[AtulJoshi1206]

Issue number: closes #8567

Summary

Changes

Exceptions raised by a Depends() dependency are now handled exactly as if the route had raised them.

solve_dependencies() wraps anything a dependency raises in DependencyResolutionError, which only subclasses Exception. _call_exception_handler() looked only at the wrapper, so three things never applied:

• handlers registered for the original exception;
• the built-in ServiceError responses;
• the validation error responses.

The wrapper then escaped resolve().

What this PR does:

• Handles the cause. ApiGatewayResolver._call_exception_handler(), the single dispatch point for resolve() and resolve_async(), now handles the wrapper's __cause__, unless the app registered a handler for DependencyResolutionError itself.

• Keeps the fallback unchanged. If nothing handles the original exception, the caller still re-raises the original DependencyResolutionError unchanged: same object, traceback and __cause__. The existing test_depends_exception_raises_dependency_resolution_error contract and the debug-mode 500 are unchanged.

• Scope. This covers every proxy resolver (REST, HTTP API, ALB, Function URL, VPC Lattice, Bedrock Agent) and HttpResolverLocal, since they all dispatch through this method. AppSync and the Bedrock function resolver don't support Depends().

• Tests, in tests/functional/event_handler/required_dependencies/test_depends.py:

  • a ServiceError returns its status code and body;
  • a custom exception_handler runs;
  • a nested dependency;
  • an explicit DependencyResolutionError handler still wins;
  • resolve_async(), handled and unhandled;
  • a parametrized app.resolve() test over the REST, HTTP API, ALB and VPC Lattice v2 fixtures.

  The 8 bug tests fail on develop, and the 2 controls pass on both.

Checks:

• pytest tests/functional/event_handler tests/unit/event_handler: 1171 passed, 1 skipped.
• ruff check and ruff format --check: clean.
• mypy: no new errors.

User experience

Before: with the docs example dependency_injection_with_request.py, a request without x-user-id makes app.resolve() raise DependencyResolutionError. The invocation fails and the client gets a 5xx instead of a 401, and @app.exception_handler(MyError) never runs for a MyError raised in a dependency.

After: the same request returns 401 {"statusCode": 401, "message": "Missing authentication"}, and exception handlers run for exceptions raised in dependencies, the same as for route errors.

Risks

• Catch-all handlers: a catch-all @app.exception_handler(Exception) now receives the original exception (e.g. UnauthorizedError) instead of DependencyResolutionError, the same as for route errors.
• Workaround handlers: apps that registered a DependencyResolutionError handler as a workaround are unaffected. It still receives the wrapper, with the original exception as __cause__.

AI assistance: prepared with Claude Code; the change was reviewed and the tests were run locally.

---

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🤖 Generated with Claude Code

[boring-cyborg]

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[leandrodamascena]

Thanks @AtulJoshi1206! I reproduced it on develop with the docs example and confirmed the 401 with this fix. Also checked nested dependencies, enable_validation=True, resolve_async and the catch-all handler, all behave like a route raising the same exception. And thanks for so many PRs improving Powertools lately, really appreciate it. Approving.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.93%. Comparing base (93e577c) to head (92d5c8d).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8568   +/-   ##
========================================
  Coverage    96.93%   96.93%           
========================================
  Files          318      318           
  Lines        16002    16005    +3     
  Branches      1419     1420    +1     
========================================
+ Hits         15511    15514    +3     
  Misses         349      349           
  Partials       142      142           

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[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud