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diff --git a/src/tools/clippy/tests/ui/needless_lifetimes.fixed b/src/tools/clippy/tests/ui/needless_lifetimes.fixed
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+++ b/src/tools/clippy/tests/ui/needless_lifetimes.fixed
@@ -0,0 +1,548 @@
+// 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,
+ dyn_drop,
+ clippy::get_first
+)]
+
+#[macro_use]
+extern crate macro_rules;
+
+fn distinct_lifetimes(_x: &u8, _y: &u8, _z: u8) {}
+
+fn distinct_and_static(_x: &u8, _y: &u8, _z: &'static u8) {}
+
+// No error; same lifetime on two params.
+fn same_lifetime_on_input<'a>(_x: &'a u8, _y: &'a u8) {}
+
+// No error; static involved.
+fn only_static_on_input(_x: &u8, _y: &u8, _z: &'static u8) {}
+
+fn mut_and_static_input(_x: &mut u8, _y: &'static str) {}
+
+fn in_and_out(x: &u8, _y: u8) -> &u8 {
+ x
+}
+
+// No error; multiple input refs.
+fn multiple_in_and_out_1<'a>(x: &'a u8, _y: &'a u8) -> &'a u8 {
+ x
+}
+
+// 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>(x: &'a u8, _y: &u8) -> &'a u8 {
+ x
+}
+
+// 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<'b>(_x: &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()
+}
+
+// No error; static involved.
+fn in_static_and_out<'a>(x: &'a u8, _y: &'static u8) -> &'a u8 {
+ x
+}
+
+// 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>(x: &'a u8, _y: &u8) -> Result<&'a u8, ()> {
+ Ok(x)
+}
+
+// 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<'b>(_x: &u8, y: &'b u8) -> Result<&'b u8, ()> {
+ Ok(y)
+}
+
+// No error; two input refs.
+fn deep_reference_2<'a>(x: Result<&'a u8, &'a u8>) -> &'a u8 {
+ x.unwrap()
+}
+
+fn deep_reference_3(x: &u8, _y: u8) -> Result<&u8, ()> {
+ Ok(x)
+}
+
+// Where-clause, but without lifetimes.
+fn where_clause_without_lt<T>(x: &u8, _y: u8) -> Result<&u8, ()>
+where
+ T: Copy,
+{
+ Ok(x)
+}
+
+type Ref<'r> = &'r u8;
+
+// No error; same lifetime on two params.
+fn lifetime_param_1<'a>(_x: Ref<'a>, _y: &'a u8) {}
+
+fn lifetime_param_2(_x: Ref<'_>, _y: &u8) {}
+
+// No error; bounded lifetime.
+fn lifetime_param_3<'a, 'b: 'a>(_x: Ref<'a>, _y: &'b u8) {}
+
+// No error; bounded lifetime.
+fn lifetime_param_4<'a, 'b>(_x: Ref<'a>, _y: &'b u8)
+where
+ 'b: 'a,
+{
+}
+
+struct Lt<'a, I: 'static> {
+ x: &'a I,
+}
+
+// No error; fn bound references `'a`.
+fn fn_bound<'a, F, I>(_m: Lt<'a, I>, _f: F) -> Lt<'a, I>
+where
+ F: Fn(Lt<'a, I>) -> Lt<'a, I>,
+{
+ unreachable!()
+}
+
+fn fn_bound_2<F, I>(_m: Lt<'_, I>, _f: F) -> Lt<'_, I>
+where
+ for<'x> F: Fn(Lt<'x, I>) -> Lt<'x, I>,
+{
+ unreachable!()
+}
+
+// No error; see below.
+fn fn_bound_3<'a, F: FnOnce(&'a i32)>(x: &'a i32, f: F) {
+ f(x);
+}
+
+fn fn_bound_3_cannot_elide() {
+ let x = 42;
+ let p = &x;
+ let mut q = &x;
+ // This will fail if we elide lifetimes of `fn_bound_3`.
+ fn_bound_3(p, |y| q = y);
+}
+
+// No error; multiple input refs.
+fn fn_bound_4<'a, F: FnOnce() -> &'a ()>(cond: bool, x: &'a (), f: F) -> &'a () {
+ if cond { x } else { f() }
+}
+
+struct X {
+ x: u8,
+}
+
+impl X {
+ fn self_and_out(&self) -> &u8 {
+ &self.x
+ }
+
+ // 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>(&'s self, _x: &u8) -> &'s u8 {
+ &self.x
+ }
+
+ // 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<'t>(&self, x: &'t u8) -> &'t u8 {
+ x
+ }
+
+ fn distinct_self_and_in(&self, _x: &u8) {}
+
+ // 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> {
+ // 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!()
+}
+
+fn struct_with_lt(_foo: Foo<'_>) -> &str {
+ unimplemented!()
+}
+
+// No warning; two input lifetimes (named on the reference, anonymous on `Foo`).
+fn struct_with_lt2<'a>(_foo: &'a Foo) -> &'a str {
+ unimplemented!()
+}
+
+// No warning; two input lifetimes (anonymous on the reference, named on `Foo`).
+fn struct_with_lt3<'a>(_foo: &Foo<'a>) -> &'a str {
+ unimplemented!()
+}
+
+// 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>(_foo: &'a Foo<'_>) -> &'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<'b>(_foo: &Foo<'b>) -> &'b str {
+ unimplemented!()
+}
+
+trait WithLifetime<'a> {}
+
+type WithLifetimeAlias<'a> = dyn WithLifetime<'a>;
+
+// Should not warn because it won't build without the lifetime.
