iOS TextField spell check style (#125432)

When using a Material TextField on iOS, the spell check selection style now defaults to the red iOS-style, not Android's blue.

packages/flutter/lib/src/cupertino/text_field.dart

@@ -887,6 +887,27 @@ class CupertinoTextField extends StatefulWidget {
         return null;
     }
   });
+
+  /// Returns a new [SpellCheckConfiguration] where the given configuration has
+  /// had any missing values replaced with their defaults for the iOS platform.
+  static SpellCheckConfiguration inferIOSSpellCheckConfiguration(
+    SpellCheckConfiguration? configuration,
+  ) {
+    if (configuration == null
+      || configuration == const SpellCheckConfiguration.disabled()) {
+      return const SpellCheckConfiguration.disabled();
+    }
+
+    return configuration.copyWith(
+      misspelledTextStyle: configuration.misspelledTextStyle
+        ?? CupertinoTextField.cupertinoMisspelledTextStyle,
+      misspelledSelectionColor: configuration.misspelledSelectionColor
+        ?? CupertinoTextField.kMisspelledSelectionColor,
+      spellCheckSuggestionsToolbarBuilder:
+        configuration.spellCheckSuggestionsToolbarBuilder
+          ?? CupertinoTextField.defaultSpellCheckSuggestionsToolbarBuilder,
+    );
+  }
 }
 
 class _CupertinoTextFieldState extends State<CupertinoTextField> with RestorationMixin, AutomaticKeepAliveClientMixin<CupertinoTextField> implements TextSelectionGestureDetectorBuilderDelegate, AutofillClient {
@@ -1298,18 +1319,9 @@ class _CupertinoTextFieldState extends State<CupertinoTextField> with Restoratio
     // ensure that configuration uses Cupertino text style for misspelled words
     // unless a custom style is specified.
     final SpellCheckConfiguration spellCheckConfiguration =
-      widget.spellCheckConfiguration != null &&
-      widget.spellCheckConfiguration != const SpellCheckConfiguration.disabled()
-        ? widget.spellCheckConfiguration!.copyWith(
-            misspelledTextStyle: widget.spellCheckConfiguration!.misspelledTextStyle
-              ?? CupertinoTextField.cupertinoMisspelledTextStyle,
-            misspelledSelectionColor: widget.spellCheckConfiguration!.misspelledSelectionColor
-              ?? CupertinoTextField.kMisspelledSelectionColor,
-            spellCheckSuggestionsToolbarBuilder:
-              widget.spellCheckConfiguration!.spellCheckSuggestionsToolbarBuilder
-                ?? CupertinoTextField.defaultSpellCheckSuggestionsToolbarBuilder,
-          )
-        : const SpellCheckConfiguration.disabled();
+        CupertinoTextField.inferIOSSpellCheckConfiguration(
+          widget.spellCheckConfiguration,
+        );
 
     final Widget paddedEditable = Padding(
       padding: widget.padding,

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

@@ -833,6 +833,25 @@ class TextField extends StatefulWidget {
     }
   }
 
+  /// Returns a new [SpellCheckConfiguration] where the given configuration has
+  /// had any missing values replaced with their defaults for the Android
+  /// platform.
+  static SpellCheckConfiguration inferAndroidSpellCheckConfiguration(
+    SpellCheckConfiguration? configuration,
+  ) {
+    if (configuration == null
+      || configuration == const SpellCheckConfiguration.disabled()) {
+      return const SpellCheckConfiguration.disabled();
+    }
+    return configuration.copyWith(
+      misspelledTextStyle: configuration.misspelledTextStyle
+        ?? TextField.materialMisspelledTextStyle,
+      spellCheckSuggestionsToolbarBuilder:
+        configuration.spellCheckSuggestionsToolbarBuilder
+          ?? TextField.defaultSpellCheckSuggestionsToolbarBuilder,
+    );
+  }
+
   @override
   State<TextField> createState() => _TextFieldState();
 
@@ -1236,19 +1255,24 @@ class _TextFieldState extends State<TextField> with RestorationMixin implements
     ];
 
