Reland "Fix `Chip.shape`'s side is not used when provided in Material 3" (#133856)

fixes [Chip border side color not working in Material3](https://github.com/flutter/flutter/issues/132922)
Relands https://github.com/flutter/flutter/pull/132941 with an updated fix and a regression test.

<details>
<summary>expand to view the code sample</summary> 

```dart
import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      theme: ThemeData(useMaterial3: true),
      home: const Example(),
    );
  }
}

class Example extends StatelessWidget {
  const Example({super.key});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Chips'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
          children: <Widget>[
            const RawChip(
              shape: RoundedRectangleBorder(
                side: BorderSide(color: Colors.amber),
              ),
              side: BorderSide(color: Colors.red),
              label: Text('RawChip'),
            ),
            const Chip(
              shape: RoundedRectangleBorder(
                side: BorderSide(color: Colors.amber),
              ),
              side: BorderSide(color: Colors.red),
              label: Text('Chip'),
            ),
            ActionChip(
              shape: const RoundedRectangleBorder(
                side: BorderSide(color: Colors.amber),
              ),
              side: const BorderSide(color: Colors.red),
              label: const Text('ActionChip'),
              onPressed: () {},
            ),
            FilterChip(
              shape: const RoundedRectangleBorder(
                side: BorderSide(color: Colors.amber),
              ),
              side: const BorderSide(color: Colors.red),
              label: const Text('FilterChip'),
              onSelected: (value) {},
            ),
            ChoiceChip(
              shape: const RoundedRectangleBorder(
                side: BorderSide(color: Colors.amber),
              ),
              side: const BorderSide(color: Colors.red),
              label: const Text('ChoiceChip'),
              selected: false,
              onSelected: (value) {},
            ),
            InputChip(
              shape: const RoundedRectangleBorder(
                side: BorderSide(color: Colors.amber),
              ),
              side: const BorderSide(color: Colors.red),
              label: const Text('InputChip'),
              onSelected: (value) {},
            ),
          ],
        ),
      ),
    );
  }
}
```

</details>

<img src="https://github.com/flutter/flutter/assets/48603081/f713fd84-cf9a-4e52-8cdb-5faba63d8e91" height="450" /> <img src="https://github.com/flutter/flutter/assets/48603081/a142efc7-041e-4e6e-87cf-e6c4ebe735f3" height="450" />

<img src="https://github.com/flutter/flutter/assets/48603081/377df55b-499f-403f-96c5-0be0334795dc" height="450" /> <img src="https://github.com/flutter/flutter/assets/48603081/731a2752-7822-4605-8e9c-db0a71dd6f08" height="450" />

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

@@ -992,13 +992,21 @@ class _RawChipState extends State<RawChip> with MaterialStateMixin, TickerProvid
 
   OutlinedBorder _getShape(ThemeData theme, ChipThemeData chipTheme, ChipThemeData chipDefaults) {
     final BorderSide? resolvedSide = MaterialStateProperty.resolveAs<BorderSide?>(widget.side, materialStates)
-      ?? MaterialStateProperty.resolveAs<BorderSide?>(chipTheme.side, materialStates)
-      ?? MaterialStateProperty.resolveAs<BorderSide?>(chipDefaults.side, materialStates);
+      ?? MaterialStateProperty.resolveAs<BorderSide?>(chipTheme.side, materialStates);
     final OutlinedBorder resolvedShape = MaterialStateProperty.resolveAs<OutlinedBorder?>(widget.shape, materialStates)
       ?? MaterialStateProperty.resolveAs<OutlinedBorder?>(chipTheme.shape, materialStates)
       ?? MaterialStateProperty.resolveAs<OutlinedBorder?>(chipDefaults.shape, materialStates)
+      // TODO(tahatesser): Remove this fallback when Material 2 is deprecated.
       ?? const StadiumBorder();
-    return resolvedShape.copyWith(side: resolvedSide);
+    // If the side is provided, shape uses the provided side.
+    if (resolvedSide != null) {
+      return resolvedShape.copyWith(side: resolvedSide);
+    }
+    // If the side is not provided and the shape's side is not [BorderSide.none],
+    // then the shape's side is used. Otherwise, the default side is used.
+    return resolvedShape.side != BorderSide.none
+      ? resolvedShape
+      : resolvedShape.copyWith(side: chipDefaults.side);
   }
 
   Color? resolveColor({

packages/flutter/test/material/chip_test.dart

@@ -3503,6 +3503,85 @@ void main() {
     expect(calledDelete, isTrue);
   });
 
