Merge remote-tracking branch 'upstream/master' into rustup

8 files changed, 318 insertions, 75 deletions

diff --git a/clippy_lints/src/methods/expect_fun_call.rs b/clippy_lints/src/methods/expect_fun_call.rs
index e2c2997594a..4d8fb217f7f 100644
--- a/clippy_lints/src/methods/expect_fun_call.rs
+++ b/clippy_lints/src/methods/expect_fun_call.rs
@@ -91,7 +91,7 @@ pub(super) fn check<'tcx>(
             },
             hir::ExprKind::Path(ref p) => matches!(
                 cx.qpath_res(p, arg.hir_id),
-                hir::def::Res::Def(hir::def::DefKind::Const | hir::def::DefKind::Static{..}, _)
+                hir::def::Res::Def(hir::def::DefKind::Const | hir::def::DefKind::Static { .. }, _)
             ),
             _ => false,
         }
diff --git a/clippy_lints/src/methods/is_empty.rs b/clippy_lints/src/methods/is_empty.rs
new file mode 100644
index 00000000000..7fe66062251
--- /dev/null
+++ b/clippy_lints/src/methods/is_empty.rs
@@ -0,0 +1,49 @@
+use clippy_utils::consts::constant_is_empty;
+use clippy_utils::diagnostics::span_lint;
+use clippy_utils::{find_binding_init, path_to_local};
+use rustc_hir::{Expr, HirId};
+use rustc_lint::{LateContext, LintContext};
+use rustc_middle::lint::in_external_macro;
+use rustc_span::sym;
+
+use super::CONST_IS_EMPTY;
+
+/// Expression whose initialization depend on a constant conditioned by a `#[cfg(…)]` directive will
+/// not trigger the lint.
+pub(super) fn check(cx: &LateContext<'_>, expr: &'_ Expr<'_>, receiver: &Expr<'_>) {
+    if in_external_macro(cx.sess(), expr.span) || !receiver.span.eq_ctxt(expr.span) {
+        return;
+    }
+    let init_expr = expr_or_init(cx, receiver);
+    if !receiver.span.eq_ctxt(init_expr.span) {
+        return;
+    }
+    if let Some(init_is_empty) = constant_is_empty(cx, init_expr) {
+        span_lint(
+            cx,
+            CONST_IS_EMPTY,
+            expr.span,
+            &format!("this expression always evaluates to {init_is_empty:?}"),
+        );
+    }
+}
+
+fn is_under_cfg(cx: &LateContext<'_>, id: HirId) -> bool {
+    cx.tcx
+        .hir()
+        .parent_id_iter(id)
+        .any(|id| cx.tcx.hir().attrs(id).iter().any(|attr| attr.has_name(sym::cfg)))
+}
+
+/// Similar to [`clippy_utils::expr_or_init`], but does not go up the chain if the initialization
+/// value depends on a `#[cfg(…)]` directive.
+fn expr_or_init<'a, 'b, 'tcx: 'b>(cx: &LateContext<'tcx>, mut expr: &'a Expr<'b>) -> &'a Expr<'b> {
+    while let Some(init) = path_to_local(expr)
+        .and_then(|id| find_binding_init(cx, id))
+        .filter(|init| cx.typeck_results().expr_adjustments(init).is_empty())
+        .filter(|init| !is_under_cfg(cx, init.hir_id))
+    {
+        expr = init;
+    }
+    expr
+}
diff --git a/clippy_lints/src/methods/iter_nth.rs b/clippy_lints/src/methods/iter_nth.rs
index 12104310405..5b0b70b4b96 100644
--- a/clippy_lints/src/methods/iter_nth.rs
+++ b/clippy_lints/src/methods/iter_nth.rs
@@ -1,10 +1,10 @@
-use super::utils::derefs_to_slice;
-use crate::methods::iter_nth_zero;
-use clippy_utils::diagnostics::span_lint_and_help;
-use clippy_utils::ty::is_type_diagnostic_item;
+use clippy_utils::diagnostics::span_lint_and_then;
+use clippy_utils::ty::get_type_diagnostic_name;
+use rustc_errors::Applicability;
 use rustc_hir as hir;
 use rustc_lint::LateContext;
 use rustc_span::symbol::sym;
+use rustc_span::Span;
 
 use super::ITER_NTH;
 
