Add extra_unused_type_parameters lint

CHANGELOG.md

@@ -4383,6 +4383,7 @@ Released 2018-09-13
 [`extend_from_slice`]: https://rust-lang.github.io/rust-clippy/master/index.html#extend_from_slice
 [`extend_with_drain`]: https://rust-lang.github.io/rust-clippy/master/index.html#extend_with_drain
 [`extra_unused_lifetimes`]: https://rust-lang.github.io/rust-clippy/master/index.html#extra_unused_lifetimes
+[`extra_unused_type_parameters`]: https://rust-lang.github.io/rust-clippy/master/index.html#extra_unused_type_parameters
 [`fallible_impl_from`]: https://rust-lang.github.io/rust-clippy/master/index.html#fallible_impl_from
 [`field_reassign_with_default`]: https://rust-lang.github.io/rust-clippy/master/index.html#field_reassign_with_default
 [`filetype_is_file`]: https://rust-lang.github.io/rust-clippy/master/index.html#filetype_is_file

README.md

@@ -5,7 +5,7 @@
 
 A collection of lints to catch common mistakes and improve your [Rust](https://github.com/rust-lang/rust) code.
 
-[There are over 550 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
+[There are over 600 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
 
 Lints are divided into categories, each with a default [lint level](https://doc.rust-lang.org/rustc/lints/levels.html).
 You can choose how much Clippy is supposed to ~~annoy~~ help you by changing the lint level by category.

book/src/README.md

@@ -6,7 +6,7 @@
 A collection of lints to catch common mistakes and improve your
 [Rust](https://github.com/rust-lang/rust) code.
 
-[There are over 550 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
+[There are over 600 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
 
 Lints are divided into categories, each with a default [lint
 level](https://doc.rust-lang.org/rustc/lints/levels.html). You can choose how

clippy_lints/src/declared_lints.rs

@@ -156,6 +156,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::exhaustive_items::EXHAUSTIVE_STRUCTS_INFO,
     crate::exit::EXIT_INFO,
     crate::explicit_write::EXPLICIT_WRITE_INFO,
+    crate::extra_unused_type_parameters::EXTRA_UNUSED_TYPE_PARAMETERS_INFO,
     crate::fallible_impl_from::FALLIBLE_IMPL_FROM_INFO,
     crate::float_literal::EXCESSIVE_PRECISION_INFO,
     crate::float_literal::LOSSY_FLOAT_LITERAL_INFO,

