Typed environment variables and Lightning CSS

Two features land in this update: typed environment variables and opt-in Lightning CSS. One tightens the boundary between your config and your code; the other speeds up how Ossido processes your CSS.

Typed environment variables

Environment config has always been stringly-typed and easy to get wrong - a missing variable surfaces as a runtime undefined deep inside a request. Ossido now lets you declare a single, typed source of truth: an Environment struct in Rust. Its fields are parsed and validated from the OS environment at startup, and the ones you mark #[public] are exposed to the frontend with generated TypeScript types.

// src/env.rs
use ossido::Environment;

#[Environment]
pub struct Environment {
    #[public]
    API_URL: String,

    #[public]
    ANALYTICS_ENABLED: Option<bool>,

    // Server-only secret - never leaves the backend.
    DATABASE_URL: String,
}

A required field that is missing or unparseable panics at startup with the offending variable name, so a bad config fails loudly on boot instead of three screens into a request. Read any field in Rust with the get_env! macro:

use ossido::get_env;

let db = get_env!(DATABASE_URL); // String
let analytics = get_env!(ANALYTICS_ENABLED, false); // bool

On the frontend, only #[public] fields are available, fully typed from the generated .ossido/types.ts:

import { getEnv } from '@ossido-labs/ossido/env';

const apiUrl = getEnv('API_URL'); // string
const enabled = getEnv('ANALYTICS_ENABLED', false); // boolean

A second argument to get_env! or getEnv is a fallback that collapses an Option<T> value to a concrete T. Secrets stay in Rust - only public fields are serialized into the page, so a connection string can never leak into the client bundle. The whole feature is optional: define no struct and nothing changes. Full details in Environment Variables.

Lightning CSS

Ossido can now process CSS with Lightning CSS - a fast, Rust-based transformer and minifier - in place of Vite's default PostCSS pipeline. It's opt-in; turn it on in ossido.config.ts:

const config: OssidoConfig = {
  lightningcss: true,
};

That switches on the transformer in dev and build, and minification in the production build, using a sensible default set of browser targets. Point it at your own browserslist query when you need to:

const config: OssidoConfig = {
  lightningcss: { targets: '>= 0.25%, not dead' },
};

You get autoprefixing and modern-CSS lowering (nesting, custom media, colour functions) driven by those targets, minified production bundles, and CSS Modules that keep working - all running in Rust instead of PostCSS + esbuild. Vite plugins like @tailwindcss/vite are unaffected and compose cleanly. More in Styling → Lightning CSS.

Get started

Both features are documented in full:

• Environment Variables
• Lightning CSS

Upgrading

Bump the ossido crate and the @ossido-labs/ossido package to 0.1.4, and update the CLI:

cargo install ossido_cli --version 0.1.4 --locked

The full diff is in the 0.1.4 release notes (0.1.3...0.1.4).