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Configuring Rustfmt

Rustfmt is designed to be very configurable. You can create a TOML file called rustfmt.toml or .rustfmt.toml, place it in the project or any other parent directory and it will apply the options in that file.

A possible content of rustfmt.toml or .rustfmt.toml might look like this:

indent_style = "Block"
reorder_imports = false

Each configuration option is either stable or unstable. Stable options can be used directly, while unstable options are opt-in. To enable unstable options, set unstable_features = true in rustfmt.toml or pass --unstable-features to rustfmt.

Configuration file resolution

As mentioned above, rustfmt searches for a rustfmt.toml or .rustfmt.toml in the directory it is run and all parent directories.

If none of these directories contain such a file, both your home directory and a directory called rustfmt in your global config directory (e.g. .config/rustfmt/) are checked as well.

If any of these directories contain such a file, rustfmt is configured with the union of configuration options in all such files. The configuration options are applied in order of reverse proximity to the directory rustfmt is run in. For example, consider a directory structure

outer
|-- rustfmt.toml
|-- outer.rs
|-- inner
    |-- rustfmt.toml
    |-- inner.rs
    |-- lib_inner.rs

Where outer/rustfmt.toml is

max_width = 80
array_width = 50
ignore = ['inner/inner.rs']

and outer/inner/rustfmt.toml is

max_width = 70
ignore = ['./lib_inner.rs']

If run in the inner directory, rustfmt's internal configuration will include

max_width = 70
array_width = 50
ignore = ['./lib_inner.rs', './inner.rs']

If run in the root outer directory, rustfmt's internal configuration will include

max_width = 80
array_width = 50
ignore = ['inner/inner.rs']

Configuration Options

Below you can find a detailed visual guide on all the supported configuration options of rustfmt.

Note that the below list reflects the configuration options available on the latest version of rustfmt in source control. Some newer options may not be available yet in a released version of rustfmt.

For version- and channel-specific configurations, please visit https://rust-lang.github.io/rustfmt/.

array_width

Maximum width of an array literal before falling back to vertical formatting.

  • Default value: 60
  • Possible values: any positive integer that is less than or equal to the value specified for max_width
  • Stable: Yes

By default this option is set as a percentage of max_width provided by width_heuristics, but a value set directly for array_width will take precedence.

See also max_width and width_heuristics

attr_fn_like_width

Maximum width of the args of a function-like attributes before falling back to vertical formatting.

  • Default value: 70
  • Possible values: any positive integer that is less than or equal to the value specified for max_width
  • Stable: Yes

By default this option is set as a percentage of max_width provided by width_heuristics, but a value set directly for attr_fn_like_width will take precedence.

See also max_width and width_heuristics

binop_separator

Where to put a binary operator when a binary expression goes multiline.

  • Default value: "Front"
  • Possible values: "Front", "Back"
  • Stable: Yes

"Front" (default):

fn main() {
    let or = foofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoo
        || barbarbarbarbarbarbarbarbarbarbarbarbarbarbarbar;

    let sum = 123456789012345678901234567890
        + 123456789012345678901234567890
        + 123456789012345678901234567890;

    let range = aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
        ..bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb;
}

"Back":

fn main() {
    let or = foofoofoofoofoofoofoofoofoofoofoofoofoofoofoofoo ||
        barbarbarbarbarbarbarbarbarbarbarbarbarbarbarbar;

    let sum = 123456789012345678901234567890 +
        123456789012345678901234567890 +
        123456789012345678901234567890;

    let range = aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa..
        bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb;
}

blank_lines_lower_bound

Minimum number of blank lines which must be put between items. If two items have fewer blank lines between them, additional blank lines are inserted.

  • Default value: 0
  • Possible values: unsigned integer
  • Stable: No (tracking issue: #3382)

Example

Original Code (rustfmt will not change it with the default value of 0):

#![rustfmt::skip]

fn foo() {
    println!("a");
}
fn bar() {
    println!("b");
    println!("c");
}

1

fn foo() {
    println!("a");
}

fn bar() {
    println!("b");
    println!("c");
}

blank_lines_upper_bound

Maximum number of blank lines which can be put between items. If more than this number of consecutive empty lines are found, they are trimmed down to match this integer.

  • Default value: 1
  • Possible values: any non-negative integer
  • Stable: No (tracking issue: #3381)

Example

Original Code:

#![rustfmt::skip]

fn foo() {
    println!("a");
}



fn bar() {
    println!("b");


    println!("c");
}

1 (default):

fn foo() {
    println!("a");
}

fn bar() {
    println!("b");

    println!("c");
}

2:

fn foo() {
    println!("a");
}


fn bar() {
    println!("b");


    println!("c");
}

See also: blank_lines_lower_bound

brace_style

Brace style for items

  • Default value: "SameLineWhere"
  • Possible values: "AlwaysNextLine", "PreferSameLine", "SameLineWhere"
  • Stable: No (tracking issue: #3376)

Functions

"SameLineWhere" (default):

fn lorem() {
    // body
}

fn lorem(ipsum: usize) {
    // body
}

fn lorem<T>(ipsum: T)
where
    T: Add + Sub + Mul + Div,
{
    // body
}

"AlwaysNextLine":

fn lorem()
{
    // body
}

fn lorem(ipsum: usize)
{
    // body
}

fn lorem<T>(ipsum: T)
where
    T: Add + Sub + Mul + Div,
{
    // body
}

"PreferSameLine":

fn lorem() {
    // body
}

fn lorem(ipsum: usize) {
    // body
}

fn lorem<T>(ipsum: T)
where
    T: Add + Sub + Mul + Div, {
    // body
}

Structs and enums

"SameLineWhere" (default):

struct Lorem {
    ipsum: bool,
}

struct Dolor<T>
where
    T: Eq,
{
    sit: T,
}

"AlwaysNextLine":

struct Lorem
{
    ipsum: bool,
}

struct Dolor<T>
where
    T: Eq,
{
    sit: T,
}

"PreferSameLine":

struct Lorem {
    ipsum: bool,
}

struct Dolor<T>
where
    T: Eq, {
    sit: T,
}

chain_width

Maximum width of a chain to fit on one line.

