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Prevent clippy::needless_lifetimes false positive in async function definition #7901

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Nov 2, 2021
Merged

Prevent clippy::needless_lifetimes false positive in async function definition #7901

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3f84010
Examine lifetimes in `OpaqueDef` bounds as well
samueltardieu Oct 30, 2021
9bcf966
Add test case for `clippy::needless_lifetimes` in async context
samueltardieu Oct 30, 2021
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6 changes: 5 additions & 1 deletion clippy_lints/src/lifetimes.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -378,11 +378,15 @@ impl<'a, 'tcx> Visitor<'tcx> for RefVisitor<'a, 'tcx> {

fn visit_ty(&mut self, ty: &'tcx Ty<'_>) {
match ty.kind {
TyKind::OpaqueDef(item, _) => {
TyKind::OpaqueDef(item, bounds) => {
let map = self.cx.tcx.hir();
let item = map.item(item);
walk_item(self, item);
walk_ty(self, ty);
self.lts.extend(bounds.iter().filter_map(|bound| match bound {
GenericArg::Lifetime(l) => Some(RefLt::Named(l.name.ident().name)),
_ => None,
}));
},
TyKind::BareFn(&BareFnTy { decl, .. }) => {
let mut sub_visitor = RefVisitor::new(self.cx);
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5 changes: 5 additions & 0 deletions tests/ui/needless_lifetimes.rs
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Expand Up @@ -27,6 +27,11 @@ fn multiple_in_and_out_2<'a, 'b>(x: &'a u8, _y: &'b u8) -> &'a u8 {
x
}

// 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
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44 changes: 22 additions & 22 deletions tests/ui/needless_lifetimes.stderr
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Expand Up @@ -19,133 +19,133 @@ LL | fn in_and_out<'a>(x: &'a u8, _y: u8) -> &'a u8 {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:45:1
--> $DIR/needless_lifetimes.rs:50:1
|
LL | fn deep_reference_3<'a>(x: &'a u8, _y: u8) -> Result<&'a u8, ()> {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:50:1
--> $DIR/needless_lifetimes.rs:55:1
|
LL | fn where_clause_without_lt<'a, T>(x: &'a u8, _y: u8) -> Result<&'a u8, ()>
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:62:1
--> $DIR/needless_lifetimes.rs:67:1
|
LL | fn lifetime_param_2<'a, 'b>(_x: Ref<'a>, _y: &'b u8) {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:86:1
--> $DIR/needless_lifetimes.rs:91:1
|
LL | fn fn_bound_2<'a, F, I>(_m: Lt<'a, I>, _f: F) -> Lt<'a, I>
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:116:5
--> $DIR/needless_lifetimes.rs:121:5
|
LL | fn self_and_out<'s>(&'s self) -> &'s u8 {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:125:5
--> $DIR/needless_lifetimes.rs:130:5
|
LL | fn distinct_self_and_in<'s, 't>(&'s self, _x: &'t u8) {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:144:1
--> $DIR/needless_lifetimes.rs:149:1
|
LL | fn struct_with_lt<'a>(_foo: Foo<'a>) -> &'a str {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:174:1
--> $DIR/needless_lifetimes.rs:179:1
|
LL | fn trait_obj_elided2<'a>(_arg: &'a dyn Drop) -> &'a str {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:180:1
--> $DIR/needless_lifetimes.rs:185:1
|
LL | fn alias_with_lt<'a>(_foo: FooAlias<'a>) -> &'a str {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:199:1
--> $DIR/needless_lifetimes.rs:204:1
|
LL | fn named_input_elided_output<'a>(_arg: &'a str) -> &str {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:207:1
--> $DIR/needless_lifetimes.rs:212:1
|
LL | fn trait_bound_ok<'a, T: WithLifetime<'static>>(_: &'a u8, _: T) {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:243:1
--> $DIR/needless_lifetimes.rs:248:1
|
LL | fn out_return_type_lts<'a>(e: &'a str) -> Cow<'a> {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:250:9
--> $DIR/needless_lifetimes.rs:255:9
|
LL | fn needless_lt<'a>(x: &'a u8) {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:254:9
--> $DIR/needless_lifetimes.rs:259:9
|
LL | fn needless_lt<'a>(_x: &'a u8) {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:267:9
--> $DIR/needless_lifetimes.rs:272:9
|
LL | fn baz<'a>(&'a self) -> impl Foo + 'a {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:296:5
--> $DIR/needless_lifetimes.rs:301:5
|
LL | fn impl_trait_elidable_nested_named_lifetimes<'a>(i: &'a i32, f: impl for<'b> Fn(&'b i32) -> &'b i32) -> &'a i32 {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:299:5
--> $DIR/needless_lifetimes.rs:304:5
|
LL | fn impl_trait_elidable_nested_anonymous_lifetimes<'a>(i: &'a i32, f: impl Fn(&i32) -> &i32) -> &'a i32 {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:308:5
--> $DIR/needless_lifetimes.rs:313:5
|
LL | fn generics_elidable<'a, T: Fn(&i32) -> &i32>(i: &'a i32, f: T) -> &'a i32 {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:320:5
--> $DIR/needless_lifetimes.rs:325:5
|
LL | fn where_clause_elidadable<'a, T>(i: &'a i32, f: T) -> &'a i32
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:335:5
--> $DIR/needless_lifetimes.rs:340:5
|
LL | fn pointer_fn_elidable<'a>(i: &'a i32, f: fn(&i32) -> &i32) -> &'a i32 {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:348:5
--> $DIR/needless_lifetimes.rs:353:5
|
LL | fn nested_fn_pointer_3<'a>(_: &'a i32) -> fn(fn(&i32) -> &i32) -> i32 {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
--> $DIR/needless_lifetimes.rs:351:5
--> $DIR/needless_lifetimes.rs:356:5
|
LL | fn nested_fn_pointer_4<'a>(_: &'a i32) -> impl Fn(fn(&i32)) {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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