$ show magefile/mage
Mage is a build tool written in Go that replaces Makefiles with plain Go functions. Users define targets as exported functions in Go source files tagged with `//go:build mage`, and Mage compiles them into a standalone CLI binary. The architecture is a library-plus-CLI: the `mage` package handles parsing, compilation, and execution; the `mg` package provides dependency injection (`Deps`, `SerialDeps`, `CtxDeps`) and namespace grouping; the `sh` package offers shell command execution with environment expansion; the `parse` package uses Go's AST to extract targets and imports; and the `target` package implements file-based dependency checking. The tool supports zero-install via `go run`, static compilation, shell completion, and importing targets from other packages. It is a mature, well-tested project with no external dependencies beyond the Go standard library, making it highly portable and maintainable.
The LLM identified 5 files worth highlighting for reuse:
Implements `Deps`, `SerialDeps`, and `CtxDeps` functions that ensure each dependency function is executed exactly once per build, with support for context cancellation and error propagation. This is a clean, reusable pattern for managing task dependencies in build systems, extractable to any Go project needing ordered, deduplicated function execution.
Provides `Run`, `Output`, `Exec`, `RunCmd`, and `OutCmd` functions that wrap `os/exec` with automatic environment variable expansion (using `os.ExpandEnv`), stdout/stderr capture, and consistent error handling. The package is self-contained and can be reused in any Go project that needs to run shell commands with minimal boilerplate.
Parses Go source files to discover exported functions, imports, and namespace structs using `go/ast` and `go/parser`. It handles build tags, comment annotations (`mage:import`, `mage:multiline`), and generates structured target metadata. This is a non-trivial use of Go's AST that could be adapted for other code-generation or introspection tools.
Implements file-based target checking similar to Makefile rules: given a list of target files and source files, it determines which targets need rebuilding based on modification times. The package is self-contained and can be reused in any build system that needs incremental build logic.
Generates shell completion scripts for bash, zsh, fish, and PowerShell by introspecting the compiled mage binary's target list. The completion logic is self-contained and demonstrates a pattern for dynamically generating completions from a CLI tool's own help output.