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"
array_width = 80
reorder_imported_names = true

Configuration Options

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

array_horizontal_layout_threshold

How many elements array must have before rustfmt uses horizontal layout.
Use this option to prevent a huge array from being vertically formatted.

• Default value: 0
• Possible values: any positive integer

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

0 (default):

// Each element will be placed on its own line.
let a = vec![
    0,
    1,
    2,
    3,
    4,
    ...
    999,
    1000,
];

1000:

// Each element will be placed on the same line as much as possible.
let a = vec![
    0, 1, 2, 3, 4, ...
    ..., 999, 1000,
];

indent_style

Indent on expressions or items.

• Default value: "Block"
• Possible values: "Block", "Visual"

Array

"Block" (default):

let lorem = vec![
    "ipsum",
    "dolor",
    "sit",
    "amet",
    "consectetur",
    "adipiscing",
    "elit",
];

"Visual":

let lorem = vec!["ipsum",
                 "dolor",
                 "sit",
                 "amet",
                 "consectetur",
                 "adipiscing",
                 "elit"];

Control flow

"Block" (default):

if lorem_ipsum &&
    dolor_sit &&
    amet_consectetur
{
    // ...
}

"Visual":

if lorem_ipsum &&
   dolor_sit &&
   amet_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
}

Functaion calls

"Block" (default):

lorem(
    "lorem",
    "ipsum",
    "dolor",
    "sit",
    "amet",
    "consectetur",
    "adipiscing",
    "elit",
);

"Visual":

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):

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

"Visual":

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

See also: struct_lit_multiline_style, 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
}

See also: where_density, where_layout.

array_width

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

• Default value: 60
• Possible values: any positive integer

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

Lines shorter than array_width:

let lorem = vec!["ipsum", "dolor", "sit", "amet", "consectetur", "adipiscing", "elit"];

Lines longer than array_width:

See indent_style.

attributes_on_same_line_as_field

Try to put attributes on the same line as fields

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

true (default):

struct Lorem {
    #[serde(rename = "Ipsum")] ipsum: usize,
    #[serde(rename = "Dolor")] dolor: usize,
    #[serde(rename = "Amet")] amet: usize,
}

false:

struct Lorem {
    #[serde(rename = "Ipsum")]
    ipsum: usize,
    #[serde(rename = "Dolor")]
    dolor: usize,
    #[serde(rename = "Amet")]
    amet: usize,
}

attributes_on_same_line_as_variant

Try to put attributes on the same line as variants

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

true (default):

enum Lorem {
    #[serde(skip_serializing)] Ipsum,
    #[serde(skip_serializing)] Dolor,
    #[serde(skip_serializing)] Amet,
}

false:

enum Lorem {
    #[serde(skip_serializing)]
    Ipsum,
    #[serde(skip_serializing)]
    Dolor,
    #[serde(skip_serializing)]
    Amet,
}

binop_separator

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

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

"Front" (default):

let or = foo
    || bar
    || foobar;

let sum = 1234
    + 5678
    + 910;

let range = aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
    ..bbbbbbbbbbbbbbbbbbbbbbbbbbbbb;

"Back":

let or = foo ||
    bar ||
    foobar;

let sum = 1234 +
    5678 +
    910;

let range = aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa..
    bbbbbbbbbbbbbbbbbbbbbbbbbbbbb;

chain_indent

Indentation of chain

• Default value: "Block"
• Possible values: "Block", "Visual"

"Block" (default):

let lorem = ipsum
    .dolor()
    .sit()
    .amet()
    .consectetur()
    .adipiscing()
    .elit();

"Visual":

let lorem = ipsum.dolor()
                 .sit()
                 .amet()
                 .consectetur()
                 .adipiscing()
                 .elit();

See also chain_width.

chain_width

Maximum length of a chain to fit on a single line

• Default value: 60
• Possible values: any positive integer

Lines shorter than chain_width:

let lorem = ipsum.dolor().sit().amet().consectetur().adipiscing().elit();

Lines longer than chain_width:

See chain_indent.

chain_split_single_child

Split a chain with a single child if its length exceeds chain_width.

