Formatter specification

In order to keep the design of treefmt simple, we support only formatters which adhere to a certain standard. This document outlines this standard. If the formatter you would like to use doesn’t comply with the rules, you should create a wrapper script that transforms the usage to match the specification.

Command-line interface

In order to be integrated to treefmt’s workflow, the formatter’s CLI must adhere to the following specification:
<command> [options] [...<files>]
<command> is the name of the formatting tool.
[options] is any number of flags and options that the formatter accepts.
[...<files>] is one or more files given to the formatter for processing.
$ rustfmt --edition 2018 src/ src/
Whenever a formatter is invoked with a list of files, it should processes only the specified files. Files that are not passed should never be formatted.
If, and only if, a file has changed, the formatter will write the new content in place of the original one.

Other requirements

You must ensure that the formatter you’re planning to use:
Preserves code validity: This is a strong contract; the syntax and semantics must never be broken by the formatter.
Is idempotent: if it is run twice on a file, the file should not change on the second invocation.
treefmt guarantees that the formatter won’t traverse the file system if a list of files is passed to it.

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