Fix error message for unbounded viewports (flutter#123035)

Fix error message for unbounded viewports

Author: Piinks

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

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'box.dart';
 import 'object.dart';
 
 export 'package:flutter/foundation.dart' show debugPrint;
@@ -311,3 +312,80 @@ bool debugAssertAllRenderVarsUnset(String reason, { bool debugCheckIntrinsicSize
   }());
   return true;
 }
+
+/// Returns true if the given [Axis] is bounded within the given
+/// [BoxConstraints] in both the main and cross axis, throwing an exception
+/// otherwise.
+///
+/// This is used by viewports during `performLayout` and `computeDryLayout`
+/// because bounded constraints are required in order to layout their children.
+bool debugCheckHasBoundedAxis(Axis axis, BoxConstraints constraints) {
+  assert(() {
+    if (!constraints.hasBoundedHeight || !constraints.hasBoundedWidth) {
+      switch (axis) {
+        case Axis.vertical:
+          if (!constraints.hasBoundedHeight) {
+            throw FlutterError.fromParts(<DiagnosticsNode>[
+              ErrorSummary('Vertical viewport was given unbounded height.'),
+              ErrorDescription(
+                'Viewports expand in the scrolling direction to fill their container. '
+                'In this case, a vertical viewport was given an unlimited amount of '
+                'vertical space in which to expand. This situation typically happens '
+                'when a scrollable widget is nested inside another scrollable widget.',
+              ),
+              ErrorHint(
+                'If this widget is always nested in a scrollable widget there '
+                'is no need to use a viewport because there will always be enough '
+                'vertical space for the children. In this case, consider using a '
+                'Column or Wrap instead. Otherwise, consider using a '
+                'CustomScrollView to concatenate arbitrary slivers into a '
+                'single scrollable.',
+              ),
+            ]);
+          }
+          if (!constraints.hasBoundedWidth) {
+            throw FlutterError(
+              'Vertical viewport was given unbounded width.\n'
+              'Viewports expand in the cross axis to fill their container and '
+              'constrain their children to match their extent in the cross axis. '
+              'In this case, a vertical viewport was given an unlimited amount of '
+              'horizontal space in which to expand.',
+            );
+          }
+          break;
+        case Axis.horizontal:
+          if (!constraints.hasBoundedWidth) {
+            throw FlutterError.fromParts(<DiagnosticsNode>[
+              ErrorSummary('Horizontal viewport was given unbounded width.'),
+              ErrorDescription(
+                'Viewports expand in the scrolling direction to fill their container. '
+                'In this case, a horizontal viewport was given an unlimited amount of '
+                'horizontal space in which to expand. This situation typically happens '
+                'when a scrollable widget is nested inside another scrollable widget.',
+              ),
+              ErrorHint(
+                'If this widget is always nested in a scrollable widget there '
+                'is no need to use a viewport because there will always be enough '
+                'horizontal space for the children. In this case, consider using a '
+                'Row or Wrap instead. Otherwise, consider using a '
+                'CustomScrollView to concatenate arbitrary slivers into a '
+                'single scrollable.',
+              ),
+            ]);
+          }
+          if (!constraints.hasBoundedHeight) {
+            throw FlutterError(
+              'Horizontal viewport was given unbounded height.\n'
+              'Viewports expand in the cross axis to fill their container and '
+              'constrain their children to match their extent in the cross axis. '
+              'In this case, a horizontal viewport was given an unlimited amount of '
+              'vertical space in which to expand.',
+            );
+          }
+          break;
+      }
+    }
+    return true;
+  }());
+  return true;
+}

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

@@ -9,6 +9,7 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter/semantics.dart';
 
 import 'box.dart';
+import 'debug.dart';
 import 'layer.dart';
 import 'object.dart';
 import 'sliver.dart';
@@ -1388,73 +1389,7 @@ class RenderViewport extends RenderViewportBase<SliverPhysicalContainerParentDat
 