@@ -12,28 +12,33 @@ pub(super) fn check<'tcx>(
     cx: &LateContext<'tcx>,
     expr: &hir::Expr<'_>,
     iter_recv: &'tcx hir::Expr<'tcx>,
-    nth_recv: &hir::Expr<'_>,
-    nth_arg: &hir::Expr<'_>,
-    is_mut: bool,
-) {
-    let mut_str = if is_mut { "_mut" } else { "" };
-    let caller_type = if derefs_to_slice(cx, iter_recv, cx.typeck_results().expr_ty(iter_recv)).is_some() {
-        "slice"
-    } else if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(iter_recv), sym::Vec) {
-        "`Vec`"
-    } else if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(iter_recv), sym::VecDeque) {
-        "`VecDeque`"
-    } else {
-        iter_nth_zero::check(cx, expr, nth_recv, nth_arg);
-        return; // caller is not a type that we want to lint
+    iter_method: &str,
+    iter_span: Span,
+    nth_span: Span,
+) -> bool {
+    let caller_type = match get_type_diagnostic_name(cx, cx.typeck_results().expr_ty(iter_recv).peel_refs()) {
+        Some(sym::Vec) => "`Vec`",
+        Some(sym::VecDeque) => "`VecDeque`",
+        _ if cx.typeck_results().expr_ty_adjusted(iter_recv).peel_refs().is_slice() => "slice",
+        // caller is not a type that we want to lint
+        _ => return false,
     };
 
-    span_lint_and_help(
+    span_lint_and_then(
         cx,
         ITER_NTH,
         expr.span,
-        &format!("called `.iter{mut_str}().nth()` on a {caller_type}"),
-        None,
-        &format!("calling `.get{mut_str}()` is both faster and more readable"),
+        &format!("called `.{iter_method}().nth()` on a {caller_type}"),
+        |diag| {
+            let get_method = if iter_method == "iter_mut" { "get_mut" } else { "get" };
+            diag.span_suggestion_verbose(
+                iter_span.to(nth_span),
+                format!("`{get_method}` is equivalent but more concise"),
+                get_method,
+                Applicability::MachineApplicable,
+            );
+        },
     );
+
+    true
 }
diff --git a/clippy_lints/src/methods/map_clone.rs b/clippy_lints/src/methods/map_clone.rs
index 27e17b43b01..c3c7a3a0033 100644
--- a/clippy_lints/src/methods/map_clone.rs
+++ b/clippy_lints/src/methods/map_clone.rs
@@ -86,8 +86,11 @@ pub(super) fn check(cx: &LateContext<'_>, e: &hir::Expr<'_>, recv: &hir::Expr<'_
                                     }
                                 }
                             },
-                            hir::ExprKind::Call(call, [_]) => {
-                                if let hir::ExprKind::Path(qpath) = call.kind {
+                            hir::ExprKind::Call(call, args) => {
+                                if let hir::ExprKind::Path(qpath) = call.kind
+                                    && let [arg] = args
+                                    && ident_eq(name, arg)
+                                {
                                     handle_path(cx, call, &qpath, e, recv);
                                 }
                             },
@@ -118,7 +121,9 @@ fn handle_path(
         if let ty::Adt(_, args) = cx.typeck_results().expr_ty(recv).kind()
             && let args = args.as_slice()
             && let Some(ty) = args.iter().find_map(|generic_arg| generic_arg.as_type())
-            && ty.is_ref()
+            && let ty::Ref(_, ty, Mutability::Not) = ty.kind()
+            && let ty::FnDef(_, lst) = cx.typeck_results().expr_ty(arg).kind()
+            && lst.iter().all(|l| l.as_type() == Some(*ty))
         {
             lint_path(cx, e.span, recv.span, is_copy(cx, ty.peel_refs()));
         }
diff --git a/clippy_lints/src/methods/mod.rs b/clippy_lints/src/methods/mod.rs
index 8a24ccea3a1..b6c474212cd 100644
--- a/clippy_lints/src/methods/mod.rs
+++ b/clippy_lints/src/methods/mod.rs
@@ -36,6 +36,7 @@ mod inefficient_to_string;
 mod inspect_for_each;
 mod into_iter_on_ref;
 mod is_digit_ascii_radix;
+mod is_empty;
 mod iter_cloned_collect;
 mod iter_count;
 mod iter_filter;
@@ -118,6 +119,7 @@ mod unnecessary_literal_unwrap;
 mod unnecessary_result_map_or_else;
 mod unnecessary_sort_by;
 mod unnecessary_to_owned;
+mod unused_enumerate_index;
 mod unwrap_expect_used;
 mod useless_asref;
 mod utils;
@@ -1235,12 +1237,11 @@ declare_clippy_lint! {
 