     // Set configuration as disabled if not otherwise specified. If specified,
-    // ensure that configuration uses Material text style for misspelled words
-    // unless a custom style is specified.
-    final SpellCheckConfiguration spellCheckConfiguration =
-      widget.spellCheckConfiguration != null &&
-      widget.spellCheckConfiguration != const SpellCheckConfiguration.disabled()
-        ? widget.spellCheckConfiguration!.copyWith(
-            misspelledTextStyle: widget.spellCheckConfiguration!.misspelledTextStyle
-              ?? TextField.materialMisspelledTextStyle,
-            spellCheckSuggestionsToolbarBuilder:
-              widget.spellCheckConfiguration!.spellCheckSuggestionsToolbarBuilder
-                ?? TextField.defaultSpellCheckSuggestionsToolbarBuilder,
-          )
-        : const SpellCheckConfiguration.disabled();
+    // ensure that configuration uses the correct style for misspelled words for
+    // the current platform, unless a custom style is specified.
+    final SpellCheckConfiguration spellCheckConfiguration;
+    switch (defaultTargetPlatform) {
+      case TargetPlatform.iOS:
+      case TargetPlatform.macOS:
+        spellCheckConfiguration =
+            CupertinoTextField.inferIOSSpellCheckConfiguration(
+              widget.spellCheckConfiguration,
+            );
+      case TargetPlatform.android:
+      case TargetPlatform.fuchsia:
+      case TargetPlatform.linux:
+      case TargetPlatform.windows:
+        spellCheckConfiguration = TextField.inferAndroidSpellCheckConfiguration(
+          widget.spellCheckConfiguration,
+        );
+    }
 
     TextSelectionControls? textSelectionControls = widget.selectionControls;
     final bool paintCursorAboveText;

packages/flutter/test/material/text_field_test.dart

@@ -16257,6 +16257,64 @@ void main() {
         expect(spellCheckToolbar, isA<SpellCheckSuggestionsToolbar>());
     }
   }, variant: const TargetPlatformVariant(<TargetPlatform>{ TargetPlatform.android, TargetPlatform.iOS }));
+
+  testWidgets('Builds the corresponding default spell check configuration by platform', (WidgetTester tester) async {
+    tester.binding.platformDispatcher.nativeSpellCheckServiceDefinedTestValue =
+      true;
+
+    final SpellCheckConfiguration expectedConfiguration;
+    switch (defaultTargetPlatform) {
+      case TargetPlatform.iOS:
+      case TargetPlatform.macOS:
+        expectedConfiguration = SpellCheckConfiguration(
+          misspelledTextStyle: CupertinoTextField.cupertinoMisspelledTextStyle,
+          misspelledSelectionColor: CupertinoTextField.kMisspelledSelectionColor,
+          spellCheckService: DefaultSpellCheckService(),
+          spellCheckSuggestionsToolbarBuilder: CupertinoTextField.defaultSpellCheckSuggestionsToolbarBuilder,
+        );
+      case TargetPlatform.android:
+      case TargetPlatform.fuchsia:
+      case TargetPlatform.linux:
+      case TargetPlatform.windows:
+        expectedConfiguration = SpellCheckConfiguration(
+          misspelledTextStyle: TextField.materialMisspelledTextStyle,
+          spellCheckService: DefaultSpellCheckService(),
+          spellCheckSuggestionsToolbarBuilder: TextField.defaultSpellCheckSuggestionsToolbarBuilder,
+        );
+    }
+    await tester.pumpWidget(
+      const MaterialApp(
+        home: Scaffold(
+          body: Center(
+            child: TextField(
+              autofocus: true,
+              spellCheckConfiguration: SpellCheckConfiguration(),
+            ),
+          ),
+        ),
+      ),
+    );
+
+    final EditableTextState editableTextState =
+        tester.state<EditableTextState>(find.byType(EditableText));
+
+    expect(
+      editableTextState.spellCheckConfiguration.misspelledTextStyle,
+      expectedConfiguration.misspelledTextStyle,
+    );
+    expect(
+      editableTextState.spellCheckConfiguration.misspelledSelectionColor,
+      expectedConfiguration.misspelledSelectionColor,
+    );
+    expect(
+      editableTextState.spellCheckConfiguration.spellCheckService.runtimeType,
+      expectedConfiguration.spellCheckService.runtimeType,
+    );
+    expect(
+      editableTextState.spellCheckConfiguration.spellCheckSuggestionsToolbarBuilder,
+      expectedConfiguration.spellCheckSuggestionsToolbarBuilder,
+    );
+  }, variant: const TargetPlatformVariant(<TargetPlatform>{ TargetPlatform.android, TargetPlatform.iOS }));
 }
 
 /// A Simple widget for testing the obscure text.