Why does mkIf cause recursion errors in platform checks?

mkIf is evaluated lazily, meaning the option path is still visible during initial module evaluation. If that path is invalid on the current platform, Nix throws a missing option or recursion error.

What is the recommended way to hide options from a specific platform?

Use optionalAttrs with a platform check like isDarwin or !isDarwin. This is evaluated at parse time, ensuring the option path is completely hidden from the platform where it doesn't belong.

How do I handle config-dependent logic within a platform-specific block?

The best practice is to nest a mkIf statement inside an optionalAttrs block. This allows the platform check to happen at parse time while the configuration check remains lazy.

Can I use config values inside optionalAttrs?

Generally no. Referencing config or cfg inside an optionalAttrs condition usually causes infinite recursion because optionalAttrs needs to be resolved early in the evaluation process.

Nix Platform-Specific Configuration

Name: Nix Platform-Specific Configuration
Author: edmundmiller

byedmundmiller

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デプロイメントとDevOps

Prevents infinite recursion errors in Nix modules by implementing standardized patterns for cross-platform NixOS and nix-darwin configurations.

概要

This skill provides Claude with specialized logic to handle the complexities of writing multi-platform Nix modules. It addresses the common 'infinite recursion' problem that occurs when developers mistakenly use lazy evaluation tools like mkIf for platform-specific option paths. By teaching Claude the distinction between parse-time checks using optionalAttrs and lazy checks using mkIf, this skill ensures that system configurations for NixOS and macOS remain robust, modular, and error-free.

主な機能

Provides patterns for nesting mkIf within platform-specific blocks
Standardizes cross-platform module structures for Darwin and NixOS
Automates debugging of problematic config references in option defaults
Implements optionalAttrs for parse-time platform detection
40 GitHub stars
Resolves infinite recursion in Nix evaluation logic

ユースケース

Fixing evaluation errors like _module.freeformType or anon-43 in complex dotfiles
Porting system-level configurations between NixOS and nix-darwin safely
Creating a single Nix module that supports both macOS and Linux environments

概要

主な機能

Provides patterns for nesting mkIf within platform-specific blocks
Standardizes cross-platform module structures for Darwin and NixOS
Automates debugging of problematic config references in option defaults
Implements optionalAttrs for parse-time platform detection
40 GitHub stars
Resolves infinite recursion in Nix evaluation logic

ユースケース

Fixing evaluation errors like _module.freeformType or anon-43 in complex dotfiles
Porting system-level configurations between NixOS and nix-darwin safely
Creating a single Nix module that supports both macOS and Linux environments