Improve `needless_lifetimes`

3 files changed, 168 insertions, 60 deletions

diff --git a/clippy_lints/src/lifetimes.rs b/clippy_lints/src/lifetimes.rs
index 13878eda0f1..996eb277426 100644
--- a/clippy_lints/src/lifetimes.rs
+++ b/clippy_lints/src/lifetimes.rs
@@ -1,4 +1,4 @@
-use clippy_utils::diagnostics::span_lint;
+use clippy_utils::diagnostics::{span_lint, span_lint_and_then};
 use clippy_utils::trait_ref_of_method;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_hir::intravisit::nested_filter::{self as hir_nested_filter, NestedFilter};
@@ -151,6 +151,7 @@ fn check_fn_inner<'tcx>(
         .params
         .iter()
         .filter(|param| matches!(param.kind, GenericParamKind::Type { .. }));
+
     for typ in types {
         for pred in generics.bounds_for_param(cx.tcx.hir().local_def_id(typ.hir_id)) {
             if pred.origin == PredicateOrigin::WhereClause {
@@ -187,15 +188,30 @@ fn check_fn_inner<'tcx>(
             }
         }
     }
-    if could_use_elision(cx, decl, body, trait_sig, generics.params) {
-        span_lint(
+
+    if let Some(elidable_lts) = could_use_elision(cx, decl, body, trait_sig, generics.params) {
+        let lts = elidable_lts
+            .iter()
+            // In principle, the result of the call to `Node::ident` could be `unwrap`ped, as `DefId` should refer to a
+            // `Node::GenericParam`.
+            .filter_map(|&(def_id, _)| cx.tcx.hir().get_by_def_id(def_id).ident())
+            .map(|ident| ident.to_string())
+            .collect::<Vec<_>>()
+            .join(", ");
+
+        span_lint_and_then(
             cx,
             NEEDLESS_LIFETIMES,
             span.with_hi(decl.output.span().hi()),
-            "explicit lifetimes given in parameter types where they could be elided \
-             (or replaced with `'_` if needed by type declaration)",
+            &format!("the following explicit lifetimes could be elided: {lts}"),
+            |diag| {
+                if let Some(span) = elidable_lts.iter().find_map(|&(_, span)| span) {
+                    diag.span_help(span, "replace with `'_` in generic arguments such as here");
+                }
+            },
         );
     }
+
     if report_extra_lifetimes {
         self::report_extra_lifetimes(cx, decl, generics);
     }
@@ -220,13 +236,14 @@ fn explicit_self_type<'tcx>(cx: &LateContext<'tcx>, func: &FnDecl<'tcx>, ident:
     }
 }
 
+#[expect(clippy::too_many_lines)]
 fn could_use_elision<'tcx>(
     cx: &LateContext<'tcx>,
     func: &'tcx FnDecl<'_>,
     body: Option<BodyId>,
     trait_sig: Option<&[Ident]>,
     named_generics: &'tcx [GenericParam<'_>],
-) -> bool {
+) -> Option<Vec<(LocalDefId, Option<Span>)>> {
     // There are two scenarios where elision works:
     // * no output references, all input references have different LT
     // * output references, exactly one input reference with same LT
@@ -253,7 +270,7 @@ fn could_use_elision<'tcx>(
     }
 
     if input_visitor.abort() || output_visitor.abort() {
-        return false;
+        return None;
     }
 
     let input_lts = input_visitor.lts;
@@ -261,7 +278,7 @@ fn could_use_elision<'tcx>(
 
     if let Some(trait_sig) = trait_sig {
         if explicit_self_type(cx, func, trait_sig.first().copied()) {
-            return false;
+            return None;
         }
     }
 
@@ -270,7 +287,7 @@ fn could_use_elision<'tcx>(
 
         let first_ident = body.params.first().and_then(|param| param.pat.simple_ident());
         if explicit_self_type(cx, func, first_ident) {
-            return false;
+            return None;
         }
 
         let mut checker = BodyLifetimeChecker {
@@ -278,14 +295,14 @@ fn could_use_elision<'tcx>(
         };
         checker.visit_expr(body.value);
         if checker.lifetimes_used_in_body {
-            return false;
+            return None;
         }
     }
 
     // check for lifetimes from higher scopes
     for lt in input_lts.iter().chain(output_lts.iter()) {
         if !allowed_lts.contains(lt) {
-            return false;
+            return None;
         }
     }
 
