sgl-project/sglang · error · ValueError

name must be provided

Error message

name must be provided

What it means

process_name_for_reasoning builds a '<name>_reasoning_content' output key from a generation expression's name and requires a non-empty name. When expr.name is None/empty (e.g. sgen called without name=), ValueError is raised because there is no key to attach reasoning output to.

Source

Thrown at python/sglang/lang/ir.py:630

    def __init__(self):
        super().__init__()

    def __repr__(self):
        return "CommitLazy()"


class SglSeparateReasoning(SglExpr):
    def __init__(self, model_type: str, expr: SglExpr):
        super().__init__()
        self.model_type = model_type

        self.expr = expr
        self.name = None
        self._process_expr(expr)

    def process_name_for_reasoning(self, name):
        if not name:
            raise ValueError("name must be provided")
        return f"{name}_reasoning_content"

    def _process_expr(self, expr):
        if isinstance(expr, SglGen):
            self.name = self.process_name_for_reasoning(expr.name)
        elif isinstance(expr, SglSelect):
            self.name = self.process_name_for_reasoning(expr.name)
        elif isinstance(expr, SglExprList):
            for x in expr.expr_list:
                self._process_expr(x)

    def __repr__(self):
        return f"SeparateReasoning(model_type={self.model_type}, name={self.name})"

View on GitHub (pinned to 0132848349)

Solutions

1. Pass an explicit name to the generation call: sgen(..., name="answer")
2. Check that every gen/select inside the function that reasoning applies to has a unique non-empty name

Example fix

# before
gen("...", temperature=0.7)

# after
gen("...", name="answer", temperature=0.7)

if not getattr(gen_expr, "name", None):
    gen_expr.name = "answer"  # or raise early with context
result = separate_reasoning(gen_expr)

try:
    out = separate_reasoning(expr)
except ValueError as e:
    if "name must be provided" in str(e):
        expr.name = expr.name or "answer"
        out = separate_reasoning(expr)
    else:
        raise

When it happens

Trigger: Using separate reasoning (e.g. _execute_separate_reasoning path) with a SglGen/SglSelect expression that was created without a name parameter, so process_name_for_reasoning receives a falsy name.

Common situations: Adding sgen(...) calls without name="..." in an SGL function and then enabling reasoning separation; relying on older code where names were auto-generated.

Understand the failure class

Background: Missing required parameter errors: what 'X is required' and 'the required X param is missing' mean, and how to fix them — this error's family across 27 libraries.

Related errors

• invalid reasoning effort: {effort!r}
• invalid Inkling reasoning_effort: {value!r}
• v_cache must be provided
• q can only be None when only_qv=True
• q must be provided unless qv is provided with only_qv=True

AI-assisted analysis of sgl-project/sglang@0132848349 (2026-08-28). Data as JSON: /api/errors/6e980e03b4743d4b. Report an issue: GitHub.