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Sarj Sarj Sarj Standards

no-hidden-constructor-fallback

Constructor option silently falls back to application settings when omitted.

SARJ095 Rule source Tests Catalog JSON

Why

Hidden configuration lookup obscures dependencies and makes construction vary with ambient application state.

Fix

Require the constructor argument and resolve any default at the composition root or call site.

Examples

Before — flagged Constructor reads an implicit default from settings
app/config.py
from pydantic_settings import BaseSettings




class Settings(BaseSettings):
    MODEL: str = "model"




settings = Settings()
app/service.py
from app.config import settings




class Generator:
    def __init__(self, *, model: str | None = None) -> None:
        self.model = model or settings.MODEL




generator = Generator(model="explicit")
pyproject.toml
[project]
name = 'example'
version = '0.1.0'
After — preferred Constructor requires its dependency
app/config.py
from pydantic_settings import BaseSettings




class Settings(BaseSettings):
    MODEL: str = "model"




settings = Settings()
app/service.py
class Generator:
    def __init__(self, *, model: str) -> None:
        self.model = model




generator = Generator(model="explicit")
pyproject.toml
[project]
name = 'example'
version = '0.1.0'