rust-analyzer/docs/user/assists.md

Assists

Cursor position or selection is signified by ┃ character.

add_custom_impl

Adds impl block for derived trait.

// BEFORE
#[derive(Deb┃ug, Display)]
struct S;

// AFTER
#[derive(Display)]
struct S;

impl Debug for S {
    $0
}

add_derive

Adds a new #[derive()] clause to a struct or enum.

// BEFORE
struct Point {
    x: u32,
    y: u32,┃
}

// AFTER
#[derive($0)]
struct Point {
    x: u32,
    y: u32,
}

add_explicit_type

Specify type for a let binding.

// BEFORE
fn main() {
    let x┃ = 92;
}

// AFTER
fn main() {
    let x: i32 = 92;
}

add_function

Adds a stub function with a signature matching the function under the cursor.

// BEFORE
struct Baz;
fn baz() -> Baz { Baz }
fn foo() {
    bar┃("", baz());
}


// AFTER
struct Baz;
fn baz() -> Baz { Baz }
fn foo() {
    bar("", baz());
}

fn bar(arg: &str, baz: Baz) {
    ${0:todo!()}
}

add_hash

Adds a hash to a raw string literal.

// BEFORE
fn main() {
    r#"Hello,┃ World!"#;
}

// AFTER
fn main() {
    r##"Hello, World!"##;
}

add_impl

Adds a new inherent impl for a type.

// BEFORE
struct Ctx<T: Clone> {
    data: T,┃
}

// AFTER
struct Ctx<T: Clone> {
    data: T,
}

impl<T: Clone> Ctx<T> {
    $0
}

add_impl_default_members

Adds scaffold for overriding default impl members.

// BEFORE
trait Trait {
    Type X;
    fn foo(&self);
    fn bar(&self) {}
}

impl Trait for () {
    Type X = ();
    fn foo(&self) {}┃

}

// AFTER
trait Trait {
    Type X;
    fn foo(&self);
    fn bar(&self) {}
}

impl Trait for () {
    Type X = ();
    fn foo(&self) {}
    $0fn bar(&self) {}

}

add_impl_missing_members

Adds scaffold for required impl members.

// BEFORE
trait Trait<T> {
    Type X;
    fn foo(&self) -> T;
    fn bar(&self) {}
}

impl Trait<u32> for () {┃

}

// AFTER
trait Trait<T> {
    Type X;
    fn foo(&self) -> T;
    fn bar(&self) {}
}

impl Trait<u32> for () {
    fn foo(&self) -> u32 {
        ${0:todo!()}
    }

}

add_new

Adds a new inherent impl for a type.

// BEFORE
struct Ctx<T: Clone> {
     data: T,┃
}

// AFTER
struct Ctx<T: Clone> {
     data: T,
}

impl<T: Clone> Ctx<T> {
    fn $0new(data: T) -> Self { Self { data } }
}

add_turbo_fish

Adds ::<_> to a call of a generic method or function.

// BEFORE
fn make<T>() -> T { todo!() }
fn main() {
    let x = make┃();
}

// AFTER
fn make<T>() -> T { todo!() }
fn main() {
    let x = make::<${0:_}>();
}

apply_demorgan

Apply De Morgan's law. This transforms expressions of the form !l || !r into !(l && r). This also works with &&. This assist can only be applied with the cursor on either || or &&, with both operands being a negation of some kind. This means something of the form !x or x != y.

// BEFORE
fn main() {
    if x != 4 ||┃ !y {}
}

// AFTER
fn main() {
    if !(x == 4 && y) {}
}

auto_import

If the name is unresolved, provides all possible imports for it.

// BEFORE
fn main() {
    let map = HashMap┃::new();
}

// AFTER
use std::collections::HashMap;

fn main() {
    let map = HashMap::new();
}

change_return_type_to_result

Change the function's return type to Result.