  • Default value: 60
  • Possible values: any positive integer that is less than or equal to the value specified for max_width
  • Stable: Yes

By default this option is set as a percentage of max_width provided by width_heuristics, but a value set directly for chain_width will take precedence.

See also max_width and width_heuristics

combine_control_expr

Combine control expressions with function calls.

  • Default value: true
  • Possible values: true, false
  • Stable: No (tracking issue: #3369)

true (default):

fn example() {
    // If
    foo!(if x {
        foo();
    } else {
        bar();
    });

    // IfLet
    foo!(if let Some(..) = x {
        foo();
    } else {
        bar();
    });

    // While
    foo!(while x {
        foo();
        bar();
    });

    // WhileLet
    foo!(while let Some(..) = x {
        foo();
        bar();
    });

    // ForLoop
    foo!(for x in y {
        foo();
        bar();
    });

    // Loop
    foo!(loop {
        foo();
        bar();
    });
}

false:

fn example() {
    // If
    foo!(
        if x {
            foo();
        } else {
            bar();
        }
    );

    // IfLet
    foo!(
        if let Some(..) = x {
            foo();
        } else {
            bar();
        }
    );

    // While
    foo!(
        while x {
            foo();
            bar();
        }
    );

    // WhileLet
    foo!(
        while let Some(..) = x {
            foo();
            bar();
        }
    );

    // ForLoop
    foo!(
        for x in y {
            foo();
            bar();
        }
    );

    // Loop
    foo!(
        loop {
            foo();
            bar();
        }
    );
}

comment_width

Maximum length of comments. No effect unlesswrap_comments = true.

  • Default value: 80
  • Possible values: any positive integer
  • Stable: No (tracking issue: #3349)

Note: A value of 0 results in wrap_comments being applied regardless of a line's width.

80 (default; comments shorter than comment_width):

// Lorem ipsum dolor sit amet, consectetur adipiscing elit.

60 (comments longer than comment_width):

// Lorem ipsum dolor sit amet,
// consectetur adipiscing elit.

See also wrap_comments.

condense_wildcard_suffixes

Replace strings of _ wildcards by a single .. in tuple patterns

  • Default value: false
  • Possible values: true, false
  • Stable: No (tracking issue: #3384)

false (default):

fn main() {
    let (lorem, ipsum, _, _) = (1, 2, 3, 4);
    let (lorem, ipsum, ..) = (1, 2, 3, 4);
}

true:

fn main() {
    let (lorem, ipsum, ..) = (1, 2, 3, 4);
}

control_brace_style

Brace style for control flow constructs

  • Default value: "AlwaysSameLine"
  • Possible values: "AlwaysNextLine", "AlwaysSameLine", "ClosingNextLine"
  • Stable: No (tracking issue: #3377)

"AlwaysSameLine" (default):

fn main() {
    if lorem {
        println!("ipsum!");
    } else {
        println!("dolor!");
    }
}

"AlwaysNextLine":

fn main() {
    if lorem
    {
        println!("ipsum!");
    }
    else
    {
        println!("dolor!");
    }
}

"ClosingNextLine":

fn main() {
    if lorem {
        println!("ipsum!");
    }
    else {
        println!("dolor!");
    }
}

edition

Specifies which edition is used by the parser.

  • Default value: "2015"
  • Possible values: "2015", "2018", "2021"
  • Stable: Yes

Rustfmt is able to pick up the edition used by reading the Cargo.toml file if executed through the Cargo's formatting tool cargo fmt. Otherwise, the edition needs to be specified in your config file:

edition = "2018"

empty_item_single_line

Put empty-body functions and impls on a single line

  • Default value: true
  • Possible values: true, false
  • Stable: No (tracking issue: #3356)

true (default):

fn lorem() {}

impl Lorem {}

false:

fn lorem() {
}

impl Lorem {
}

See also brace_style, control_brace_style.

enum_discrim_align_threshold

The maximum length of enum variant having discriminant, that gets vertically aligned with others. Variants without discriminants would be ignored for the purpose of alignment.

Note that this is not how much whitespace is inserted, but instead the longest variant name that doesn't get ignored when aligning.

  • Default value : 0
  • Possible values: any positive integer
  • Stable: No (tracking issue: #3372)

0 (default):

enum Bar {
    A = 0,
    Bb = 1,
    RandomLongVariantGoesHere = 10,
    Ccc = 71,
}

enum Bar {
    VeryLongVariantNameHereA = 0,
    VeryLongVariantNameHereBb = 1,
    VeryLongVariantNameHereCcc = 2,
}

20:

enum Foo {
    A   = 0,
    Bb  = 1,
    RandomLongVariantGoesHere = 10,
    Ccc = 2,
}

enum Bar {
    VeryLongVariantNameHereA = 0,
    VeryLongVariantNameHereBb = 1,
    VeryLongVariantNameHereCcc = 2,
}

error_on_line_overflow

Error if Rustfmt is unable to get all lines within max_width, except for comments and string literals. If this happens, then it is a bug in Rustfmt. You might be able to work around the bug by refactoring your code to avoid long/complex expressions, usually by extracting a local variable or using a shorter name.

  • Default value: false
  • Possible values: true, false
  • Stable: No (tracking issue: #3391)

See also max_width.

error_on_unformatted

Error if unable to get comments or string literals within max_width, or they are left with trailing whitespaces.