clippy_lints/src/extra_unused_type_parameters.rs

@@ -0,0 +1,178 @@
+use clippy_utils::diagnostics::span_lint_and_help;
+use clippy_utils::trait_ref_of_method;
+use rustc_data_structures::fx::FxHashMap;
+use rustc_errors::MultiSpan;
+use rustc_hir::intravisit::{walk_impl_item, walk_item, walk_param_bound, walk_ty, Visitor};
+use rustc_hir::{
+    GenericParamKind, Generics, ImplItem, ImplItemKind, Item, ItemKind, PredicateOrigin, Ty, TyKind, WherePredicate,
+};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_middle::hir::nested_filter;
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_span::{def_id::DefId, Span};
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for type parameters in generics that are never used anywhere else.
+    ///
+    /// ### Why is this bad?
+    /// Functions cannot infer the value of unused type parameters; therefore, calling them
+    /// requires using a turbofish, which serves no purpose but to satisfy the compiler.
+    ///
+    /// ### Example
+    /// ```rust
+    /// // unused type parameters
+    /// fn unused_ty<T>(x: u8) {
+    ///     // ..
+    /// }
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// fn no_unused_ty(x: u8) {
+    ///     // ..
+    /// }
+    /// ```
+    #[clippy::version = "1.69.0"]
+    pub EXTRA_UNUSED_TYPE_PARAMETERS,
+    complexity,
+    "unused type parameters in function definitions"
+}
+declare_lint_pass!(ExtraUnusedTypeParameters => [EXTRA_UNUSED_TYPE_PARAMETERS]);
+
+/// A visitor struct that walks a given function and gathers generic type parameters, plus any
+/// trait bounds those parameters have.
+struct TypeWalker<'cx, 'tcx> {
+    cx: &'cx LateContext<'tcx>,
+    /// Collection of all the type parameters and their spans.
+    ty_params: FxHashMap<DefId, Span>,
+    /// Collection of any (inline) trait bounds corresponding to each type parameter.
+    bounds: FxHashMap<DefId, Span>,
+    /// The entire `Generics` object of the function, useful for querying purposes.
+    generics: &'tcx Generics<'tcx>,
+    /// The value of this will remain `true` if *every* parameter:
+    ///   1. Is a type parameter, and
+    ///   2. Goes unused in the function.
+    /// Otherwise, if any type parameters end up being used, or if any lifetime or const-generic
+    /// parameters are present, this will be set to `false`.
+    all_params_unused: bool,
+}
+
+impl<'cx, 'tcx> TypeWalker<'cx, 'tcx> {
+    fn new(cx: &'cx LateContext<'tcx>, generics: &'tcx Generics<'tcx>) -> Self {
+        let mut all_params_unused = true;
+        let ty_params = generics
+            .params
+            .iter()
+            .filter_map(|param| {
+                if let GenericParamKind::Type { .. } = param.kind {
+                    Some((param.def_id.into(), param.span))
+                } else {
+                    if !param.is_elided_lifetime() {
+                        all_params_unused = false;
+                    }
+                    None
+                }
+            })
+            .collect();
+        Self {
+            cx,
+            ty_params,
+            bounds: FxHashMap::default(),
+            generics,
+            all_params_unused,
+        }
+    }
+
+    fn emit_lint(&self) {
+        let (msg, help) = match self.ty_params.len() {
+            0 => return,
+            1 => (
+                "type parameter goes unused in function definition",
+                "consider removing the parameter",
+            ),
+            _ => (
+                "type parameters go unused in function definition",
+                "consider removing the parameters",
+            ),
+        };
+
+        let source_map = self.cx.tcx.sess.source_map();
+        let span = if self.all_params_unused {
+            self.generics.span.into() // Remove the entire list of generics
+        } else {
+            MultiSpan::from_spans(
+                self.ty_params
+                    .iter()
+                    .map(|(def_id, &span)| {
+                        // Extend the span past any trait bounds, and include the comma at the end.
+                        let span_to_extend = self.bounds.get(def_id).copied().map_or(span, Span::shrink_to_hi);
+                        let comma_range = source_map.span_extend_to_next_char(span_to_extend, '>', false);
+                        let comma_span = source_map.span_through_char(comma_range, ',');
+                        span.with_hi(comma_span.hi())
+                    })
+                    .collect(),
+            )
+        };
+
+        span_lint_and_help(self.cx, EXTRA_UNUSED_TYPE_PARAMETERS, span, msg, None, help);
+    }
+}
+
+impl<'cx, 'tcx> Visitor<'tcx> for TypeWalker<'cx, 'tcx> {
+    type NestedFilter = nested_filter::OnlyBodies;
+
+    fn visit_ty(&mut self, t: &'tcx Ty<'tcx>) {
+        if let Some((def_id, _)) = t.peel_refs().as_generic_param() {
+            if self.ty_params.remove(&def_id).is_some() {
+                self.all_params_unused = false;
+            }
+        } else if let TyKind::OpaqueDef(id, _, _) = t.kind {
+            // Explicitly walk OpaqueDef. Normally `walk_ty` would do the job, but it calls
+            // `visit_nested_item`, which checks that `Self::NestedFilter::INTER` is set. We're
+            // using `OnlyBodies`, so the check ends up failing and the type isn't fully walked.
+            let item = self.nested_visit_map().item(id);
+            walk_item(self, item);
+        } else {
+            walk_ty(self, t);
+        }
+    }
+
+    fn visit_where_predicate(&mut self, predicate: &'tcx WherePredicate<'tcx>) {
+        if let WherePredicate::BoundPredicate(predicate) = predicate {
+            // Collect spans for bounds that appear in the list of generics (not in a where-clause)
+            // for use in forming the help message
+            if let Some((def_id, _)) = predicate.bounded_ty.peel_refs().as_generic_param()
+                && let PredicateOrigin::GenericParam = predicate.origin
+            {
+                self.bounds.insert(def_id, predicate.span);
+            }
+            // Only walk the right-hand side of where-bounds
+            for bound in predicate.bounds {
+                walk_param_bound(self, bound);
+            }
+        }
+    }
+
+    fn nested_visit_map(&mut self) -> Self::Map {
+        self.cx.tcx.hir()
+    }
+}
+
+impl<'tcx> LateLintPass<'tcx> for ExtraUnusedTypeParameters {
+    fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'tcx>) {
+        if let ItemKind::Fn(_, generics, _) = item.kind {
+            let mut walker = TypeWalker::new(cx, generics);
+            walk_item(&mut walker, item);
+            walker.emit_lint();
+        }
+    }
+
+    fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx ImplItem<'tcx>) {
+        // Only lint on inherent methods, not trait methods.
+        if let ImplItemKind::Fn(..) = item.kind && trait_ref_of_method(cx, item.owner_id.def_id).is_none() {
+            let mut walker = TypeWalker::new(cx, item.generics);
+            walk_impl_item(&mut walker, item);
+            walker.emit_lint();
+        }
+    }
+}

