fix(Semantics): Ensure semantics properties take priority over button's (flutter#174473)

Fixes flutter#157689

Flutter packages PR counterpart:
- flutter/packages#9815



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Author: pedromassango

engine/src/flutter/lib/web_ui/lib/src/engine/semantics/semantics.dart

@@ -2055,14 +2055,14 @@ class SemanticsObject {
       return EngineSemanticsRole.image;
     } else if (isCheckable) {
       return EngineSemanticsRole.checkable;
+    } else if (isLink) {
+      return EngineSemanticsRole.link;
     } else if (isButton) {
       return EngineSemanticsRole.button;
     } else if (isScrollContainer) {
       return EngineSemanticsRole.scrollable;
     } else if (scopesRoute) {
       return EngineSemanticsRole.route;
-    } else if (isLink) {
-      return EngineSemanticsRole.link;
     } else if (isHeader) {
       return EngineSemanticsRole.header;
     } else if (isButtonLike) {

engine/src/flutter/lib/web_ui/test/engine/semantics/semantics_test.dart

@@ -4377,6 +4377,34 @@ void _testLink() {
     expect(object.element.tagName.toLowerCase(), 'a');
     expect(object.element.getAttribute('href'), 'https://flutter.dev');
   });
+
+  test('a node that is both a link and a button is rendered as a link', () {
+    semantics()
+      ..debugOverrideTimestampFunction(() => _testTime)
+      ..semanticsEnabled = true;
+
+    const String url = 'https://flutter.dev';
+    final SemanticsTester tester = SemanticsTester(owner());
+    tester.updateNode(
+      id: 0,
+      linkUrl: url,
+      flags: const ui.SemanticsFlags(isLink: true, isButton: true),
+      label: 'link button label',
+      rect: const ui.Rect.fromLTRB(0, 0, 100, 50),
+    );
+    tester.apply();
+
+    tester.expectSemantics('<a style="display: block;">link button label</a>');
+    final SemanticsObject node = owner().debugSemanticsTree![0]!;
+    expect(node.semanticRole?.kind, EngineSemanticsRole.link);
+    expect(node.linkUrl, url);
+    expect(
+      node.semanticRole?.debugSemanticBehaviorTypes,
+      containsAll(<Type>[Focusable, Tappable, LabelAndValue]),
+    );
+
+    semantics().semanticsEnabled = false;
+  });
 }
 
 void _testTabs() {

packages/flutter/lib/src/semantics/semantics.dart

@@ -6003,6 +6003,7 @@ class SemanticsConfiguration {
     _actionsAsBits |= child._effectiveActionsAsBits;
     _customSemanticsActions.addAll(child._customSemanticsActions);
     _flags = _flags.merge(child._flags);
+    _linkUrl ??= child._linkUrl;
     _textSelection ??= child._textSelection;
     _scrollPosition ??= child._scrollPosition;
     _scrollExtentMax ??= child._scrollExtentMax;

packages/flutter/test/widgets/semantics_merge_test.dart

@@ -4,7 +4,6 @@
 
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
-import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 import 'semantics_tester.dart';
@@ -141,4 +140,55 @@ void main() {
 
     semantics.dispose();
   });
+
+  testWidgets('LinkUri from child is passed up to the parent when merging nodes', (
+    WidgetTester tester,
+  ) async {
+    final SemanticsTester semantics = SemanticsTester(tester);
+    final Uri uri = Uri.parse('https://flutter.com');
+    const String label = 'test1';
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: MergeSemantics(
+          child: Semantics(
+            linkUrl: uri,
+            link: true,
+            child: ElevatedButton(
+              onPressed: () {},
+              child: const Text(label),
+              onFocusChange: (bool value) {},
+            ),
+          ),
+        ),
+      ),
+    );
+
+    expect(
+      semantics,
+      hasSemantics(
+        TestSemantics.root(
+          children: <TestSemantics>[
+            TestSemantics.rootChild(
+              id: 1,
+              linkUrl: uri,
+              flags: <SemanticsFlag>[
+                SemanticsFlag.isButton,
+                SemanticsFlag.hasEnabledState,
+                SemanticsFlag.isEnabled,
+                SemanticsFlag.isFocusable,
+                SemanticsFlag.isLink,
+              ],
+              actions: <SemanticsAction>[SemanticsAction.tap, SemanticsAction.focus],
+              label: label,
+            ),
+          ],
+        ),
+        ignoreRect: true,
+        ignoreTransform: true,
+      ),
+    );
+
+    semantics.dispose();
+  });
 }