Fix single ToggleButton border painting bugs (#73780)

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

@@ -424,7 +424,9 @@ class ToggleButtons extends StatelessWidget {
       ?? toggleButtonsTheme.borderRadius
       ?? BorderRadius.zero;
 
-    if (direction == Axis.horizontal) {
+    if (length == 1) {
+      return resultingBorderRadius;
+    } else if (direction == Axis.horizontal) {
       if (_isFirstButton(index, length, textDirection)) {
         return BorderRadius.only(
           topLeft: resultingBorderRadius.topLeft,
@@ -466,7 +468,14 @@ class ToggleButtons extends StatelessWidget {
       ?? toggleButtonsTheme.borderWidth
       ?? _defaultBorderWidth;
 
-    if (direction == Axis.horizontal) {
+    if (length == 1) {
+      return BorderRadius.only(
+        topLeft: resultingBorderRadius.topLeft - Radius.circular(resultingBorderWidth / 2.0),
+        bottomLeft: resultingBorderRadius.bottomLeft - Radius.circular(resultingBorderWidth / 2.0),
+        topRight: resultingBorderRadius.topRight - Radius.circular(resultingBorderWidth / 2.0),
+        bottomRight: resultingBorderRadius.bottomRight - Radius.circular(resultingBorderWidth / 2.0),
+      );
+    } else if (direction == Axis.horizontal) {
       if (_isFirstButton(index, length, textDirection)) {
         return BorderRadius.only(
           topLeft: resultingBorderRadius.topLeft - Radius.circular(resultingBorderWidth / 2.0),
@@ -1269,11 +1278,12 @@ class _SelectToggleButtonRenderObject extends RenderShiftedBox {
     const double sweepAngle = math.pi / 2.0;
     final RRect rrect = RRect.fromRectAndCorners(
       center,
-      topLeft: borderRadius.topLeft,
-      topRight: borderRadius.topRight,
-      bottomLeft: borderRadius.bottomLeft,
-      bottomRight: borderRadius.bottomRight,
+      topLeft: (borderRadius.topLeft.x * borderRadius.topLeft.y != 0.0) ? borderRadius.topLeft : Radius.zero,
+      topRight: (borderRadius.topRight.x * borderRadius.topRight.y != 0.0) ? borderRadius.topRight : Radius.zero,
+      bottomLeft: (borderRadius.bottomLeft.x * borderRadius.bottomLeft.y != 0.0) ? borderRadius.bottomLeft : Radius.zero,
+      bottomRight: (borderRadius.bottomRight.x * borderRadius.bottomRight.y != 0.0) ? borderRadius.bottomRight : Radius.zero,
     ).scaleRadii();
+
     final Rect tlCorner = Rect.fromLTWH(
       rrect.left,
       rrect.top,
@@ -1299,8 +1309,25 @@ class _SelectToggleButtonRenderObject extends RenderShiftedBox {
       rrect.brRadiusY * 2,
     );
 
+    final Paint leadingPaint = leadingBorderSide.toPaint();
+    // Only one button.
+    if (isFirstButton && isLastButton) {
+      final Path leadingPath = Path();
+      final double startX = (rrect.brRadiusX == 0.0) ? outer.right : rrect.right - rrect.brRadiusX;
+      leadingPath..moveTo(startX, rrect.bottom)
+        ..lineTo(rrect.left + rrect.blRadiusX, rrect.bottom)
+        ..addArc(blCorner, math.pi / 2.0, sweepAngle)
+        ..lineTo(rrect.left, rrect.top + rrect.tlRadiusY)
+        ..addArc(tlCorner, math.pi, sweepAngle)
+        ..lineTo(rrect.right - rrect.trRadiusX, rrect.top)
+        ..addArc(trCorner, math.pi * 3.0 / 2.0, sweepAngle)
+        ..lineTo(rrect.right, rrect.bottom - rrect.brRadiusY)
+        ..addArc(brCorner, 0, sweepAngle);
+      context.canvas.drawPath(leadingPath, leadingPaint);
+      return;
+    }
+
     if (direction == Axis.horizontal) {
-      final Paint leadingPaint = leadingBorderSide.toPaint();
       switch (textDirection) {
         case TextDirection.ltr:
           if (isLastButton) {
@@ -1339,7 +1366,6 @@ class _SelectToggleButtonRenderObject extends RenderShiftedBox {
               ..lineTo(outer.right - rrect.trRadiusX, rrect.top)
               ..moveTo(rrect.left + borderSide.width / 2.0 + rrect.tlRadiusX, rrect.bottom)
               ..lineTo(outer.right - rrect.trRadiusX, rrect.bottom);
-
             context.canvas.drawPath(horizontalPaths, horizontalPaint);
           }
           break;
@@ -1385,14 +1411,12 @@ class _SelectToggleButtonRenderObject extends RenderShiftedBox {
           break;
       }
     } else {
-      final Paint leadingPaint = leadingBorderSide.toPaint();
       switch (verticalDirection) {
         case VerticalDirection.down:
           if (isLastButton) {
             final Path topPath = Path();
             topPath..moveTo(outer.left, outer.top + leadingBorderSide.width / 2)
               ..lineTo(outer.right, outer.top + leadingBorderSide.width / 2);
-
             context.canvas.drawPath(topPath, leadingPaint);
 