clippy_lints/src/lib.rs

@@ -122,6 +122,7 @@ mod excessive_bools;
 mod exhaustive_items;
 mod exit;
 mod explicit_write;
+mod extra_unused_type_parameters;
 mod fallible_impl_from;
 mod float_literal;
 mod floating_point_arithmetic;
@@ -910,6 +911,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_late_pass(|_| Box::new(permissions_set_readonly_false::PermissionsSetReadonlyFalse));
     store.register_late_pass(|_| Box::new(size_of_ref::SizeOfRef));
     store.register_late_pass(|_| Box::new(multiple_unsafe_ops_per_block::MultipleUnsafeOpsPerBlock));
+    store.register_late_pass(|_| Box::new(extra_unused_type_parameters::ExtraUnusedTypeParameters));
     // add lints here, do not remove this comment, it's used in `new_lint`
 }
 

tests/ui/extra_unused_type_parameters.rs

@@ -0,0 +1,69 @@
+#![allow(unused, clippy::needless_lifetimes)]
+#![warn(clippy::extra_unused_type_parameters)]
+
+fn unused_ty<T>(x: u8) {}
+
+fn unused_multi<T, U>(x: u8) {}
+
+fn unused_with_lt<'a, T>(x: &'a u8) {}
+
+fn used_ty<T>(x: T, y: u8) {}
+
+fn used_ref<'a, T>(x: &'a T) {}
+
+fn used_ret<T: Default>(x: u8) -> T {
+    T::default()
+}
+
+fn unused_bounded<T: Default, U>(x: U) {}
+
+fn unused_where_clause<T, U>(x: U)
+where
+    T: Default,
+{
+}
+
+fn some_unused<A, B, C, D: Iterator<Item = (B, C)>, E>(b: B, c: C) {}
+
+fn used_opaque<A>(iter: impl Iterator<Item = A>) -> usize {
+    iter.count()
+}
+
+fn used_ret_opaque<A>() -> impl Iterator<Item = A> {
+    std::iter::empty()
+}
+
+fn used_vec_box<T>(x: Vec<Box<T>>) {}
+
+fn used_body<T: Default + ToString>() -> String {
+    T::default().to_string()
+}
+
+fn used_closure<T: Default + ToString>() -> impl Fn() {
+    || println!("{}", T::default().to_string())
+}
+
+struct S;
+
+impl S {
+    fn unused_ty_impl<T>(&self) {}
+}
+
+// Don't lint on trait methods
+trait Foo {
+    fn bar<T>(&self);
+}
+
+impl Foo for S {
+    fn bar<T>(&self) {}
+}
+
+fn skip_index<A, Iter>(iter: Iter, index: usize) -> impl Iterator<Item = A>
+where
+    Iter: Iterator<Item = A>,
+{
+    iter.enumerate()
+        .filter_map(move |(i, a)| if i == index { None } else { Some(a) })
+}
+
+fn main() {}

tests/ui/extra_unused_type_parameters.stderr

@@ -0,0 +1,59 @@
+error: type parameter goes unused in function definition
+  --> $DIR/extra_unused_type_parameters.rs:4:13
+   |
+LL | fn unused_ty<T>(x: u8) {}
+   |             ^^^
+   |
+   = help: consider removing the parameter
+   = note: `-D clippy::extra-unused-type-parameters` implied by `-D warnings`
+
+error: type parameters go unused in function definition
+  --> $DIR/extra_unused_type_parameters.rs:6:16
+   |
+LL | fn unused_multi<T, U>(x: u8) {}
+   |                ^^^^^^
+   |
+   = help: consider removing the parameters
+
+error: type parameter goes unused in function definition
+  --> $DIR/extra_unused_type_parameters.rs:8:23
+   |
+LL | fn unused_with_lt<'a, T>(x: &'a u8) {}
+   |                       ^
+   |
+   = help: consider removing the parameter
+
+error: type parameter goes unused in function definition
+  --> $DIR/extra_unused_type_parameters.rs:18:19
+   |
+LL | fn unused_bounded<T: Default, U>(x: U) {}
+   |                   ^^^^^^^^^^^
+   |
+   = help: consider removing the parameter
+
+error: type parameter goes unused in function definition
+  --> $DIR/extra_unused_type_parameters.rs:20:24
+   |
+LL | fn unused_where_clause<T, U>(x: U)
+   |                        ^^
+   |
+   = help: consider removing the parameter
+
+error: type parameters go unused in function definition
+  --> $DIR/extra_unused_type_parameters.rs:26:16
+   |
+LL | fn some_unused<A, B, C, D: Iterator<Item = (B, C)>, E>(b: B, c: C) {}
+   |                ^^       ^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^
+   |
+   = help: consider removing the parameters
+
+error: type parameter goes unused in function definition
+  --> $DIR/extra_unused_type_parameters.rs:49:22
+   |
+LL |     fn unused_ty_impl<T>(&self) {}
+   |                      ^^^
+   |
+   = help: consider removing the parameter
+
+error: aborting due to 7 previous errors
+

