# OpenLogi Cross-Platform cfg-Gating Strategy: Rust Conditional Compilation for Multi-OS Support

> Master Rust cfg-gating in OpenLogi to build cross-platform applications for macOS Linux and Windows. Leverage Cargo for efficient conditional compilation and optimize your multi-OS support.

- Repository: [Xuan Zhang/OpenLogi](https://github.com/AprilNEA/OpenLogi)
- Tags: architecture
- Published: 2026-08-24

---

**OpenLogi uses Rust's `#[cfg]` attributes and Cargo's target-specific dependencies to compile platform-specific code only on relevant operating systems, enabling a single codebase to support macOS, Linux, and Windows without runtime overhead.**

OpenLogi is a cross-platform automation framework that runs natively on macOS, Linux, and Windows. Managing disparate platform APIs while maintaining a unified public interface requires a disciplined approach to **conditional compilation**. This article examines the **OpenLogi cross-platform cfg-gating strategy** as implemented in the AprilNEA/OpenLogi repository, demonstrating how the project leverages Rust's compile-time configuration system to isolate OS-specific implementations.

## The Four Layers of Conditional Compilation

The OpenLogi codebase organizes platform-specific logic into four distinct layers, each serving a specific architectural purpose. This hierarchy ensures that platform dependencies are both explicit and minimal.

### Crate-Level Gating

At the highest level, the project uses **target-specific dependencies** in [`Cargo.toml`](https://github.com/AprilNEA/OpenLogi/blob/main/Cargo.toml) to ensure platform-only libraries are never compiled on the wrong OS. This prevents linking errors and keeps the build graph minimal.

According to the OpenLogi source code, the configuration uses `target.'cfg(...)'` tables:

```toml
[target.'cfg(target_os = "macos")'.dependencies]
async-hid = "0.5"
macos-api = { git = "https://github.com/Apple/macOS-api" }

[target.'cfg(target_os = "linux")'.dependencies]
evdev = "0.12"
linux-permissions = "1.0"

[target.'cfg(target_os = "windows")'.dependencies]
winapi = { version = "0.3", features = ["winuser"] }

```

### Module-Level Gating

Large OS-specific implementations are split into separate modules within the same crate. The entry point uses `#[cfg(target_os = "...")]` to conditionally compile only the relevant module.

In [`crates/openlogi-hook/src/lib.rs`](https://github.com/AprilNEA/OpenLogi/blob/main/crates/openlogi-hook/src/lib.rs), the input-hook subsystem declares three top-level modules:

```rust
#[cfg(target_os = "macos")]
mod macos;
#[cfg(target_os = "linux")]
mod linux;
#[cfg(target_os = "windows")]
mod windows;

```

The public API (`Hook::start()`) is defined once in the parent module, while the internals differ per OS. This pattern keeps the public API identical across platforms while isolating implementation details.

### Item-Level Gating

Individual structs, functions, or `impl` blocks that call platform APIs are guarded at the item level. This fine-grained control prevents accidental use of OS-specific functions on incompatible targets.

In [`crates/openlogi-inject/src/inject.rs`](https://github.com/AprilNEA/OpenLogi/blob/main/crates/openlogi-inject/src/inject.rs), input synthesis functions are gated as follows:

```rust
#[cfg(target_os = "windows")]
pub fn send_key_windows(vk: u16) { /* Windows API */ }

#[cfg(target_os = "macos")]
pub fn send_key_macos(keycode: u32) { /* CGEvent API */ }

```

### Runtime Abstractions

The strategy exposes **platform-agnostic traits** (e.g., `HidBackend`) that each OS module implements. The rest of the codebase works against the trait without caring about the concrete OS, enabling compile-time polymorphism.

In [`crates/openlogi-hid/src/lib.rs`](https://github.com/AprilNEA/OpenLogi/blob/main/crates/openlogi-hid/src/lib.rs), the trait abstraction appears as:

```rust
pub trait HidBackend {
    fn open(&self, vid: u16, pid: u16) -> Result<Box<dyn Device>, HidError>;
}

// macOS implementation (only compiled on macOS)
#[cfg(target_os = "macos")]
mod macos_impl {
    use super::HidBackend;
    pub struct MacBackend;
    impl HidBackend for MacBackend {
        fn open(&self, vid: u16, pid: u16) -> Result<Box<dyn Device>, HidError> {
            /* macOS-specific code */
        }
    }
}

```

## Implementation Patterns in the Source Tree

OpenLogi applies these layers consistently across its crate structure. Specific files demonstrate distinct aspects of the cfg-gating strategy.

### Transport Layer Selection

[`crates/openlogi-hid/src/transport.rs`](https://github.com/AprilNEA/OpenLogi/blob/main/crates/openlogi-hid/src/transport.rs) serves as the central hub that selects the correct OS transport implementation. The file uses `#[cfg(target_os = "...")]` to re-export a single `Transport` type that aliases to the platform-specific implementation:

```rust
// crates/openlogi-hid/src/transport.rs
#[cfg(target_os = "macos")]
mod macos;
#[cfg(target_os = "linux")]
mod linux;
#[cfg(target_os = "windows")]
mod windows;

// Public type used by the rest of the code base
pub use self::{macos::Transport as TransportMac,
               linux::Transport as TransportLinux,
               windows::Transport as TransportWindows};

```

### Input Hook Entry Points

The [`crates/openlogi-hook/src/lib.rs`](https://github.com/AprilNEA/OpenLogi/blob/main/crates/openlogi-hook/src/lib.rs) file demonstrates crate-level gating for the input-hook subsystem. It contains three top-level modules (`macos`, `linux`, `windows`), each guarded by `#[cfg(target_os = "...")]`. The public API remains consistent while the internal event loop implementations vary by platform.

