[Mairramer]

This PR proposes a standardized Extensible Constant Pattern for Flutter federated plugins.

Historically, platform-specific constant domains (such as camera pixel formats, biometric authentication types, media surface formats, and store modes) have been modeled as standard Dart enums. Because standard enums represent closed sets, adding a new constant when an underlying OS introduces a feature triggers a compile-time breaking change for downstream consumers due to Dart's exhaustiveness checks.

This RFC outlines the architectural trade-offs, specifies the canonical class pattern (final class with value equality, fromString, and knownValues), validates it against the camera package's ImageFormatGroup (PR flutter/packages#11765), and surveys applications across other official plugins in flutter/packages (local_auth, video_player, file_selector, in_app_purchase).

Converting the document Extensible Enums for Plugins and expanding it with more details.

Tracking issue: flutter/flutter#189696

Pre-launch Checklist

• I read RFC 000.0001: Taxonomy and followed the file and path naming and metadata standards.
• I read RFC 000.0002: Process and confirmed this proposal meets the threshold for a full RFC.
• I read and agree to the Code of Conduct.
• I signed the CLA.
• I have linked an issue from flutter/flutter with the label design doc.
• All existing and new tests are passing.
• I have enabled "Allow edits from maintainers" on this PR so the bot can automatically assign an RFC number (or I will run dart run bin/assign_rfc_number.dart locally when instructed).

If you need help, consider asking for advice on the #hackers channel on Discord.

[bparrishMines]

@Mairramer Thanks for converting this document. We are currently reviewing #32, which will create a consistent style across Flutter repos. I think we forgot to link this RFC in the PR yesterday. I linked your doc in #32 (comment), but feel free to leave more comments. I think flutter/packages and flutter/flutter can share a style doc based on the use cases.

[dcharkes]

I already reviewed the original design doc which was converted now to this RFC. 👍

[jtmcdole]

If the original design doc was already approved / accepted, we can move forward with this. @dcharkes for info.

[Piinks]

I agree with @bparrishMines to keep both, aligned & cross-linked. PR #32 (710.0000) establishing the concise repo-wide flutter/flutter style-guide & breaking-change policy, and this (440.0000) the federated-plugin architecture companion covering cross-package SemVer compatibility, platform-specific extension constants, channel string serialization, knownValues, and plugin migration strategy, while harmonizing their class templates.

[Piinks]

LGTM - assigning rfc number as this was a previously approved proposal being ported over.

[github-actions]

Assigned RFC 440.0001.