tests/ui/needless_lifetimes.fixed

@@ -5,6 +5,7 @@
 #![allow(
     unused,
     clippy::boxed_local,
+    clippy::extra_unused_type_parameters,
     clippy::needless_pass_by_value,
     clippy::unnecessary_wraps,
     dyn_drop,

tests/ui/needless_lifetimes.rs

@@ -5,6 +5,7 @@
 #![allow(
     unused,
     clippy::boxed_local,
+    clippy::extra_unused_type_parameters,
     clippy::needless_pass_by_value,
     clippy::unnecessary_wraps,
     dyn_drop,

tests/ui/needless_lifetimes.stderr

@@ -1,5 +1,5 @@
 error: the following explicit lifetimes could be elided: 'a, 'b
-  --> $DIR/needless_lifetimes.rs:17:1
+  --> $DIR/needless_lifetimes.rs:18:1
    |
 LL | fn distinct_lifetimes<'a, 'b>(_x: &'a u8, _y: &'b u8, _z: u8) {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -12,7 +12,7 @@ LL + fn distinct_lifetimes(_x: &u8, _y: &u8, _z: u8) {}
    |
 
 error: the following explicit lifetimes could be elided: 'a, 'b
-  --> $DIR/needless_lifetimes.rs:19:1
+  --> $DIR/needless_lifetimes.rs:20:1
    |
 LL | fn distinct_and_static<'a, 'b>(_x: &'a u8, _y: &'b u8, _z: &'static u8) {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -24,7 +24,7 @@ LL + fn distinct_and_static(_x: &u8, _y: &u8, _z: &'static u8) {}
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:29:1
+  --> $DIR/needless_lifetimes.rs:30:1
    |
 LL | fn in_and_out<'a>(x: &'a u8, _y: u8) -> &'a u8 {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -36,7 +36,7 @@ LL + fn in_and_out(x: &u8, _y: u8) -> &u8 {
    |
 
 error: the following explicit lifetimes could be elided: 'b
-  --> $DIR/needless_lifetimes.rs:41:1
+  --> $DIR/needless_lifetimes.rs:42:1
    |
 LL | fn multiple_in_and_out_2a<'a, 'b>(x: &'a u8, _y: &'b u8) -> &'a u8 {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -48,7 +48,7 @@ LL + fn multiple_in_and_out_2a<'a>(x: &'a u8, _y: &u8) -> &'a u8 {
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:48:1
+  --> $DIR/needless_lifetimes.rs:49:1
    |
 LL | fn multiple_in_and_out_2b<'a, 'b>(_x: &'a u8, y: &'b u8) -> &'b u8 {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -60,7 +60,7 @@ LL + fn multiple_in_and_out_2b<'b>(_x: &u8, y: &'b u8) -> &'b u8 {
    |
 
 error: the following explicit lifetimes could be elided: 'b
-  --> $DIR/needless_lifetimes.rs:65:1
+  --> $DIR/needless_lifetimes.rs:66:1
    |
 LL | fn deep_reference_1a<'a, 'b>(x: &'a u8, _y: &'b u8) -> Result<&'a u8, ()> {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -72,7 +72,7 @@ LL + fn deep_reference_1a<'a>(x: &'a u8, _y: &u8) -> Result<&'a u8, ()> {
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:72:1
+  --> $DIR/needless_lifetimes.rs:73:1
    |
 LL | fn deep_reference_1b<'a, 'b>(_x: &'a u8, y: &'b u8) -> Result<&'b u8, ()> {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -84,7 +84,7 @@ LL + fn deep_reference_1b<'b>(_x: &u8, y: &'b u8) -> Result<&'b u8, ()> {
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:81:1
+  --> $DIR/needless_lifetimes.rs:82:1
    |
 LL | fn deep_reference_3<'a>(x: &'a u8, _y: u8) -> Result<&'a u8, ()> {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -96,7 +96,7 @@ LL + fn deep_reference_3(x: &u8, _y: u8) -> Result<&u8, ()> {
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:86:1
+  --> $DIR/needless_lifetimes.rs:87:1
    |
 LL | fn where_clause_without_lt<'a, T>(x: &'a u8, _y: u8) -> Result<&'a u8, ()>
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -108,7 +108,7 @@ LL + fn where_clause_without_lt<T>(x: &u8, _y: u8) -> Result<&u8, ()>
    |
 
 error: the following explicit lifetimes could be elided: 'a, 'b
-  --> $DIR/needless_lifetimes.rs:98:1
+  --> $DIR/needless_lifetimes.rs:99:1
    |
 LL | fn lifetime_param_2<'a, 'b>(_x: Ref<'a>, _y: &'b u8) {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -120,7 +120,7 @@ LL + fn lifetime_param_2(_x: Ref<'_>, _y: &u8) {}
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:122:1
+  --> $DIR/needless_lifetimes.rs:123:1
    |
 LL | fn fn_bound_2<'a, F, I>(_m: Lt<'a, I>, _f: F) -> Lt<'a, I>
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -132,7 +132,7 @@ LL + fn fn_bound_2<F, I>(_m: Lt<'_, I>, _f: F) -> Lt<'_, I>
    |
 