 declare_clippy_lint! {
     /// ### What it does
-    /// Checks for usage of `.iter().nth()` (and the related
-    /// `.iter_mut().nth()`) on standard library types with *O*(1) element access.
+    /// Checks for usage of `.iter().nth()`/`.iter_mut().nth()` on standard library types that have
+    /// equivalent `.get()`/`.get_mut()` methods.
     ///
     /// ### Why is this bad?
-    /// `.get()` and `.get_mut()` are more efficient and more
-    /// readable.
+    /// `.get()` and `.get_mut()` are equivalent but more concise.
     ///
     /// ### Example
     /// ```no_run
@@ -1256,7 +1257,7 @@ declare_clippy_lint! {
     /// ```
     #[clippy::version = "pre 1.29.0"]
     pub ITER_NTH,
-    perf,
+    style,
     "using `.iter().nth()` on a standard library type with O(1) element access"
 }
 
@@ -2848,7 +2849,7 @@ declare_clippy_lint! {
     /// the file is created from scratch, or ensure `truncate` is
     /// called so that the truncation behaviour is explicit. `truncate(true)`
     /// will ensure the file is entirely overwritten with new data, whereas
-    /// `truncate(false)` will explicitely keep the default behavior.
+    /// `truncate(false)` will explicitly keep the default behavior.
     ///
     /// ### Example
     /// ```rust,no_run
@@ -2862,7 +2863,7 @@ declare_clippy_lint! {
     ///
     /// OpenOptions::new().create(true).truncate(true);
     /// ```
-    #[clippy::version = "1.75.0"]
+    #[clippy::version = "1.77.0"]
     pub SUSPICIOUS_OPEN_OPTIONS,
     suspicious,
     "suspicious combination of options for opening a file"
@@ -3182,8 +3183,8 @@ declare_clippy_lint! {
 declare_clippy_lint! {
     /// ### What it does
     ///
-    /// Checks an argument of `seek` method of `Seek` trait
-    /// and if it start seek from `SeekFrom::Current(0)`, suggests `stream_position` instead.
+    /// Checks if the `seek` method of the `Seek` trait is called with `SeekFrom::Current(0)`,
+    /// and if it is, suggests using `stream_position` instead.
     ///
     /// ### Why is this bad?
     ///
@@ -3590,7 +3591,7 @@ declare_clippy_lint! {
     /// ```
     #[clippy::version = "1.73.0"]
     pub READONLY_WRITE_LOCK,
-    nursery,
+    perf,
     "acquiring a write lock when a read lock would work"
 }
 
@@ -3816,7 +3817,7 @@ declare_clippy_lint! {
     /// ```no_run
     /// let _ = std::iter::empty::<Result<i32, ()>>().flatten();
     /// ```
-    #[clippy::version = "1.76.0"]
+    #[clippy::version = "1.77.0"]
     pub RESULT_FILTER_MAP,
     complexity,
     "filtering `Result` for `Ok` then force-unwrapping, which can be one type-safe operation"
@@ -3825,7 +3826,7 @@ declare_clippy_lint! {
 declare_clippy_lint! {
     /// ### What it does
     /// Checks for usage of `.filter(Option::is_some)` that may be replaced with a `.flatten()` call.
-    /// This lint will require additional changes to the follow-up calls as it appects the type.
+    /// This lint will require additional changes to the follow-up calls as it affects the type.
     ///
     /// ### Why is this bad?
     /// This pattern is often followed by manual unwrapping of the `Option`. The simplification
@@ -3842,7 +3843,7 @@ declare_clippy_lint! {
     /// // example code which does not raise clippy warning
     /// vec![Some(1)].into_iter().flatten();
     /// ```
-    #[clippy::version = "1.76.0"]
+    #[clippy::version = "1.77.0"]
     pub ITER_FILTER_IS_SOME,
     pedantic,
     "filtering an iterator over `Option`s for `Some` can be achieved with `flatten`"
@@ -3851,7 +3852,7 @@ declare_clippy_lint! {
 declare_clippy_lint! {
     /// ### What it does
     /// Checks for usage of `.filter(Result::is_ok)` that may be replaced with a `.flatten()` call.
-    /// This lint will require additional changes to the follow-up calls as it appects the type.
+    /// This lint will require additional changes to the follow-up calls as it affects the type.
     ///
     /// ### Why is this bad?
     /// This pattern is often followed by manual unwrapping of `Result`. The simplification
@@ -3868,7 +3869,7 @@ declare_clippy_lint! {
     /// // example code which does not raise clippy warning
     /// vec![Ok::<i32, String>(1)].into_iter().flatten();
     /// ```
-    #[clippy::version = "1.76.0"]
+    #[clippy::version = "1.77.0"]
     pub ITER_FILTER_IS_OK,
     pedantic,
     "filtering an iterator over `Result`s for `Ok` can be achieved with `flatten`"
@@ -3895,7 +3896,7 @@ declare_clippy_lint! {
     /// option.is_some_and(|a| a > 10);
     /// result.is_ok_and(|a| a > 10);
     /// ```
-    #[clippy::version = "1.76.0"]
+    #[clippy::version = "1.77.0"]
     pub MANUAL_IS_VARIANT_AND,
     pedantic,
     "using `.map(f).unwrap_or_default()`, which is more succinctly expressed as `is_some_and(f)` or `is_ok_and(f)`"
@@ -3925,7 +3926,7 @@ declare_clippy_lint! {
     /// `"\r\n"`), for example during the parsing of a specific file format in which precisely one newline type is
     /// valid.
     /// ```
-    #[clippy::version = "1.76.0"]
+    #[clippy::version = "1.77.0"]
     pub STR_SPLIT_AT_NEWLINE,
     pedantic,
     "splitting a trimmed string at hard-coded newlines"
@@ -4044,6 +4045,31 @@ declare_clippy_lint! {
     "calling `.get().is_some()` or `.get().is_none()` instead of `.contains()` or `.contains_key()`"
 }
 
