[Bugfix] Fix ImportError in get_chat_template for builtin chat-template names

[waynehacking8]

Motivation

lmdeploy serve api_server ... --chat-template <name> and lmdeploy chat ... --chat-template <name> crash with ImportError whenever <name> is a builtin chat-template name (anything that is not a .json file path):

ImportError: cannot import name 'DEPRECATED_CHAT_TEMPLATE_NAMES' from 'lmdeploy.model'

Fixes #4533.

Root cause

get_chat_template (lmdeploy/cli/utils.py) imports DEPRECATED_CHAT_TEMPLATE_NAMES and REMOVED_CHAT_TEMPLATE_NAMES from lmdeploy.model. Those lists were removed in #4252 ([AsyncEngine Refactor 2/N] Remove deprecates from chat template), which cleaned up model.py, cli.py, async_engine.py and the tests but left the import — and its two guard blocks — dangling in cli/utils.py. The two names now exist nowhere in the repo, so the import raises before reaching the registry validation.

The crash only fires on the else branch (a builtin name that is not a file), which is why it went unnoticed: passing no --chat-template, or a .json file path, both return earlier. It is reachable from both lmdeploy/cli/serve.py (serve api_server) and lmdeploy/cli/chat.py (chat).

Modification

Complete the #4252 refactor in get_chat_template: drop the dead import and the removed-/deprecated-name guard blocks, keep the existing MODELS registry check, and remove the now-unused module-level logger. Unknown names are still rejected — by the registry assert, which lists the builtin templates.

BC-breaking (Optional)

No. Builtin names that previously crashed now work; unknown names still raise (an AssertionError from the registry check instead of an ImportError).

Use cases (Optional)

lmdeploy chat <model_path> --chat-template internlm2
lmdeploy serve api_server <model_path> --chat-template qwen

Checklist

1. Added regression tests in tests/test_lmdeploy/test_utils.py (GPU-free, no model load):
   • test_get_chat_template_builtin_name — get_chat_template('llama2') returns a ChatTemplateConfig. Fails with ImportError on current main, passes with this fix.
   • test_get_chat_template_unregistered_name — an unregistered name raises AssertionError (registry check), not ImportError.
   • test_get_chat_template_none — None in → None out.
2. Verified locally: reverting only the cli/utils.py change makes test_get_chat_template_builtin_name fail at cli/utils.py:85: ImportError; with the fix all three pass. pre-commit (ruff-check / docformatter / copyright) is clean.

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