 error: the following explicit lifetimes could be elided: 's
-  --> $DIR/needless_lifetimes.rs:152:5
+  --> $DIR/needless_lifetimes.rs:153:5
    |
 LL |     fn self_and_out<'s>(&'s self) -> &'s u8 {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -144,7 +144,7 @@ LL +     fn self_and_out(&self) -> &u8 {
    |
 
 error: the following explicit lifetimes could be elided: 't
-  --> $DIR/needless_lifetimes.rs:159:5
+  --> $DIR/needless_lifetimes.rs:160:5
    |
 LL |     fn self_and_in_out_1<'s, 't>(&'s self, _x: &'t u8) -> &'s u8 {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -156,7 +156,7 @@ LL +     fn self_and_in_out_1<'s>(&'s self, _x: &u8) -> &'s u8 {
    |
 
 error: the following explicit lifetimes could be elided: 's
-  --> $DIR/needless_lifetimes.rs:166:5
+  --> $DIR/needless_lifetimes.rs:167:5
    |
 LL |     fn self_and_in_out_2<'s, 't>(&'s self, x: &'t u8) -> &'t u8 {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -168,7 +168,7 @@ LL +     fn self_and_in_out_2<'t>(&self, x: &'t u8) -> &'t u8 {
    |
 
 error: the following explicit lifetimes could be elided: 's, 't
-  --> $DIR/needless_lifetimes.rs:170:5
+  --> $DIR/needless_lifetimes.rs:171:5
    |
 LL |     fn distinct_self_and_in<'s, 't>(&'s self, _x: &'t u8) {}
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -180,7 +180,7 @@ LL +     fn distinct_self_and_in(&self, _x: &u8) {}
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:189:1
+  --> $DIR/needless_lifetimes.rs:190:1
    |
 LL | fn struct_with_lt<'a>(_foo: Foo<'a>) -> &'a str {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -192,7 +192,7 @@ LL + fn struct_with_lt(_foo: Foo<'_>) -> &str {
    |
 
 error: the following explicit lifetimes could be elided: 'b
-  --> $DIR/needless_lifetimes.rs:207:1
+  --> $DIR/needless_lifetimes.rs:208:1
    |
 LL | fn struct_with_lt4a<'a, 'b>(_foo: &'a Foo<'b>) -> &'a str {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -204,7 +204,7 @@ LL + fn struct_with_lt4a<'a>(_foo: &'a Foo<'_>) -> &'a str {
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:215:1
+  --> $DIR/needless_lifetimes.rs:216:1
    |
 LL | fn struct_with_lt4b<'a, 'b>(_foo: &'a Foo<'b>) -> &'b str {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -216,7 +216,7 @@ LL + fn struct_with_lt4b<'b>(_foo: &Foo<'b>) -> &'b str {
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:230:1
+  --> $DIR/needless_lifetimes.rs:231:1
    |
 LL | fn trait_obj_elided2<'a>(_arg: &'a dyn Drop) -> &'a str {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -228,7 +228,7 @@ LL + fn trait_obj_elided2(_arg: &dyn Drop) -> &str {
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:236:1
+  --> $DIR/needless_lifetimes.rs:237:1
    |
 LL | fn alias_with_lt<'a>(_foo: FooAlias<'a>) -> &'a str {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -240,7 +240,7 @@ LL + fn alias_with_lt(_foo: FooAlias<'_>) -> &str {
    |
 
