Makes text selection match the native behavior (#79308)

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

@@ -3042,22 +3042,43 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin {
     // If text is obscured, the entire sentence should be treated as one word.
     if (obscureText) {
       return TextSelection(baseOffset: 0, extentOffset: _plainText.length);
-    // If the word is a space, on iOS try to select the previous word instead.
-    // On Android try to select the previous word instead only if the text is read only.
+    // On iOS, select the previous word if there is a previous word, or select
+    // to the end of the next word if there is a next word. Select nothing if
+    // there is neither a previous word nor a next word.
+    //
+    // If the platform is Android and the text is read only, try to select the
+    // previous word if there is one; otherwise, select the single whitespace at
+    // the position.
     } else if (_isWhitespace(_plainText.codeUnitAt(position.offset))
         && position.offset > 0) {
       assert(defaultTargetPlatform != null);
       final TextRange? previousWord = _getPreviousWord(word.start);
       switch (defaultTargetPlatform) {
         case TargetPlatform.iOS:
+          if (previousWord == null) {
+            final TextRange? nextWord = _getNextWord(word.start);
+            if (nextWord == null) {
+              return TextSelection.collapsed(offset: position.offset);
+            }
+            return TextSelection(
+              baseOffset: position.offset,
+              extentOffset: nextWord.end,
+            );
+          }
           return TextSelection(
-            baseOffset: previousWord!.start,
+            baseOffset: previousWord.start,
             extentOffset: position.offset,
           );
         case TargetPlatform.android:
           if (readOnly) {
+            if (previousWord == null) {
+              return TextSelection(
+                baseOffset: position.offset,
+                extentOffset: position.offset + 1,
+              );
+            }
             return TextSelection(
-              baseOffset: previousWord!.start,
+              baseOffset: previousWord.start,
               extentOffset: position.offset,
             );
           }

packages/flutter/test/rendering/editable_test.dart

@@ -499,6 +499,136 @@ void main() {
     expect(currentSelection.extentOffset, 9);
   }, skip: isBrowser); // https://github.com/flutter/flutter/issues/61026
 
