Introduce {bool exclusive = false} parameter to File.create({recursive}) method

[aam]

Desktop OSs allow for a file to be created in exclusive mode enabling simple concurrency-serializing mechanism.

from https://man7.org/linux/man-pages/man2/open.2.html

       O_EXCL Ensure that this call creates the file: if this flag is
              specified in conjunction with O_CREAT, and pathname
              already exists, then open() fails with the error EEXIST.

https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/open-wopen

EEXIST | _O_CREAT and _O_EXCL flags specified, but filename already exists.

This currently is not available for Dart apps.
This can be fixed via new optional exclusive parameter to https://api.flutter.dev/flutter/dart-io/File/create.html:

Future<File>> create(
{bool recursive = false,
bool exclusive = false}
)

[a-siva]

//cc @itsjustkevin

[itsjustkevin]

Hey @aam please forgive my ignorance here, but is adding an additional parameter a breaking change if it has a default? There is usually a bit more context in these breaking change requests.

[aam]

@itsjustkevin yeah, unfortunately even adding optional parameter with default value is a breaking change since it will break all the code that implemented that class - potentially internal code that is used in testing, code that provided mock implementation of File class. Code that implemented File class with its own implementation of Future<File> create({bool recursive = false}) now has to be changed to Future<File> create({bool recursive = false, recursive = false})

[itsjustkevin]

Thanks for the breakdown @aam that was really helpful in understanding the scope of the change request!

Reaching out to @Hixie @grouma and @vsmenon to review this breaking change request.

[Hixie]

We should add exclusive to package:file before we add it here, to reduce the impact of the breaking change. Other than that, SGTM. cc @tvolkert

[aam]

We should add exclusive to package:file before we add it here,

Yeah, package:file is part of dart sdk build, so has to be addressed before File in dart:io dart sdk change can land.

[vsmenon]

We should study the breaking change impact, but lgtm.