 error: the following explicit lifetimes could be elided: 'b
-  --> $DIR/needless_lifetimes.rs:254:1
+  --> $DIR/needless_lifetimes.rs:255:1
    |
 LL | fn alias_with_lt4a<'a, 'b>(_foo: &'a FooAlias<'b>) -> &'a str {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -252,7 +252,7 @@ LL + fn alias_with_lt4a<'a>(_foo: &'a FooAlias<'_>) -> &'a str {
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:262:1
+  --> $DIR/needless_lifetimes.rs:263:1
    |
 LL | fn alias_with_lt4b<'a, 'b>(_foo: &'a FooAlias<'b>) -> &'b str {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -264,7 +264,7 @@ LL + fn alias_with_lt4b<'b>(_foo: &FooAlias<'b>) -> &'b str {
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:266:1
+  --> $DIR/needless_lifetimes.rs:267:1
    |
 LL | fn named_input_elided_output<'a>(_arg: &'a str) -> &str {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -276,7 +276,7 @@ LL + fn named_input_elided_output(_arg: &str) -> &str {
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:274:1
+  --> $DIR/needless_lifetimes.rs:275:1
    |
 LL | fn trait_bound_ok<'a, T: WithLifetime<'static>>(_: &'a u8, _: T) {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -288,7 +288,7 @@ LL + fn trait_bound_ok<T: WithLifetime<'static>>(_: &u8, _: T) {
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:310:1
+  --> $DIR/needless_lifetimes.rs:311:1
    |
 LL | fn out_return_type_lts<'a>(e: &'a str) -> Cow<'a> {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -300,7 +300,7 @@ LL + fn out_return_type_lts(e: &str) -> Cow<'_> {
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:317:9
+  --> $DIR/needless_lifetimes.rs:318:9
    |
 LL |         fn needless_lt<'a>(x: &'a u8) {}
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -312,7 +312,7 @@ LL +         fn needless_lt(x: &u8) {}
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:321:9
+  --> $DIR/needless_lifetimes.rs:322:9
    |
 LL |         fn needless_lt<'a>(_x: &'a u8) {}
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -324,7 +324,7 @@ LL +         fn needless_lt(_x: &u8) {}
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:334:9
+  --> $DIR/needless_lifetimes.rs:335:9
    |
 LL |         fn baz<'a>(&'a self) -> impl Foo + 'a {
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -336,7 +336,7 @@ LL +         fn baz(&self) -> impl Foo + '_ {
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:366:5
+  --> $DIR/needless_lifetimes.rs:367:5
    |
 LL |     fn impl_trait_elidable_nested_anonymous_lifetimes<'a>(i: &'a i32, f: impl Fn(&i32) -> &i32) -> &'a i32 {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -348,7 +348,7 @@ LL +     fn impl_trait_elidable_nested_anonymous_lifetimes(i: &i32, f: impl Fn(&
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:375:5
+  --> $DIR/needless_lifetimes.rs:376:5
    |
 LL |     fn generics_elidable<'a, T: Fn(&i32) -> &i32>(i: &'a i32, f: T) -> &'a i32 {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -360,7 +360,7 @@ LL +     fn generics_elidable<T: Fn(&i32) -> &i32>(i: &i32, f: T) -> &i32 {
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:387:5
+  --> $DIR/needless_lifetimes.rs:388:5
    |
 LL |     fn where_clause_elidadable<'a, T>(i: &'a i32, f: T) -> &'a i32
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -372,7 +372,7 @@ LL +     fn where_clause_elidadable<T>(i: &i32, f: T) -> &i32
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:402:5
+  --> $DIR/needless_lifetimes.rs:403:5
    |
 LL |     fn pointer_fn_elidable<'a>(i: &'a i32, f: fn(&i32) -> &i32) -> &'a i32 {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -384,7 +384,7 @@ LL +     fn pointer_fn_elidable(i: &i32, f: fn(&i32) -> &i32) -> &i32 {
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:415:5
+  --> $DIR/needless_lifetimes.rs:416:5
    |
 LL |     fn nested_fn_pointer_3<'a>(_: &'a i32) -> fn(fn(&i32) -> &i32) -> i32 {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -396,7 +396,7 @@ LL +     fn nested_fn_pointer_3(_: &i32) -> fn(fn(&i32) -> &i32) -> i32 {
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:418:5
+  --> $DIR/needless_lifetimes.rs:419:5
    |
 LL |     fn nested_fn_pointer_4<'a>(_: &'a i32) -> impl Fn(fn(&i32)) {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -408,7 +408,7 @@ LL +     fn nested_fn_pointer_4(_: &i32) -> impl Fn(fn(&i32)) {
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:440:9
+  --> $DIR/needless_lifetimes.rs:441:9
    |
 LL |         fn implicit<'a>(&'a self) -> &'a () {
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -420,7 +420,7 @@ LL +         fn implicit(&self) -> &() {
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:443:9
+  --> $DIR/needless_lifetimes.rs:444:9
    |
 LL |         fn implicit_mut<'a>(&'a mut self) -> &'a () {
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -432,7 +432,7 @@ LL +         fn implicit_mut(&mut self) -> &() {
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:454:9
+  --> $DIR/needless_lifetimes.rs:455:9
    |
 LL |         fn lifetime_elsewhere<'a>(self: Box<Self>, here: &'a ()) -> &'a () {
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -444,7 +444,7 @@ LL +         fn lifetime_elsewhere(self: Box<Self>, here: &()) -> &() {
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:460:9
+  --> $DIR/needless_lifetimes.rs:461:9
    |
 LL |         fn implicit<'a>(&'a self) -> &'a ();
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -456,7 +456,7 @@ LL +         fn implicit(&self) -> &();
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:461:9
+  --> $DIR/needless_lifetimes.rs:462:9
    |
 LL |         fn implicit_provided<'a>(&'a self) -> &'a () {
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -468,7 +468,7 @@ LL +         fn implicit_provided(&self) -> &() {
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:470:9
+  --> $DIR/needless_lifetimes.rs:471:9
    |
 LL |         fn lifetime_elsewhere<'a>(self: Box<Self>, here: &'a ()) -> &'a ();
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -480,7 +480,7 @@ LL +         fn lifetime_elsewhere(self: Box<Self>, here: &()) -> &();
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:471:9
+  --> $DIR/needless_lifetimes.rs:472:9
    |
 LL |         fn lifetime_elsewhere_provided<'a>(self: Box<Self>, here: &'a ()) -> &'a () {
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -492,7 +492,7 @@ LL +         fn lifetime_elsewhere_provided(self: Box<Self>, here: &()) -> &() {
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:480:5
+  --> $DIR/needless_lifetimes.rs:481:5
    |
 LL |     fn foo<'a>(x: &'a u8, y: &'_ u8) {}
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -504,7 +504,7 @@ LL +     fn foo(x: &u8, y: &'_ u8) {}
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:482:5
+  --> $DIR/needless_lifetimes.rs:483:5
    |
 LL |     fn bar<'a>(x: &'a u8, y: &'_ u8, z: &'_ u8) {}
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -516,7 +516,7 @@ LL +     fn bar(x: &u8, y: &'_ u8, z: &'_ u8) {}
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:489:5
+  --> $DIR/needless_lifetimes.rs:490:5
    |
 LL |     fn one_input<'a>(x: &'a u8) -> &'a u8 {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -528,7 +528,7 @@ LL +     fn one_input(x: &u8) -> &u8 {
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:494:5
+  --> $DIR/needless_lifetimes.rs:495:5
    |
 LL |     fn multiple_inputs_output_not_elided<'a, 'b>(x: &'a u8, y: &'b u8, z: &'b u8) -> &'b u8 {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -540,7 +540,7 @@ LL +     fn multiple_inputs_output_not_elided<'b>(x: &u8, y: &'b u8, z: &'b u8)
    |
 
