[Swift 6] Fix mutable state error in FirebaseDataEncoder.swift

[ncooke3]

error:

Var '_iso8601Formatter' is not concurrency-safe because it is nonisolated global shared mutable state

[gemini-code-assist]

Hello @ncooke3, 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!

Summary of Changes

This pull request addresses a Swift 6 concurrency safety error in FirebaseDataEncoder.swift. The error was due to the _iso8601Formatter being a nonisolated global shared mutable state. To fix this, the code was modified to make _iso8601Formatter a computed property with a getter that instantiates a new ISO8601DateFormatter each time it's accessed.

Highlights

• Concurrency Safety: Fixes a Swift 6 concurrency safety error related to mutable shared state.
• ISO8601DateFormatter: Modifies _iso8601Formatter to be a computed property, ensuring a new instance is created each time, avoiding shared mutable state issues.

Changelog

• FirebaseSharedSwift/Sources/third_party/FirebaseDataEncoder/FirebaseDataEncoder.swift
  • Changed _iso8601Formatter from a variable with an immediately executed closure to a computed property with a getter that returns a new ISO8601DateFormatter instance.

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Trivia time!

What is the primary use case for the ISO 8601 standard?

Click here for the answer

The primary use case for the ISO 8601 standard is to provide an unambiguous and well-defined method of representing dates and times, avoiding misinterpretations caused by different cultural or national conventions.

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[gemini-code-assist]

Code Review

The pull request addresses a concurrency issue with the _iso8601Formatter in FirebaseDataEncoder.swift. The original implementation used a nonisolated global shared mutable state, which is not concurrency-safe. The fix involves changing the variable to a computed property with a getter that creates a new ISO8601DateFormatter instance each time it's accessed. This ensures that each thread or concurrent context has its own instance of the formatter, preventing race conditions and data corruption. The change appears to be correct and addresses the issue effectively.

Summary of Findings

• Concurrency Safety: The original implementation of _iso8601Formatter as a nonisolated global shared mutable state was not concurrency-safe. The fix addresses this by making it a computed property that returns a new instance each time, ensuring thread safety.

Merge Readiness

The pull request appears to correctly address the concurrency issue. Given the severity of concurrency issues, I recommend that this pull request be merged after verifying that the change does not introduce any performance regressions due to the repeated creation of ISO8601DateFormatter instances. I am unable to directly approve this pull request, and recommend that others review and approve this code before merging.

[google-oss-bot]

	1 Warning
⚠️	Did you forget to add a changelog entry? (Add #no-changelog to the PR description to silence this warning.)

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