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

false (default):

let files = fs::read_dir("tests/coverage/source").expect("Couldn't read source dir");

true:

let files = fs::read_dir("tests/coverage/source")
    .expect("Couldn't read source dir");

See also chain_width.

combine_control_expr

Combine control expressions with function calls.

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

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

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

Comments shorter than comment_width:

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

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

false (default):

let (lorem, ipsum, _, _) = (1, 2, 3, 4);

true:

let (lorem, ipsum, ..) = (1, 2, 3, 4);

control_brace_style

Brace style for control flow constructs

• Default value: "AlwaysSameLine"
• Possible values: "AlwaysNextLine", "AlwaysSameLine", "ClosingNextLine"

"AlwaysSameLine" (default):

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

"AlwaysNextLine":

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

"ClosingNextLine":

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

disable_all_formatting

Don't reformat anything

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

error_on_line_overflow

Error if unable to get all lines within max_width

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

See also max_width.

error_on_line_overflow_comments

Error if unable to get all comment lines within comment_width.

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

See also comment_width.

fn_args_density

Argument density in functions

• Default value: "Tall"
• Possible values: "Compressed", "CompressedIfEmpty", "Tall", "Vertical"

"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
    }
}

"CompressedIfEmpty":

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_args_paren_newline

If function argument parenthesis goes on a newline

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

false (default):

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

true:

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

brace_style

Brace style for items

• Default value: "SameLineWhere"
• Possible values: "AlwaysNextLine", "PreferSameLine", "SameLineWhere"

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,
}

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

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

Function call shorter than fn_call_width:

lorem("lorem", "ipsum", "dolor", "sit", "amet", "consectetur", "adipiscing", "elit");

Function call longer than fn_call_width:

See indent_style.

fn_empty_single_line

Put empty-body functions on a single line

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

true (default):

fn lorem() {}

false:

fn lorem() {
}

See also control_brace_style.

fn_return_indent

Location of return type in function declaration

• Default value: "WithArgs"
• Possible values: "WithArgs", "WithWhereClause"

"WithArgs" (default):

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

"WithWhereClause":

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

Note: This option only takes effect when indent_style is set to "Visual".

fn_single_line

Put single-expression functions on a single line

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

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

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_format_strings

Always format string literals

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

See format_strings.

See also max_width.

format_strings

Format string literals where necessary

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

false (default):

let lorem = "ipsum dolor sit amet consectetur adipiscing elit lorem ipsum dolor sit";

true:

let lorem =
    "ipsum dolor sit amet consectetur \
     adipiscing elit lorem ipsum dolor sit";

See also force_format_strings, max_width.

hard_tabs

Use tab characters for indentation, spaces for alignment

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

false (default):

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

true:

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

See also: tab_spaces.

impl_empty_single_line

Put empty-body implementations on a single line

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

true (default):

impl Lorem {}

false:

impl Lorem {
}

See also brace_style.

indent_match_arms

Indent match arms instead of keeping them at the same indentation level as the match keyword

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

true (default):

match lorem {
    Lorem::Ipsum => (),
    Lorem::Dolor => (),
    Lorem::Sit => (),
    Lorem::Amet => (),
}

false:

match lorem {
Lorem::Ipsum => (),
Lorem::Dolor => (),
Lorem::Sit => (),
Lorem::Amet => (),
}

See also: match_block_trailing_comma, wrap_match_arms.

imports_indent

Indent style of imports

• Default Value: "Visual"
• Possible values: "Block", "Visual"

"Visual" (default):

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

"Block":

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

See also: imports_layout.

imports_layout

Item layout inside a imports block

• Default value: "Mixed"
• Possible values: "Horizontal", "HorizontalVertical", "Mixed", "Vertical"

"Mixed" (default):

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

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

"Horizontal":

Note: This option forces to put everything on one line and may exceeds max_width.

