rust/tests/ui/needless_lifetimes.rs

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// run-rustfix
// aux-build:macro_rules.rs
#![warn(clippy::needless_lifetimes)]
#![allow(
unused,
clippy::boxed_local,
clippy::extra_unused_type_parameters,
clippy::needless_pass_by_value,
clippy::unnecessary_wraps,
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dyn_drop,
clippy::get_first
)]
#[macro_use]
extern crate macro_rules;
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fn distinct_lifetimes<'a, 'b>(_x: &'a u8, _y: &'b u8, _z: u8) {}
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fn distinct_and_static<'a, 'b>(_x: &'a u8, _y: &'b u8, _z: &'static u8) {}
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// No error; same lifetime on two params.
fn same_lifetime_on_input<'a>(_x: &'a u8, _y: &'a u8) {}
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// No error; static involved.
fn only_static_on_input(_x: &u8, _y: &u8, _z: &'static u8) {}
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fn mut_and_static_input(_x: &mut u8, _y: &'static str) {}
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fn in_and_out<'a>(x: &'a u8, _y: u8) -> &'a u8 {
x
}
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// No error; multiple input refs.
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fn multiple_in_and_out_1<'a>(x: &'a u8, _y: &'a u8) -> &'a u8 {
x
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}
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// Error; multiple input refs, but the output lifetime is not elided, i.e., the following is valid:
// fn multiple_in_and_out_2a<'a>(x: &'a u8, _y: &u8) -> &'a u8
// ^^^
fn multiple_in_and_out_2a<'a, 'b>(x: &'a u8, _y: &'b u8) -> &'a u8 {
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x
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}
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// Error; multiple input refs, but the output lifetime is not elided, i.e., the following is valid:
// fn multiple_in_and_out_2b<'b>(_x: &u8, y: &'b u8) -> &'b u8
// ^^^
fn multiple_in_and_out_2b<'a, 'b>(_x: &'a u8, y: &'b u8) -> &'b u8 {
y
}
// No error; multiple input refs
async fn func<'a>(args: &[&'a str]) -> Option<&'a str> {
args.get(0).cloned()
}
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// No error; static involved.
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fn in_static_and_out<'a>(x: &'a u8, _y: &'static u8) -> &'a u8 {
x
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}
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// Error; multiple input refs, but the output lifetime is not elided, i.e., the following is valid:
// fn deep_reference_1a<'a>(x: &'a u8, _y: &u8) -> Result<&'a u8, ()>
// ^^^
fn deep_reference_1a<'a, 'b>(x: &'a u8, _y: &'b u8) -> Result<&'a u8, ()> {
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Ok(x)
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}
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// Error; multiple input refs, but the output lifetime is not elided, i.e., the following is valid:
// fn deep_reference_1b<'b>(_x: &u8, y: &'b u8) -> Result<&'b u8, ()>
// ^^^
fn deep_reference_1b<'a, 'b>(_x: &'a u8, y: &'b u8) -> Result<&'b u8, ()> {
Ok(y)
}
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// No error; two input refs.
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fn deep_reference_2<'a>(x: Result<&'a u8, &'a u8>) -> &'a u8 {
x.unwrap()
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}
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fn deep_reference_3<'a>(x: &'a u8, _y: u8) -> Result<&'a u8, ()> {
Ok(x)
}
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// Where-clause, but without lifetimes.
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fn where_clause_without_lt<'a, T>(x: &'a u8, _y: u8) -> Result<&'a u8, ()>
where
T: Copy,
{
Ok(x)
}
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type Ref<'r> = &'r u8;
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// No error; same lifetime on two params.
fn lifetime_param_1<'a>(_x: Ref<'a>, _y: &'a u8) {}
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fn lifetime_param_2<'a, 'b>(_x: Ref<'a>, _y: &'b u8) {}
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// No error; bounded lifetime.
fn lifetime_param_3<'a, 'b: 'a>(_x: Ref<'a>, _y: &'b u8) {}
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// No error; bounded lifetime.
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fn lifetime_param_4<'a, 'b>(_x: Ref<'a>, _y: &'b u8)
where
'b: 'a,
{
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}
struct Lt<'a, I: 'static> {
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x: &'a I,
}
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// No error; fn bound references `'a`.
fn fn_bound<'a, F, I>(_m: Lt<'a, I>, _f: F) -> Lt<'a, I>
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where
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F: Fn(Lt<'a, I>) -> Lt<'a, I>,
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{
unreachable!()
}
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fn fn_bound_2<'a, F, I>(_m: Lt<'a, I>, _f: F) -> Lt<'a, I>
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where
for<'x> F: Fn(Lt<'x, I>) -> Lt<'x, I>,
{
unreachable!()
}
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// No error; see below.
