Fixing some issues around handling multiple firestore DBs

[joehan]

Description

Fixes some issues related to handling multiple Firestore DBs during emulation and deployment. Fixes #9742 and #8114

[gemini-code-assist]

Summary of Changes

Hello @joehan, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the Firebase Firestore emulator by introducing comprehensive support for multiple Firestore databases. It addresses long-standing limitations and bugs, allowing developers to configure, emulate, and manage security rules for several Firestore instances within a single project. This change improves the development workflow for applications utilizing multiple Firestore databases by making the emulator more robust and feature-complete.

Highlights

• Multi-Database Emulation: The Firestore emulator now fully supports emulating multiple Firestore databases simultaneously, removing previous limitations.
• Firebase.json Multi-DB Fix: Resolved issues where configuring multiple Firestore databases in firebase.json would lead to errors, specifically addressing Cannot deploy indexes in a project with multiple firestore dbs: TypeError: Cannot read properties of undefined (reading 'map') #8114.
• Database-Specific Security Rules: Security rules can now be applied and updated on a per-database basis within the emulator, enhancing flexibility for multi-database setups.
• Improved Configuration Handling: The configuration parsing for firestore:rules and firestore:indexes now correctly includes all database configurations, ensuring comprehensive coverage.

🧠 New Feature in Public Preview: You can now enable Memory to help Gemini Code Assist learn from your team's feedback. This makes future code reviews more consistent and personalized to your project's style. Click here to enable Memory in your admin console.

Using Gemini Code Assist

The full guide for Gemini Code Assist can be found on our documentation page, here are some quick tips.

Invoking Gemini

You can request assistance from Gemini at any point by creating a comment using either /gemini <command> or @gemini-code-assist <command>. Below is a summary of the supported commands on the current page.

Feature	Command	Description
Code Review	/gemini review	Performs a code review for the current pull request in its current state.
Pull Request Summary	/gemini summary	Provides a summary of the current pull request in its current state.
Comment	@gemini-code-assist	Responds in comments when explicitly tagged, both in pull request comments and review comments.
Help	/gemini help	Displays a list of available commands.

Customization

To customize Gemini Code Assist for GitHub experience, repository maintainers can create a configuration file and/or provide a custom code review style guide (such as PEP-8 for Python) by creating and adding files to a .gemini/ folder in the base of the repository. Detailed instructions can be found here.

Limitations & Feedback

Gemini Code Assist may make mistakes. Please leave feedback on any instances where its feedback is incorrect or counter productive. You can react with 👍 and 👎 on @gemini-code-assist comments. If you're interested in giving your feedback about your experience with Gemini Code Assist for Github and other Google products, sign up here.

You can also get AI-powered code generation, chat, as well as code reviews directly in the IDE at no cost with the Gemini Code Assist IDE Extension.

Footnotes

1. Review the Privacy Notices, Generative AI Prohibited Use Policy, Terms of Service, and learn how to configure Gemini Code Assist in GitHub here. Gemini can make mistakes, so double check it and use code with caution. ↩

[gemini-code-assist]

Code Review

The pull request successfully addresses the issues related to handling multiple Firestore databases during emulation and deployment. The changes in src/emulator/controller.ts correctly adapt the rule processing logic to support multiple configurations, and the FirestoreEmulatorArgs and updateRules method in src/emulator/firestoreEmulator.ts have been updated to reflect this. The new test cases in src/firestore/fsConfig.spec.ts provide good coverage for the getFirestoreConfig function's behavior with firestore:rules and firestore:indexes filters. However, there are a couple of areas that need attention to ensure correctness and efficiency.

[aalej]

I can't seem to run the Firestore emulators. Given this test case https://github.com/aalej/pulls-9770, running firebase emulators:start will raise

Jan 21, 2026 9:50:13 PM com.google.cloud.datastore.emulator.firestore.CloudFirestore main
SEVERE: Exiting due to unexpected exception.
java.io.FileNotFoundException: [object Object],[object Object] (No such file or directory)
	at java.base/java.io.FileInputStream.open0(Native Method)
	at java.base/java.io.FileInputStream.open(FileInputStream.java:213)
	at java.base/java.io.FileInputStream.<init>(FileInputStream.java:152)
	at com.google.common.io.Files$FileByteSource.openStream(Files.java:140)
	at com.google.common.io.Files$FileByteSource.read(Files.java:170)
	at com.google.common.io.ByteSource$AsCharSource.read(ByteSource.java:534)
	at com.google.cloud.datastore.emulator.firestore.CloudFirestore.init(CloudFirestore.java:186)
	at com.google.cloud.datastore.emulator.firestore.CloudFirestore.startLocally(CloudFirestore.java:120)
	at com.google.cloud.datastore.emulator.firestore.CloudFirestore.main(CloudFirestore.java:101)

Exception in thread "main" java.lang.NoClassDefFoundError: com/google/common/util/LegacySystemExit
	at com.google.cloud.datastore.emulator.firestore.CloudFirestore.main(CloudFirestore.java:106)
Caused by: java.lang.ClassNotFoundException: com.google.common.util.LegacySystemExit
	at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:641)
	at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:525)
	... 1 more

[joehan]

@aalej I had jetski split out the emulator changes - this should be good to rereview and hopefully get in for tommorrow