 error: the following explicit lifetimes could be elided: 'a
-  --> $DIR/needless_lifetimes.rs:507:13
+  --> $DIR/needless_lifetimes.rs:508:13
    |
 LL |             fn one_input<'a>(x: &'a u8) -> &'a u8 {
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

tests/ui/new_without_default.rs

@@ -1,4 +1,9 @@
-#![allow(dead_code, clippy::missing_safety_doc, clippy::extra_unused_lifetimes)]
+#![allow(
+    dead_code,
+    clippy::missing_safety_doc,
+    clippy::extra_unused_lifetimes,
+    clippy::extra_unused_type_parameters
+)]
 #![warn(clippy::new_without_default)]
 
 pub struct Foo;

tests/ui/new_without_default.stderr

@@ -1,5 +1,5 @@
 error: you should consider adding a `Default` implementation for `Foo`
-  --> $DIR/new_without_default.rs:7:5
+  --> $DIR/new_without_default.rs:12:5
    |
 LL | /     pub fn new() -> Foo {
 LL | |         Foo
@@ -17,7 +17,7 @@ LL + }
    |
 
 error: you should consider adding a `Default` implementation for `Bar`
-  --> $DIR/new_without_default.rs:15:5
+  --> $DIR/new_without_default.rs:20:5
    |
 LL | /     pub fn new() -> Self {
 LL | |         Bar
@@ -34,7 +34,7 @@ LL + }
    |
 
 error: you should consider adding a `Default` implementation for `LtKo<'c>`
-  --> $DIR/new_without_default.rs:79:5
+  --> $DIR/new_without_default.rs:84:5
    |
 LL | /     pub fn new() -> LtKo<'c> {
 LL | |         unimplemented!()
@@ -51,7 +51,7 @@ LL + }
    |
 
 error: you should consider adding a `Default` implementation for `NewNotEqualToDerive`
-  --> $DIR/new_without_default.rs:172:5
+  --> $DIR/new_without_default.rs:177:5
    |
 LL | /     pub fn new() -> Self {
 LL | |         NewNotEqualToDerive { foo: 1 }
@@ -68,7 +68,7 @@ LL + }
    |
 
 error: you should consider adding a `Default` implementation for `FooGenerics<T>`
-  --> $DIR/new_without_default.rs:180:5
+  --> $DIR/new_without_default.rs:185:5
    |
 LL | /     pub fn new() -> Self {
 LL | |         Self(Default::default())
@@ -85,7 +85,7 @@ LL + }
    |
 
 error: you should consider adding a `Default` implementation for `BarGenerics<T>`
-  --> $DIR/new_without_default.rs:187:5
+  --> $DIR/new_without_default.rs:192:5
    |
 LL | /     pub fn new() -> Self {
 LL | |         Self(Default::default())
@@ -102,7 +102,7 @@ LL + }
    |
 
 error: you should consider adding a `Default` implementation for `Foo<T>`
-  --> $DIR/new_without_default.rs:198:9
+  --> $DIR/new_without_default.rs:203:9
    |
 LL | /         pub fn new() -> Self {
 LL | |             todo!()

tests/ui/redundant_field_names.fixed

@@ -1,7 +1,7 @@
 // run-rustfix
 
 #![warn(clippy::redundant_field_names)]
-#![allow(clippy::no_effect, dead_code, unused_variables)]
+#![allow(clippy::extra_unused_type_parameters, clippy::no_effect, dead_code, unused_variables)]
 