  • Default value: false
  • Possible values: true, false
  • Stable: No (tracking issue: #3392)

fn_params_layout

Control the layout of parameters in a function signature

  • Default value: "Tall"
  • Possible values: "Compressed", "Tall", "Vertical"
  • Stable: Yes

"Tall" (default):

trait Lorem {
    fn lorem(ipsum: Ipsum, dolor: Dolor, sit: Sit, amet: Amet);

    fn lorem(ipsum: Ipsum, dolor: Dolor, sit: Sit, amet: Amet) {
        // body
    }

    fn lorem(
        ipsum: Ipsum,
        dolor: Dolor,
        sit: Sit,
        amet: Amet,
        consectetur: Consectetur,
        adipiscing: Adipiscing,
        elit: Elit,
    );

    fn lorem(
        ipsum: Ipsum,
        dolor: Dolor,
        sit: Sit,
        amet: Amet,
        consectetur: Consectetur,
        adipiscing: Adipiscing,
        elit: Elit,
    ) {
        // body
    }
}

"Compressed":

trait Lorem {
    fn lorem(ipsum: Ipsum, dolor: Dolor, sit: Sit, amet: Amet);

    fn lorem(ipsum: Ipsum, dolor: Dolor, sit: Sit, amet: Amet) {
        // body
    }

    fn lorem(
        ipsum: Ipsum, dolor: Dolor, sit: Sit, amet: Amet, consectetur: Consectetur,
        adipiscing: Adipiscing, elit: Elit,
    );

    fn lorem(
        ipsum: Ipsum, dolor: Dolor, sit: Sit, amet: Amet, consectetur: Consectetur,
        adipiscing: Adipiscing, elit: Elit,
    ) {
        // body
    }
}

"Vertical":

trait Lorem {
    fn lorem(
        ipsum: Ipsum,
        dolor: Dolor,
        sit: Sit,
        amet: Amet,
    );

    fn lorem(
        ipsum: Ipsum,
        dolor: Dolor,
        sit: Sit,
        amet: Amet,
    ) {
        // body
    }

    fn lorem(
        ipsum: Ipsum,
        dolor: Dolor,
        sit: Sit,
        amet: Amet,
        consectetur: Consectetur,
        adipiscing: Adipiscing,
        elit: Elit,
    );

    fn lorem(
        ipsum: Ipsum,
        dolor: Dolor,
        sit: Sit,
        amet: Amet,
        consectetur: Consectetur,
        adipiscing: Adipiscing,
        elit: Elit,
    ) {
        // body
    }
}

fn_call_width

Maximum width of the args of a function call before falling back to vertical formatting.

  • Default value: 60
  • Possible values: any positive integer that is less than or equal to the value specified for max_width
  • Stable: Yes

By default this option is set as a percentage of max_width provided by width_heuristics, but a value set directly for fn_call_width will take precedence.

See also max_width and width_heuristics

fn_single_line

Put single-expression functions on a single line

  • Default value: false
  • Possible values: true, false
  • Stable: No (tracking issue: #3358)

false (default):

fn lorem() -> usize {
    42
}

fn lorem() -> usize {
    let ipsum = 42;
    ipsum
}

true:

fn lorem() -> usize { 42 }

fn lorem() -> usize {
    let ipsum = 42;
    ipsum
}

See also control_brace_style.

force_explicit_abi

Always print the abi for extern items

  • Default value: true
  • Possible values: true, false
  • Stable: Yes

Note: Non-"C" ABIs are always printed. If false then "C" is removed.

true (default):

extern "C" {
    pub static lorem: c_int;
}

false:

extern {
    pub static lorem: c_int;
}

force_multiline_blocks

Force multiline closure and match arm bodies to be wrapped in a block

  • Default value: false
  • Possible values: false, true
  • Stable: No (tracking issue: #3374)

false (default):

fn main() {
    result.and_then(|maybe_value| match maybe_value {
        None => foo(),
        Some(value) => bar(),
    });

    match lorem {
        None => |ipsum| {
            println!("Hello World");
        },
        Some(dolor) => foo(),
    }
}

true:

fn main() {
    result.and_then(|maybe_value| {
        match maybe_value {
            None => foo(),
            Some(value) => bar(),
        }
    });

    match lorem {
        None => {
            |ipsum| {
                println!("Hello World");
            }
        }
        Some(dolor) => foo(),
    }
}

format_code_in_doc_comments

Format code snippet included in doc comments.

  • Default value: false
  • Possible values: true, false
  • Stable: No (tracking issue: #3348)

false (default):

/// Adds one to the number given.
///
/// # Examples
///
/// ```rust
/// let five=5;
///
/// assert_eq!(
///     6,
///     add_one(5)
/// );
/// # fn add_one(x: i32) -> i32 {
/// #     x + 1
/// # }
/// ```
fn add_one(x: i32) -> i32 {
    x + 1
}

true

/// Adds one to the number given.
///
/// # Examples
///
/// ```rust
/// let five = 5;
///
/// assert_eq!(6, add_one(5));
/// # fn add_one(x: i32) -> i32 {
/// #     x + 1
/// # }
/// ```
fn add_one(x: i32) -> i32 {
    x + 1
}

format_generated_files

Format generated files. A file is considered as generated if the file starts with // @generated.

  • Default value: false
  • Possible values: true, false
  • Stable: No

format_macro_matchers

Format the metavariable matching patterns in macros.

  • Default value: false
  • Possible values: true, false
  • Stable: No (tracking issue: #3354)

false (default):

macro_rules! foo {
    ($a: ident : $b: ty) => {
        $a(42): $b;
    };
    ($a: ident $b: ident $c: ident) => {
        $a = $b + $c;
    };
}

true:

macro_rules! foo {
    ($a:ident : $b:ty) => {
        $a(42): $b;
    };
    ($a:ident $b:ident $c:ident) => {
        $a = $b + $c;
    };
}

See also format_macro_bodies.

format_macro_bodies

Format the bodies of macros.

  • Default value: true
  • Possible values: true, false
  • Stable: No (tracking issue: #3355)

true (default):

macro_rules! foo {
    ($a: ident : $b: ty) => {
        $a(42): $b;
    };
    ($a: ident $b: ident $c: ident) => {
        $a = $b + $c;
    };
}

false:

macro_rules! foo {
    ($a: ident : $b: ty) => { $a(42): $b; };
    ($a: ident $b: ident $c: ident) => { $a=$b+$c; };
}

See also format_macro_matchers.

format_strings

Format string literals where necessary

  • Default value: false
  • Possible values: true, false
  • Stable: No (tracking issue: #3353)

false (default):

fn main() {
    let lorem = "ipsum dolor sit amet consectetur adipiscing elit lorem ipsum dolor sit amet consectetur adipiscing";
}

true:

fn main() {
    let lorem = "ipsum dolor sit amet consectetur adipiscing elit lorem ipsum dolor sit amet \
                 consectetur adipiscing";
}

See also max_width.

hard_tabs

Use tab characters for indentation, spaces for alignment

  • Default value: false
  • Possible values: true, false
  • Stable: Yes

false (default):

fn lorem() -> usize {
    42 // spaces before 42
}

true:

fn lorem() -> usize {
	42 // tabs before 42
}

See also: tab_spaces.

hide_parse_errors

Do not show parse errors if the parser failed to parse files.

