rust/Configurations.md

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 Options

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

indent_style

Indent on expressions or items.

• Default value: "Block"
• Possible values: "Block", "Visual"
• Stable: No

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
}

use_small_heuristics

Whether to use different formatting for items and expressions if they satisfy a heuristic notion of 'small'.

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

true (default):

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 };
}

false:

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
    };
}

binop_separator

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

• Default value: "Front"
• Possible values: "Front", "Back"
• Stable: No

"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;
}

combine_control_expr

Combine control expressions with function calls.

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

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

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

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

"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!");
    }
}

disable_all_formatting

Don't reformat anything

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

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

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

fn_args_density

Argument density in functions

• Default value: "Tall"
• Possible values: "Compressed", "Tall", "Vertical"
• Stable: No

"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
    }
}

brace_style

Brace style for items

• Default value: "SameLineWhere"
• Possible values: "AlwaysNextLine", "PreferSameLine", "SameLineWhere"
• Stable: No

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,
}

empty_item_single_line

Put empty-body functions and impls on a single line

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

true (default):

fn lorem() {}

impl Lorem {}

false:

fn lorem() {
}

impl Lorem {
}

See also brace_style, control_brace_style.

fn_single_line

Put single-expression functions on a single line

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

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.

where_single_line

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

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

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.

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;
}

format_strings

Format string literals where necessary

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

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.

imports_indent

Indent style of imports

• Default Value: "Visual"
• Possible values: "Block", "Visual"
• Stable: No

"Visual" (default):

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

"Block":

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

"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,
};

merge_imports

Merge multiple imports into a single nested import.

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

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};

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: No

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 {}

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

false (default):

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

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

newline_style

Unix or Windows line endings

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

normalize_comments

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

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

false (default):

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

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

true:

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

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

remove_nested_parens

Remove nested parens.

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

false (default):

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

true:

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

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: No

true (default):

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

false:

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

reorder_modules

Reorder mod declarations alphabetically in group.

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

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 semantic of the original source code.

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

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
    }
}

report_todo

Report TODO items in comments.

• Default value: "Never"
• Possible values: "Always", "Unnumbered", "Never"
• Stable: No

Warns about any comments containing TODO in them when set to "Always". If it contains a #X (with X being a number) in parentheses following the TODO, "Unnumbered" will ignore it.

See also report_fixme.

report_fixme

Report FIXME items in comments.

• Default value: "Never"
• Possible values: "Always", "Unnumbered", "Never"
• Stable: No

Warns about any comments containing FIXME in them when set to "Always". If it contains a #X (with X being a number) in parentheses following the FIXME, "Unnumbered" will ignore it.

See also report_todo.

skip_children

Don't reformat out of line modules

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

space_after_colon

Leave a space after the colon.

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

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

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.

struct_field_align_threshold

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

• Default value : 0
• Possible values: any positive integer
• Stable: No

0 (default):

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

20:

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

spaces_around_ranges

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

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

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,
    }
}

spaces_within_parens_and_brackets

Put spaces within non-empty generic arguments, parentheses, and square brackets

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

false (default):

// generic arguments
fn lorem<T: Eq>(t: T) {
    // body
}

// non-empty parentheses
fn lorem<T: Eq>(t: T) {
    let lorem = (ipsum, dolor);
}

// non-empty square brackets
fn lorem<T: Eq>(t: T) {
    let lorem: [usize; 2] = [ipsum, dolor];
}

true:

// generic arguments
fn lorem< T: Eq >( t: T ) {
    // body
}

// non-empty parentheses
fn lorem< T: Eq >( t: T ) {
    let lorem = ( ipsum, dolor );
}

// non-empty square brackets
fn lorem< T: Eq >( t: T ) {
    let lorem: [ usize; 2 ] = [ ipsum, dolor ];
}

struct_lit_single_line

Put small struct literals on a single line

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

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.

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

"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

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

"Wide" (default):

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

"Compressed":

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

use_field_init_shorthand

Use field initialize shorthand if possible.

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

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 };
}

use_try_shorthand

Replace uses of the try! macro by the ? shorthand

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

false (default):

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

true:

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

wrap_comments

Break comments to fit on the line

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

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.

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

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.

write_mode

What Write Mode to use when none is supplied: Replace, Overwrite, Display, Diff, Coverage

• Default value: "Overwrite"
• Possible values: "Checkstyle", "Coverage", "Diff", "Display", "Overwrite", "Plain", "Replace"
• Stable: No

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: unsigned integer
• Stable: No

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 (default):

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


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


    println!("c");
}

See also: blank_lines_lower_bound

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

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");
}

remove_blank_lines_at_start_or_end_of_block

Remove blank lines at the start or the end of a block.

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

true

fn foo() {
    let msg = {
        let mut str = String::new();
        str.push_str("hello, ");
        str.push_str("world!");
        str
    };
    println!("{}", msg);
}

false

fn foo() {

    let msg = {

        let mut str = String::new();
        str.push_str("hello, ");
        str.push_str("world!");
        str

    };
    println!("{}", msg);

}

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

hide_parse_errors

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

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

color

Whether to use colored output or not.

• Default value: "Auto"
• Possible values: "Auto", "Always", "Never"
• Stable: No

unstable_features

Enable unstable features on stable channel.

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

license_template_path

Check whether beginnings of files match a license template.

• Default value: `""``
• Possible values: path to a license template file
• Stable: No

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.

ignore

Skip formatting the specified files and directories.

• Default value: format every files
• Possible values: See an example below
• Stable: No

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",
]