🐛 Avoid Interceptors.clear removes ImplyContentTypeInterceptor (#…

…1975)

Resolves #1973

### New Pull Request Checklist

- [x] I have read the
[Documentation](https://pub.dev/documentation/dio/latest/)
- [x] I have searched for a similar pull request in the
[project](https://github.com/cfug/dio/pulls) and found none
- [x] I have updated this branch with the latest `main` branch to avoid
conflicts (via merge from master or rebase)
- [x] I have added the required tests to prove the fix/feature I'm
adding
- [x] I have updated the documentation (if necessary)
- [x] I have run the tests without failures
- [x] I have updated the `CHANGELOG.md` in the corresponding package

### Additional context and info (if any)

The PR only addresses `clear`. However, lists can be modified in various
ways which might also remove/replace the interceptor. We might need to
rethink an extra internal interceptors list.

dio/CHANGELOG.md

@@ -12,6 +12,7 @@ See the [Migration Guide][] for the complete breaking changes list.**
 - Reduce cases in which browsers would trigger a CORS preflight request.
 - Add warnings in debug mode when using `sendTimeout` and `onSendProgress` with an empty request body.
 - Fix `receiveTimeout` not working correctly on web.
+- Fix `ImplyContentTypeInterceptor` can be removed by `Interceptors.clear()` by default.
 
 ## 5.3.2
 

dio/lib/src/interceptor.dart

@@ -319,6 +319,17 @@ class Interceptors extends ListMixin<Interceptor> {
     }
   }
 
+  /// The default [ImplyContentTypeInterceptor] will be removed only if
+  /// [keepImplyContentTypeInterceptor] is false.
+  @override
+  void clear({bool keepImplyContentTypeInterceptor = true}) {
+    if (keepImplyContentTypeInterceptor) {
+      _list.removeWhere((e) => e is! ImplyContentTypeInterceptor);
+    } else {
+      super.clear();
+    }
+  }
+
   /// Remove the default imply content type interceptor.
   void removeImplyContentTypeInterceptor() {
     _list.removeWhere((e) => e is ImplyContentTypeInterceptor);

dio/test/interceptor_test.dart

@@ -583,6 +583,7 @@ void main() {
       expect(tokenRequestCounts, 1);
       expect(result, 3);
       expect(myInter.requestCount, predicate((int e) => e > 0));
+      // The `ImplyContentTypeInterceptor` will be replaced.
       dio.interceptors[0] = myInter;
       dio.interceptors.clear();
       expect(dio.interceptors.isEmpty, true);
@@ -659,6 +660,9 @@ void main() {
     expect(interceptors.length, equals(2));
     expect(interceptors, isNotEmpty);
     interceptors.clear();
+    expect(interceptors.length, equals(1));
+    expect(interceptors.single, isA<ImplyContentTypeInterceptor>());
+    interceptors.clear(keepImplyContentTypeInterceptor: false);
     expect(interceptors.length, equals(0));
     expect(interceptors, isEmpty);
   });