Check lifetimes in Fn traits in generic bounds.

Add tests.

clippy_lints/src/lifetimes.rs

@@ -103,6 +103,11 @@ fn check_fn_inner<'a, 'tcx>(
     let mut bounds_lts = Vec::new();
     for typ in generics.ty_params() {
         for bound in &typ.bounds {
+            let mut visitor = RefVisitor::new(cx);
+            walk_ty_param_bound(&mut visitor, bound);
+            if visitor.lts.iter().any(|lt| matches!(lt, RefLt::Named(_))) {
+                return;
+            }
             if let TraitTyParamBound(ref trait_ref, _) = *bound {
                 let params = &trait_ref
                     .trait_ref

tests/ui/lifetimes.rs

@@ -53,6 +53,10 @@ fn fn_bound_2<'a, F, I>(_m: Lt<'a, I>, _f: F) -> Lt<'a, I>
     where for<'x> F: Fn(Lt<'x, I>) -> Lt<'x, I>
 { unreachable!() }
 
+fn fn_bound_3<'a, F: FnOnce(&'a ())>(x: &'a (), f: F) {} // no error, referenced
+
+fn fn_bound_4<'a, F: FnOnce() -> &'a ()>(x: &'a (), f: F) {} // no error, referenced
+
 struct X {
     x: u8,
 }

tests/ui/lifetimes.stderr

@@ -45,45 +45,45 @@ error: explicit lifetimes given in parameter types where they could be elided
    | |__________________^
 
 error: explicit lifetimes given in parameter types where they could be elided
-  --> $DIR/lifetimes.rs:61:5
+  --> $DIR/lifetimes.rs:65:5
    |
-61 |     fn self_and_out<'s>(&'s self) -> &'s u8 { &self.x }
+65 |     fn self_and_out<'s>(&'s self) -> &'s u8 { &self.x }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: explicit lifetimes given in parameter types where they could be elided
-  --> $DIR/lifetimes.rs:65:5
+  --> $DIR/lifetimes.rs:69:5
    |
-65 |     fn distinct_self_and_in<'s, 't>(&'s self, _x: &'t u8) { }
+69 |     fn distinct_self_and_in<'s, 't>(&'s self, _x: &'t u8) { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: explicit lifetimes given in parameter types where they could be elided
-  --> $DIR/lifetimes.rs:81:1
+  --> $DIR/lifetimes.rs:85:1
    |
-81 | fn struct_with_lt<'a>(_foo: Foo<'a>) -> &'a str { unimplemented!() }
+85 | fn struct_with_lt<'a>(_foo: Foo<'a>) -> &'a str { unimplemented!() }
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: explicit lifetimes given in parameter types where they could be elided
-   --> $DIR/lifetimes.rs:101:1
-    |
-101 | fn trait_obj_elided2<'a>(_arg: &'a Drop) -> &'a str { unimplemented!() }
-    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
 error: explicit lifetimes given in parameter types where they could be elided
    --> $DIR/lifetimes.rs:105:1
     |
-105 | fn alias_with_lt<'a>(_foo: FooAlias<'a>) -> &'a str { unimplemented!() }
+105 | fn trait_obj_elided2<'a>(_arg: &'a Drop) -> &'a str { unimplemented!() }
     | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: explicit lifetimes given in parameter types where they could be elided
-   --> $DIR/lifetimes.rs:116:1
+   --> $DIR/lifetimes.rs:109:1
     |
-116 | fn named_input_elided_output<'a>(_arg: &'a str) -> &str { unimplemented!() }
+109 | fn alias_with_lt<'a>(_foo: FooAlias<'a>) -> &'a str { unimplemented!() }
-    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: explicit lifetimes given in parameter types where they could be elided
    --> $DIR/lifetimes.rs:120:1
     |
-120 | fn trait_bound_ok<'a, T: WithLifetime<'static>>(_: &'a u8, _: T) { unimplemented!() }
+120 | fn named_input_elided_output<'a>(_arg: &'a str) -> &str { unimplemented!() }
+    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: explicit lifetimes given in parameter types where they could be elided
+   --> $DIR/lifetimes.rs:124:1
+    |
+124 | fn trait_bound_ok<'a, T: WithLifetime<'static>>(_: &'a u8, _: T) { unimplemented!() }
     | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to 14 previous errors