+  test('selects readonly renderEditable matches native behavior for android', () {
+    // Regression test for https://github.com/flutter/flutter/issues/79166.
+    final TargetPlatform? previousPlatform = debugDefaultTargetPlatformOverride;
+    debugDefaultTargetPlatformOverride = TargetPlatform.android;
+    const String text = '  test';
+    final TextSelectionDelegate delegate = FakeEditableTextState()
+      ..textEditingValue = const TextEditingValue(text: text);
+    final ViewportOffset viewportOffset = ViewportOffset.zero();
+    late TextSelection currentSelection;
+    final RenderEditable editable = RenderEditable(
+      backgroundCursorColor: Colors.grey,
+      selectionColor: Colors.black,
+      textDirection: TextDirection.ltr,
+      cursorColor: Colors.red,
+      readOnly: true,
+      offset: viewportOffset,
+      textSelectionDelegate: delegate,
+      onSelectionChanged: (TextSelection selection, RenderEditable renderObject, SelectionChangedCause cause) {
+        currentSelection = selection;
+      },
+      startHandleLayerLink: LayerLink(),
+      endHandleLayerLink: LayerLink(),
+      text: const TextSpan(
+        text: text,
+        style: TextStyle(
+          height: 1.0, fontSize: 10.0, fontFamily: 'Ahem',
+        ),
+      ),
+      selection: const TextSelection.collapsed(
+        offset: 4,
+      ),
+    );
+
+    layout(editable);
+
+    // Select the second white space, where the text position = 1.
+    editable.selectWordsInRange(from: const Offset(10, 2), cause:SelectionChangedCause.longPress);
+    pumpFrame();
+    expect(currentSelection.isCollapsed, false);
+    expect(currentSelection.baseOffset, 1);
+    expect(currentSelection.extentOffset, 2);
+    debugDefaultTargetPlatformOverride = previousPlatform;
+  });
+
+  test('selects renderEditable matches native behavior for iOS case 1', () {
+    // Regression test for https://github.com/flutter/flutter/issues/79166.
+    final TargetPlatform? previousPlatform = debugDefaultTargetPlatformOverride;
+    debugDefaultTargetPlatformOverride = TargetPlatform.iOS;
+    const String text = '  test';
+    final TextSelectionDelegate delegate = FakeEditableTextState()
+      ..textEditingValue = const TextEditingValue(text: text);
+    final ViewportOffset viewportOffset = ViewportOffset.zero();
+    late TextSelection currentSelection;
+    final RenderEditable editable = RenderEditable(
+      backgroundCursorColor: Colors.grey,
+      selectionColor: Colors.black,
+      textDirection: TextDirection.ltr,
+      cursorColor: Colors.red,
+      offset: viewportOffset,
+      textSelectionDelegate: delegate,
+      onSelectionChanged: (TextSelection selection, RenderEditable renderObject, SelectionChangedCause cause) {
+        currentSelection = selection;
+      },
+      startHandleLayerLink: LayerLink(),
+      endHandleLayerLink: LayerLink(),
+      text: const TextSpan(
+        text: text,
+        style: TextStyle(
+          height: 1.0, fontSize: 10.0, fontFamily: 'Ahem',
+        ),
+      ),
+      selection: const TextSelection.collapsed(
+        offset: 4,
+      ),
+    );
+
+    layout(editable);
+
+    // Select the second white space, where the text position = 1.
+    editable.selectWordsInRange(from: const Offset(10, 2), cause:SelectionChangedCause.longPress);
+    pumpFrame();
+    expect(currentSelection.isCollapsed, false);
+    expect(currentSelection.baseOffset, 1);
+    expect(currentSelection.extentOffset, 6);
+    debugDefaultTargetPlatformOverride = previousPlatform;
+  });
+
+  test('selects renderEditable matches native behavior for iOS case 2', () {
+    // Regression test for https://github.com/flutter/flutter/issues/79166.
+    final TargetPlatform? previousPlatform = debugDefaultTargetPlatformOverride;
+    debugDefaultTargetPlatformOverride = TargetPlatform.iOS;
+    const String text = '   ';
+    final TextSelectionDelegate delegate = FakeEditableTextState()
+      ..textEditingValue = const TextEditingValue(text: text);
+    final ViewportOffset viewportOffset = ViewportOffset.zero();
+    late TextSelection currentSelection;
+    final RenderEditable editable = RenderEditable(
+      backgroundCursorColor: Colors.grey,
+      selectionColor: Colors.black,
+      textDirection: TextDirection.ltr,
+      cursorColor: Colors.red,
+      offset: viewportOffset,
+      textSelectionDelegate: delegate,
+      onSelectionChanged: (TextSelection selection, RenderEditable renderObject, SelectionChangedCause cause) {
+        currentSelection = selection;
+      },
+      startHandleLayerLink: LayerLink(),
+      endHandleLayerLink: LayerLink(),
+      text: const TextSpan(
+        text: text,
+        style: TextStyle(
+          height: 1.0, fontSize: 10.0, fontFamily: 'Ahem',
+        ),
+      ),
+      selection: const TextSelection.collapsed(
+        offset: 4,
+      ),
+    );
+
+    layout(editable);
+
+    // Select the second white space, where the text position = 1.
+    editable.selectWordsInRange(from: const Offset(10, 2), cause:SelectionChangedCause.longPress);
+    pumpFrame();
+    expect(currentSelection.isCollapsed, true);
+    expect(currentSelection.baseOffset, 1);
+    expect(currentSelection.extentOffset, 1);
+    debugDefaultTargetPlatformOverride = previousPlatform;
+  });
+
   test('selects correct place when offsets are flipped', () {
     const String text = 'abc def ghi';
     final TextSelectionDelegate delegate = FakeEditableTextState()