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

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

"HorizontalVertical":

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

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

"Vertical":

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

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

match_arm_forces_newline

Consistently put match arms (block based or not) in a newline.

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

false (default):

match x {
    // a non-empty block
    X0 => {
        f();
    }
    // an empty block
    X1 => {}
    // a non-block
    X2 => println!("ok"),
}

true:

match x {
    // a non-empty block
    X0 => {
        f();
    }
    // an empty block
    X1 =>
        {}
    // a non-block
    X2 => {
        println!("ok")
    }
}

See also: wrap_match_arms.

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

false (default):

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

true:

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

See also: indent_match_arms, trailing_comma, wrap_match_arms.

match_pattern_separator_break_point

Put a match sub-patterns' separator (|) in front or back.

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

"Back" (default):

match m {
    Variant::Tag |
    Variant::Tag2 |
    Variant::Tag3 |
    Variant::Tag4 |
    Variant::Tag5 |
    Variant::Tag6 => {}
}

Front:

match m {
    Variant::Tag
    | Variant::Tag2
    | Variant::Tag3
    | Variant::Tag4
    | Variant::Tag5
    | Variant::Tag6 => {}
}

max_width

Maximum width of each line

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

See also error_on_line_overflow.

merge_derives

Merge multiple derives into a single one.

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

true (default):

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

false:

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

multiline_closure_forces_block

Force multiline closure bodies to be wrapped in a block

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

false (default):

result.and_then(|maybe_value| match maybe_value {
    None => ...,
    Some(value) => ...,
})

true:

result.and_then(|maybe_value| {
    match maybe_value {
        None => ...,
        Some(value) => ...,
    }
})

multiline_match_arm_forces_block

Force multiline match arm bodies to be wrapped in a block

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

false (default):

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

true:

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

newline_style

Unix or Windows line endings

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

normalize_comments

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

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

false (default):

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

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

true:

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

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

reorder_imported_names

Reorder lists of names in import statements alphabetically

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

false (default):

use super::{lorem, ipsum, dolor, sit};

true:

use super::{dolor, ipsum, lorem, sit};

See also reorder_imports.

reorder_imports

Reorder import statements alphabetically

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

false (default):

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

true:

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

See also reorder_imported_names, reorder_imports_in_group.

reorder_imports_in_group

Reorder import statements in group

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

Note: This option takes effect only when reorder_imports is set to true.

false (default):

use std::mem;
use std::io;

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

true:

use std::io;
use std::mem;

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

See also reorder_imports.

reorder_extern_crates

Reorder extern crate statements alphabetically

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

true (default):

extern crate dolor;
extern crate ipsum;
extern crate lorem;
extern crate sit;

false:

extern crate lorem;
extern crate ipsum;
extern crate dolor;
extern crate sit;

See also reorder_extern_crates_in_group.

reorder_extern_crates_in_group

Reorder extern crate statements in group

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

Note: This option takes effect only when reorder_imports is set to true.

true (default):

extern crate a;
extern crate b;

extern crate dolor;
extern crate ipsum;
extern crate lorem;
extern crate sit;

false:

extern crate b;
extern crate a;

extern crate lorem;
extern crate ipsum;
extern crate dolor;
extern crate sit;

See also reorder_extern_crates.

report_todo

Report TODO items in comments.

• Default value: "Never"
• Possible values: "Always", "Unnumbered", "Never"

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"

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.

single_line_if_else_max_width

Maximum line length for single line if-else expressions.

• Default value: 50
• Possible values: any positive integer

Note: A value of 0 results in if-else expressions being broken regardless of their line's width.

Lines shorter than single_line_if_else_max_width:

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

Lines longer than single_line_if_else_max_width:

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

See also: control_brace_style.

skip_children

Don't reformat out of line modules

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

space_after_bound_colon

Leave a space after the colon in a trait or lifetime bound

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

true (default):

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

false:

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

See also: space_before_bound.