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fn fn_bound_3<'a, F: FnOnce(&'a i32)>(x: &'a i32, f: F) {
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f(x);
}
fn fn_bound_3_cannot_elide() {
let x = 42;
let p = &x;
let mut q = &x;
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// This will fail if we elide lifetimes of `fn_bound_3`.
fn_bound_3(p, |y| q = y);
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}
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// No error; multiple input refs.
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fn fn_bound_4<'a, F: FnOnce() -> &'a ()>(cond: bool, x: &'a (), f: F) -> &'a () {
if cond { x } else { f() }
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}
struct X {
x: u8,
}
impl X {
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fn self_and_out<'s>(&'s self) -> &'s u8 {
&self.x
}
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// Error; multiple input refs, but the output lifetime is not elided, i.e., the following is valid:
// fn self_and_in_out_1<'s>(&'s self, _x: &u8) -> &'s u8
// ^^^
fn self_and_in_out_1<'s, 't>(&'s self, _x: &'t u8) -> &'s u8 {
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&self.x
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}
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// Error; multiple input refs, but the output lifetime is not elided, i.e., the following is valid:
// fn self_and_in_out_2<'t>(&self, x: &'t u8) -> &'t u8
// ^^^^^
fn self_and_in_out_2<'s, 't>(&'s self, x: &'t u8) -> &'t u8 {
x
}
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fn distinct_self_and_in<'s, 't>(&'s self, _x: &'t u8) {}
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// No error; same lifetimes on two params.
fn self_and_same_in<'s>(&'s self, _x: &'s u8) {}
}
struct Foo<'a>(&'a u8);
impl<'a> Foo<'a> {
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// No error; lifetime `'a` not defined in method.
fn self_shared_lifetime(&self, _: &'a u8) {}
// No error; bounds exist.
fn self_bound_lifetime<'b: 'a>(&self, _: &'b u8) {}
}
fn already_elided<'a>(_: &u8, _: &'a u8) -> &'a u8 {
unimplemented!()
}
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fn struct_with_lt<'a>(_foo: Foo<'a>) -> &'a str {
unimplemented!()
}
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// No warning; two input lifetimes (named on the reference, anonymous on `Foo`).
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fn struct_with_lt2<'a>(_foo: &'a Foo) -> &'a str {
unimplemented!()
}
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// No warning; two input lifetimes (anonymous on the reference, named on `Foo`).
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fn struct_with_lt3<'a>(_foo: &Foo<'a>) -> &'a str {
unimplemented!()
}
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// Warning; two input lifetimes, but the output lifetime is not elided, i.e., the following is
// valid:
// fn struct_with_lt4a<'a>(_foo: &'a Foo<'_>) -> &'a str
// ^^
fn struct_with_lt4a<'a, 'b>(_foo: &'a Foo<'b>) -> &'a str {
unimplemented!()
}
// Warning; two input lifetimes, but the output lifetime is not elided, i.e., the following is
// valid:
// fn struct_with_lt4b<'b>(_foo: &Foo<'b>) -> &'b str
// ^^^^
fn struct_with_lt4b<'a, 'b>(_foo: &'a Foo<'b>) -> &'b str {
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unimplemented!()
}
trait WithLifetime<'a> {}
type WithLifetimeAlias<'a> = dyn WithLifetime<'a>;
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// Should not warn because it won't build without the lifetime.
fn trait_obj_elided<'a>(_arg: &'a dyn WithLifetime) -> &'a str {
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unimplemented!()
}
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// Should warn because there is no lifetime on `Drop`, so this would be
// unambiguous if we elided the lifetime.
fn trait_obj_elided2<'a>(_arg: &'a dyn Drop) -> &'a str {
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unimplemented!()
}
type FooAlias<'a> = Foo<'a>;
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fn alias_with_lt<'a>(_foo: FooAlias<'a>) -> &'a str {
unimplemented!()
}
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// No warning; two input lifetimes (named on the reference, anonymous on `FooAlias`).
