How do I set up Fenix with Nix flakes?

Add Fenix as a flake input in your flake.nix, ensuring nixpkgs follows it, then use fenix.packages for toolchains. The README provides a full example with outputs for flakes.

Fenix vs rustup: which should I use for Rust?

Use Fenix if you're in a Nix environment and need reproducible, declarative toolchain management. Rustup is better for simple, traditional setups without Nix integration.

Does Fenix support stable Rust versions?

Yes, Fenix supports stable, beta, and nightly channels through functions like 'stable' and 'toolchainOf', allowing you to pin specific versions as shown in the examples.

How to cross-compile to WASM with Fenix?

Use the 'targets' output, such as 'targets.wasm32-unknown-unknown.latest.rust-std', combined with a toolchain for cross-compilation, as demonstrated in the naersk example.

What is the monthly branch in Fenix?

It's a branch updated on the first of each month for using rust nightly with less frequent updates, ideal for projects that don't need daily toolchain changes.

How do I use rust-analyzer nightly with Fenix?

Fenix includes 'rust-analyzer-nightly' as a derivation, available via overlays or packages. The README shows how to add it to systemPackages or VS Code extensions.

fenix

MPL-2.0Nix

Provides Rust toolchains, rust-analyzer nightly, and VS Code extensions for Nix, serving as a replacement for rustup and nixpkgs-mozilla.

GitHub

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What is fenix?

Fenix is a Nix-based project that delivers Rust toolchains, rust-analyzer nightly, and its VS Code extension, designed to replace rustup and the rust overlay from nixpkgs-mozilla. It provides flexible integration methods including flakes, packages, and overlays, making Rust development reproducible and declarative within Nix ecosystems. It offers Rust toolchain profiles (minimal, default, complete, and latest nightly), cross-compilation support, and a binary cache for faster builds.

Target Audience

Rust developers working within Nix-based environments who need reproducible and declarative toolchain management, particularly those using Nix flakes, overlays, or packages for their projects. It is also suitable for developers requiring cross-compilation to targets like WASM, Android, or macOS.

Value Proposition

Developers choose Fenix over alternatives like rustup or nixpkgs-mozilla because it integrates seamlessly with Nix, offering reproducible builds, flexible toolchain customization, and support for multiple integration methods. Its binary cache and cross-compilation capabilities further enhance development efficiency within Nix ecosystems.

Overview

Rust toolchains and rust-analyzer nightly for Nix [maintainers=@figsoda, @eureka-cpu]

Use Cases

Best For

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Managing Rust toolchains declaratively within Nix flakes, packages, or overlays.
Cross-compiling Rust projects to targets like WASM, Android, or macOS using Nix.
Pinning specific Rust toolchain versions (stable, beta, nightly, or custom dates) for reproducible builds.
Using nightly builds of rust-analyzer and its VS Code extension in Nix-based development environments.
Creating custom Rust toolchains from manifests, toolchain files, or specific channel/date combinations.
Reducing build times with binary caching via Cachix for supported platforms (x86_64-darwin, aarch64-darwin, x86_64-linux).

Not Ideal For

Projects not using Nix or preferring the simplicity of rustup for toolchain management.
Teams requiring absolute latest nightly components without any compatibility risks, as Fenix's 'latest' profile can have incompatibilities.
Environments needing binary caching for platforms not supported by Fenix's Cachix cache (e.g., aarch64-linux).
Developers using older nixpkgs with overlays, where caching issues may require complex workarounds.

Pros & Cons

Pros

Flexible Nix Integration

Supports multiple integration methods—flakes, packages, and overlays—as shown in the README usage examples, accommodating various Nix workflows seamlessly.

Extensive Cross-Compilation

Offers toolchains for numerous targets like WASM, Android, and macOS, enabling declarative cross-compilation within Nix, with detailed target lists provided.

Efficient Binary Caching

Includes a Cachix binary cache for x86_64-darwin, aarch64-darwin, and x86_64-linux, significantly reducing build times for supported platforms.

Precise Toolchain Control

Allows creating toolchains from manifests, toolchain files, or specific channel/date combinations, giving fine-grained version pinning for reproducibility.

Cons

Limited Cache Coverage

Binary caching is only available for three platforms, and using overlays with older nixpkgs may not be cached, requiring a workaround as noted in the README issue #79.

Nightly Stability Risks

The 'latest' profile provides the most recent components but risks incompatibility between them, as admitted in the README, which can break builds.

Nix Dependency Complexity

Requires familiarity with Nix concepts and setup, making it less accessible than rustup for developers new to Nix or preferring simpler toolchains.

Open Source Alternative To

fenix is an open-source alternative to the following products:

n

nixpkgs-mozilla

nixpkgs-mozilla is a collection of Nix expressions for building Mozilla software, providing Firefox and other Mozilla applications within the Nix package manager ecosystem.

rustup

rustup is the official toolchain installer for the Rust programming language, allowing users to manage multiple Rust versions and associated components.

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