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

0 (default):

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

20:

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

space_after_struct_lit_field_colon

Leave a space after the colon in a struct literal field

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

true (default):

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

false:

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

See also: space_before_struct_lit_field_colon.

space_after_type_annotation_colon

Leave a space after the colon in a type annotation

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

true (default):

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

false:

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

See also: space_before_type_annotation.

space_before_bound

Leave a space before the colon in a trait or lifetime bound

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

false (default):

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

true:

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

See also: space_after_bound_colon.

space_before_struct_lit_field_colon

Leave a space before the colon in a struct literal field

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

false (default):

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

true:

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

See also: space_after_struct_lit_field_colon.

space_before_type_annotation

Leave a space before the colon in a type annotation

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

false (default):

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

true:

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

See also: space_after_type_annotation_colon.

spaces_around_ranges

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

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

false (default):

let lorem = 0..10;

true:

let lorem = 0 .. 10;

spaces_within_angle_brackets

Put spaces within non-empty generic arguments

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

false (default):

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

true:

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

See also: spaces_within_parens, spaces_within_square_brackets.

spaces_within_parens

Put spaces within non-empty parentheses

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

false (default):

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

true:

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

See also: spaces_within_angle_brackets, spaces_within_square_brackets.

spaces_within_square_brackets

Put spaces within non-empty square brackets

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

false (default):

let lorem: [usize; 2] = [ipsum, dolor];

true:

let lorem: [ usize; 2 ] = [ ipsum, dolor ];

See also: spaces_within_parens, spaces_within_angle_brackets.

struct_lit_multiline_style

Multiline style on literal structs

• Default value: "PreferSingle"
• Possible values: "ForceMulti", "PreferSingle"

"PreferSingle" (default):

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

"ForceMulti":

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

See also: indent_style, struct_lit_width.

struct_lit_width

Maximum width in the body of a struct lit before falling back to vertical formatting

• Default value: 18
• Possible values: any positive integer

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

Lines shorter than struct_lit_width:

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

Lines longer than struct_lit_width:

See indent_style.

See also: struct_lit_multiline_style, indent_style.

struct_variant_width

Maximum width in the body of a struct variant before falling back to vertical formatting

• Default value: 35
• Possible values: any positive integer

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

Struct variants shorter than struct_variant_width:

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

Struct variants longer than struct_variant_width:

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

tab_spaces

Number of spaces per tab

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

4 (default):

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

2:

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

See also: hard_tabs.

take_source_hints

Retain some formatting characteristics from the source code

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

false (default):

lorem
    .ipsum()
    .dolor(|| { sit.amet().consectetur().adipiscing().elit(); });

true:

lorem
    .ipsum()
    .dolor(|| {
               sit.amet()
                   .consectetur()
                   .adipiscing()
                   .elit();
           });

Note: This only applies if the call chain within the inner closure had already been formatted on separate lines before running rustfmt.

trailing_comma

How to handle trailing commas for lists

• Default value: "Vertical"
• Possible values: "Always", "Never", "Vertical"

"Vertical" (default):

let Lorem { ipsum, dolor, sit } = amet;
let Lorem {
    ipsum,
    dolor,
    sit,
    amet,
    consectetur,
    adipiscing,
} = elit;

"Always":

let Lorem { ipsum, dolor, sit, } = amet;
let Lorem {
    ipsum,
    dolor,
    sit,
    amet,
    consectetur,
    adipiscing,
} = elit;

"Never":

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

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"

"Wide" (default):

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

"Compressed":

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

use_try_shorthand

Replace uses of the try! macro by the ? shorthand

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

false (default):

let lorem = try!(ipsum.map(|dolor|dolor.sit()));

true:

let lorem = ipsum.map(|dolor| dolor.sit())?;

where_density

Density of a where clause.

• Default value: "Vertical"
• Possible values: "Compressed", "CompressedIfEmpty", "Tall", "Vertical"

"Vertical" (default):

trait Lorem {
    fn ipsum<Dolor>(dolor: Dolor) -> Sit
    where
        Dolor: Eq;

    fn ipsum<Dolor>(dolor: Dolor) -> Sit
    where
        Dolor: Eq,
    {
        // body
    }
}

Note: where_density = "Vertical" currently produces the same output as where_density = "Tall".