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fn alias_with_lt2<'a>(_foo: &'a FooAlias) -> &'a str {
unimplemented!()
}
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// No warning; two input lifetimes (anonymous on the reference, named on `FooAlias`).
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fn alias_with_lt3<'a>(_foo: &FooAlias<'a>) -> &'a str {
unimplemented!()
}
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// Warning; two input lifetimes, but the output lifetime is not elided, i.e., the following is
// valid:
// fn alias_with_lt4a<'a>(_foo: &'a FooAlias<'_>) -> &'a str
// ^^
fn alias_with_lt4a<'a, 'b>(_foo: &'a FooAlias<'b>) -> &'a str {
unimplemented!()
}
// Warning; two input lifetimes, but the output lifetime is not elided, i.e., the following is
// valid:
// fn alias_with_lt4b<'b>(_foo: &FooAlias<'b>) -> &'b str
// ^^^^^^^^^
fn alias_with_lt4b<'a, 'b>(_foo: &'a FooAlias<'b>) -> &'b str {
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unimplemented!()
}
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fn named_input_elided_output<'a>(_arg: &'a str) -> &str {
unimplemented!()
}
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fn elided_input_named_output<'a>(_arg: &str) -> &'a str {
unimplemented!()
}
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fn trait_bound_ok<'a, T: WithLifetime<'static>>(_: &'a u8, _: T) {
unimplemented!()
}
fn trait_bound<'a, T: WithLifetime<'a>>(_: &'a u8, _: T) {
unimplemented!()
}
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// Don't warn on these; see issue #292.
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fn trait_bound_bug<'a, T: WithLifetime<'a>>() {
unimplemented!()
}
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// See issue #740.
struct Test {
vec: Vec<usize>,
}
impl Test {
fn iter<'a>(&'a self) -> Box<dyn Iterator<Item = usize> + 'a> {
unimplemented!()
}
}
trait LintContext<'a> {}
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fn f<'a, T: LintContext<'a>>(_: &T) {}
fn test<'a>(x: &'a [u8]) -> u8 {
let y: &'a u8 = &x[5];
*y
}
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// Issue #3284: give hint regarding lifetime in return type.
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struct Cow<'a> {
x: &'a str,
}
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fn out_return_type_lts<'a>(e: &'a str) -> Cow<'a> {
unimplemented!()
}
// Make sure we still warn on implementations
mod issue4291 {
trait BadTrait {
fn needless_lt<'a>(x: &'a u8) {}
}
impl BadTrait for () {
fn needless_lt<'a>(_x: &'a u8) {}
}
}
mod issue2944 {
trait Foo {}
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struct Bar;
struct Baz<'a> {
bar: &'a Bar,
}
impl<'a> Foo for Baz<'a> {}
impl Bar {
fn baz<'a>(&'a self) -> impl Foo + 'a {
Baz { bar: self }
}
}
}
mod nested_elision_sites {
// issue #issue2944
// closure trait bounds subject to nested elision
// don't lint because they refer to outer lifetimes
fn trait_fn<'a>(i: &'a i32) -> impl Fn() -> &'a i32 {
move || i
}
fn trait_fn_mut<'a>(i: &'a i32) -> impl FnMut() -> &'a i32 {
move || i
}
fn trait_fn_once<'a>(i: &'a i32) -> impl FnOnce() -> &'a i32 {
move || i
}
// don't lint
fn impl_trait_in_input_position<'a>(f: impl Fn() -> &'a i32) -> &'a i32 {
f()
}
fn impl_trait_in_output_position<'a>(i: &'a i32) -> impl Fn() -> &'a i32 {
move || i
}
// lint
fn impl_trait_elidable_nested_named_lifetimes<'a>(i: &'a i32, f: impl for<'b> Fn(&'b i32) -> &'b i32) -> &'a i32 {
f(i)
}