+  // This is a regression test for https://github.com/flutter/flutter/pull/133615.
+  testWidgets('Material3 - Custom shape without provided side uses default side', (WidgetTester tester) async {
+    final ThemeData theme = ThemeData(useMaterial3: true);
+    await tester.pumpWidget(
+      MaterialApp(
+        theme: theme,
+        home: const Material(
+          child: Center(
+            child: RawChip(
+              // No side provided.
+              shape: StadiumBorder(),
+              label: Text('RawChip'),
+            ),
+          ),
+        ),
+      ),
+    );
+
+    // Chip should have the default side.
+    expect(
+      getMaterial(tester).shape,
+      StadiumBorder(side: BorderSide(color: theme.colorScheme.outline)),
+    );
+  });
+
+  testWidgets("Material3 - RawChip.shape's side is used when provided", (WidgetTester tester) async {
+    Widget buildChip({ OutlinedBorder? shape, BorderSide? side }) {
+      return MaterialApp(
+        theme: ThemeData(useMaterial3: true),
+        home: Material(
+          child: Center(
+            child: RawChip(
+              shape: shape,
+              side: side,
+              label: const Text('RawChip'),
+            ),
+          ),
+        ),
+      );
+    }
+
+    // Test [RawChip.shape] with a side.
+    await tester.pumpWidget(buildChip(
+      shape: const RoundedRectangleBorder(
+        side: BorderSide(color: Color(0xffff00ff)),
+        borderRadius: BorderRadius.all(Radius.circular(7.0)),
+      )),
+    );
+
+    // Chip should have the provided shape and the side from [RawChip.shape].
+    expect(
+      getMaterial(tester).shape,
+      const RoundedRectangleBorder(
+        side: BorderSide(color: Color(0xffff00ff)),
+        borderRadius: BorderRadius.all(Radius.circular(7.0)),
+      ),
+    );
+
+    // Test [RawChip.shape] with a side and [RawChip.side].
+    await tester.pumpWidget(buildChip(
+      shape: const RoundedRectangleBorder(
+        side: BorderSide(color: Color(0xffff00ff)),
+        borderRadius: BorderRadius.all(Radius.circular(7.0)),
+      ),
+      side: const BorderSide(color: Color(0xfffff000))),
+    );
+    await tester.pumpAndSettle();
+
+    // Chip use shape from [RawChip.shape] and the side from [RawChip.side].
+    // [RawChip.shape]'s side should be ignored.
+    expect(
+      getMaterial(tester).shape,
+      const RoundedRectangleBorder(
+        side: BorderSide(color: Color(0xfffff000)),
+        borderRadius: BorderRadius.all(Radius.circular(7.0)),
+      ),
+    );
+  });
+
   group('Material 2', () {
     // These tests are only relevant for Material 2. Once Material 2
     // support is deprecated and the APIs are removed, these tests

packages/flutter/test/material/chip_theme_test.dart

@@ -928,6 +928,64 @@ void main() {
       )),
     );
   });
+
+  testWidgets("Material3 - RawChip.shape's side is used when provided", (WidgetTester tester) async {
+    Widget buildChip({ OutlinedBorder? shape, BorderSide? side }) {
+      return MaterialApp(
+        theme: ThemeData(
+          useMaterial3: true,
+          chipTheme: ChipThemeData(
+            shape: shape,
+            side: side,
+          ),
+        ),
+        home: const Material(
+          child: Center(
+            child: RawChip(
+              label: Text('RawChip'),
+            ),
+          ),
+        ),
+      );
+    }
+
+    // Test [RawChip.shape] with a side.
+    await tester.pumpWidget(buildChip(
+      shape: const RoundedRectangleBorder(
+        side: BorderSide(color: Color(0xffff00ff)),
+        borderRadius: BorderRadius.all(Radius.circular(7.0)),
+      )),
+    );
+
+    // Chip should have the provided shape and the side from [RawChip.shape].
+    expect(
+      getMaterial(tester).shape,
+      const RoundedRectangleBorder(
+        side: BorderSide(color: Color(0xffff00ff)),
+        borderRadius: BorderRadius.all(Radius.circular(7.0)),
+      ),
+    );
+
+    // Test [RawChip.shape] with a side and [RawChip.side].
+    await tester.pumpWidget(buildChip(
+      shape: const RoundedRectangleBorder(
+        side: BorderSide(color: Color(0xffff00ff)),
+        borderRadius: BorderRadius.all(Radius.circular(7.0)),
+      ),
+      side: const BorderSide(color: Color(0xfffff000))),
+    );
+    await tester.pumpAndSettle();
+
+    // Chip use shape from [RawChip.shape] and the side from [RawChip.side].
+    // [RawChip.shape]'s side should be ignored.
+    expect(
+      getMaterial(tester).shape,
+      const RoundedRectangleBorder(
+        side: BorderSide(color: Color(0xfffff000)),
+        borderRadius: BorderRadius.all(Radius.circular(7.0)),
+      ),
+    );
+  });
 }
 
 class _MaterialStateOutlinedBorder extends StadiumBorder implements MaterialStateOutlinedBorder {