Fix RabbitMQ 4.x crash: global QoS not supported on classic queues

[Azd325]

RabbitMQ 4.0 removed support for global QoS prefetch (basic.qos with global=true) on classic queues. When Kombu connected to a RabbitMQ 4.x broker, qos_semantics_matches_spec returned False (because the version was not < 3.3), causing Celery to set global=True in its QoS call, which RabbitMQ 4.x immediately rejected with:

540 NOT_IMPLEMENTED - queue does not support global qos

This crashed workers on startup before they could consume any tasks.

Fix the version boundary check in both pyamqp and librabbitmq transports to return True (per-channel QoS) for RabbitMQ >= 4.0:

Before: version < (3, 3)
After: version < (3, 3) or version >= (4, 0)

This restores the correct behavior:

• RabbitMQ < 3.3: True (spec-compliant per-channel QoS)
• RabbitMQ 3.3–3.x: False (global QoS semantics)
• RabbitMQ 4.0+: True (global QoS removed, per-channel only)

RabbitMQ deprecation announcement (2021):
https://www.rabbitmq.com/blog/2021/08/21/4.0-deprecation-announcements

RabbitMQ 4.x classic queues docs (global QoS removal):
https://www.rabbitmq.com/docs/classic-queues

Closes: #2469

[Copilot]

Pull request overview

This PR fixes a startup crash when Kombu connects to a RabbitMQ 4.x broker using the pyamqp or librabbitmq transports. RabbitMQ 4.0 removed support for global QoS prefetch on classic queues, but the old version boundary check (version < (3, 3)) returned False for all RabbitMQ ≥ 3.3, causing Celery to set global=True in its QoS call — which RabbitMQ 4.x rejects with a 540 NOT_IMPLEMENTED error.

Changes:

• Fix the version boundary in pyamqp.Transport.qos_semantics_matches_spec to return True for RabbitMQ ≥ 4.0.
• Apply the same fix symmetrically to librabbitmq.Transport.qos_semantics_matches_spec, and add safe handling for a missing version key in both transports.
• Add comprehensive unit tests for both transports covering all version boundary cases and the missing-version edge case.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
kombu/transport/pyamqp.py	Core fix: adds RabbitMQ 4.0+ condition and safe version key handling
kombu/transport/librabbitmq.py	Same fix applied symmetrically to the librabbitmq transport
t/unit/transport/test_pyamqp.py	New tests for all QoS version boundary cases in pyamqp
t/unit/transport/test_librabbitmq.py	New tests for all QoS version boundary cases in librabbitmq, including the AttributeError path

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.24%. Comparing base (6cc2228) to head (3a99f4f).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
kombu/transport/librabbitmq.py	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2481      +/-   ##
==========================================
+ Coverage   82.23%   82.24%   +0.01%     
==========================================
  Files          79       79              
  Lines       10080    10088       +8     
  Branches     1150     1152       +2     
==========================================
+ Hits         8289     8297       +8     
  Misses       1589     1589              
  Partials      202      202              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[auvipy]

we should keep support for both old and new versions for easier migrations

[auvipy]

also can you improve test coverage?

[auvipy]

@ChickenBenny

[ChickenBenny]

LGTM! 🚀

[auvipy]

the codecov is showing very low coverage