fn impl_trait_elidable_nested_anonymous_lifetimes<'a>(i: &'a i32, f: impl Fn(&i32) -> &i32) -> &'a i32 {
f(i)
}
// don't lint
fn generics_not_elidable<'a, T: Fn() -> &'a i32>(f: T) -> &'a i32 {
f()
}
// lint
fn generics_elidable<'a, T: Fn(&i32) -> &i32>(i: &'a i32, f: T) -> &'a i32 {
f(i)
}
// don't lint
fn where_clause_not_elidable<'a, T>(f: T) -> &'a i32
where
T: Fn() -> &'a i32,
{
f()
}
// lint
fn where_clause_elidadable<'a, T>(i: &'a i32, f: T) -> &'a i32
where
T: Fn(&i32) -> &i32,
{
f(i)
}
// don't lint
fn pointer_fn_in_input_position<'a>(f: fn(&'a i32) -> &'a i32, i: &'a i32) -> &'a i32 {
f(i)
}
fn pointer_fn_in_output_position<'a>(_: &'a i32) -> fn(&'a i32) -> &'a i32 {
|i| i
}
// lint
fn pointer_fn_elidable<'a>(i: &'a i32, f: fn(&i32) -> &i32) -> &'a i32 {
f(i)
}
// don't lint
fn nested_fn_pointer_1<'a>(_: &'a i32) -> fn(fn(&'a i32) -> &'a i32) -> i32 {
|f| 42
}
fn nested_fn_pointer_2<'a>(_: &'a i32) -> impl Fn(fn(&'a i32)) {
|f| ()
}
// lint
fn nested_fn_pointer_3<'a>(_: &'a i32) -> fn(fn(&i32) -> &i32) -> i32 {
|f| 42
}
fn nested_fn_pointer_4<'a>(_: &'a i32) -> impl Fn(fn(&i32)) {
|f| ()
}
}
mod issue6159 {
use std::ops::Deref;
pub fn apply_deref<'a, T, F, R>(x: &'a T, f: F) -> R
where
T: Deref,
F: FnOnce(&'a T::Target) -> R,
{
f(x.deref())
}
}
mod issue7296 {
use std::rc::Rc;
use std::sync::Arc;
struct Foo;
impl Foo {
fn implicit<'a>(&'a self) -> &'a () {
&()
}
fn implicit_mut<'a>(&'a mut self) -> &'a () {
&()
}
fn explicit<'a>(self: &'a Arc<Self>) -> &'a () {
&()
}
fn explicit_mut<'a>(self: &'a mut Rc<Self>) -> &'a () {
&()
}
fn lifetime_elsewhere<'a>(self: Box<Self>, here: &'a ()) -> &'a () {
&()
}
}
trait Bar {
fn implicit<'a>(&'a self) -> &'a ();
fn implicit_provided<'a>(&'a self) -> &'a () {
&()
}
fn explicit<'a>(self: &'a Arc<Self>) -> &'a ();
fn explicit_provided<'a>(self: &'a Arc<Self>) -> &'a () {
&()
}
fn lifetime_elsewhere<'a>(self: Box<Self>, here: &'a ()) -> &'a ();
fn lifetime_elsewhere_provided<'a>(self: Box<Self>, here: &'a ()) -> &'a () {
&()
}
}
}
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mod pr_9743_false_negative_fix {
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#![allow(unused)]
fn foo<'a>(x: &'a u8, y: &'_ u8) {}
fn bar<'a>(x: &'a u8, y: &'_ u8, z: &'_ u8) {}
}
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mod pr_9743_output_lifetime_checks {
#![allow(unused)]
// lint: only one input
fn one_input<'a>(x: &'a u8) -> &'a u8 {
unimplemented!()
}
// lint: multiple inputs, output would not be elided
fn multiple_inputs_output_not_elided<'a, 'b>(x: &'a u8, y: &'b u8, z: &'b u8) -> &'b u8 {
unimplemented!()
}
// don't lint: multiple inputs, output would be elided (which would create an ambiguity)
fn multiple_inputs_output_would_be_elided<'a, 'b>(x: &'a u8, y: &'b u8, z: &'b u8) -> &'a u8 {
unimplemented!()
}
}
mod in_macro {
macro_rules! local_one_input_macro {
() => {
fn one_input<'a>(x: &'a u8) -> &'a u8 {
unimplemented!()
}
};
}
// lint local macro expands to function with needless lifetimes
local_one_input_macro!();
// no lint on external macro
macro_rules::needless_lifetime!();
macro_rules! expanded_lifetime {
($l:lifetime) => {
fn f<$l>(arg: &$l str) -> &$l str {
arg
}
}
}
expanded_lifetime!('a);
}
mod issue5787 {
use std::sync::MutexGuard;
struct Foo;
impl Foo {
// doesn't get linted without async
pub async fn wait<'a, T>(&self, guard: MutexGuard<'a, T>) -> MutexGuard<'a, T> {
guard
}
}
async fn foo<'a>(_x: &i32, y: &'a str) -> &'a str {
y
}
}
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fn main() {}