   @override
   Size computeDryLayout(BoxConstraints constraints) {
-    assert(() {
-      if (!constraints.hasBoundedHeight || !constraints.hasBoundedWidth) {
-        switch (axis) {
-          case Axis.vertical:
-            if (!constraints.hasBoundedHeight) {
-              throw FlutterError.fromParts(<DiagnosticsNode>[
-                ErrorSummary('Vertical viewport was given unbounded height.'),
-                ErrorDescription(
-                  'Viewports expand in the scrolling direction to fill their container. '
-                  'In this case, a vertical viewport was given an unlimited amount of '
-                  'vertical space in which to expand. This situation typically happens '
-                  'when a scrollable widget is nested inside another scrollable widget.',
-                ),
-                ErrorHint(
-                  'If this widget is always nested in a scrollable widget there '
-                  'is no need to use a viewport because there will always be enough '
-                  'vertical space for the children. In this case, consider using a '
-                  'Column or Wrap instead. Otherwise, consider using a '
-                  'CustomScrollView to concatenate arbitrary slivers into a '
-                  'single scrollable.',
-                ),
-              ]);
-            }
-            if (!constraints.hasBoundedWidth) {
-              throw FlutterError(
-                'Vertical viewport was given unbounded width.\n'
-                'Viewports expand in the cross axis to fill their container and '
-                'constrain their children to match their extent in the cross axis. '
-                'In this case, a vertical viewport was given an unlimited amount of '
-                'horizontal space in which to expand.',
-              );
-            }
-            break;
-          case Axis.horizontal:
-            if (!constraints.hasBoundedWidth) {
-              throw FlutterError.fromParts(<DiagnosticsNode>[
-                ErrorSummary('Horizontal viewport was given unbounded width.'),
-                ErrorDescription(
-                  'Viewports expand in the scrolling direction to fill their container. '
-                  'In this case, a horizontal viewport was given an unlimited amount of '
-                  'horizontal space in which to expand. This situation typically happens '
-                  'when a scrollable widget is nested inside another scrollable widget.',
-                ),
-                ErrorHint(
-                  'If this widget is always nested in a scrollable widget there '
-                  'is no need to use a viewport because there will always be enough '
-                  'horizontal space for the children. In this case, consider using a '
-                  'Row or Wrap instead. Otherwise, consider using a '
-                  'CustomScrollView to concatenate arbitrary slivers into a '
-                  'single scrollable.',
-                ),
-              ]);
-            }
-            if (!constraints.hasBoundedHeight) {
-              throw FlutterError(
-                'Horizontal viewport was given unbounded height.\n'
-                'Viewports expand in the cross axis to fill their container and '
-                'constrain their children to match their extent in the cross axis. '
-                'In this case, a horizontal viewport was given an unlimited amount of '
-                'vertical space in which to expand.',
-              );
-            }
-            break;
-        }
-      }
-      return true;
-    }());
+    assert(debugCheckHasBoundedAxis(axis, constraints));
     return constraints.biggest;
   }
 
@@ -1858,17 +1793,48 @@ class RenderShrinkWrappingViewport extends RenderViewportBase<SliverLogicalConta
   late double _shrinkWrapExtent;
   bool _hasVisualOverflow = false;
 
+  bool _debugCheckHasBoundedCrossAxis() {
+    assert(() {
+      switch (axis) {
+        case Axis.vertical:
+          if (!constraints.hasBoundedWidth) {
+            throw FlutterError(
+              'Vertical viewport was given unbounded width.\n'
+              'Viewports expand in the cross axis to fill their container and '
+              'constrain their children to match their extent in the cross axis. '
+              'In this case, a vertical shrinkwrapping viewport was given an '
+              'unlimited amount of horizontal space in which to expand.',
+            );
+          }
+          break;
+        case Axis.horizontal:
+          if (!constraints.hasBoundedHeight) {
+            throw FlutterError(
+              'Horizontal viewport was given unbounded height.\n'
+              'Viewports expand in the cross axis to fill their container and '
+              'constrain their children to match their extent in the cross axis. '
+              'In this case, a horizontal shrinkwrapping viewport was given an '
+              'unlimited amount of vertical space in which to expand.',
+            );
+          }
+          break;
+      }
+      return true;
+    }());
+    return true;
+  }
+
   @override
   void performLayout() {
     final BoxConstraints constraints = this.constraints;
     if (firstChild == null) {
+      // Shrinkwrapping viewport only requires the cross axis to be bounded.
+      assert(_debugCheckHasBoundedCrossAxis());
       switch (axis) {
         case Axis.vertical:
-          assert(constraints.hasBoundedWidth);
           size = Size(constraints.maxWidth, constraints.minHeight);
           break;
         case Axis.horizontal:
-          assert(constraints.hasBoundedHeight);
           size = Size(constraints.minWidth, constraints.maxHeight);
           break;
       }
@@ -1882,14 +1848,14 @@ class RenderShrinkWrappingViewport extends RenderViewportBase<SliverLogicalConta
 
