yact

Yet another commit transformer-- but this one will finally help you truly forget about formatting!

yact is a tool that applies code formatters / prettifiers to your staged changes, seamlessly updating what you commit. Additionally, it works well when staging only some changes within a file-- it merges the formatting changes back into your worktree (accepting the worktree version in case of a conflict). It's like another programmer cleaning up your commits behind the scenes!

yact is designed to avoid the following issues that plague other popular auto-formatters / auto-formatting strategies:

1. Putting formatting changes in your worktree, aborting the commit, and forcing you to add back the formatting updates to whatever you staged. 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.
3. Format on write can sometimes be jarring. For example, when writing a new function and then saving, the function will be reduced to a minimal form (ex. int main(){}).

Requirements and installation

• This crate depends on libgit2, but this should be built automatically if it is not installed on the target system.
• For the time being, build and install yact from source:
  1. Install Rust
  2. cargo install --git https://github.com/NelsonAPenn/yact --bin yact
• yact does not install formatting tools for you. This does require that any desired external formatters be installed and on the system path.

Usage

1. Create a config file named yactrc.toml in the workspace root. Below are some example config files that will apply to most people. Note that the configuration file is dependent on what languages and formatters your team prefers, so these may require modification.

# Configuration file for yact. See https://github.com/NelsonAPenn/yact for more
# information.
#
# Created from the Rust sample config file.

# Note if the Rust edition you are using is later than 2015, you may need to
# create a .rustfmt.toml file in the workspace root specifying the edition.
[[items]]
glob = "**/*.rs"
transformers = [{ External = "Rustfmt" }]

[[items]]
glob = "**/*.md"
transformers = [{ Builtin = "TrailingWhitespace" }]

# Configuration file for yact. See https://github.com/NelsonAPenn/yact for more
# information.
#
# Created from the C / C++ sample config file.
items = [
    { glob = "**/*.cpp", transformers = [{External = "ClangFormat"}] },
    { glob = "**/*.hpp", transformers = [{External = "ClangFormat"}] },
    { glob = "**/*.h", transformers = [{External = "ClangFormat"}] },
    { glob = "**/*.c", transformers = [{External = "ClangFormat"}] },

    # clang-format also works for JSON. If it's already installed, may as well
    # use it rather than configuring a different tool.
    { glob = "**/*.json", transformers = [{External = "ClangFormat"}] },
   
    { glob = "**/*.md", transformers = [{ Builtin = "TrailingWhitespace" }]},
]

# Configuration file for yact. See https://github.com/NelsonAPenn/yact for more
# information.
#
# Created from the web development sample config file.

# "Npm" can be replaced with "Yarn", or the field can be removed entirely to
# use a global installation of prettier.
#
# package_json_directory can also be specified, e.g.
#
# transformers = [{External = { Prettier = { package_manager_type="Yarn", package_json_directory = "webapp"}}]
items = [
    { glob = "**/*.js", transformers = [{External = { Prettier = { package_manager_type = "Npm" } }}] },
    { glob = "**/*.ts", transformers = [{External = { Prettier = { package_manager_type = "Npm" }}}] },
    { glob = "**/*.jsx", transformers = [{External = { Prettier = { package_manager_type = "Npm" }}}] },
    { glob = "**/*.tsx", transformers = [{External = { Prettier = { package_manager_type = "Npm" }}}] },
    { glob = "**/*.html", transformers = [{External = { Prettier = { package_manager_type = "Npm" }}}] },
    { glob = "**/*.json", transformers = [{External = { Prettier = { package_manager_type = "Npm" }}}] },
    { glob = "**/*.md", transformers = [{External = { Prettier = { package_manager_type = "Npm" }}}] },
]

# Configuration file for yact. See https://github.com/NelsonAPenn/yact for more
# information.
#
# Created from the Python sample config file.

# To use a virtual environment, run `git commit` from the activated environment
# or provide the virtual environment path (recommended to be within repository
# root), for example `{ RuffFormat = { venv_path = ".venv" }}`
items = [
    { glob = "**/*.py", transformers = [{ External = { RuffFormat = {}}}] },
    { glob = "**/*.pyi", transformers = [{ External = { RuffFormat = {}}}] },

    { glob = "**/*.md", transformers = [{ Builtin = "TrailingWhitespace" }]},
]

# Configuration file for yact. See https://github.com/NelsonAPenn/yact for more
# information.
#
# Created from the Golang sample config file.
[[items]]
glob = "**/*.go"
transformers = [{ External = "Gofmt" }]

[[items]]
glob = "**/*.md"
transformers = [{ Builtin = "TrailingWhitespace" }]

2. Update your pre-commit git hook to run yact. For example, on Unix systems, run the following command from the root of the repository you'd like to use yact in.

ln -s "$(which yact)" .git/hooks/pre-commit

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
• DenoFmt
• Prettier
• RuffFormat
• Gofmt

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

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

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.