  • Default value: false
  • Possible values: true, false
  • Stable: No (tracking issue: #3390)

ignore

Skip formatting files and directories that match the specified pattern. The pattern format is the same as .gitignore. Be sure to use Unix/forwardslash / style paths. This path style will work on all platforms. Windows style paths with backslashes \ are not supported.

  • Default value: format every file
  • Possible values: See an example below
  • Stable: Yes

Example

If you want to ignore specific files, put the following to your config file:

ignore = [
    "src/types.rs",
    "src/foo/bar.rs",
]

If you want to ignore every file under examples/, put the following to your config file:

ignore = [
    "examples",
]

If you want to ignore every file under the directory where you put your rustfmt.toml:

ignore = ["/"]

imports_indent

Indent style of imports

  • Default Value: "Block"
  • Possible values: "Block", "Visual"
  • Stable: No (tracking issue: #3360)

"Block" (default):

use foo::{
    xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx, yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy,
    zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz,
};

"Visual":

use foo::{xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx, yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy,
          zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz};

See also: imports_layout.

imports_layout

Item layout inside a imports block

  • Default value: "Mixed"
  • Possible values: "Horizontal", "HorizontalVertical", "Mixed", "Vertical"
  • Stable: No (tracking issue: #3361)

"Mixed" (default):

use foo::{xxxxxxxxxxxxxxxxxx, yyyyyyyyyyyyyyyyyy, zzzzzzzzzzzzzzzzzz};

use foo::{
    aaaaaaaaaaaaaaaaaa, bbbbbbbbbbbbbbbbbb, cccccccccccccccccc, dddddddddddddddddd,
    eeeeeeeeeeeeeeeeee, ffffffffffffffffff,
};

"Horizontal":

Note: This option forces all imports onto one line and may exceed max_width.

use foo::{xxx, yyy, zzz};

use foo::{aaa, bbb, ccc, ddd, eee, fff};

"HorizontalVertical":

use foo::{xxxxxxxxxxxxxxxxxx, yyyyyyyyyyyyyyyyyy, zzzzzzzzzzzzzzzzzz};

use foo::{
    aaaaaaaaaaaaaaaaaa,
    bbbbbbbbbbbbbbbbbb,
    cccccccccccccccccc,
    dddddddddddddddddd,
    eeeeeeeeeeeeeeeeee,
    ffffffffffffffffff,
};

"Vertical":

use foo::{
    xxx,
    yyy,
    zzz,
};

use foo::{
    aaa,
    bbb,
    ccc,
    ddd,
    eee,
    fff,
};

indent_style

Indent on expressions or items.

  • Default value: "Block"
  • Possible values: "Block", "Visual"
  • Stable: No (tracking issue: #3346)

Array

"Block" (default):

fn main() {
    let lorem = vec![
        "ipsum",
        "dolor",
        "sit",
        "amet",
        "consectetur",
        "adipiscing",
        "elit",
    ];
}

"Visual":

fn main() {
    let lorem = vec!["ipsum",
                     "dolor",
                     "sit",
                     "amet",
                     "consectetur",
                     "adipiscing",
                     "elit"];
}

Control flow

"Block" (default):

fn main() {
    if lorem_ipsum
        && dolor_sit
        && amet_consectetur
        && lorem_sit
        && dolor_consectetur
        && amet_ipsum
        && lorem_consectetur
    {
        // ...
    }
}

"Visual":

fn main() {
    if lorem_ipsum
       && dolor_sit
       && amet_consectetur
       && lorem_sit
       && dolor_consectetur
       && amet_ipsum
       && lorem_consectetur
    {
        // ...
    }
}

See also: control_brace_style.

Function arguments

"Block" (default):

fn lorem() {}

fn lorem(ipsum: usize) {}

fn lorem(
    ipsum: usize,
    dolor: usize,
    sit: usize,
    amet: usize,
    consectetur: usize,
    adipiscing: usize,
    elit: usize,
) {
    // body
}

"Visual":

fn lorem() {}

fn lorem(ipsum: usize) {}

fn lorem(ipsum: usize,
         dolor: usize,
         sit: usize,
         amet: usize,
         consectetur: usize,
         adipiscing: usize,
         elit: usize) {
    // body
}

Function calls

"Block" (default):

fn main() {
    lorem(
        "lorem",
        "ipsum",
        "dolor",
        "sit",
        "amet",
        "consectetur",
        "adipiscing",
        "elit",
    );
}

"Visual":

fn main() {
    lorem("lorem",
          "ipsum",
          "dolor",
          "sit",
          "amet",
          "consectetur",
          "adipiscing",
          "elit");
}

Generics

"Block" (default):

fn lorem<
    Ipsum: Eq = usize,
    Dolor: Eq = usize,
    Sit: Eq = usize,
    Amet: Eq = usize,
    Adipiscing: Eq = usize,
    Consectetur: Eq = usize,
    Elit: Eq = usize,
>(
    ipsum: Ipsum,
    dolor: Dolor,
    sit: Sit,
    amet: Amet,
    adipiscing: Adipiscing,
    consectetur: Consectetur,
    elit: Elit,
) -> T {
    // body
}

"Visual":

fn lorem<Ipsum: Eq = usize,
         Dolor: Eq = usize,
         Sit: Eq = usize,
         Amet: Eq = usize,
         Adipiscing: Eq = usize,
         Consectetur: Eq = usize,
         Elit: Eq = usize>(
    ipsum: Ipsum,
    dolor: Dolor,
    sit: Sit,
    amet: Amet,
    adipiscing: Adipiscing,
    consectetur: Consectetur,
    elit: Elit)
    -> T {
    // body
}

Struct

"Block" (default):

fn main() {
    let lorem = Lorem {
        ipsum: dolor,
        sit: amet,
    };
}

"Visual":

fn main() {
    let lorem = Lorem { ipsum: dolor,
                        sit: amet };
}

See also: struct_lit_single_line, indent_style.

