Configure Treefmt

The treefmt.toml configuration file consists of a mixture of global options and formatter sections:

[global]
excludes = ["*.md", "*.dat"]

[formatter.elm]
command = "elm-format"
options = ["--yes"]
includes = ["*.elm"]

[formatter.go]
command = "gofmt"
options = ["-w"]
includes = ["*.go"]

[formatter.python]
command = "black"
includes = ["*.py"]

# use the priority field to control the order of execution

# run shellcheck first
[formatter.shellcheck]
command = "shellcheck"
includes = ["*.sh"]
priority = 0    # default is 0, but we set it here for clarity

# shfmt second
[formatter.shfmt]
command = "shfmt"
options = ["-s", "-w"]
includes = ["*.sh"]
priority = 1

Global Options

• excludes - an optional list of glob patterns used to exclude certain files from all formatters.

Formatter Options

• command - the command to invoke when applying the formatter.
• options - an optional list of args to be passed to command.
• includes - a list of glob patterns used to determine whether the formatter should be applied against a given path.
• excludes - an optional list of glob patterns used to exclude certain files from this formatter.
• priority - influences the order of execution. Greater precedence is given to lower numbers, with the default being 0.

Same file, multiple formatters?

For each file, treefmt determines a list of formatters based on the configured includes / excludes rules. This list is then sorted, first by priority (lower the value, higher the precedence) and secondly by formatter name (lexicographically).

The resultant sequence of formatters is used to create a batch key, and similarly matched files get added to that batch until it is full, at which point the files are passed to each formatter in turn.

This means that treefmt guarantees only one formatter will be operating on a given file at any point in time. Another consequence is that formatting is deterministic for a given file and a given treefmt configuration.

By setting the priority fields appropriately, you can control the order in which those formatters are applied for any files they both happen to match on.

Glob patterns format

This is a variant of the Unix glob pattern. It supports all the usual selectors such as * and ?.

Examples

• *.go - match all files in the project that end with a ".go" file extension.
• vendor/* - match all files under the vendor folder, recursively.

Supported Formatters

Any formatter that follows the spec is supported out of the box.

Already 60+ formatters are supported.

To find examples, take a look at https://github.com/numtide/treefmt-nix/tree/main/examples.

If you are a Nix user, you might also like https://github.com/numtide/treefmt-nix, which uses Nix to pull in the right formatter package and seamlessly integrates both together.