// BEFORE
fn foo() -> i32┃ { 42i32 }

// AFTER
fn foo() -> Result<i32, ${0:_}> { Ok(42i32) }

change_visibility

Adds or changes existing visibility specifier.

// BEFORE
┃fn frobnicate() {}

// AFTER
pub(crate) fn frobnicate() {}

convert_to_guarded_return

Replace a large conditional with a guarded return.

// BEFORE
fn main() {
    ┃if cond {
        foo();
        bar();
    }
}

// AFTER
fn main() {
    if !cond {
        return;
    }
    foo();
    bar();
}

fill_match_arms

Adds missing clauses to a match expression.

// BEFORE
enum Action { Move { distance: u32 }, Stop }

fn handle(action: Action) {
    match action {
        ┃
    }
}

// AFTER
enum Action { Move { distance: u32 }, Stop }

fn handle(action: Action) {
    match action {
        $0Action::Move { distance } => {}
        Action::Stop => {}
    }
}

fix_visibility

Makes inaccessible item public.

// BEFORE
mod m {
    fn frobnicate() {}
}
fn main() {
    m::frobnicate┃() {}
}

// AFTER
mod m {
    $0pub(crate) fn frobnicate() {}
}
fn main() {
    m::frobnicate() {}
}

flip_binexpr

Flips operands of a binary expression.

// BEFORE
fn main() {
    let _ = 90 +┃ 2;
}

// AFTER
fn main() {
    let _ = 2 + 90;
}

flip_comma

Flips two comma-separated items.

// BEFORE
fn main() {
    ((1, 2),┃ (3, 4));
}

// AFTER
fn main() {
    ((3, 4), (1, 2));
}

flip_trait_bound

Flips two trait bounds.

// BEFORE
fn foo<T: Clone +┃ Copy>() { }

// AFTER
fn foo<T: Copy + Clone>() { }

inline_local_variable

Inlines local variable.

// BEFORE
fn main() {
    let x┃ = 1 + 2;
    x * 4;
}

// AFTER
fn main() {
    (1 + 2) * 4;
}

introduce_variable

Extracts subexpression into a variable.

// BEFORE
fn main() {
    ┃(1 + 2)┃ * 4;
}

// AFTER
fn main() {
    let var_name = (1 + 2);
    var_name * 4;
}

invert_if

Apply invert_if This transforms if expressions of the form if !x {A} else {B} into if x {B} else {A} This also works with !=. This assist can only be applied with the cursor on if.

// BEFORE
fn main() {
    if┃ !y { A } else { B }
}

// AFTER
fn main() {
    if y { B } else { A }
}

make_raw_string

Adds r# to a plain string literal.

// BEFORE
fn main() {
    "Hello,┃ World!";
}

// AFTER
fn main() {
    r#"Hello, World!"#;
}

make_usual_string

Turns a raw string into a plain string.

// BEFORE
fn main() {
    r#"Hello,┃ "World!""#;
}

// AFTER
fn main() {
    "Hello, \"World!\"";
}

merge_imports

Merges two imports with a common prefix.

// BEFORE
use std::┃fmt::Formatter;
use std::io;

// AFTER
use std::{fmt::Formatter, io};

merge_match_arms

Merges identical match arms.

// BEFORE
enum Action { Move { distance: u32 }, Stop }

fn handle(action: Action) {
    match action {
        ┃Action::Move(..) => foo(),
        Action::Stop => foo(),
    }
}

// AFTER
enum Action { Move { distance: u32 }, Stop }

fn handle(action: Action) {
    match action {
        Action::Move(..) | Action::Stop => foo(),
    }
}

move_arm_cond_to_match_guard

Moves if expression from match arm body into a guard.