Where predicates

"Block" (default):

fn lorem<Ipsum, Dolor, Sit, Amet>() -> T
where
    Ipsum: Eq,
    Dolor: Eq,
    Sit: Eq,
    Amet: Eq,
{
    // body
}

"Visual":

fn lorem<Ipsum, Dolor, Sit, Amet>() -> T
    where Ipsum: Eq,
          Dolor: Eq,
          Sit: Eq,
          Amet: Eq
{
    // body
}

inline_attribute_width

Write an item and its attribute on the same line if their combined width is below a threshold

  • Default value: 0
  • Possible values: any positive integer
  • Stable: No (tracking issue: #3343)

Example

0 (default):

#[cfg(feature = "alloc")]
use core::slice;

50:

#[cfg(feature = "alloc")] use core::slice;

license_template_path

Check whether beginnings of files match a license template.

  • Default value: ""
  • Possible values: path to a license template file
  • Stable: No (tracking issue: #3352)

A license template is a plain text file which is matched literally against the beginning of each source file, except for {}-delimited blocks, which are matched as regular expressions. The following license template therefore matches strings like // Copyright 2017 The Rust Project Developers., // Copyright 2018 The Rust Project Developers., etc.:

// Copyright {\d+} The Rust Project Developers.

\{, \} and \\ match literal braces / backslashes.

match_arm_blocks

Wrap the body of arms in blocks when it does not fit on the same line with the pattern of arms

  • Default value: true
  • Possible values: true, false
  • Stable: No (tracking issue: #3373)

true (default):

fn main() {
    match lorem {
        true => {
            foooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo(x)
        }
        false => println!("{}", sit),
    }
}

false:

fn main() {
    match lorem {
        true =>
            foooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo(x),
        false => println!("{}", sit),
    }
}

See also: match_block_trailing_comma.

match_arm_leading_pipes

Controls whether to include a leading pipe on match arms

  • Default value: Never
  • Possible values: Always, Never, Preserve
  • Stable: Yes

Never (default):

// Leading pipes are from this:
// fn foo() {
//     match foo {
//         | "foo" | "bar" => {}
//         | "baz"
//         | "something relatively long"
//         | "something really really really realllllllllllllly long" => println!("x"),
//         | "qux" => println!("y"),
//         _ => {}
//     }
// }

// Are removed:
fn foo() {
    match foo {
        "foo" | "bar" => {}
        "baz"
        | "something relatively long"
        | "something really really really realllllllllllllly long" => println!("x"),
        "qux" => println!("y"),
        _ => {}
    }
}

Always:

// Leading pipes are emitted on all arms of this:
// fn foo() {
//     match foo {
//         "foo" | "bar" => {}
//         "baz"
//         | "something relatively long"
//         | "something really really really realllllllllllllly long" => println!("x"),
//         "qux" => println!("y"),
//         _ => {}
//     }
// }

// Becomes:
fn foo() {
    match foo {
        | "foo" | "bar" => {}
        | "baz"
        | "something relatively long"
        | "something really really really realllllllllllllly long" => println!("x"),
        | "qux" => println!("y"),
        | _ => {}
    }
}

Preserve:

fn foo() {
    match foo {
        | "foo" | "bar" => {}
        | "baz"
        | "something relatively long"
        | "something really really really realllllllllllllly long" => println!("x"),
        | "qux" => println!("y"),
        _ => {}
    }

    match baz {
        "qux" => {}
        "foo" | "bar" => {}
        _ => {}
    }
}

match_block_trailing_comma

Put a trailing comma after a block based match arm (non-block arms are not affected)

  • Default value: false
  • Possible values: true, false
  • Stable: Yes

false (default):

fn main() {
    match lorem {
        Lorem::Ipsum => {
            println!("ipsum");
        }
        Lorem::Dolor => println!("dolor"),
    }
}

true:

fn main() {
    match lorem {
        Lorem::Ipsum => {
            println!("ipsum");
        },
        Lorem::Dolor => println!("dolor"),
    }
}

See also: trailing_comma, match_arm_blocks.

max_width

Maximum width of each line

  • Default value: 100
  • Possible values: any positive integer
  • Stable: Yes

See also error_on_line_overflow.

merge_derives

Merge multiple derives into a single one.

  • Default value: true
  • Possible values: true, false
  • Stable: Yes

true (default):

#[derive(Eq, PartialEq, Debug, Copy, Clone)]
pub enum Foo {}

false:

#[derive(Eq, PartialEq)]
#[derive(Debug)]
#[derive(Copy, Clone)]
pub enum Foo {}

imports_granularity

Merge together related imports based on their paths.

  • Default value: Preserve
  • Possible values: Preserve, Crate, Module, Item, One
  • Stable: No

Preserve (default):

Do not perform any merging and preserve the original structure written by the developer.

use foo::b;
use foo::b::{f, g};
use foo::{a, c, d::e};
use qux::{h, i};

Crate:

Merge imports from the same crate into a single use statement. Conversely, imports from different crates are split into separate statements.

use foo::{
    a, b,
    b::{f, g},
    c,
    d::e,
};
use qux::{h, i};

Module:

Merge imports from the same module into a single use statement. Conversely, imports from different modules are split into separate statements.

use foo::b::{f, g};
use foo::d::e;
use foo::{a, b, c};
use qux::{h, i};

Item:

Flatten imports so that each has its own use statement.

use foo::a;
use foo::b;
use foo::b::f;
use foo::b::g;
use foo::c;
use foo::d::e;
use qux::h;
use qux::i;

One:

Merge all imports into a single use statement as long as they have the same visibility.

pub use foo::{x, y};
use {
    bar::{
        a,
        b::{self, f, g},
        c,
        d::e,
    },
    qux::{h, i},
};

merge_imports

This option is deprecated. Use imports_granularity = "Crate" instead.

