Tooltip update can cause assert (#7338)

We were trying to update the tooltip overlay entry, but that cannot work
because the overlay entry might have already built. Instead, we keep the
old value.

Fixes #7151

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

@@ -110,18 +110,6 @@ class _TooltipState extends State<Tooltip> with SingleTickerProviderStateMixin {
       _removeEntry();
   }
 
-  @override
-  void didUpdateConfig(Tooltip oldConfig) {
-    super.didUpdateConfig(oldConfig);
-    if (_entry != null &&
-        (config.message != oldConfig.message ||
-         config.height != oldConfig.height ||
-         config.padding != oldConfig.padding ||
-         config.verticalOffset != oldConfig.verticalOffset ||
-         config.preferBelow != oldConfig.preferBelow))
-      _entry.markNeedsBuild();
-  }
-
   void ensureTooltipVisible() {
     if (_entry != null) {
       _timer?.cancel();
@@ -129,22 +117,24 @@ class _TooltipState extends State<Tooltip> with SingleTickerProviderStateMixin {
       _controller.forward();
       return;  // Already visible.
     }
-    RenderBox box = context.findRenderObject();
-    Point target = box.localToGlobal(box.size.center(Point.origin));
-    _entry = new OverlayEntry(builder: (BuildContext context) {
-      return new _TooltipOverlay(
-        message: config.message,
-        height: config.height,
-        padding: config.padding,
-        animation: new CurvedAnimation(
-          parent: _controller,
-          curve: Curves.fastOutSlowIn
-        ),
-        target: target,
-        verticalOffset: config.verticalOffset,
-        preferBelow: config.preferBelow
-      );
-    });
+    final RenderBox box = context.findRenderObject();
+    final Point target = box.localToGlobal(box.size.center(Point.origin));
+    // We create this widget outside of the overlay entry's builder to prevent
+    // updated values from happening to leak into the overlay when the overlay
+    // rebuilds.
+    final Widget overlay = new _TooltipOverlay(
+      message: config.message,
+      height: config.height,
+      padding: config.padding,
+      animation: new CurvedAnimation(
+        parent: _controller,
+        curve: Curves.fastOutSlowIn
+      ),
+      target: target,
+      verticalOffset: config.verticalOffset,
+      preferBelow: config.preferBelow
+    );
+    _entry = new OverlayEntry(builder: (BuildContext context) => overlay);
     Overlay.of(context, debugRequiredFor: config).insert(_entry);
     GestureBinding.instance.pointerRouter.addGlobalRoute(_handlePointerEvent);
     _controller.forward();

packages/flutter/test/material/tooltip_test.dart

@@ -473,4 +473,36 @@ void main() {
 
     semantics.dispose();
   });
+
+  testWidgets('Tooltip overlay does not update', (WidgetTester tester) async {
+    Widget buildApp(String text) {
+      return new MaterialApp(
+        home: new Center(
+          child: new Tooltip(
+            message: text,
+            child: new Container(
+              width: 100.0,
+              height: 100.0,
+              decoration: new BoxDecoration(
+                backgroundColor: Colors.green[500]
+              )
+            )
+          )
+        )
+      );
+    }
+
+    await tester.pumpWidget(buildApp(tooltipText));
+    await tester.longPress(find.byType(Tooltip));
+    expect(find.text(tooltipText), findsOneWidget);
+    await tester.pumpWidget(buildApp('NEW'));
+    expect(find.text(tooltipText), findsOneWidget);
+    await tester.tapAt(const Point(5.0, 5.0));
+    await tester.pump();
+    await tester.pump(const Duration(seconds: 1));
+    expect(find.text(tooltipText), findsNothing);
+    await tester.longPress(find.byType(Tooltip));
+    expect(find.text(tooltipText), findsNothing);
+  });
+
 }

packages/flutter_test/lib/src/controller.dart

@@ -267,6 +267,26 @@ class WidgetController {
     });
   }
 
+  /// Dispatch a pointer down / pointer up sequence (with a delay of
+  /// [kLongPressTimeout] + [kPressTimeout] between the two events) at the
+  /// center of the given widget, assuming it is exposed. If the center of the
+  /// widget is not exposed, this might send events to another
+  /// object.
+  Future<Null> longPress(Finder finder, { int pointer: 1 }) {
+    return longPressAt(getCenter(finder), pointer: pointer);
+  }
+
+  /// Dispatch a pointer down / pointer up sequence at the given location with
+  /// a delay of [kLongPressTimeout] + [kPressTimeout] between the two events.
+  Future<Null> longPressAt(Point location, { int pointer: 1 }) {
+    return TestAsyncUtils.guard(() async {
+      TestGesture gesture = await startGesture(location, pointer: pointer);
+      await pump(kLongPressTimeout + kPressTimeout);
+      await gesture.up();
+      return null;
+    });
+  }
+
   /// Attempts a fling gesture starting from the center of the given
   /// widget, moving the given distance, reaching the given velocity.
   ///