             final Paint endingPaint = trailingBorderSide.toPaint();
@@ -1403,7 +1427,6 @@ class _SelectToggleButtonRenderObject extends RenderShiftedBox {
               ..lineTo(rrect.right - rrect.blRadiusX, rrect.bottom)
               ..addArc(brCorner, math.pi / 2.0, -sweepAngle)
               ..lineTo(rrect.right, rrect.top + leadingBorderSide.width / 2.0);
-
             context.canvas.drawPath(endingPath, endingPaint);
           } else if (isFirstButton) {
             final Path leadingPath = Path();
@@ -1413,7 +1436,6 @@ class _SelectToggleButtonRenderObject extends RenderShiftedBox {
               ..lineTo(rrect.right - rrect.trRadiusX, rrect.top)
               ..addArc(trCorner, math.pi * 3.0 / 2.0, sweepAngle)
               ..lineTo(rrect.right, outer.bottom);
-
             context.canvas.drawPath(leadingPath, leadingPaint);
           } else {
             final Path topPath = Path();
@@ -1427,7 +1449,6 @@ class _SelectToggleButtonRenderObject extends RenderShiftedBox {
               ..lineTo(rrect.left, outer.bottom)
               ..moveTo(rrect.right, outer.top + leadingBorderSide.width)
               ..lineTo(rrect.right, outer.bottom);
-
             context.canvas.drawPath(paths, paint);
           }
           break;

packages/flutter/test/material/toggle_buttons_test.dart

@@ -891,13 +891,6 @@ void main() {
       expect(
         toggleButtonRenderObject,
         paints
-          // trailing side
-          ..path(
-            style: PaintingStyle.stroke,
-            color: theme.colorScheme.onSurface.withOpacity(0.12),
-            strokeWidth: defaultBorderWidth,
-          )
-          // leading side, top and bottom
           ..path(
             style: PaintingStyle.stroke,
             color: theme.colorScheme.onSurface.withOpacity(0.12),
@@ -925,13 +918,6 @@ void main() {
       expect(
         toggleButtonRenderObject,
         paints
-          // trailing side
-          ..path(
-            style: PaintingStyle.stroke,
-            color: theme.colorScheme.onSurface.withOpacity(0.12),
-            strokeWidth: defaultBorderWidth,
-          )
-          // leading side, top and bottom
           ..path(
             style: PaintingStyle.stroke,
             color: theme.colorScheme.onSurface.withOpacity(0.12),
@@ -958,13 +944,6 @@ void main() {
       expect(
         toggleButtonRenderObject,
         paints
-          // trailing side
-          ..path(
-            style: PaintingStyle.stroke,
-            color: theme.colorScheme.onSurface.withOpacity(0.12),
-            strokeWidth: defaultBorderWidth,
-          )
-          // leading side, top and bottom
           ..path(
             style: PaintingStyle.stroke,
             color: theme.colorScheme.onSurface.withOpacity(0.12),
@@ -1005,13 +984,6 @@ void main() {
       expect(
         toggleButtonRenderObject,
         paints
-          // trailing side
-          ..path(
-            style: PaintingStyle.stroke,
-            color: borderColor,
-            strokeWidth: customWidth,
-          )
-          // leading side, top and bottom
           ..path(
             style: PaintingStyle.stroke,
             color: borderColor,
@@ -1041,13 +1013,6 @@ void main() {
       expect(
         toggleButtonRenderObject,
         paints
-          // trailing side
-          ..path(
-            style: PaintingStyle.stroke,
-            color: selectedBorderColor,
-            strokeWidth: customWidth,
-          )
-          // leading side, top and bottom
           ..path(
             style: PaintingStyle.stroke,
             color: selectedBorderColor,
@@ -1076,13 +1041,6 @@ void main() {
       expect(
         toggleButtonRenderObject,
         paints
-          // trailing side
-          ..path(
-            style: PaintingStyle.stroke,
-            color: disabledBorderColor,
-            strokeWidth: customWidth,
-          )
-          // leading side, top and bottom
           ..path(
             style: PaintingStyle.stroke,
             color: disabledBorderColor,
@@ -1510,6 +1468,80 @@ void main() {
     },
   );
 
