IndexError: list index out of range——vLLM LoRA 加载 Qwen3.5 崩溃，choices[0] 的无保护访问

(EngineCore_DP0 pid=2550193) ERROR 03-09 16:48:25 [core.py:1100]
  File "vllm/lora/layers/column_parallel_linear.py", line 268, in set_lora
    if (lora_a_i := lora_a[i]) is not None:
                    ~~~~~~^^^
IndexError: list index out of range

File "anthropic/experimental_pass_through/adapters/streaming_iterator.py", line 819
    if chunk.choices[0].finish_reason is not None:
       ~~~~~~~~~~~~~^^^
IndexError: list index out of range

vllm serve /opt/nas/n/model/Qwen3.5-2B \
  --gpu-memory-utilization 0.6 \
  --enable-lora \
  --lora-modules M1=/opt/nas/n/ms-swift/output/lora/2B/checkpoint-1640

LoRA 适配器激活
  → model_manager.activate_adapter(lora_id)
  → module.set_lora(lora_a, lora_b)
  → column_parallel_linear.py:268
  → lora_a[i]  ← i 的值超出 lora_a 列表长度
  → IndexError

streaming_iterator.py:346   → chunk.choices[0]
streaming_iterator.py:594   → chunk.choices[0]
streaming_iterator.py:819   → chunk.choices[0].finish_reason
transformation.py:1401      → chunk.choices[0]
transformation.py:1603      → chunk.choices[0]

// Objects/listobject.c
PyObject *
PyList_GetItem(PyObject *op, Py_ssize_t i)
{
    if (!PyList_Check(op)) {
        PyErr_BadInternalCall();
        return NULL;
    }
    // 关键检查！
    if (i < 0 || i >= Py_SIZE(op)) {
        if (indexerr == NULL) {
            indexerr = PyUnicode_FromString(
                "list index out of range");
        }
        PyErr_SetObject(PyExc_IndexError, indexerr);
        return NULL;
    }
    return ((PyListObject *)op)->ob_item[i];
}

if (i < 0 || i >= Py_SIZE(op)) {
    // → 抛出 IndexError
}

// Python/ceval.c (简化)
case TARGET(BINARY_SUBSCR): {
    PyObject *sub = POP();   // 索引值
    PyObject *container = TOP();  // 列表对象
    PyObject *res = PyObject_GetItem(container, sub);
    // PyObject_GetItem → PyList_GetItem → 检查边界 → IndexError
    if (res == NULL)
        goto error;
    SET_TOP(res);
    Py_DECREF(container);
    Py_DECREF(sub);
    DISPATCH();
}

# ❌ 错误：假设 lora_a 足够长
for i, module in enumerate(target_modules):
    lora_a_i = lora_a[i]  # lora_a 可能比 target_modules 短

# ✅ 正确：先检查长度
for i, module in enumerate(target_modules):
    if i >= len(lora_a):
        logger.warning(f"lora_a has no entry for module {i}, skipping")
        continue
    lora_a_i = lora_a[i]

# ❌ 错误：假设 choices 永远非空
first_choice = response.choices[0]

# ✅ 正确：防御式访问
if not response.choices:
    logger.warning("Empty choices in response, skipping")
    return None
first_choice = response.choices[0]

# ❌ 错误：假设用户传了参数
filename = sys.argv[1]  # python script.py → IndexError

# ✅ 正确
if len(sys.argv) < 2:
    print("Usage: python script.py <filename>")
    sys.exit(1)
filename = sys.argv[1]

# ❌ 错误：假设 split 结果有 3 段
name, version, arch = package_string.split("-")  # "nginx-1.24" → IndexError

# ✅ 正确
parts = package_string.split("-")
if len(parts) == 2:
    name, version = parts
    arch = "amd64"  # 默认值
elif len(parts) == 3:
    name, version, arch = parts

# ❌ 错误：边遍历边删除
items = [1, 2, 3, 4, 5]
for i in range(len(items)):
    if items[i] % 2 == 0:
        del items[i]  # 列表变短，后续 i 越界

# ✅ 正确：列表推导式新建
items = [x for x in items if x % 2 != 0]

Traceback 最后三行：
  File "xxx.py", line N, in func
    xxx[i]
IndexError: list index out of range

→ 列表名：xxx（可能是动态计算的结果）
→ 下标：i（看上一行的赋值或循环变量）
→ 检查 len(xxx) vs i

try:
    value = some_list[index]
except IndexError:
    logger.error(
        f"IndexError: len(some_list)={len(some_list)}, "
        f"index={index}, type={type(index)}"
    )
    raise

import pdb; pdb.set_trace()
# 然后：
# (Pdb) len(lora_a)
# (Pdb) i
# (Pdb) type(i)
# (Pdb) lora_a[:10]  # 看前 10 个元素