@@ -301,14 +318,14 @@ fn could_use_elision<'tcx>(
         for lt in input_visitor.nested_elision_site_lts {
             if let RefLt::Named(def_id) = lt {
                 if allowed_lts.contains(&cx.tcx.item_name(def_id.to_def_id())) {
-                    return false;
+                    return None;
                 }
             }
         }
         for lt in output_visitor.nested_elision_site_lts {
             if let RefLt::Named(def_id) = lt {
                 if allowed_lts.contains(&cx.tcx.item_name(def_id.to_def_id())) {
-                    return false;
+                    return None;
                 }
             }
         }
@@ -316,32 +333,47 @@ fn could_use_elision<'tcx>(
 
     // no input lifetimes? easy case!
     if input_lts.is_empty() {
-        false
+        None
     } else if output_lts.is_empty() {
         // no output lifetimes, check distinctness of input lifetimes
 
         // only unnamed and static, ok
         let unnamed_and_static = input_lts.iter().all(|lt| *lt == RefLt::Unnamed || *lt == RefLt::Static);
         if unnamed_and_static {
-            return false;
+            return None;
+        }
+        // we have no output reference, so we can elide explicit lifetimes that occur at most once
+        let elidable_lts = named_lifetime_occurrences(&input_lts)
+            .into_iter()
+            .filter_map(|(def_id, occurrences)| {
+                if occurrences <= 1 {
+                    Some((def_id, input_visitor.sample_generic_arg_span.get(&def_id).copied()))
+                } else {
+                    None
+                }
+            })
+            .collect::<Vec<_>>();
+        if elidable_lts.is_empty() {
+            None
+        } else {
+            Some(elidable_lts)
         }
-        // we have no output reference, so we only need all distinct lifetimes
-        input_lts.len() == unique_lifetimes(&input_lts)
     } else {
         // we have output references, so we need one input reference,
         // and all output lifetimes must be the same
-        if unique_lifetimes(&output_lts) > 1 {
-            return false;
-        }
         if input_lts.len() == 1 {
             match (&input_lts[0], &output_lts[0]) {
-                (&RefLt::Named(n1), &RefLt::Named(n2)) if n1 == n2 => true,
-                (&RefLt::Named(_), &RefLt::Unnamed) => true,
-                _ => false, /* already elided, different named lifetimes
-                             * or something static going on */
+                (&RefLt::Named(n1), &RefLt::Named(n2)) if n1 == n2 => {
+                    Some(vec![(n1, input_visitor.sample_generic_arg_span.get(&n1).copied())])
+                },
+                (&RefLt::Named(n), &RefLt::Unnamed) => {
+                    Some(vec![(n, input_visitor.sample_generic_arg_span.get(&n).copied())])
+                },
+                _ => None, /* already elided, different named lifetimes
+                            * or something static going on */
             }
         } else {
-            false
+            None
         }
     }
 }
@@ -358,10 +390,24 @@ fn allowed_lts_from(tcx: TyCtxt<'_>, named_generics: &[GenericParam<'_>]) -> FxH
     allowed_lts
 }
 
-/// Number of unique lifetimes in the given vector.
+/// Number of times each named lifetime occurs in the given slice. Returns a vector to preserve
+/// relative order.
 #[must_use]
-fn unique_lifetimes(lts: &[RefLt]) -> usize {
-    lts.iter().collect::<FxHashSet<_>>().len()
+fn named_lifetime_occurrences(lts: &[RefLt]) -> Vec<(LocalDefId, usize)> {
+    let mut occurrences = Vec::new();
+    for lt in lts {
+        if let &RefLt::Named(curr_def_id) = lt {
+            if let Some(i) = occurrences
+                .iter()
+                .position(|&(prev_def_id, _)| prev_def_id == curr_def_id)
+            {
+                occurrences[i].1 += 1;
+            } else {
+                occurrences.push((curr_def_id, 1));
+            }
+        }
+    }
+    occurrences
 }
 