// BEFORE
enum Action { Move { distance: u32 }, Stop }

fn handle(action: Action) {
    match action {
        Action::Move { distance } => ┃if distance > 10 { foo() },
        _ => (),
    }
}

// AFTER
enum Action { Move { distance: u32 }, Stop }

fn handle(action: Action) {
    match action {
        Action::Move { distance } if distance > 10 => foo(),
        _ => (),
    }
}

move_bounds_to_where_clause

Moves inline type bounds to a where clause.

// BEFORE
fn apply<T, U, ┃F: FnOnce(T) -> U>(f: F, x: T) -> U {
    f(x)
}

// AFTER
fn apply<T, U, F>(f: F, x: T) -> U where F: FnOnce(T) -> U {
    f(x)
}

move_guard_to_arm_body

Moves match guard into match arm body.

// BEFORE
enum Action { Move { distance: u32 }, Stop }

fn handle(action: Action) {
    match action {
        Action::Move { distance } ┃if distance > 10 => foo(),
        _ => (),
    }
}

// AFTER
enum Action { Move { distance: u32 }, Stop }

fn handle(action: Action) {
    match action {
        Action::Move { distance } => if distance > 10 { foo() },
        _ => (),
    }
}

remove_dbg

Removes dbg!() macro call.

// BEFORE
fn main() {
    ┃dbg!(92);
}

// AFTER
fn main() {
    92;
}

remove_hash

Removes a hash from a raw string literal.

// BEFORE
fn main() {
    r#"Hello,┃ World!"#;
}

// AFTER
fn main() {
    r"Hello, World!";
}

remove_mut

Removes the mut keyword.

// BEFORE
impl Walrus {
    fn feed(&mut┃ self, amount: u32) {}
}

// AFTER
impl Walrus {
    fn feed(&self, amount: u32) {}
}

reorder_fields

Reorder the fields of record literals and record patterns in the same order as in the definition.

// BEFORE
struct Foo {foo: i32, bar: i32};
const test: Foo = ┃Foo {bar: 0, foo: 1}

// AFTER
struct Foo {foo: i32, bar: i32};
const test: Foo = Foo {foo: 1, bar: 0}

replace_if_let_with_match

Replaces if let with an else branch with a match expression.

// BEFORE
enum Action { Move { distance: u32 }, Stop }

fn handle(action: Action) {
    ┃if let Action::Move { distance } = action {
        foo(distance)
    } else {
        bar()
    }
}

// AFTER
enum Action { Move { distance: u32 }, Stop }

fn handle(action: Action) {
    match action {
        Action::Move { distance } => foo(distance),
        _ => bar(),
    }
}

replace_let_with_if_let

Replaces let with an if-let.

// BEFORE

fn main(action: Action) {
    ┃let x = compute();
}

fn compute() -> Option<i32> { None }

// AFTER

fn main(action: Action) {
    if let Some(x) = compute() {
    }
}

fn compute() -> Option<i32> { None }

replace_qualified_name_with_use

Adds a use statement for a given fully-qualified name.

// BEFORE
fn process(map: std::collections::┃HashMap<String, String>) {}

// AFTER
use std::collections::HashMap;

fn process(map: HashMap<String, String>) {}

replace_unwrap_with_match

Replaces unwrap a match expression. Works for Result and Option.

// BEFORE
enum Result<T, E> { Ok(T), Err(E) }
fn main() {
    let x: Result<i32, i32> = Result::Ok(92);
    let y = x.┃unwrap();
}

// AFTER
enum Result<T, E> { Ok(T), Err(E) }
fn main() {
    let x: Result<i32, i32> = Result::Ok(92);
    let y = match x {
        Ok(a) => a,
        _ => unreachable!(),
    };
}

split_import

Wraps the tail of import into braces.

// BEFORE
use std::┃collections::HashMap;

// AFTER
use std::{collections::HashMap};

unwrap_block

This assist removes if...else, for, while and loop control statements to just keep the body.

// BEFORE
fn foo() {
    if true {┃
        println!("foo");
    }
}

// AFTER
fn foo() {
    println!("foo");
}