yact

Yet another commit transformer-- but this one is different than the rest!

Enter the forbidden fruit of your development process.

Features

yact is focused on (in order):

1. Seamlessly applying formatters with minimal disturbance to your workflow or git history (better than other solutions).
   • Transparently transforms staged changes for commit
   • Merges the resulting formatting changes back into working tree
2. Using the first-party implementation (libgit2) whenever possible when working with git repositories.
3. Performance
4. Efficiency

yact provides both a method for configuring what transformers to run on which files in a project as well as a method for integrating with other pre-commit management tools (like pre-commit).

Requirements and installation

• Requires libgit2
• For the time being, build and install yact from source:
  1. Install Rust / cargo
  2. cargo install --git https://github.com/NelsonAPenn/yact

Usage

1. Create a config file named .yactrc.toml in the workspace root.

# Example .yactrc.toml
items = [
    { pathspec = "**/*.rs", transformers = [ {RawCommand = "Rustfmt"} ]},
    { pathspec = "**/*.md", transformers = [ {Builtin = "TrailingWhitespace" }]},
    { pathspec = "*.md", transformers = [ {Builtin = "TrailingWhitespace"} ]}
]

2. Update your pre-commit git hook to run yact. This can be as simple as placing the script below at .git/hooks/pre-commit

#!/bin/sh

yact

Note on pathspecs: at the present time, pathspec defined in the above items is a git pathspec, which differs subtly from shell globs. Importantly, ** matches one or more directories rather than zero or more. Because of this, two separate rules are often required to be defined to match all the files of one filetype. This behavior may change in the future.

Transformers

yact defines a transformer as any process that applies some sort of formatting to a file. yact includes builtin transformers (written in native Rust) and transformers that invoke another process.

The standard interface for transformers that are a separate process are a command that reads a source file in from stdin and writes the formatter version to stdout, returning a nonzero exit code if the operation failed.

yact has the following builtin transformers:

• TrailingWhitespace: trims trailing whitespace and ensures the source file ends in a newline.

Additionally, yact has options for the following popular transformers (simply providing the correct command-line arguments to them):

• Rustfmt
• ClangFormat

Finally, yact provides a catch-all System transformer where command, env, and args can be configured. Example below.

[[items]]
pathspec = "**/*.rs"
transformers = [ { System = { command = "rustfmt", env = {}, args = ["--emit", "stdout"] }}]

Why another tool?

There are many wonderful tools out there that help you quit spending time aligning lines of code, remove common mistakes, and sometimes even automatically make common simplifications to your code. There are also tools that help integrate these tools with your git workflow. However, the tools of the latter class usually exhibit a couple main classes of problems.

1. Making you readd your changes. This is just annoying.
2. Not playing nice in cases when some changes are staged and some are unstaged and still in progress. Some tools result in borkage; others make you git add -p twice, which is again, just annoying.

yact is a standalone binary which operates on low-level git objects directly, formatting staged changes behind the scenes without ever pushing the onus back on you, and updating your working tree in the most correct way possible.

Considerations

yact will never bork your git history. However, yact will take liberty in modifying your working tree as it sees fit. This is done in a fairly safe manner, merging formatting changes back into your worktree but keeping the worktree's version in case of conflicts.

How it works

yact dives into git plumbing to manage staged changes as perfectly as it can. It uses bindings to libgit2 to do things right.

General flow:

1. (If used as pre-commit hook management replacement) iterate diff and find the right transformer for each file.
2. Create new blob as transformation of staged blob
3. Diff new blob and work tree.
4. Merge diff into worktree.
5. (If used as a pre-commit hook management replacement) create new tree and bump commit to point to new tree.