 #[macro_use]
 extern crate derive_new;

tests/ui/redundant_field_names.rs

@@ -1,7 +1,7 @@
 // run-rustfix
 
 #![warn(clippy::redundant_field_names)]
-#![allow(clippy::no_effect, dead_code, unused_variables)]
+#![allow(clippy::extra_unused_type_parameters, clippy::no_effect, dead_code, unused_variables)]
 
 #[macro_use]
 extern crate derive_new;

tests/ui/seek_to_start_instead_of_rewind.fixed

@@ -26,7 +26,7 @@ fn seek_to_start_false_method(t: &mut StructWithSeekMethod) {
 
 // This should NOT trigger clippy warning because
 // StructWithSeekMethod does not implement std::io::Seek;
-fn seek_to_start_method_owned_false<T>(mut t: StructWithSeekMethod) {
+fn seek_to_start_method_owned_false(mut t: StructWithSeekMethod) {
     t.seek(SeekFrom::Start(0));
 }
 
@@ -38,7 +38,7 @@ fn seek_to_start_false_trait(t: &mut StructWithSeekTrait) {
 
 // This should NOT trigger clippy warning because
 // StructWithSeekMethod does not implement std::io::Seek;
-fn seek_to_start_false_trait_owned<T>(mut t: StructWithSeekTrait) {
+fn seek_to_start_false_trait_owned(mut t: StructWithSeekTrait) {
     t.seek(SeekFrom::Start(0));
 }
 

tests/ui/seek_to_start_instead_of_rewind.rs

@@ -26,7 +26,7 @@ fn seek_to_start_false_method(t: &mut StructWithSeekMethod) {
 
 // This should NOT trigger clippy warning because
 // StructWithSeekMethod does not implement std::io::Seek;
-fn seek_to_start_method_owned_false<T>(mut t: StructWithSeekMethod) {
+fn seek_to_start_method_owned_false(mut t: StructWithSeekMethod) {
     t.seek(SeekFrom::Start(0));
 }
 
@@ -38,7 +38,7 @@ fn seek_to_start_false_trait(t: &mut StructWithSeekTrait) {
 
 // This should NOT trigger clippy warning because
 // StructWithSeekMethod does not implement std::io::Seek;
-fn seek_to_start_false_trait_owned<T>(mut t: StructWithSeekTrait) {
+fn seek_to_start_false_trait_owned(mut t: StructWithSeekTrait) {
     t.seek(SeekFrom::Start(0));
 }
 

tests/ui/type_repetition_in_bounds.rs

@@ -1,4 +1,5 @@
 #![deny(clippy::type_repetition_in_bounds)]
+#![allow(clippy::extra_unused_type_parameters)]
 
 use std::ops::{Add, AddAssign, Div, DivAssign, Mul, MulAssign, Sub, SubAssign};
 

tests/ui/type_repetition_in_bounds.stderr

@@ -1,5 +1,5 @@
 error: this type has already been used as a bound predicate
-  --> $DIR/type_repetition_in_bounds.rs:8:5
+  --> $DIR/type_repetition_in_bounds.rs:9:5
    |
 LL |     T: Clone,
    |     ^^^^^^^^
@@ -12,7 +12,7 @@ LL | #![deny(clippy::type_repetition_in_bounds)]
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: this type has already been used as a bound predicate
-  --> $DIR/type_repetition_in_bounds.rs:25:5
+  --> $DIR/type_repetition_in_bounds.rs:26:5
    |
 LL |     Self: Copy + Default + Ord,
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -20,7 +20,7 @@ LL |     Self: Copy + Default + Ord,
    = help: consider combining the bounds: `Self: Clone + Copy + Default + Ord`
 
 error: this type has already been used as a bound predicate
-  --> $DIR/type_repetition_in_bounds.rs:85:5
+  --> $DIR/type_repetition_in_bounds.rs:86:5
    |
 LL |     T: Clone,
    |     ^^^^^^^^
@@ -28,7 +28,7 @@ LL |     T: Clone,
    = help: consider combining the bounds: `T: ?Sized + Clone`
 
 error: this type has already been used as a bound predicate
-  --> $DIR/type_repetition_in_bounds.rs:90:5
+  --> $DIR/type_repetition_in_bounds.rs:91:5
    |
 LL |     T: ?Sized,
    |     ^^^^^^^^^