[flutter_hook_config] Add the flutter_hook_config package

[bdero]

Towards flutter/flutter#186299

Adds flutter_hook_config, a package:hooks protocol extension owned by Flutter. It lets the Flutter SDK pass engine host-tool paths (such as impellerc and libtessellator) to build and link hooks in a typed way, resolved through the same artifact lookup flutter_tools uses for its own build steps, so --local-engine propagates to hooks instead of silently using stale cached tools.

Originally proposed in flutter/packages#11701. Per review there, the package belongs in this repo: flutter_tools depends on it, so keeping it in flutter/packages would create a circular repo dependency. This moves it here unchanged apart from the repo onboarding bits (SDK constraint, allowed dependencies, labeler, README) and a bump to hooks: ^2.0.0.

What a Flutter build hook looks like with it:

import 'package:flutter_hook_config/flutter_hook_config.dart';
import 'package:hooks/hooks.dart';

void main(List<String> args) async {
  await build(args, (input, output) async {
    if (input.config.buildForFlutter) {
      final impellerc = input.config.flutter.impellerc; // absolute Uri
      // ... invoke impellerc to compile a shader bundle ...
    } else {
      // Plain `dart` build, or a Flutter SDK without this extension:
      // fall back to the hook's own tool discovery.
    }
  });
}

v1 exposes impellerc, libtessellator, and an engineVersion for cache invalidation; more host artifacts can be added later as null-checked fields. Pure Dart, depends on hooks: ^2.0.0, starts at 0.1.0 while the shape stabilizes.

Pre-Review Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the AI contribution guidelines and understand my responsibilities, or I am not using AI tools.
• I read the Tree Hygiene page, which explains my responsibilities.
• I read and followed the Flutter style guide and ran the auto-formatter.
• I signed the CLA.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [vector_math]
• I linked to at least one issue that this PR fixes in the description above.
• I followed the version and CHANGELOG instructions, using semantic versioning and the repository CHANGELOG style, or I have commented below to indicate which documented exception this PR falls under[^1].
• I updated/added any relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or I have commented below to indicate which test exemption this PR falls under[^1].
• All existing and new tests are passing.

[bdero]

Migrated from flutter/packages#11701.

FYI @dcharkes, I also updated this to use hooks v2.

[bdero]

Copying publishing notes from previous PR:

Note for shipping this: flutter_hook_config is a brand-new package, so on its first publish the release workflow will publish it under the bot publisher account rather than the flutter.dev verified publisher. Someone on the Flutter team with publisher-account access will need to do the one-time transfer from the package's Admin tab on pub.dev afterward (per the packages release process docs; access is tracked internally at b/191674407). Happy to coordinate in #hackers-ecosystem.

Also flagging: the top-level README.md row and the issue_tracker URL reference pub.dev/packages/flutter_hook_config and the flutter/flutter label p: flutter_hook_config, neither of which exists yet, so the badges/links will 404 until the package publishes and the label is created.

[Piinks]

I am not aware of this being owned by the framework team. Let's discuss if that is expected. Removing the triage label for now.

[bdero]

@Piinks Ah whoopsies, I added that label by accident. This is more tools-esque.

[dcharkes]

All the comments from flutter/packages#11701 have been addressed. LGTM!

[stuartmorgan-g]

Note for shipping this: flutter_hook_config is a brand-new package, so on its first publish the release workflow will publish it under the bot publisher account rather than the flutter.dev verified publisher. Someone on the Flutter team with publisher-account access will need to do the one-time transfer from the package's Admin tab on pub.dev afterward

Except it isn't a new package; what appears to be a placeholder package, with no useful metadata about where it came from, was published 5 months ago. So the publishing failed.

Does one of you own that package?

(The only clue to ownership I can find in the package is that it is "Copyright 2025, the Dart project authors", so hopefully that means someone on the Dart team is the package owner.)

[bdero]

Ugh, no. I thought I had checked if the name was taken, but I guess not. :/ This was actually my second choice name, as the first name I chose was also taken. Another good name would be flutter_hook_extensions... making a follow-up to rename now. I can also back it out and reland if you'd prefer.

[dcharkes]

I'm also not owning it. But it seems that package is just being name-squatted, which is against the pub.dev policy: https://pub.dev/policy#name-squatting I've pinged the pub team to unsquat it.