cistell 0.1.2

Configuration library with field provenance and secret support

Cistell

A powerful, transparent configuration library with provenance tracking and secret support for Rust and Python.

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Overview

Cistell is a configuration resolution engine providing zero-boilerplate settings loading with robust accountability. Built heavily in Rust, it brings performance, type safety, and correctness across two ecosystems:

• Rust (cistell-core, cistell-macros): Native library with a convenient #[derive(Config)] procedural macro.
• Python (cistell): Performant bindings that serve as an idiomatic drop-in replacement for the original pure-Python cistell, extending its features with exact provenance APIs and fast resolution.

There's no more guessing where a config value came from. cistell tells you exactly how it resolved each field across 7 different possible priority layers, all while keeping secrets secure.

Features & Highlights

• Field Provenance Tracking: Inquire exactly where any configuration state was materialized from.
• Priority Resolution Chain: Values fall through an exact, strictly ordered 7-level priority chain.
• Secret Management: Built-in Secret<T> wrapper (Rust) and secret=True kwargs (Python) natively redact sensitive config properties across logs and display operations.
• Zero-Boilerplate Derivation: Simple attribute tagging configures fallback defaults and variable names.

Quick Start (Rust)

Add cistell-core to your Cargo.toml:

[dependencies]
cistell-core = "0.1.0"

use cistell_core::{Config, Secret};

#[derive(Config, Debug)]
struct ServerConfig {
    #[config(default = "127.0.0.1")]
    host: String,

    #[config(default = 8080)]
    port: u16,

    #[config(env = "API_KEY")]
    api_key: Secret<String>,
}

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let cfg = ServerConfig::load()?;

    println!("Resolved Host: {}", cfg.host);
    // Explain the provenance
    println!("Provenance:\n{}", cistell_core::explain(&cfg));

    Ok(())
}

Quick Start (Python)

Install via pip or uv:

pip install cistell

from cistell import ConfigBase, ConfigField

class MySettings(ConfigBase):
    host = ConfigField("127.0.0.1")
    port = ConfigField(8080)
    api_key = ConfigField("default-key", secret=True)

cfg = MySettings()

print(cfg.host)
print(cfg.api_key) # prints 'default-key'

# Inspect how values were resolved
print(cfg.explain())

# Export a redacted immutable dictionary
print(cfg.safe_dict())

Priority Chain

When resolving a field, Cistell checks the following layers in exact descending order of priority.

Priority Level	Source	Description
1	Explicit/Overridden	Programmatically set at runtime via instantiation or context overrides.
2	Environment Variable	Matches PREFIX_FIELD_NAME (or specifically configured env key).
3	Environment File	Value parsed statically from a .env file.
4	Selected Config File	Value loaded from a specifically pointed config.toml, config.yaml, or .json.
5	pyproject.toml	Defaults pulled directly from Python packaging [tool.yourapp] namespace (if applicable).
6	Default Config File	The default generic configuration file found in the working directory.
7	Hardcoded Defaults	Fallback static definition assigned via macro #[config(default = ...)] or python ConfigField(default).

Feature Flags (Rust)

You can opt-in to parsing requirements in your Cargo.toml for cistell-core:

Feature	Default	Description
toml	✅	TOML file support
yaml	❌	YAML file support
json	❌	JSON file support
serde	❌	Enable Serialize/Deserialize on Secret<T>
zeroize	❌	Enable zero-on-drop mapping for Secret<T>

Secret Fields

Keeping secrets out of crash reports and debug prints is critical. By using Secret<T> (Rust) or ConfigField(secret=True) (Python), any underlying representation correctly implements traits or __repr__ functions that output "***" rendering it harmless to standard printing vectors out of the box.

Provenance

Need to figure out if your port was configured by .env, Docker env injection, or fell-back to the code default?

Use cfg.explain() to log the materialized source configuration on startup. Use cfg.safe_dict() to retrieve an inert representation of configuration states. Both functions intrinsically hide secret parameters gracefully.

Python Compatibility

• Minimum Version: Python 3.12+
• Dependencies: No Python dependencies. All complex loading natively invokes Rust via PyO3.
• Available natively via pre-built wheels across Linux (manylinux), macOS (x86_64, arm64), and Windows.

License

Cistell is distributed freely under the MIT License. CENSE).