fix: read beam.search_type from config instead of hardcoding 'default'

[nedalaltiti]

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What does this PR do ?

Fixes CTC beam decoding configuration by reading beam.search_type from the decoding config instead of hardcoding search_type="default" when strategy="beam" in AbstractCTCDecoding.__init__.

This enables intended behavior for LM-aware beam search backends (e.g., pyctcdecode) when users set beam.search_type and provide kenlm_path.

Collection: [ASR]

Changelog

• Update AbstractCTCDecoding.__init__ to pass:

  • from search_type="default"
  • to search_type=self.cfg.beam.get("search_type", "default")

• Keeps backward compatibility via the "default" fallback when beam.search_type is not set.

Usage

from omegaconf import OmegaConf

ctc_cfg = OmegaConf.create({
    "strategy": "beam",
    "beam": {
        "beam_size": 32,
        "search_type": "pyctcdecode",
        "kenlm_path": "/path/to/lm.arpa",
        "beam_alpha": 0.5,
        "beam_beta": 0.1,
    },
})

model.change_decoding_strategy(decoding_cfg=ctc_cfg, decoder_type="ctc")

# After this fix, the configured search_type is preserved
assert model.ctc_decoding.decoding.search_type == "pyctcdecode"

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PR Type:

• New Feature
• Bugfix
• Documentation

Additional Information

• Related to [ASR][CTC] Beam decoding ignores beam.search_type (search_type hardcoded to "default") #15400

Diff summary:

• search_type="default"

• search_type=self.cfg.beam.get("search_type", "default")

Reviewer: @nithinraok

[nedalaltiti]

Hi @nithinraok, could you please add the Run CICD label to trigger the CI tests? Also requesting your review on this ASR fix.

Note: The reformat_with_isort_and_black check failure is a CI infrastructure issue — the changed-files action cannot resolve fork commit SHAs with pull_request_target. It is unrelated to this code change. Happy to rebase or adjust if needed.