  • Default value: false
  • Possible values: true, false

false (default):

use foo::{a, c, d};
use foo::{b, g};
use foo::{e, f};

true:

use foo::{a, b, c, d, e, f, g};

newline_style

Unix or Windows line endings

  • Default value: "Auto"
  • Possible values: "Auto", "Native", "Unix", "Windows"
  • Stable: Yes

Auto (default):

The newline style is detected automatically on a per-file basis. Files with mixed line endings will be converted to the first detected line ending style.

Native

Line endings will be converted to \r\n on Windows and \n on all other platforms.

Unix

Line endings will be converted to \n.

Windows

Line endings will be converted to \r\n.

normalize_comments

Convert /* */ comments to // comments where possible

  • Default value: false
  • Possible values: true, false
  • Stable: No (tracking issue: #3350)

false (default):

// Lorem ipsum:
fn dolor() -> usize {}

/* sit amet: */
fn adipiscing() -> usize {}

true:

// Lorem ipsum:
fn dolor() -> usize {}

// sit amet:
fn adipiscing() -> usize {}

normalize_doc_attributes

Convert #![doc] and #[doc] attributes to //! and /// doc comments.

  • Default value: false
  • Possible values: true, false
  • Stable: No (tracking issue: #3351)

false (default):

#![doc = "Example documentation"]

#[doc = "Example item documentation"]
pub enum Foo {}

true:

//! Example documentation

/// Example item documentation
pub enum Foo {}

preserve_block_start_blank_lines

Preserves blanks lines at the start of the block. Note that this will preserve newlines, but strip any other whitespace on those lines.

  • Default value: false
  • Possible values: true, false
  • Stable: No

false (default):

fn say_hi() {
    println!("hi");
}

true:

fn say_hi() {


    println!("hi");
}

preserve_closure_block_wrapping

Preserves block wraping arround closures. For example, useful when the closure || can be confused with OR.

  • Default value: false
  • Possible values: true, false
  • Stable: No

true:

Original block wrapping is preserved:

fn main() {
    let explicit_conversion_preserves_semantics =
        || { !is_mod || (is_mod && attrs.map_or(true, |a| a.is_empty())) };
}

false (default):

Block is not preserved:

fn main() {
    let explicit_conversion_preserves_semantics =
        || !is_mod || (is_mod && attrs.map_or(true, |a| a.is_empty()));
}

overflow_delimited_expr

When structs, slices, arrays, and block/array-like macros are used as the last argument in an expression list, allow them to overflow (like blocks/closures) instead of being indented on a new line.

  • Default value: false
  • Possible values: true, false
  • Stable: No (tracking issue: #3370)

false (default):

fn example() {
    foo(ctx, |param| {
        action();
        foo(param)
    });

    foo(
        ctx,
        Bar {
            x: value,
            y: value2,
        },
    );

    foo(
        ctx,
        &[
            MAROON_TOMATOES,
            PURPLE_POTATOES,
            ORGANE_ORANGES,
            GREEN_PEARS,
            RED_APPLES,
        ],
    );

    foo(
        ctx,
        vec![
            MAROON_TOMATOES,
            PURPLE_POTATOES,
            ORGANE_ORANGES,
            GREEN_PEARS,
            RED_APPLES,
        ],
    );
}

true:

fn example() {
    foo(ctx, |param| {
        action();
        foo(param)
    });

    foo(ctx, Bar {
        x: value,
        y: value2,
    });

    foo(ctx, &[
        MAROON_TOMATOES,
        PURPLE_POTATOES,
        ORGANE_ORANGES,
        GREEN_PEARS,
        RED_APPLES,
    ]);

    foo(ctx, vec![
        MAROON_TOMATOES,
        PURPLE_POTATOES,
        ORGANE_ORANGES,
        GREEN_PEARS,
        RED_APPLES,
    ]);
}

remove_nested_parens

Remove nested parens.

  • Default value: true,
  • Possible values: true, false
  • Stable: Yes

true (default):

fn main() {
    (foo());
}

false:

fn main() {
    ((((foo()))));
}

reorder_impl_items

Reorder impl items. type and const are put first, then macros and methods.

  • Default value: false
  • Possible values: true, false
  • Stable: No (tracking issue: #3363)

false (default)

struct Dummy;

impl Iterator for Dummy {
    fn next(&mut self) -> Option<Self::Item> {
        None
    }

    type Item = i32;
}

true

struct Dummy;

impl Iterator for Dummy {
    type Item = i32;

    fn next(&mut self) -> Option<Self::Item> {
        None
    }
}

reorder_imports

Reorder import and extern crate statements alphabetically in groups (a group is separated by a newline).

  • Default value: true
  • Possible values: true, false
  • Stable: Yes

true (default):

use dolor;
use ipsum;
use lorem;
use sit;

false:

use lorem;
use ipsum;
use dolor;
use sit;

group_imports

Controls the strategy for how imports are grouped together.

  • Default value: Preserve
  • Possible values: Preserve, StdExternalCrate
  • Stable: No

Preserve (default):

Preserve the source file's import groups.

use super::update::convert_publish_payload;
use chrono::Utc;

use alloc::alloc::Layout;
use juniper::{FieldError, FieldResult};
use uuid::Uuid;

use std::sync::Arc;

use broker::database::PooledConnection;

use super::schema::{Context, Payload};
use crate::models::Event;
use core::f32;

StdExternalCrate:

Discard existing import groups, and create three groups for:

  1. std, core and alloc,
  2. external crates,
  3. self, super and crate imports.
use alloc::alloc::Layout;
use core::f32;
use std::sync::Arc;

use broker::database::PooledConnection;
use chrono::Utc;
use juniper::{FieldError, FieldResult};
use uuid::Uuid;

use super::schema::{Context, Payload};
use super::update::convert_publish_payload;
use crate::models::Event;

reorder_modules

Reorder mod declarations alphabetically in group.

  • Default value: true
  • Possible values: true, false
  • Stable: Yes

true (default)

mod a;
mod b;

mod dolor;
mod ipsum;
mod lorem;
mod sit;

false

mod b;
mod a;

mod lorem;
mod ipsum;
mod dolor;
mod sit;

Note mod with #[macro_export] will not be reordered since that could change the semantics of the original source code.

required_version

Require a specific version of rustfmt. If you want to make sure that the specific version of rustfmt is used in your CI, use this option.