 const CLOSURE_TRAIT_BOUNDS: [LangItem; 3] = [LangItem::Fn, LangItem::FnMut, LangItem::FnOnce];
@@ -370,6 +416,7 @@ const CLOSURE_TRAIT_BOUNDS: [LangItem; 3] = [LangItem::Fn, LangItem::FnMut, Lang
 struct RefVisitor<'a, 'tcx> {
     cx: &'a LateContext<'tcx>,
     lts: Vec<RefLt>,
+    sample_generic_arg_span: FxHashMap<LocalDefId, Span>,
     nested_elision_site_lts: Vec<RefLt>,
     unelided_trait_object_lifetime: bool,
 }
@@ -379,6 +426,7 @@ impl<'a, 'tcx> RefVisitor<'a, 'tcx> {
         Self {
             cx,
             lts: Vec::new(),
+            sample_generic_arg_span: FxHashMap::default(),
             nested_elision_site_lts: Vec::new(),
             unelided_trait_object_lifetime: false,
         }
@@ -472,6 +520,22 @@ impl<'a, 'tcx> Visitor<'tcx> for RefVisitor<'a, 'tcx> {
             _ => walk_ty(self, ty),
         }
     }
+
+    fn visit_generic_arg(&mut self, generic_arg: &'tcx GenericArg<'tcx>) {
+        if let GenericArg::Lifetime(l) = generic_arg
+            && let LifetimeName::Param(def_id, _) = l.name
+        {
+            self.sample_generic_arg_span.entry(def_id).or_insert(l.span);
+        }
+        // Replace with `walk_generic_arg` if/when https://github.com/rust-lang/rust/pull/103692 lands.
+        // walk_generic_arg(self, generic_arg);
+        match generic_arg {
+            GenericArg::Lifetime(lt) => self.visit_lifetime(lt),
+            GenericArg::Type(ty) => self.visit_ty(ty),
+            GenericArg::Const(ct) => self.visit_anon_const(&ct.value),
+            GenericArg::Infer(inf) => self.visit_infer(inf),
+        }
+    }
 }
 
 /// Are any lifetimes mentioned in the `where` clause? If so, we don't try to
diff --git a/tests/ui/needless_lifetimes.rs b/tests/ui/needless_lifetimes.rs
index fc686b1dac0..3fe12214294 100644
--- a/tests/ui/needless_lifetimes.rs
+++ b/tests/ui/needless_lifetimes.rs
@@ -419,4 +419,12 @@ mod issue7296 {
     }
 }
 
+mod false_negative {
+    #![allow(unused)]
+
+    fn foo<'a>(x: &'a u8, y: &'_ u8) {}
+
+    fn bar<'a>(x: &'a u8, y: &'_ u8, z: &'_ u8) {}
+}
+
 fn main() {}
diff --git a/tests/ui/needless_lifetimes.stderr b/tests/ui/needless_lifetimes.stderr
index 3c428fd4674..94787b95181 100644
--- a/tests/ui/needless_lifetimes.stderr
+++ b/tests/ui/needless_lifetimes.stderr
@@ -1,4 +1,4 @@
-error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
+error: the following explicit lifetimes could be elided: 'a, 'b
   --> $DIR/needless_lifetimes.rs:11:1
    |
 LL | fn distinct_lifetimes<'a, 'b>(_x: &'a u8, _y: &'b u8, _z: u8) {}
@@ -6,185 +6,221 @@ LL | fn distinct_lifetimes<'a, 'b>(_x: &'a u8, _y: &'b u8, _z: u8) {}
    |
    = note: `-D clippy::needless-lifetimes` implied by `-D warnings`
 