"CompressedIfEmpty":

trait Lorem {
    fn ipsum<Dolor>(dolor: Dolor) -> Sit
    where Dolor: Eq;

    fn ipsum<Dolor>(dolor: Dolor) -> Sit
    where
        Dolor: Eq,
    {
        // body
    }
}

"Compressed":

trait Lorem {
    fn ipsum<Dolor>(dolor: Dolor) -> Sit
    where Dolor: Eq;

    fn ipsum<Dolor>(dolor: Dolor) -> Sit
    where Dolor: Eq {
        // body
    }
}

"Tall":

trait Lorem {
    fn ipsum<Dolor>(dolor: Dolor) -> Sit
    where
        Dolor: Eq;

    fn ipsum<Dolor>(dolor: Dolor) -> Sit
    where
        Dolor: Eq,
    {
        // body
    }
}

Note: where_density = "Tall" currently produces the same output as where_density = "Vertical".

See also: where_layout, indent_style.

where_layout

Element layout inside a where clause

• Default value: "Vertical"
• Possible values: "Horizontal", "HorizontalVertical", "Mixed", "Vertical"

"Vertical" (default):

fn lorem<Ipsum, Dolor>(ipsum: Ipsum, dolor: Dolor)
    where Ipsum: IpsumDolorSitAmet,
          Dolor: DolorSitAmetConsectetur
{
    // body
}

fn lorem<Ipsum, Dolor, Sit, Amet>(ipsum: Ipsum, dolor: Dolor, sit: Sit, amet: Amet)
    where Ipsum: IpsumDolorSitAmet,
          Dolor: DolorSitAmetConsectetur,
          Sit: SitAmetConsecteturAdipiscing,
          Amet: AmetConsecteturAdipiscingElit
{
    // body
}

"Horizontal":

fn lorem<Ipsum, Dolor>(ipsum: Ipsum, dolor: Dolor)
    where Ipsum: IpsumDolorSitAmet, Dolor: DolorSitAmetConsectetur
{
    // body
}

fn lorem<Ipsum, Dolor, Sit, Amet>(ipsum: Ipsum, dolor: Dolor, sit: Sit, amet: Amet)
    where Ipsum: IpsumDolorSitAmet, Dolor: DolorSitAmetConsectetur, Sit: SitAmetConsecteturAdipiscing, Amet: AmetConsecteturAdipiscingElit
{
    // body
}

"HorizontalVertical":

fn lorem<Ipsum, Dolor>(ipsum: Ipsum, dolor: Dolor)
    where Ipsum: IpsumDolorSitAmet, Dolor: DolorSitAmetConsectetur
{
    // body
}

fn lorem<Ipsum, Dolor, Sit, Amet>(ipsum: Ipsum, dolor: Dolor, sit: Sit, amet: Amet)
    where Ipsum: IpsumDolorSitAmet,
          Dolor: DolorSitAmetConsectetur,
          Sit: SitAmetConsecteturAdipiscing,
          Amet: AmetConsecteturAdipiscingElit
{
    // body
}

"Mixed":

fn lorem<Ipsum, Dolor>(ipsum: Ipsum, dolor: Dolor)
    where Ipsum: IpsumDolorSitAmet, Dolor: DolorSitAmetConsectetur
{
    // body
}

fn lorem<Ipsum, Dolor, Sit, Amet>(ipsum: Ipsum, dolor: Dolor, sit: Sit, amet: Amet)
    where Ipsum: IpsumDolorSitAmet, Dolor: DolorSitAmetConsectetur,
          Sit: SitAmetConsecteturAdipiscing, Amet: AmetConsecteturAdipiscingElit
{
    // body
}

See also: where_density, indent_style.

wrap_comments

Break comments to fit on the line

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

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.

wrap_match_arms

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

true (default):

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

false:

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

See also: indent_match_arms, 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"