Complete October 2021 GraphQL spec compliance

[spawnia]

Full October 2021 Spec Compliance 🎉

This PR completes webonyx/graphql-php's compliance with the October 2021 GraphQL specification.
After auditing the spec against the implementation, SingleFieldSubscription (section 5.2.3.1) was the last remaining gap.

Changes

Rewrite SingleFieldSubscription validation to match the reference graphql-js implementation:

• Expand fragments (inline and named) before counting root fields — previously only top-level selections were counted, missing fields contributed via fragments
• Reject introspection fields (__schema, __type, __typename) at the subscription root
• Reject @skip/@include directives on top-level selections
• Handle fragment cycle detection and type condition matching

Test plan

• 21 new/updated tests mirroring graphql-js's SingleFieldSubscriptionsRule-test.ts (40 assertions)
• Full test suite passes across PHP 7.4–8.5: make test
• Static analysis passes across PHP 7.4–8.5: make stan
• Benchmarks show no regression

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Updates the subscription validation rule to align SingleFieldSubscription with the October 2021 GraphQL spec, particularly around fragment expansion at the subscription root and additional root-level restrictions.

Changes:

• Rework SingleFieldSubscription validation to expand inline/named fragments before counting top-level subscription fields.
• Add new validation failures for introspection fields and @skip/@include directives at the subscription root.
• Add/extend PHPUnit coverage for fragment expansion, recursion handling, introspection fields, directive rejection, and the “no subscription type” skip behavior; document the change in the changelog.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/Validator/Rules/SingleFieldSubscription.php	Rewrites validation logic to expand fragments, reject introspection fields, and reject @skip/@include at the subscription root.
tests/Validator/SingleFieldSubscriptionsTest.php	Adds extensive tests mirroring graphql-js coverage for the updated subscription rule behavior.
CHANGELOG.md	Records the spec-compliance fix under Unreleased.

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 13 out of 13 changed files in this pull request and generated 3 comments.

[simPod]

AI review note: the @skip/@include rejection appears to be current-draft / graphql-js 17 behavior, not October 2021 behavior. If the intent is to match current graphql-js, the code direction makes sense, but the README/changelog wording around “October 2021 compliance” is misleading.

[simPod]

AI review:

@skip/@include are only checked on the operation’s immediate top-level selections here, but subscription root fields can also be contributed by expanded fragments. That means this currently accepts a root field with a forbidden directive when it comes from a fragment:

subscription sub {
  ...frag
}

fragment frag on SubscriptionRoot {
  catSubscribe @include(if: true) {
    meows
  }
}

The draft/reference CollectSubscriptionFields logic applies the directive check during recursive collection, so fragment-contributed root selections should be checked as they are collected too.