-error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
+error: the following explicit lifetimes could be elided: 'a, 'b
   --> $DIR/needless_lifetimes.rs:13:1
    |
 LL | fn distinct_and_static<'a, 'b>(_x: &'a u8, _y: &'b u8, _z: &'static u8) {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
+error: the following explicit lifetimes could be elided: 'a
   --> $DIR/needless_lifetimes.rs:23:1
    |
 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)
+error: the following explicit lifetimes could be elided: 'a
   --> $DIR/needless_lifetimes.rs:57:1
    |
 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)
+error: the following explicit lifetimes could be elided: 'a
   --> $DIR/needless_lifetimes.rs:62:1
    |
 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)
+error: the following explicit lifetimes could be elided: 'a, 'b
   --> $DIR/needless_lifetimes.rs:74:1
    |
 LL | fn lifetime_param_2<'a, 'b>(_x: Ref<'a>, _y: &'b u8) {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: replace with `'_` in generic arguments such as here
+  --> $DIR/needless_lifetimes.rs:74:37
+   |
+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)
+error: the following explicit lifetimes could be elided: 'a
   --> $DIR/needless_lifetimes.rs:98:1
    |
 LL | fn fn_bound_2<'a, F, I>(_m: Lt<'a, I>, _f: F) -> Lt<'a, I>
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: replace with `'_` in generic arguments such as here
+  --> $DIR/needless_lifetimes.rs:98:32
+   |
+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)
+error: the following explicit lifetimes could be elided: 's
   --> $DIR/needless_lifetimes.rs:128:5
    |
 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)
+error: the following explicit lifetimes could be elided: 's, 't
   --> $DIR/needless_lifetimes.rs:137:5
    |
 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)
+error: the following explicit lifetimes could be elided: 'a
   --> $DIR/needless_lifetimes.rs:156:1
    |
 LL | fn struct_with_lt<'a>(_foo: Foo<'a>) -> &'a str {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: replace with `'_` in generic arguments such as here
+  --> $DIR/needless_lifetimes.rs:156:33
+   |
+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)
+error: the following explicit lifetimes could be elided: 'a
   --> $DIR/needless_lifetimes.rs:186:1
    |
 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)
+error: the following explicit lifetimes could be elided: 'a
   --> $DIR/needless_lifetimes.rs:192:1
    |
 LL | fn alias_with_lt<'a>(_foo: FooAlias<'a>) -> &'a str {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: replace with `'_` in generic arguments such as here
+  --> $DIR/needless_lifetimes.rs:192:37
+   |
+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)
+error: the following explicit lifetimes could be elided: 'a
   --> $DIR/needless_lifetimes.rs:211:1
    |
 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)
+error: the following explicit lifetimes could be elided: 'a
   --> $DIR/needless_lifetimes.rs:219:1
    |
 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)
+error: the following explicit lifetimes could be elided: 'a
   --> $DIR/needless_lifetimes.rs:255:1
    |
 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)
+error: the following explicit lifetimes could be elided: 'a
   --> $DIR/needless_lifetimes.rs:262:9
    |
 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)
+error: the following explicit lifetimes could be elided: 'a
   --> $DIR/needless_lifetimes.rs:266:9
    |
 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)
+error: the following explicit lifetimes could be elided: 'a
   --> $DIR/needless_lifetimes.rs:279:9
    |
 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)
+error: the following explicit lifetimes could be elided: 'a
   --> $DIR/needless_lifetimes.rs:311:5
    |
 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)
+error: the following explicit lifetimes could be elided: 'a
   --> $DIR/needless_lifetimes.rs:320:5
    |
 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)
+error: the following explicit lifetimes could be elided: 'a
   --> $DIR/needless_lifetimes.rs:332:5
    |
 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)
+error: the following explicit lifetimes could be elided: 'a
   --> $DIR/needless_lifetimes.rs:347:5
    |
 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)
+error: the following explicit lifetimes could be elided: 'a
   --> $DIR/needless_lifetimes.rs:360:5
    |
 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)
+error: the following explicit lifetimes could be elided: 'a
   --> $DIR/needless_lifetimes.rs:363:5
    |
 LL |     fn nested_fn_pointer_4<'a>(_: &'a i32) -> impl Fn(fn(&i32)) {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
+error: the following explicit lifetimes could be elided: 'a
   --> $DIR/needless_lifetimes.rs:385:9
    |
 LL |         fn implicit<'a>(&'a self) -> &'a () {
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
+error: the following explicit lifetimes could be elided: 'a
   --> $DIR/needless_lifetimes.rs:388:9
    |
 LL |         fn implicit_mut<'a>(&'a mut self) -> &'a () {
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
+error: the following explicit lifetimes could be elided: 'a
   --> $DIR/needless_lifetimes.rs:399:9
    |
 LL |         fn lifetime_elsewhere<'a>(self: Box<Self>, here: &'a ()) -> &'a () {
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
+error: the following explicit lifetimes could be elided: 'a
   --> $DIR/needless_lifetimes.rs:405:9
    |
 LL |         fn implicit<'a>(&'a self) -> &'a ();
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
+error: the following explicit lifetimes could be elided: 'a
   --> $DIR/needless_lifetimes.rs:406:9
    |
 LL |         fn implicit_provided<'a>(&'a self) -> &'a () {
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
+error: the following explicit lifetimes could be elided: 'a
   --> $DIR/needless_lifetimes.rs:415:9
    |
 LL |         fn lifetime_elsewhere<'a>(self: Box<Self>, here: &'a ()) -> &'a ();
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
+error: the following explicit lifetimes could be elided: 'a
   --> $DIR/needless_lifetimes.rs:416:9
    |
 LL |         fn lifetime_elsewhere_provided<'a>(self: Box<Self>, here: &'a ()) -> &'a () {
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 31 previous errors
+error: the following explicit lifetimes could be elided: 'a
+  --> $DIR/needless_lifetimes.rs:425:5
+   |
+LL |     fn foo<'a>(x: &'a u8, y: &'_ u8) {}
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: the following explicit lifetimes could be elided: 'a
+  --> $DIR/needless_lifetimes.rs:427:5
+   |
+LL |     fn bar<'a>(x: &'a u8, y: &'_ u8, z: &'_ u8) {}
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 33 previous errors