Set selection on tap down for desktop platforms and tap up for mobile (#105505)

Co-authored-by: Renzo Olivares <roliv@google.com>

packages/flutter/lib/src/widgets/text_selection.dart

@@ -1454,6 +1454,9 @@ class TextSelectionGestureDetectorBuilder {
   ///  * [TextSelectionGestureDetector.onTapDown], which triggers this callback.
   @protected
   void onTapDown(TapDownDetails details) {
+    if (!delegate.selectionEnabled) {
+      return;
+    }
     renderEditable.handleTapDown(details);
     // The selection overlay should only be shown when the user is interacting
     // through a touch screen (via either a finger or a stylus). A mouse shouldn't
@@ -1465,13 +1468,21 @@ class TextSelectionGestureDetectorBuilder {
       || kind == PointerDeviceKind.stylus;
 
     // Handle shift + click selection if needed.
-    if (_isShiftPressed && renderEditable.selection?.baseOffset != null) {
-      _isShiftTapping = true;
+    final bool isShiftPressedValid = _isShiftPressed && renderEditable.selection?.baseOffset != null;
     switch (defaultTargetPlatform) {
+      case TargetPlatform.android:
+      case TargetPlatform.fuchsia:
       case TargetPlatform.iOS:
+        // On mobile platforms the selection is set on tap up.
+        if (_isShiftTapping) {
+          _isShiftTapping = false;
+        }
+        break;
       case TargetPlatform.macOS:
-          // On these platforms, a shift-tapped unfocused field expands from 0,
-          // not from the previous selection.
+        // On macOS, a shift-tapped unfocused field expands from 0, not from the
+        // previous selection.
+        if (isShiftPressedValid) {
+          _isShiftTapping = true;
           final TextSelection? fromSelection = renderEditable.hasFocus
               ? null
               : const TextSelection.collapsed(offset: 0);
@@ -1480,14 +1491,23 @@ class TextSelectionGestureDetectorBuilder {
             SelectionChangedCause.tap,
             fromSelection,
           );
+          return;
+        }
+        // On macOS, a tap/click places the selection in a precise position.
+        // This differs from iOS/iPadOS, where if the gesture is done by a touch
+        // then the selection moves to the closest word edge, instead of a
+        // precise position.
+        renderEditable.selectPosition(cause: SelectionChangedCause.tap);
         break;
-        case TargetPlatform.android:
-        case TargetPlatform.fuchsia:
       case TargetPlatform.linux:
       case TargetPlatform.windows:
+        if (isShiftPressedValid) {
+          _isShiftTapping = true;
           _extendSelection(details.globalPosition, SelectionChangedCause.tap);
-          break;
+          return;
         }
+        renderEditable.selectPosition(cause: SelectionChangedCause.tap);
+        break;
     }
   }
 
@@ -1547,15 +1567,42 @@ class TextSelectionGestureDetectorBuilder {
   ///    this callback.
   @protected
   void onSingleTapUp(TapUpDetails details) {
+    if (delegate.selectionEnabled) {
+      // Handle shift + click selection if needed.
+      final bool isShiftPressedValid = _isShiftPressed && renderEditable.selection?.baseOffset != null;
+      switch (defaultTargetPlatform) {
+        case TargetPlatform.linux:
+        case TargetPlatform.macOS:
+        case TargetPlatform.windows:
+          // On desktop platforms the selection is set on tap down.
           if (_isShiftTapping) {
             _isShiftTapping = false;
+          }
+          break;
+        case TargetPlatform.android:
+        case TargetPlatform.fuchsia:
+          if (isShiftPressedValid) {
+            _isShiftTapping = true;
+            _extendSelection(details.globalPosition, SelectionChangedCause.tap);
             return;
           }
-
-    if (delegate.selectionEnabled) {
-      switch (defaultTargetPlatform) {
+          renderEditable.selectPosition(cause: SelectionChangedCause.tap);
+          break;
         case TargetPlatform.iOS:
-        case TargetPlatform.macOS:
+          if (isShiftPressedValid) {
+            // On iOS, a shift-tapped unfocused field expands from 0, not from
+            // the previous selection.
+            _isShiftTapping = true;
+            final TextSelection? fromSelection = renderEditable.hasFocus
+                ? null
+                : const TextSelection.collapsed(offset: 0);
+            _expandSelection(
+              details.globalPosition,
+              SelectionChangedCause.tap,
+              fromSelection,
+            );
+            return;
+          }
           switch (details.kind) {
             case PointerDeviceKind.mouse:
             case PointerDeviceKind.trackpad:
@@ -1566,18 +1613,11 @@ class TextSelectionGestureDetectorBuilder {
               break;
             case PointerDeviceKind.touch:
             case PointerDeviceKind.unknown:
-              // On macOS/iOS/iPadOS a touch tap places the cursor at the edge
-              // of the word.
+              // On iOS/iPadOS a touch tap places the cursor at the edge of the word.
               renderEditable.selectWordEdge(cause: SelectionChangedCause.tap);
               break;
           }
           break;
-        case TargetPlatform.android:
-        case TargetPlatform.fuchsia:
-        case TargetPlatform.linux:
-        case TargetPlatform.windows:
-          renderEditable.selectPosition(cause: SelectionChangedCause.tap);
-          break;
       }
     }
   }

packages/flutter/test/material/text_field_focus_test.dart

@@ -475,8 +475,6 @@ void main() {
 
     final TestGesture down1 = await tester.startGesture(tester.getCenter(find.byType(TextField).first), kind: PointerDeviceKind.mouse);
     await tester.pump();
-    await tester.pumpAndSettle();
-    await down1.up();
     await down1.removePointer();
 
     expect(focusNodeA.hasFocus, true);

packages/flutter/test/widgets/text_selection_test.dart

@@ -557,9 +557,9 @@ void main() {
 
     switch (defaultTargetPlatform) {
       case TargetPlatform.iOS:
-      case TargetPlatform.macOS:
         expect(renderEditable.selectWordEdgeCalled, isTrue);
         break;
+      case TargetPlatform.macOS:
       case TargetPlatform.android:
       case TargetPlatform.fuchsia:
       case TargetPlatform.linux: