Fix BlendSearch OptunaSearch warning for non-hierarchical spaces with Ray Tune domains

[Copilot]

BlendSearch issues a warning when using Ray Tune domains in non-hierarchical search spaces: "You passed a space parameter to OptunaSearch that contained unresolved search space definitions."

from ray import tune
from flaml.tune.searcher.blendsearch import BlendSearch

# Previously triggered warning
searcher = BlendSearch(
    metric='loss',
    mode='min',
    space={'lr': tune.uniform(0.001, 0.1), 'depth': tune.randint(1, 10)}
)

Changes

• blendsearch.py: Always use define-by-run mode when passing spaces to Ray's OptunaSearch, not just for hierarchical spaces. Ray's OptunaSearch expects either Optuna distributions or a callable define-by-run function, not Ray Tune domain objects.

• test_searcher.py: Add regression test capturing stderr to verify warning is eliminated.

CFO remains unaffected (doesn't use global search). The evaluated_rewards parameter continues to be correctly set to None for define-by-run mode.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• metadata.google.internal
  • Triggering command: /usr/bin/python3 /usr/bin/python3 /home/REDACTED/.local/lib/python3.12/site-packages/ray/dashboard/dashboard.py --host=127.0.0.1 --port=8265 --port-retries=50 --temp-dir=/tmp/ray --log-dir=/tmp/ray/session_2026-01-10_08-37-43_892531_3832/logs --session-dir=/tmp/ray/session_2026-01-10_08-37-43_892531_3832 --logging-rotate-bytes=536870912 --logging-rotate-backup-count=5 --gcs-address=127.0.0.1:43919 --cluster-id-hex=97d382d349ced6bc4406879caed009b547b42c9aad36ac5cd3305571 --node-ip-address=127.0.0.1 --stdout-filepath=/tmp/ray/session_2026-01-10_08-37-43_892531_3832/logs/dashboard.out --stderr-filepath=/tmp/ray/session_2026-01-10_08-37-43_892531_3832/logs/dashboard.err --minimal pull.rebase (dns block)
  • Triggering command: /usr/bin/python3 /usr/bin/python3 /home/REDACTED/.local/lib/python3.12/site-packages/ray/dashboard/dashboard.py --host=127.0.0.1 --port=8265 --port-retries=50 --temp-dir=/tmp/ray --log-dir=/tmp/ray/session_2026-01-10_08-38-34_168600_4240/logs --session-dir=/tmp/ray/session_2026-01-10_08-38-34_168600_4240 --logging-rotate-bytes=536870912 --logging-rotate-backup-count=5 --gcs-address=127.0.0.1:46054 --cluster-id-hex=fb1fa4f56b7d156e008fbba8f39cdf69844e221bfd3ffd5b729b74c4 --node-ip-address=127.0.0.1 --stdout-filepath=/tmp/ray/session_2026-01-10_08-38-34_168600_4240/logs/dashboard.out --stderr-filepath=/tmp/ray/session_2026-01-10_08-38-34_168600_4240/logs/dashboard.err --minimal .js (dns block)
  • Triggering command: /usr/bin/python3 /usr/bin/python3 /home/REDACTED/.local/lib/python3.12/site-packages/ray/dashboard/dashboard.py --host=127.0.0.1 --port=8265 --port-retries=50 --temp-dir=/tmp/ray --log-dir=/tmp/ray/session_2026-01-10_08-40-16_435306_4778/logs --session-dir=/tmp/ray/session_2026-01-10_08-40-16_435306_4778 --logging-rotate-bytes=536870912 --logging-rotate-backup-count=5 --gcs-address=127.0.0.1:45251 --cluster-id-hex=12830389913f810d52524c2e0628c76352cbd9da533c1b2c9ada2482 --node-ip-address=127.0.0.1 --stdout-filepath=/tmp/ray/session_2026-01-10_08-40-16_435306_4778/logs/dashboard.out --stderr-filepath=/tmp/ray/session_2026-01-10_08-40-16_435306_4778/logs/dashboard.err --minimal (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>BlendSearch in UDF mode</issue_title>
<issue_description>When I select the BlendSearch search algorithm, I consistently encounter the following warning, whereas it does not appear when using CFO:

You passed a space parameter to OptunaSearch that contained unresolved search space definitions. OptunaSearch should however be instantiated with fully configured search spaces only. To use Ray Tune's automatic search space conversion, pass the space definition as part of the param_space argument to tune.Tuner() instead.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes BlendSearch in UDF mode #1283

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