Go Language Toolchain

Sets up the Go development toolchain: compiler, tools, GOPATH, GOROOT, and PATH. This replaces devenv's languages.go module.

This module handles TOOLCHAIN setup (compiler, env, PATH). App-level config (building, packaging, air, gomod2nix) is in modules/go/.

Usage in .stack/config.nix:

languages.go.enable = true;

Or auto-enabled when any app has go.enable = true.