[Shopify Sync] Fix nil reservation when queue is empty

[dkeegan-figma]

Summary

Cherry-picks Shopify's fix for nil reservation bug (commit 40d568c). Prevents workers from setting @reserved_test to nil when the queue is empty, which could cause crashes or unexpected behavior.

Changes

Modified Files

• ruby/lib/ci/queue/redis/worker.rb - Updated reserve method to only set @reserved_test when test is non-nil

The Bug

Previously, when try_to_reserve_lost_test and try_to_reserve_test both returned nil (queue empty), the code would still set @reserved_test = nil, potentially causing issues with reservation tracking.

The Fix

# Before - sets @reserved_test even when nil
@reserved_test = try_to_reserve_lost_test || try_to_reserve_test

# After - only sets @reserved_test when non-nil
test = try_to_reserve_lost_test || try_to_reserve_test
@reserved_test = test if test
test

Conflict Resolution

✅ Adapted for Figma's architecture:

• Shopify's version uses reserved_tests (Set)
• Figma uses @reserved_test (single instance variable)
• Successfully adapted the nil-check logic to work with Figma's approach

Benefits

• Correctness: Prevents nil reservations
• Reliability: Avoids potential crashes from unexpected nil values
• Safety: Better reservation state management

Testing

• ✅ Ruby syntax check passes
• ✅ Logic verified through code review
• ✅ Preserves existing reservation error checking
• ⏳ Full test suite requires Redis (run in CI)

Original Shopify PR

• Shopify PR: #356
• Original commit: 40d568c
• Author: David Stosik david.stosik@shopify.com

Risk Assessment

Risk Level: Low

• Small, focused change (3 insertions, 1 deletion)
• Defensive programming improvement
• No behavior change when tests are available
• Only affects edge case when queue is exhausted

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cc: @Dkeegan