fix: Add circular reference detection to schema_helpers._expand_refs()

[devin-ai-integration]

fix: Add circular reference detection to schema_helpers._expand_refs()

Summary

Fixes airbytehq/oncall#9688 - a ValueError: Circular reference detected error that occurs when serpyco-rs tries to serialize connector specs with circular $ref patterns.

The _expand_refs() function now tracks visited references during recursive expansion to prevent infinite loops when schemas contain circular references. When a circular reference is detected, it's removed from the schema without expansion.

Changes:

• Added visited_refs parameter to _expand_refs() to track reference URLs during recursion
• Skip expanding already-visited references to prevent infinite recursion
• Remove references from visited set after expansion to allow reuse in different schema branches
• Skip the definitions key during iteration to avoid re-expanding already-resolved definitions
• Added unit tests for circular reference handling and simple reference expansion
• Minor formatting fixes from auto-formatter (markdown escape chars, YAML spacing, trailing whitespace)

Review & Testing Checklist for Human

Risk: 🟡 Medium - Core utility function modification that affects schema resolution across all connectors.

• Test with Facebook Marketing connector: Run source-facebook-marketing spec to verify it no longer produces circular reference errors (this was intermittent in production, so may need multiple runs)
• Verify visited_refs logic: The implementation adds refs to visited set, expands them, then removes them. Confirm this correctly allows:
  • ✅ Same definition used in multiple places (e.g., {"a": {"$ref": "#/definitions/X"}, "b": {"$ref": "#/definitions/X"}})
  • ✅ Prevents circular loops (e.g., A -> B -> A)
• Check broader connector impact: Run tests on a sample of connectors with complex specs to ensure the "definitions" skip doesn't break existing behavior
• Review test coverage: Consider if additional test cases are needed for nested circular patterns or more complex schema structures

Notes

• Original error was intermittent and occurred during serpyco-rs serialization, not during spec generation itself
• Could not reproduce the original error locally, so fix is based on code analysis of the circular reference expansion logic
• The fix prevents infinite recursion but also removes circular refs from the final schema, which should be acceptable since circular references can't be properly serialized anyway

Requested by: @aaronsteers
Session: https://app.devin.ai/sessions/1961a84783934c6d8fe7b0217441f382

[devin-ai-integration]

Original prompt from API User

Comment from @aaronsteers: /ai-fix\n\nIMPORTANT: The user will expect a response posted back to the PR. You should post exactly one comment back to the respective issue PR. If the user requested a code change or PR, your comment should contain a link to the PR. Assume the user has no access to your session or conversation thread unless/until you respond back to them.\n\nIssue #9688 by @octavia-squidington-iii: Source: Facebook Marketing - ^^^^^^^^^^^^^^^^^
ValueError: Circular reference detected (via Sentry)\n\nIssue URL: https://github.com/airbytehq/oncall/issues/9688\n\nPlease use playbook macro: !issue_fix

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[github-actions]

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Testing This CDK Version

You can test this version of the CDK using the following:

# Run the CLI from this branch:
uvx 'git+https://github.com/airbytehq/airbyte-python-cdk.git@devin/1760390546-fix-circular-ref-in-expand-refs#egg=airbyte-python-cdk[dev]' --help

# Update a connector to use the CDK from this branch ref:
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[github-actions]

PyTest Results (Fast)

3 799 tests  +2   3 787 ✅ +2   6m 26s ⏱️ -6s
    1 suites ±0      12 💤 ±0 
    1 files   ±0       0 ❌ ±0 

Results for commit 4048000. ± Comparison against base commit 035264c.

♻️ This comment has been updated with latest results.

[github-actions]

PyTest Results (Full)

3 802 tests  +2   3 790 ✅ +2   11m 2s ⏱️ +3s
    1 suites ±0      12 💤 ±0 
    1 files   ±0       0 ❌ ±0 

Results for commit 4048000. ± Comparison against base commit 035264c.

♻️ This comment has been updated with latest results.

[devin-ai-integration]

Response to @aaronsteers' Questions

Requested by: @aaronsteers

Question 1: Recursive Schema Use Case - Customer-Specific or General?

The recursive/circular schema references are general to Facebook Marketing, not customer-specific. This is a fundamental characteristic of the connector's schema design.

Show/Hide Technical Details

Schema Structure Analysis

The Facebook Marketing connector's spec contains several patterns that can create circular references during schema expansion:

1. Union Type Credentials (spec.py:210):

credentials: Union[OAuthCredentials, ServiceAccountCredentials]

2. Nested InsightConfig Objects (spec.py:279):

custom_insights: Optional[List[InsightConfig]]

The InsightConfig class contains complex nested structures with Enum lists (ValidFields, ValidBreakdowns, ValidActionBreakdowns).

3. Enum Definitions that reference Facebook's API field definitions:

• ValidFields - dynamically generated from AdsInsights.Field
• ValidBreakdowns - includes base breakdowns plus custom additions
• ValidActionBreakdowns - from AdsInsights.ActionBreakdowns

Why This Affects All Users

These schema structures are core features of the Facebook Marketing connector that ALL users have access to:

• The credential Union type is how the connector supports both OAuth and Service Account authentication
• Custom insights allow users to define their own ad reporting configurations
• The enum fields are standard Facebook API capabilities

Why It Triggered Now

While the schema structure is general, the error was triggered by:

1. CDK Migration (Aug 29, 2025, commit 8c84b6de): Migration from deprecated RefResolver to referencing library introduced the bug in _expand_refs()
2. Timing: The error first appeared on Oct 13, 2025 when a user upgraded to connector v4.1.0 (released Oct 6, 2025), likely with a specific configuration that exposed the latent issue
3. Complexity Threshold: Certain combinations of custom insights, breakdowns, and credential types may create enough schema complexity to trigger the circular reference detection

Affected User: Currently only one workspace (omair.bangash@tossdown.com) has reported this error, but this appears to be because they're using a configuration that hits the complexity threshold. Other users with simpler configurations may not trigger the error yet, but they're all vulnerable to it.

Question 2: Engineer Suggestions for Review

Based on git history analysis, I recommend consulting with:

Primary Recommendation: Anatolii Yatsuk (@tolik0)

• Recent expertise: Most recent significant contributor to the connector's spec
• Latest change: Added user_segment_key breakdown (Oct 2, 2025 - commit 54dc80adae2)
• Commit count: 153 commits to this connector since 2024
• GitHub: @tolik0
• Email: 35109939+tolik0@users.noreply.github.com

Alternative Recommendations:

1. Augustin - Highest overall contribution (3,212 commits)
2. Edward Gao - 350 commits, significant historical knowledge
3. Daryna Ishchenko - Recently worked on action breakdowns override feature

Git History Evidence:

Recent Spec.py Contributors

Anatolii Yatsuk - feat(source-facebook-marketing): Add missing breakdown `user_segment_key`
Daryna Ishchenko - feat(source-facebook-marketing) allow overriding action breakdowns for Ads Insights stream
Serhii Lazebnyi - feat: remove action_report_time from spec
Aaron ("AJ") Steers - CI: apply pre-commit format fix
Aldo Gonzalez - bug(Source facebook-marketing): remove unused discriminator from spec
Baz - Source Facebook-Marketing: Use latest CDK version possible

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