  • Default value: CARGO_PKG_VERSION
  • Possible values: any published version (e.g. "0.3.8")
  • Stable: No (tracking issue: #3386)

single_line_if_else_max_width

Maximum line length for single line if-else expressions. A value of 0 (zero) results in if-else expressions always being broken into multiple lines. Note this occurs when width_heuristics is set to Off.

  • Default value: 50
  • Possible values: any positive integer that is less than or equal to the value specified for max_width
  • Stable: Yes

By default this option is set as a percentage of max_width provided by width_heuristics, but a value set directly for single_line_if_else_max_width will take precedence.

See also max_width and width_heuristics

space_after_colon

Leave a space after the colon.

  • Default value: true
  • Possible values: true, false
  • Stable: No (tracking issue: #3366)

true (default):

fn lorem<T: Eq>(t: T) {
    let lorem: Dolor = Lorem {
        ipsum: dolor,
        sit: amet,
    };
}

false:

fn lorem<T:Eq>(t:T) {
    let lorem:Dolor = Lorem {
        ipsum:dolor,
        sit:amet,
    };
}

See also: space_before_colon.

space_before_colon

Leave a space before the colon.

  • Default value: false
  • Possible values: true, false
  • Stable: No (tracking issue: #3365)

false (default):

fn lorem<T: Eq>(t: T) {
    let lorem: Dolor = Lorem {
        ipsum: dolor,
        sit: amet,
    };
}

true:

fn lorem<T : Eq>(t : T) {
    let lorem : Dolor = Lorem {
        ipsum : dolor,
        sit : amet,
    };
}

See also: space_after_colon.

space_before_fn_sig_paren

Whether to put a space before the opening paren in function signatures

  • Default value: false
  • Possible values: true, false
  • Stable: No

false (default):

fn lorem() {
    // body
}

fn lorem(ipsum: usize) {
    // body
}

fn lorem<T>(ipsum: T)
where
    T: Add + Sub + Mul + Div,
{
    // body
}

true:

fn lorem () {
    // body
}

fn lorem (ipsum: usize) {
    // body
}

fn lorem<T> (ipsum: T)
where
    T: Add + Sub + Mul + Div,
{
    // body
}

spaces_around_ranges

Put spaces around the .., ..=, and ... range operators

  • Default value: false
  • Possible values: true, false
  • Stable: No (tracking issue: #3367)

false (default):

fn main() {
    let lorem = 0..10;
    let ipsum = 0..=10;

    match lorem {
        1..5 => foo(),
        _ => bar,
    }

    match lorem {
        1..=5 => foo(),
        _ => bar,
    }

    match lorem {
        1...5 => foo(),
        _ => bar,
    }
}

true:

fn main() {
    let lorem = 0 .. 10;
    let ipsum = 0 ..= 10;

    match lorem {
        1 .. 5 => foo(),
        _ => bar,
    }

    match lorem {
        1 ..= 5 => foo(),
        _ => bar,
    }

    match lorem {
        1 ... 5 => foo(),
        _ => bar,
    }
}

space_around_attr_eq

Determines if '=' are wrapped in spaces in attributes.

  • Default value: true
  • Possible values: true, false
  • Stable: No

true (default):

#[cfg(not(target_os = "pi"))]
println!("os is not pi!");

false

#[cfg(not(target_os="pi"))]
println!("os is not pi!");

struct_field_align_threshold

The maximum diff of width between struct fields to be aligned with each other.

  • Default value : 0
  • Possible values: any non-negative integer
  • Stable: No (tracking issue: #3371)

0 (default):

struct Foo {
    x: u32,
    yy: u32,
    zzz: u32,
}

20:

struct Foo {
    x:   u32,
    yy:  u32,
    zzz: u32,
}

struct_lit_single_line

Put small struct literals on a single line

  • Default value: true
  • Possible values: true, false
  • Stable: No (tracking issue: #3357)

true (default):

fn main() {
    let lorem = Lorem { foo: bar, baz: ofo };
}

false:

fn main() {
    let lorem = Lorem {
        foo: bar,
        baz: ofo,
    };
}

See also: indent_style.

struct_lit_width

Maximum width in the body of a struct literal before falling back to vertical formatting. A value of 0 (zero) results in struct literals always being broken into multiple lines. Note this occurs when width_heuristics is set to Off.

  • Default value: 18
  • Possible values: any positive integer that is less than or equal to the value specified for max_width
  • Stable: Yes

By default this option is set as a percentage of max_width provided by width_heuristics, but a value set directly for struct_lit_width will take precedence.

See also max_width, width_heuristics, and struct_lit_single_line

struct_variant_width

Maximum width in the body of a struct variant before falling back to vertical formatting. A value of 0 (zero) results in struct literals always being broken into multiple lines. Note this occurs when width_heuristics is set to Off.

  • Default value: 35
  • Possible values: any positive integer that is less than or equal to the value specified for max_width
  • Stable: Yes

By default this option is set as a percentage of max_width provided by width_heuristics, but a value set directly for struct_variant_width will take precedence.

See also max_width and width_heuristics

tab_spaces

Number of spaces per tab

  • Default value: 4
  • Possible values: any positive integer
  • Stable: Yes

4 (default):

fn lorem() {
    let ipsum = dolor();
    let sit = vec![
        "amet consectetur adipiscing elit amet",
        "consectetur adipiscing elit amet consectetur.",
    ];
}

2:

fn lorem() {
  let ipsum = dolor();
  let sit = vec![
    "amet consectetur adipiscing elit amet",
    "consectetur adipiscing elit amet consectetur.",
  ];
}

See also: hard_tabs.

trailing_comma

How to handle trailing commas for lists

  • Default value: "Vertical"
  • Possible values: "Always", "Never", "Vertical"
  • Stable: No (tracking issue: #3379)

"Vertical" (default):

fn main() {
    let Lorem { ipsum, dolor, sit } = amet;
    let Lorem {
        ipsum,
        dolor,
        sit,
        amet,
        consectetur,
        adipiscing,
    } = elit;
}

