[cloud_firestore] Fix DocumentReference comparison bug.

[slightfoot]

Description

I was just caught out by this.

void main() {
  final first = Firestore.instance.collection('a').document('b');
  final second = Firestore.instance.collection('a').document('b');
  print(first == second); // prints false
}

You expect two DocumentReferences to be equal. https://github.com/FirebaseExtended/flutterfire/blob/master/packages/cloud_firestore/cloud_firestore/lib/src/document_reference.dart#L25 shows this to be the case if the firestore instance is the same and the instance getter above does not return a singleton instead it creates a new instance each time.

This fix corrects this by firstly treating the Firestore.instance field as a singleton, and second adding a equality method that now compares the underlying app. Which now means even if you have multiple instances of the same Firestore class they will be considered equal.

Tests

• cloud_firestore package does not contain tests.

Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• If the pull request affects only one plugin, the PR title starts with the name of the plugin in brackets (e.g. [cloud_firestore])
• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See [Contributor Guide]).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (flutter analyze) does not report any problems on my PR.
• I read and followed the [Flutter Style Guide].
• I updated pubspec.yaml with an appropriate new version according to the [pub versioning philosophy].
• I updated CHANGELOG.md to add a description of the change.
• I signed the [CLA].
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate a breaking change in CHANGELOG.md and increment major revision).
• No, this is not a breaking change.

[slightfoot]

/cc @bparrishMines @collinjackson not sure who I should reference for this simple ticket. Can you have a look and tell me where the tests should go?

[bparrishMines]

@slightfoot The code looks good to me. It only lacks lacks a test and updating the pubspec.yaml and CHANGELOG. It looks like tests were placed in flutterfire/packages/cloud_firestore/cloud_firestore/example/test_driver/ for this plugin.

[mono0926]

@slightfoot

This seems redundant for me because Firestore() is practically singleton.

static Firestore get instance calls these:

1. https://github.com/FirebaseExtended/flutterfire/blob/5e380cf85fde7eefa91d520bdb3ae0bfeb2d1282/packages/cloud_firestore/cloud_firestore/lib/src/firestore.dart#L26
2. https://github.com/FirebaseExtended/flutterfire/blob/5e380cf85fde7eefa91d520bdb3ae0bfeb2d1282/packages/cloud_firestore/cloud_firestore_platform_interface/lib/cloud_firestore_platform_interface.dart#L61-L66
   • This is singleton

[mono0926]

Suggested change

	int get hashCode => _delegate.app.name.hashCode;
	int get hashCode => _delegate.app.hashCode;

@slightfoot

The hashCode of FirebaseApp is implemented appropriately, so .name seems redundant.

• https://github.com/FirebaseExtended/flutterfire/blob/5e380cf85fde7eefa91d520bdb3ae0bfeb2d1282/packages/firebase_core/firebase_core/lib/src/firebase_app.dart#L86

[duttaoindril]

Glad this is finally getting attention! i've literally had to wrap DocumentReference in a wrapper DocumentReferenceKey class I've created to use DocumentReferences as keys in all my query result maps.

• [cloud_firestore] Strip Document Reference firestore equality to solve equality & map key bug #2081 #2110
• [cloud_firestore] Incorrect DocumentReference == equals behavior on the same path on default firestore instance #2081