {
+                        return DropdownMenuItem<String>(
+                          child: Text(value),
+                        );
+                      }).toList(),
+                    );
+                  },
+                ),
+              ),
+            ),
+          ),
+        ),
+      );
+    }
+
+    await tester.pumpWidget(buildFrame());
+    expect(tester.getTopLeft(find.text('-item0-')).dx, 8);
+
+    // Show the popup menu.
+    await tester.tap(find.text('-item0-'));
+    await tester.pumpAndSettle();
+
+    expect(tester.getTopLeft(find.text('-item0-')).dx, 8);
+  });
 }