"Always":

fn main() {
    let Lorem { ipsum, dolor, sit, } = amet;
    let Lorem {
        ipsum,
        dolor,
        sit,
        amet,
        consectetur,
        adipiscing,
    } = elit;
}

"Never":

fn main() {
    let Lorem { ipsum, dolor, sit } = amet;
    let Lorem {
        ipsum,
        dolor,
        sit,
        amet,
        consectetur,
        adipiscing
    } = elit;
}

See also: match_block_trailing_comma.

trailing_semicolon

Add trailing semicolon after break, continue and return

  • Default value: true
  • Possible values: true, false
  • Stable: No (tracking issue: #3378)

true (default):

fn foo() -> usize {
    return 0;
}

false:

fn foo() -> usize {
    return 0
}

type_punctuation_density

Determines if + or = are wrapped in spaces in the punctuation of types

  • Default value: "Wide"
  • Possible values: "Compressed", "Wide"
  • Stable: No (tracking issue: #3364)

"Wide" (default):

fn lorem<Ipsum: Dolor + Sit = Amet>() {
    // body
}

"Compressed":

fn lorem<Ipsum: Dolor+Sit=Amet>() {
    // body
}

unstable_features

Enable unstable features on stable and beta channels (unstable features are available by default on nightly).

  • Default value: false
  • Possible values: true, false
  • Stable: Yes

Note - if you are setting unstable configuration options via the CLI instead of the configuration file, then you should include a unstable_features=true item before any of the unstable items.

For example:

rustfmt src/lib.rs --config unstable_features=true imports_granularity=Crate

use_field_init_shorthand

Use field initialize shorthand if possible.

  • Default value: false
  • Possible values: true, false
  • Stable: Yes

false (default):

struct Foo {
    x: u32,
    y: u32,
    z: u32,
}

fn main() {
    let x = 1;
    let y = 2;
    let z = 3;
    let a = Foo { x: x, y: y, z: z };
}

true:

struct Foo {
    x: u32,
    y: u32,
    z: u32,
}

fn main() {
    let x = 1;
    let y = 2;
    let z = 3;
    let a = Foo { x, y, z };
}

width_heuristics

This option can be used to simplify the management and bulk updates of the granular width configuration settings (fn_call_width, attr_fn_like_width, struct_lit_width, struct_variant_width, array_width, chain_width, single_line_if_else_max_width), that respectively control when formatted constructs are multi-lined/vertical based on width.

Note that explicitly provided values for the width configuration settings take precedence and override the calculated values determined by width_heuristics.

  • Default value: "Scaled"
  • Possible values: "Scaled", "Off", "Max"
  • Stable: Yes

Scaled (default):

When width_heuristics is set to Scaled, the values for the granular width settings are calculated as a ratio of the value for max_width.

The ratios are:

For example when max_width is set to 100, the width settings are:

  • fn_call_width=60
  • attr_fn_like_width=70
  • struct_lit_width=18
  • struct_variant_width=35
  • array_width=60
  • chain_width=60
  • single_line_if_else_max_width=50

and when max_width is set to 200:

  • fn_call_width=120
  • attr_fn_like_width=140
  • struct_lit_width=36
  • struct_variant_width=70
  • array_width=120
  • chain_width=120
  • single_line_if_else_max_width=100
enum Lorem {
    Ipsum,
    Dolor(bool),
    Sit { amet: Consectetur, adipiscing: Elit },
}

fn main() {
    lorem(
        "lorem",
        "ipsum",
        "dolor",
        "sit",
        "amet",
        "consectetur",
        "adipiscing",
    );

    let lorem = Lorem {
        ipsum: dolor,
        sit: amet,
    };
    let lorem = Lorem { ipsum: dolor };

    let lorem = if ipsum { dolor } else { sit };
}

Off:

When width_heuristics is set to Off, the granular width settings are functionally disabled and ignored. See the documentation for the respective width config options for specifics.

enum Lorem {
    Ipsum,
    Dolor(bool),
    Sit {
        amet: Consectetur,
        adipiscing: Elit,
    },
}

fn main() {
    lorem("lorem", "ipsum", "dolor", "sit", "amet", "consectetur", "adipiscing");

    let lorem = Lorem {
        ipsum: dolor,
        sit: amet,
    };

    let lorem = if ipsum {
        dolor
    } else {
        sit
    };
}

Max:

When width_heuristics is set to Max, then each granular width setting is set to the same value as max_width.

So if max_width is set to 200, then all the width settings are also set to 200.

  • fn_call_width=200
  • attr_fn_like_width=200
  • struct_lit_width=200
  • struct_variant_width=200
  • array_width=200
  • chain_width=200
  • single_line_if_else_max_width=200
enum Lorem {
    Ipsum,
    Dolor(bool),
    Sit { amet: Consectetur, adipiscing: Elit },
}

fn main() {
    lorem("lorem", "ipsum", "dolor", "sit", "amet", "consectetur", "adipiscing");

    let lorem = Lorem { ipsum: dolor, sit: amet };

    let lorem = if ipsum { dolor } else { sit };
}

See also:

use_try_shorthand

Replace uses of the try! macro by the ? shorthand

  • Default value: false
  • Possible values: true, false
  • Stable: Yes

false (default):

fn main() {
    let lorem = r#try!(ipsum.map(|dolor| dolor.sit()));
}

true:

fn main() {
    let lorem = ipsum.map(|dolor| dolor.sit())?;
}

where_single_line

Forces the where clause to be laid out on a single line.

  • Default value: false
  • Possible values: true, false
  • Stable: No (tracking issue: #3359)

false (default):

impl<T> Lorem for T
where
    Option<T>: Ipsum,
{
    // body
}

true:

impl<T> Lorem for T
where Option<T>: Ipsum
{
    // body
}

See also brace_style, control_brace_style.

wrap_comments

Break comments to fit on the line

  • Default value: false
  • Possible values: true, false
  • Stable: No (tracking issue: #3347)

false (default):

// Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.

true:

// Lorem ipsum dolor sit amet, consectetur adipiscing elit,
// sed do eiusmod tempor incididunt ut labore et dolore
// magna aliqua. Ut enim ad minim veniam, quis nostrud
// exercitation ullamco laboris nisi ut aliquip ex ea
// commodo consequat.