grfmt

A Go formatter written in Rust for learning purposes.

Note

This project does not aim for full Go language coverage. It exists for learning and experimentation, not as a production-ready tool.

What This Is

An exploration of formatter design under specific constraints:

• Subject: Go's gofmt formatting behavior
• Language: Rust (ownership, lifetimes, enums)
• Scope: Subset of Go syntax sufficient to explore key design trade-offs

The goal is design exploration, not to build a complete tool.

See design/ for notes on each area.

What This Is Not

• A production-ready Go formatter
• Faster or better than gofmt
• Complete Go language coverage
• A starting point for semantic analysis / compiler

Usage

grfmt fmt file.go       # Format and print
grfmt fmt -w file.go    # Format and write back
echo "..." | grfmt fmt - # From stdin

Architecture

src/
├── tokenizer.rs  # Lexer with LineMap
├── token.rs      # Token types
├── span.rs       # Byte offset ranges
├── parser.rs     # Recursive descent parser
├── ast.rs        # AST nodes
├── printer.rs    # gofmt-style printer
└── main.rs       # CLI

Limitations

Known unsupported features (documented, not planned to fix):

• Multiple type arguments: Pair[K, V]
• Type union constraints: int | string
• Comment/value alignment
• Blank line preservation

Building

cargo build
cargo test

License

MIT