alofmt

A fast, deterministic Ruby formatter powered by Prism and written in Rust. Pronounced like "elephant", but with more Aluminium Oxide.

alofmt turns this:

published=Catalog.fetch(ids).filter_map{|record|
# Keep drafts out of the index.
next unless record.published?
{id:record.id,title:record.title,topics:record.topics,metadata:record.metadata}
}.group_by{|record|record[:topics].first}.transform_values(&:count)

into this:

published =
  Catalog
    .fetch(ids)
    .filter_map do |record|
      # Keep drafts out of the index.
      next unless record.published?
      {
        id: record.id,
        title: record.title,
        topics: record.topics,
        metadata: record.metadata
      }
    end
    .group_by { |record| record[:topics].first }
    .transform_values(&:count)

Quick start

Install alofmt with Homebrew:

brew install AllyMarthaJ/tap/alofmt

Or install it with Cargo:

cargo install --locked alofmt

Then format or check a project:

alofmt --write .         # Format every Ruby file in place.
alofmt --check .         # Check formatting without changing files.
alofmt --check --diff .  # Show what would change.

alofmt finds .rb and .rbi files, respects .gitignore, and formats files in parallel. Pass one file without --write or --check to print the result, or use - to read standard input.

Highlights

• Fast: directory discovery and formatting both run in parallel.
• Deterministic: parallel work still produces stable output and reporting.
• Configurable: project policy lives in .alofmt.toml, not formatter special cases.
• Strict: invalid input, parse errors, unsupported syntax, and misspelled configuration keys fail visibly.
• Embeddable: the Rust library exposes the same formatter and allocation-free checks as the CLI.

Note

alofmt is pre-1.0. It supports a broad and growing portion of Ruby syntax. Unsupported Prism nodes return an error instead of partial or lossy output.

Configuration

The defaults are pretty standard; two-space indentation, preserved quotes, and no method-name or optional syntax special cases.

Add .alofmt.toml at the root of a project to change that:

line_width = 100
indent_width = 4
quote_style = "single"
trailing_commas = true

alofmt searches the current directory and its parents for the nearest config file. CLI options override the file for one run.

See the configuration reference for every option and its default value.

Library

Use alofmt as a Rust library when formatting needs to live inside another tool:

use alofmt::{FormatOptions, QuoteStyle, format_with_options};

let options = FormatOptions {
    quote_style: QuoteStyle::Single,
    ..FormatOptions::default()
};

let output = format_with_options(b"message = \"hello\"\n", &options)?;
assert_eq!(output, "message = 'hello'\n");
# Ok::<(), anyhow::Error>(())

Read the API documentation for the complete library interface.

More

• Behavior, safety, and performance
• Configuration reference
• Contributing

Licence

alofmt is available under the MIT licence.