### Desktop Platform Wrappers

[`crates/openlogi-desktop/src/platform/os.rs`](https://github.com/AprilNEA/OpenLogi/blob/main/crates/openlogi-desktop/src/platform/os.rs) provides a thin wrapper that forwards to the appropriate macOS or Linux implementation. This file illustrates how higher-level crates delegate to platform-specific code without exposing implementation details to consumers.

### System Tray Integration

The system-tray integration in [`crates/openlogi-agent/src/tray.rs`](https://github.com/AprilNEA/OpenLogi/blob/main/crates/openlogi-agent/src/tray.rs) uses cfg-gating to only compile tray code on supported platforms:

```rust
#[cfg(target_os = "macos")]
mod macos_tray;

#[cfg(target_os = "windows")]
mod windows_tray;

```

Linux builds exclude this functionality entirely at compile time, reducing binary size and eliminating unnecessary dependencies.

## Benefits of the cfg-Gating Strategy

This compile-time approach delivers specific advantages for cross-platform Rust development:

- **Compile-Time Safety**: Any accidental use of a platform-specific function on the wrong target immediately fails to compile. In [`crates/openlogi-permissions/src/lib.rs`](https://github.com/AprilNEA/OpenLogi/blob/main/crates/openlogi-permissions/src/lib.rs), permission handling logic uses `#[cfg]` to ensure macOS-specific entitlement checks never appear in Linux builds.
- **Single Source of Truth**: The public API—traits, enums, and CLI commands—lives in shared modules with no `#[cfg]` attributes. All OS-specific code implements the same traits, keeping the rest of the codebase platform-oblivious.
- **Modular Testing**: Each OS module can be unit-tested behind a `#[cfg(test)]` harness that forces the appropriate target. This facilitates CI jobs that run separately on Linux, macOS, and Windows, ensuring platform-specific logic is verified on its native target.

## Summary

OpenLogi's cross-platform strategy relies on Rust's conditional compilation to maintain a clean separation between platform-specific implementations and shared business logic. Key takeaways include:

- **Crate-level gating** through Cargo's `target.'cfg(...)'` dependency tables ensures platform libraries are only fetched and linked for their respective targets.
- **Module and item-level gating** using `#[cfg(target_os = "...")]` isolates OS-specific code while exposing a unified public API through trait abstractions.
- **Concrete implementations** in files like [`crates/openlogi-hid/src/transport.rs`](https://github.com/AprilNEA/OpenLogi/blob/main/crates/openlogi-hid/src/transport.rs) and [`crates/openlogi-hook/src/lib.rs`](https://github.com/AprilNEA/OpenLogi/blob/main/crates/openlogi-hook/src/lib.rs) demonstrate how to structure cross-platform crates for maintainability.
- **Compile-time elimination** of unsupported platform code prevents runtime crashes and reduces binary size compared to runtime dispatch approaches.

## Frequently Asked Questions

### How does OpenLogi prevent compiling Windows-specific code on Linux?

OpenLogi uses Rust's `#[cfg(target_os = "windows")]` attribute to gate Windows-specific functions, modules, and dependencies. The Rust compiler evaluates these conditions at compile time; if the target OS is not Windows, the compiler ignores the gated code entirely, preventing linking errors and ensuring Linux builds contain no Windows API calls.

### What is the difference between module-level and item-level cfg-gating?

**Module-level gating** applies the `#[cfg]` attribute to an entire module declaration (e.g., `#[cfg(target_os = "linux")] mod linux;`), which excludes all contents of that module from compilation on other platforms. **Item-level gating** applies to individual structs, functions, or implementations (e.g., `#[cfg(target_os = "macos")] pub fn open_device(...)`), allowing fine-grained control when multiple platforms share a module file but implement specific items differently.

### Why use trait abstractions instead of conditional compilation everywhere?

Trait abstractions in OpenLogi (such as `HidBackend`) provide a **single public interface** that the rest of the codebase can import without knowing which platform is running. While `#[cfg]` selects the correct implementation at compile time, the trait ensures type safety and allows the majority of the code to remain platform-agnostic, reducing the surface area where conditional compilation is required.

### How does Cargo support platform-specific dependencies?

Cargo supports platform-specific dependencies through `target.'cfg(...)'` tables in [`Cargo.toml`](https://github.com/AprilNEA/OpenLogi/blob/main/Cargo.toml). OpenLogi declares dependencies like `async-hid` under `[target.'cfg(target_os = "macos")'.dependencies]`, ensuring the library is only downloaded and compiled when building for macOS, keeping build times and artifact sizes minimal for Linux and Windows targets.