+  // Regression test for https://github.com/flutter/flutter/issues/73725
+  testWidgets('Border radius paint test when there is only one button', (WidgetTester tester) async {
+    final ThemeData theme = ThemeData();
+    await tester.pumpWidget(
+      Material(
+        child: boilerplate(
+          child: RepaintBoundary(
+            child: ToggleButtons(
+              borderRadius: const BorderRadius.all(Radius.circular(7.0)),
+              isSelected: const <bool>[true],
+              onPressed: (int index) {},
+              children: const <Widget>[
+                Text('First child'),
+              ],
+            ),
+          ),
+        ),
+      ),
+    );
+
+    // The only button should be laid out at the center of the screen.
+    expect(tester.getCenter(find.text('First child')), const Offset(400.0, 300.0));
+
+    final List<RenderObject> toggleButtonRenderObject = tester.allRenderObjects.where((RenderObject object) {
+      return object.runtimeType.toString() == '_SelectToggleButtonRenderObject';
+    }).toSet().toList();
+
+    // The first button paints the left, top and right sides with a path.
+    expect(
+      toggleButtonRenderObject[0],
+      paints
+      // left side, top and right - enabled.
+        ..path(
+          style: PaintingStyle.stroke,
+          color: theme.colorScheme.onSurface.withOpacity(0.12),
+          strokeWidth: _defaultBorderWidth,
+        ),
+    );
+
+    await expectLater(
+      find.byType(RepaintBoundary),
+      matchesGoldenFile('toggle_buttons.oneButton.boardsPaint.png'),
+    );
+  });
+
+  testWidgets('Border radius paint test when Radius.x or Radius.y equal 0.0', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      Material(
+        child: boilerplate(
+          child: RepaintBoundary(
+            child: ToggleButtons(
+              borderRadius: const BorderRadius.only(
+                topRight: Radius.elliptical(10, 0),
+                topLeft: Radius.elliptical(0, 10),
+                bottomRight: Radius.elliptical(0, 10),
+                bottomLeft: Radius.elliptical(10, 0),
+              ),
+              isSelected: const <bool>[true],
+              onPressed: (int index) {},
+              children: const <Widget>[
+                Text('First child'),
+              ],
+            ),
+          ),
+        ),
+      ),
+    );
+
+    await expectLater(
+      find.byType(RepaintBoundary),
+      matchesGoldenFile('toggle_buttons.oneButton.boardsPaint2.png'),
+    );
+  });
+
   testWidgets('ToggleButtons implements debugFillProperties', (WidgetTester tester) async {
     final DiagnosticPropertiesBuilder builder = DiagnosticPropertiesBuilder();
 

packages/flutter/test/material/toggle_buttons_theme_test.dart

@@ -476,13 +476,6 @@ void main() {
       expect(
         toggleButtonRenderObject,
         paints
-          // trailing side
-          ..path(
-            style: PaintingStyle.stroke,
-            color: borderColor,
-            strokeWidth: customWidth,
-          )
-          // leading side, top and bottom
           ..path(
             style: PaintingStyle.stroke,
             color: borderColor,
@@ -516,13 +509,6 @@ void main() {
       expect(
         toggleButtonRenderObject,
         paints
-          // trailing side
-          ..path(
-            style: PaintingStyle.stroke,
-            color: selectedBorderColor,
-            strokeWidth: customWidth,
-          )
-          // leading side, top and bottom
           ..path(
             style: PaintingStyle.stroke,
             color: selectedBorderColor,
@@ -555,13 +541,6 @@ void main() {
       expect(
         toggleButtonRenderObject,
         paints
-          // trailing side
-          ..path(
-            style: PaintingStyle.stroke,
-            color: disabledBorderColor,
-            strokeWidth: customWidth,
-          )
-          // leading side, top and bottom
           ..path(
             style: PaintingStyle.stroke,
             color: disabledBorderColor,