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Seven llama_sampler_init_* bindings admit keyword arguments that the ctypes function object silently drops

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
88/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
python
Domain
api

Research direction

Start in llama_cpp/llama_cpp.py at the seven llama_sampler_init_* definitions around lines 4553-4606, then read ctypes_function in llama_cpp/_ctypes_extensions.py:146-152 to confirm how the exported functions are created. Make the seven binding parameters positional-only, matching the surrounding definitions, and verify that their signatures no longer invite keyword calls.

Written by the indexing model from the issue text.

Description

Summary

In llama_cpp/llama_cpp.py, seven bindings are declared as defs whose parameters are NOT
positional-only, while every other decorated binding in the file uses /:

line (main d736646) def
4553 def llama_sampler_init_dist(seed: int) -> llama_sampler_p
4560 def llama_sampler_init_top_k(k: int) -> llama_sampler_p
4570 def llama_sampler_init_top_p(p: float, min_keep: int) -> llama_sampler_p
4580 def llama_sampler_init_min_p(p: float, min_keep: int) -> llama_sampler_p
4590 def llama_sampler_init_typical(p: float, min_keep: int) -> llama_sampler_p
4596 def llama_sampler_init_temp(t: float) -> llama_sampler_p
4606 def llama_sampler_init_temp_ext(t: float, delta: float, exponent: float) -> llama_sampler_p

ctypes_function (llama_cpp/_ctypes_extensions.py:146-152) replaces the def with the
ctypes function object:

def decorator(f):
    if enabled:
        func = getattr(lib, name)
        func.argtypes = argtypes
        func.restype = restype
        functools.wraps(f)(func)
        return func

so the name the module exports IS getattr(lib, "llama_sampler_init_top_k"). A ctypes
function object without paramflags binds no argument by name, but functools.wraps and
the (f: F) -> F typing make inspect.signature, pyright and IDEs show the def's
signature — which invites keyword calls the object cannot honour.

What happens (CPython 3.12.10, ctypes)

>>> import ctypes; lib = ctypes.CDLL(None); f = lib.abs
>>> f.argtypes = [ctypes.c_int]; f.restype = ctypes.c_int
>>> f(-3, x=1)        # an extra keyword is DROPPED silently
3
>>> f(x=-3)           # all-keyword: refused
TypeError: this function takes at least 1 argument (0 given)

Applied to these bindings:

  • llama_sampler_init_top_k(k=40) — type-checks clean, raises TypeError at run time.
  • llama_sampler_init_top_p(0.9, min_keep=2) — type-checks clean, runs, and passes ONE
    positional to a two-parameter C function: min_keep is silently dropped and the C side
    reads whatever the register/stack held for it.

No caller inside the repository is affected today (_internals.py:705-732 and the server
pass positionals), so this is a latent API hazard rather than a current bug — but the
signature is public and the failure is invisible to every static check.

Fix

Make the seven defs positional-only, as the other bindings already are:

def llama_sampler_init_top_k(k: int, /) -> llama_sampler_p: ...

(Alternatively, build the functions through a CFUNCTYPE prototype with paramflags,
which does bind by name — but the one-character fix matches the file's convention.)

Found with SemLinker, a cross-language contract checker we are developing; happy to send a PR.

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