Hacktoberfest 2026: die Issues, die Maintainer für den Oktober markiert haben – offen und einsteigerfreundlich. Hacktoberfest-Issues durchsuchen

Suppress "Placeholders have not been resolved" warning when MessagesPlaceholder use is intentional (LangChain integration)

Offen
  • Stimmt etwas nicht?
#1,667 1 Kommentar 0 Reaktionen 1 zugewiesene Person Auf GitHub ansehen

Maintainer antworten meist innerhalb von 1 Tag

@hassiebp arbeitet bereits daran.

Seit 22.5.2026.

Bewertung

Dieses Issue wurde noch nicht bewertet.

Beschreibung

bug integration-langchain integrations sdk-python

Summary

ChatPromptClient.compile() (and get_langchain_prompt() which calls it
under the hood) unconditionally logs:

Placeholders ['...'] have not been resolved. Pass them as keyword arguments to compile().

even when leaving placeholders unresolved is intentional — i.e. the
caller follows the officially documented LangChain integration pattern
where unresolved placeholders are deliberately returned as
MessagesPlaceholder for LangChain's ChatPromptTemplate to resolve at
.invoke() time.

Result: production logs are flooded with one WARNING per request, masking
real signals.

Reproduction (langfuse 4.6.1, official docs example)

from langfuse import get_client
from langchain_core.prompts import ChatPromptTemplate

langfuse = get_client()

# Create a chat prompt with a placeholder (per docs example)
langfuse.create_prompt(
    name="movie-critic-chat",
    type="chat",
    prompt=[
        {"role": "system", "content": "You are an expert movie critic"},
        {"type": "placeholder", "name": "chat_history"},
        {"role": "user", "content": "What should I watch next?"},
    ],
    labels=["production"],
)

# Documented LangChain integration:
# https://langfuse.com/docs/prompt-management/features/message-placeholders
prompt = langfuse.get_prompt("movie-critic-chat")
langchain_prompt = ChatPromptTemplate.from_template(prompt.get_langchain_prompt())

# → logs WARNING: Placeholders ['chat_history'] have not been resolved.
#   even though leaving it unresolved is EXACTLY what the docs tell you
#   to do for LangChain integration.

Why this is a problem

  1. The docs at /docs/prompt-management/features/message-placeholders
    (LangChain Python tab) endorse this exact pattern — MessagesPlaceholder
    objects in the output are the documented goal.
  2. SDK can't distinguish "intentional unresolved (LangChain hand-off)" from
    "misuse (forgot kwargs)" and warns in both cases.
  3. No public API to silence: no silent= / suppress_warnings= kwarg on
    compile() or get_langchain_prompt().
  4. logging.getLogger("langfuse").setLevel(...) is not a reliable
    workaround — see langfuse/langfuse#4976 reporting setLevel doesn't
    affect certain SDK-emitted warnings.
  5. Forces every LangChain integrator to install a logging.Filter that
    string-matches the warning message — brittle (breaks on copy edits)
    and easy to over-silence.

Suggested fix

Add a silent=True (or suppress_unresolved_warning=True) kwarg to:

  • ChatPromptClient.compile(**kwargs, silent: bool = False)
  • ChatPromptClient.get_langchain_prompt(**kwargs, silent: bool = False)

When silent=True, the
"Placeholders ['...'] have not been resolved" warning is skipped, but
other validation warnings (e.g. "Placeholder X must contain a list of
chat messages") still fire — those are genuine misuse signals.

Alternatively, get_langchain_prompt() could pass silent=True to its
internal compile() call by default, since by definition any unresolved
placeholder returned from this method is intended for LangChain.

Version info

  • langfuse-python: 4.6.1 (also reproduces on 4.5.1 + main HEAD)
  • langchain-core: 1.3.2
  • Python: 3.11

Current workaround we use

contextlib.contextmanager that scopes a logging.Filter matching the
substring "have not been resolved" over the
chat_skeleton.get_langchain_prompt() call site. Fragile (depends on
warning string), but scoped narrowly so other langfuse warnings still
propagate.

Happy to send a PR if the maintainers agree with the kwarg shape.

Vorherrschende Sprache
Python
Sterne
468
Forks
349
Ø Merge
15 Std. 51 Min.
Gemergte PRs (30 T.)
24

Entwicklungsumgebung

Erste Schritte

  1. Lesen Sie das ganze Issue und danach den Beitragsleitfaden des Projekts.
  2. Schreiben Sie ins Issue, dass Sie es übernehmen — das erspart doppelte Arbeit.
  3. Forken Sie das Repository und arbeiten Sie in einem Branch.
  4. Öffnen Sie einen Pull Request, der die Issue-Nummer nennt.

Mehr aus langfuse/langfuse-python

Alle Issues in langfuse/langfuse-python

Ähnliche Issues

Weitere Issues zu Python

Neue Issues direkt in Ihr Postfach

Eine kurze Übersicht über anfängerfreundliche GitHub-Issues.