     final double mainAxisExtent;
     final double crossAxisExtent;
+    // Shrinkwrapping viewport only requires the cross axis to be bounded.
+    assert(_debugCheckHasBoundedCrossAxis());
     switch (axis) {
       case Axis.vertical:
-        assert(constraints.hasBoundedWidth);
         mainAxisExtent = constraints.maxHeight;
         crossAxisExtent = constraints.maxWidth;
         break;
       case Axis.horizontal:
-        assert(constraints.hasBoundedHeight);
         mainAxisExtent = constraints.maxWidth;
         crossAxisExtent = constraints.maxHeight;
         break;

packages/flutter/test/rendering/debug_test.dart

@@ -261,4 +261,15 @@ void main() {
     expect(() => debugAssertAllRenderVarsUnset('ERROR'), throwsFlutterError);
     debugDisableOpacityLayers = false;
   });
+
+  test('debugCheckHasBoundedAxis warns for vertical and horizontal axis', () {
+    expect(
+      () => debugCheckHasBoundedAxis(Axis.vertical, const BoxConstraints()),
+      throwsFlutterError,
+    );
+    expect(
+      () => debugCheckHasBoundedAxis(Axis.horizontal, const BoxConstraints()),
+      throwsFlutterError,
+    );
+  });
 }

packages/flutter/test/rendering/viewport_test.dart

@@ -2188,4 +2188,76 @@ void main() {
     });
     expect(visited, true);
   });
+
+  testWidgets('Shrinkwrapping viewport asserts bounded cross axis', (WidgetTester tester) async {
+    final List<FlutterErrorDetails> errors = <FlutterErrorDetails>[];
+    FlutterError.onError = (FlutterErrorDetails error) => errors.add(error);
+    // Vertical
+    await tester.pumpWidget(Directionality(
+        textDirection: TextDirection.ltr,
+        child: ListView(
+          scrollDirection: Axis.horizontal,
+          children: <Widget>[
+            ListView(
+              shrinkWrap: true,
+              children: const <Widget>[ SizedBox.square(dimension: 500) ],
+            ),
+          ],
+        ),
+      ));
+
+    expect(errors, isNotEmpty);
+    expect(errors.first.exception, isFlutterError);
+    FlutterError error = errors.first.exception as FlutterError;
+    expect(
+      error.toString(),
+      contains('Viewports expand in the cross axis to fill their container'),
+    );
+    errors.clear();
+
+    // Horizontal
+    await tester.pumpWidget(Directionality(
+      textDirection: TextDirection.ltr,
+      child: ListView(
+        children: <Widget>[
+          ListView(
+            scrollDirection: Axis.horizontal,
+            shrinkWrap: true,
+            children: const <Widget>[ SizedBox.square(dimension: 500) ],
+          ),
+        ],
+      ),
+    ));
+
+    expect(errors, isNotEmpty);
+    expect(errors.first.exception, isFlutterError);
+    error = errors.first.exception as FlutterError;
+    expect(
+      error.toString(),
+      contains('Viewports expand in the cross axis to fill their container'),
+    );
+    errors.clear();
+
+    // No children
+    await tester.pumpWidget(Directionality(
+      textDirection: TextDirection.ltr,
+      child: ListView(
+        scrollDirection: Axis.horizontal,
+        children: <Widget>[
+          ListView(
+            shrinkWrap: true,
+          ),
+        ],
+      ),
+    ));
+
+    expect(errors, isNotEmpty);
+    expect(errors.first.exception, isFlutterError);
+    error = errors.first.exception as FlutterError;
+    expect(
+      error.toString(),
+      contains('Viewports expand in the cross axis to fill their container'),
+    );
+    errors.clear();
+  });
 }