+fn trait_obj_elided<'a>(_arg: &'a dyn WithLifetime) -> &'a str {
+ unimplemented!()
+}
+
+// Should warn because there is no lifetime on `Drop`, so this would be
+// unambiguous if we elided the lifetime.
+fn trait_obj_elided2(_arg: &dyn Drop) -> &str {
+ unimplemented!()
+}
+
+type FooAlias<'a> = Foo<'a>;
+
+fn alias_with_lt(_foo: FooAlias<'_>) -> &str {
+ unimplemented!()
+}
+
+// No warning; two input lifetimes (named on the reference, anonymous on `FooAlias`).
+fn alias_with_lt2<'a>(_foo: &'a FooAlias) -> &'a str {
+ unimplemented!()
+}
+
+// No warning; two input lifetimes (anonymous on the reference, named on `FooAlias`).
+fn alias_with_lt3<'a>(_foo: &FooAlias<'a>) -> &'a str {
+ unimplemented!()
+}
+
+// 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>(_foo: &'a FooAlias<'_>) -> &'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<'b>(_foo: &FooAlias<'b>) -> &'b str {
+ unimplemented!()
+}
+
+fn named_input_elided_output(_arg: &str) -> &str {
+ unimplemented!()
+}
+
+fn elided_input_named_output<'a>(_arg: &str) -> &'a str {
+ unimplemented!()
+}
+
+fn trait_bound_ok<T: WithLifetime<'static>>(_: &u8, _: T) {
+ unimplemented!()
+}
+fn trait_bound<'a, T: WithLifetime<'a>>(_: &'a u8, _: T) {
+ unimplemented!()
+}
+
+// Don't warn on these; see issue #292.
+fn trait_bound_bug<'a, T: WithLifetime<'a>>() {
+ unimplemented!()
+}
+
+// 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> {}
+
+fn f<'a, T: LintContext<'a>>(_: &T) {}
+
+fn test<'a>(x: &'a [u8]) -> u8 {
+ let y: &'a u8 = &x[5];
+ *y
+}
+
+// Issue #3284: give hint regarding lifetime in return type.
+struct Cow<'a> {
+ x: &'a str,
+}
+fn out_return_type_lts(e: &str) -> Cow<'_> {
+ unimplemented!()
+}
+
+// Make sure we still warn on implementations
+mod issue4291 {
+ trait BadTrait {
+ fn needless_lt(x: &u8) {}
+ }
+
+ impl BadTrait for () {
+ fn needless_lt(_x: &u8) {}
+ }
+}
+
+mod issue2944 {
+ trait Foo {}
+ struct Bar;
+ struct Baz<'a> {
+ bar: &'a Bar,
+ }
+
+ impl<'a> Foo for Baz<'a> {}
+ impl Bar {
+ fn baz(&self) -> impl Foo + '_ {
+ 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(i: &i32, f: impl Fn(&i32) -> &i32) -> &i32 {
+ f(i)
+ }
+
+ // don't lint
+ fn generics_not_elidable<'a, T: Fn() -> &'a i32>(f: T) -> &'a i32 {
+ f()
+ }
+ // lint
+ fn generics_elidable<T: Fn(&i32) -> &i32>(i: &i32, f: T) -> &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<T>(i: &i32, f: T) -> &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(i: &i32, f: fn(&i32) -> &i32) -> &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(_: &i32) -> fn(fn(&i32) -> &i32) -> i32 {
+ |f| 42
+ }
+ fn nested_fn_pointer_4(_: &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(&self) -> &() {
+ &()
+ }
+ fn implicit_mut(&mut self) -> &() {
+ &()
+ }
+
+ fn explicit<'a>(self: &'a Arc<Self>) -> &'a () {
+ &()
+ }
+ fn explicit_mut<'a>(self: &'a mut Rc<Self>) -> &'a () {
+ &()
+ }
+
+ fn lifetime_elsewhere(self: Box<Self>, here: &()) -> &() {
+ &()
+ }
+ }
+
+ trait Bar {
+ fn implicit(&self) -> &();
+ fn implicit_provided(&self) -> &() {
+ &()
+ }
+
+ fn explicit<'a>(self: &'a Arc<Self>) -> &'a ();
+ fn explicit_provided<'a>(self: &'a Arc<Self>) -> &'a () {
+ &()
+ }
+
+ fn lifetime_elsewhere(self: Box<Self>, here: &()) -> &();
+ fn lifetime_elsewhere_provided(self: Box<Self>, here: &()) -> &() {
+ &()
+ }
+ }
+}
+
+mod pr_9743_false_negative_fix {
+ #![allow(unused)]
+
+ fn foo(x: &u8, y: &'_ u8) {}
+
+ fn bar(x: &u8, y: &'_ u8, z: &'_ u8) {}
+}
+
+mod pr_9743_output_lifetime_checks {
+ #![allow(unused)]
+
+ // lint: only one input
+ fn one_input(x: &u8) -> &u8 {
+ unimplemented!()
+ }
+
+ // lint: multiple inputs, output would not be elided
+ fn multiple_inputs_output_not_elided<'b>(x: &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(x: &u8) -> &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
+ }
+}
+
+fn main() {}
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