From 7d368dcf0c00b45fef5b02c5cccb8aa5306234ba Mon Sep 17 00:00:00 2001
From: Justin McCandless <jmccandless@google.com>
Date: Tue, 14 Sep 2021 12:39:19 -0700
Subject: [PATCH] InteractiveViewer with a child of zero size (#90012)

Asserts that the InteractiveViewer child can't have zero size.
---
 .../lib/src/widgets/interactive_viewer.dart   |  4 +++
 .../test/widgets/interactive_viewer_test.dart | 36 +++++++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/packages/flutter/lib/src/widgets/interactive_viewer.dart b/packages/flutter/lib/src/widgets/interactive_viewer.dart
index b5ae9b04f7e..1a6e9a60bde 100644
--- a/packages/flutter/lib/src/widgets/interactive_viewer.dart
+++ b/packages/flutter/lib/src/widgets/interactive_viewer.dart
@@ -512,6 +512,10 @@ class _InteractiveViewerState extends State<InteractiveViewer> with TickerProvid
     final RenderBox childRenderBox = _childKey.currentContext!.findRenderObject()! as RenderBox;
     final Size childSize = childRenderBox.size;
     final Rect boundaryRect = widget.boundaryMargin.inflateRect(Offset.zero & childSize);
+    assert(
+      !boundaryRect.isEmpty,
+      "InteractiveViewer's child must have nonzero dimensions.",
+    );
     // Boundaries that are partially infinite are not allowed because Matrix4's
     // rotation and translation methods don't handle infinites well.
     assert(
diff --git a/packages/flutter/test/widgets/interactive_viewer_test.dart b/packages/flutter/test/widgets/interactive_viewer_test.dart
index 6015f42111b..871a2310f10 100644
--- a/packages/flutter/test/widgets/interactive_viewer_test.dart
+++ b/packages/flutter/test/widgets/interactive_viewer_test.dart
@@ -201,6 +201,42 @@ void main() {
       expect(transformationController.value, isNot(equals(Matrix4.identity())));
     });
 
+    testWidgets('child has no dimensions', (WidgetTester tester) async {
+      final TransformationController transformationController = TransformationController();
+      await tester.pumpWidget(
+        MaterialApp(
+          home: Scaffold(
+            body: Center(
+              child: InteractiveViewer(
+                constrained: false,
+                scaleEnabled: false,
+                transformationController: transformationController,
+                child: const SizedBox(width: 0.0, height: 0.0),
+              ),
+            ),
+          ),
+        ),
+      );
+
+      expect(transformationController.value, equals(Matrix4.identity()));
+
+      // Interacting throws an error because the child has no size.
+      final Offset childOffset = tester.getTopLeft(find.byType(SizedBox));
+      final Offset childInterior = Offset(
+        childOffset.dx + 20.0,
+        childOffset.dy + 20.0,
+      );
+      final TestGesture gesture = await tester.startGesture(childOffset);
+      addTearDown(gesture.removePointer);
+      await tester.pump();
+      await gesture.moveTo(childInterior);
+      await tester.pump();
+      await gesture.up();
+      await tester.pumpAndSettle();
+      expect(transformationController.value, equals(Matrix4.identity()));
+      expect(tester.takeException(), isAssertionError);
+    });
+
     testWidgets('no boundary', (WidgetTester tester) async {
       final TransformationController transformationController = TransformationController();
       const double minScale = 0.8;