fix(resolve): fix mutation-during-iteration bug in optionallyAllowCustomExtensionProperties

[jensneuse]

Summary

Fix SIGSEGV (segmentation violation at addr=0x8) caused by deleting Object.kvs entries while Visit() iterates over them. This occurred in optionallyAllowCustomExtensionProperties when filtering extension fields.

Changes

• Replaced mutation-during-iteration pattern with object reconstruction: instead of deleting disallowed keys inside the Visit callback, rebuild extensions with only allowed keys
• Simplified optionallyOmitErrorExtensions by removing redundant Exists() check before Del() (Del is a safe no-op on missing keys)
• Added 3 comprehensive tests providing 100% coverage of the fixed function

Test Coverage

All tests pass, including 3 new tests covering previously uncovered branches:

• Multiple non-allowed field deletions (the crash scenario)
• Non-object extension types being preserved
• Allowed fields configured but none present in extensions

Summary by CodeRabbit

Release Notes

• Bug Fixes

  • Error responses now properly handle extension field filtering, removing disallowed fields and preserving allowed ones.
  • Fixed edge cases with null extension values and missing allowed fields.

• Tests

  • Added test coverage for extension field handling in error responses.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

---

📝 Walkthrough

Walkthrough

This PR refactors error extension field handling in the GraphQL engine's loader component. It changes the extension filtering logic to either completely remove the extensions object when no fields are allowed or construct a new filtered extensions object with only permitted fields, replacing the previous in-place modification approach.

Changes

Cohort / File(s)	Summary
Error Extension Filtering Logic v2/pkg/engine/resolve/loader.go	Refactored optionallyAllowCustomExtensionProperties to replace in-place filtering with constructing a new extensions object or removing it entirely. Simplified optionallyOmitErrorExtensions to unconditionally delete extensions when feature flag is enabled.
Extension Handling Tests v2/pkg/engine/resolve/loader_hooks_test.go	Added three test cases validating extension field filtering behavior: removal of non-allowed fields, preservation of null extensions, and complete removal when no allowed fields match.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• graphql-go-tools#1217: Modifies error extension handling in the same loader component with complementary changes to extension filtering and flag-based behavior control.

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title directly and clearly describes the main change: fixing a mutation-during-iteration bug in optionallyAllowCustomExtensionProperties, which is the primary problem addressed in this PR.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

• 📝 Generate docstrings (stacked PR)
• 📝 Generate docstrings (commit on current branch)

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch jensneuse/fix-nil-object-visit

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[StarpTech]

LGTM