jjgi - Jujutsu Gi

Jujutsu Gi (着) is a linter/formatter wrapper for jj fix.

Motivation

jj fix requires tools to follow a specific convention:

[...] tools run as subprocesses that take file content on standard input and return it, with any desired changes, on standard output.

However, many linters and formatters do not work this way. They may:

• Output status messages to standard output instead of the file content
• Write results to a file instead of standard output
• Not accept standard input at all

jjgi is a wrapper that adapts these tools to work with jj fix by routing their input/output streams appropriately.

Installation

GitHub release

Pre-built binaries are available in the GitHub releases. Download and install manually, or use tools like mise:

mise install github:shihanng/jjgi@latest

Homebrew

brew install shihanng/jjgi/jjgi

Cargo

cargo install jjgi

From source

Clone this repository and run cargo install:

git clone https://github.com/shihanng/jjgi
cargo install --path .

Usage

Use jjgi inside jj's config file. Run jjgi --help to see all available flags.

The problem

For example, luacheck can accept standard input but does not produce the file content in standard output. Instead, it outputs the status to standard output:

$ cat something.lua | luacheck -
Checking stdin                                    OK

Total: 0 warnings / 0 errors in 1 file

This means that when luacheck does not report any errors, jj fix will replace the entire file with empty content (because jj fix expects the file content on standard output).

--on-success-stdout/stderr

We can set up luacheck using jjgi in the jj config file so that it works correctly with jj fix:

[fix.tools.luacheck]
command = [
  "jjgi",
  "--on-success-stdout=stdin",
  "--on-success-stderr=stdout",
  "--",
  "luacheck",
  "-",
]
patterns = ["glob:'**/*.lua'"]

How it works:

• --on-success-stdout=stdin - When luacheck exits successfully, jjgi outputs the original standard input to standard output. This ensures jj fix receives and uses the file content.
• --on-success-stderr=stdout - When luacheck exits successfully, jjgi routes the command's standard output to standard error. This allows status messages to be displayed to the user.
• -- - Separates jjgi flags from the wrapped command.

When the tool succeeds:

$ jj fix
something.lua:
Checking stdin                                    OK

Total: 0 warnings / 0 errors in 1 file

Fixed 0 commits of 1 checked.
Nothing changed.

The status messages appear because they're routed to standard error, and the original file content is preserved because standard input is routed to standard output.

--stdin-file

The --stdin-file flag stores the standard input into a temporary file that the wrapped command can refer to using {stdin_file}. This is useful when the command cannot read from standard input.

Here is an example using sort-lines. When sort-lines exits successfully, it has formatted {stdin_file} in the correct sort order. We then use the content of {stdin_file} as standard output so that the changes are applied to the actual file.

[fix.tools.sort-lines]
command = [
  "jjgi",
  "--stdin-file",
  "--on-success-stdout=stdin-file",
  "--",
  "sort-lines",
  "{stdin_file}",
]
patterns = ["glob:'**/*'"]

--on-failure-stderr

By default, jjgi uses the standard error of the wrapper command as its standard error when the command exits with an error code. However, some commands output status or error details to standard output. Using --on-failure-stderr=stdout, we can route the standard output of the command to the standard error of jjgi, allowing us to see the error details when jj fix detects a failure.

Development

How to release jjgi

Use cargo release to simultaneously push the release commit to the main branch on GitHub and publish the package to crates.io.