+declare_clippy_lint! {
+    /// ### What it does
+    /// It identifies calls to `.is_empty()` on constant values.
+    ///
+    /// ### Why is this bad?
+    /// String literals and constant values are known at compile time. Checking if they
+    /// are empty will always return the same value. This might not be the intention of
+    /// the expression.
+    ///
+    /// ### Example
+    /// ```no_run
+    /// let value = "";
+    /// if value.is_empty() {
+    ///     println!("the string is empty");
+    /// }
+    /// ```
+    /// Use instead:
+    /// ```no_run
+    /// println!("the string is empty");
+    /// ```
+    #[clippy::version = "1.78.0"]
+    pub CONST_IS_EMPTY,
+    suspicious,
+    "is_empty() called on strings known at compile time"
+}
 pub struct Methods {
     avoid_breaking_exported_api: bool,
     msrv: Msrv,
@@ -4092,6 +4118,7 @@ impl_lint_pass!(Methods => [
     CLONE_ON_COPY,
     CLONE_ON_REF_PTR,
     COLLAPSIBLE_STR_REPLACE,
+    CONST_IS_EMPTY,
     ITER_OVEREAGER_CLONED,
     CLONED_INSTEAD_OF_COPIED,
     FLAT_MAP_OPTION,
@@ -4403,6 +4430,7 @@ impl Methods {
                     zst_offset::check(cx, expr, recv);
                 },
                 ("all", [arg]) => {
+                    unused_enumerate_index::check(cx, expr, recv, arg);
                     if let Some(("cloned", recv2, [], _, _)) = method_call(recv) {
                         iter_overeager_cloned::check(
                             cx,
@@ -4421,23 +4449,26 @@ impl Methods {
                         unnecessary_lazy_eval::check(cx, expr, recv, arg, "and");
                     }
                 },
-                ("any", [arg]) => match method_call(recv) {
-                    Some(("cloned", recv2, [], _, _)) => iter_overeager_cloned::check(
-                        cx,
-                        expr,
-                        recv,
-                        recv2,
-                        iter_overeager_cloned::Op::NeedlessMove(arg),
-                        false,
-                    ),
-                    Some(("chars", recv, _, _, _))
-                        if let ExprKind::Closure(arg) = arg.kind
-                            && let body = cx.tcx.hir().body(arg.body)
-                            && let [param] = body.params =>
-                    {
-                        string_lit_chars_any::check(cx, expr, recv, param, peel_blocks(body.value), &self.msrv);
-                    },
-                    _ => {},
+                ("any", [arg]) => {
+                    unused_enumerate_index::check(cx, expr, recv, arg);
+                    match method_call(recv) {
+                        Some(("cloned", recv2, [], _, _)) => iter_overeager_cloned::check(
+                            cx,
+                            expr,
+                            recv,
+                            recv2,
+                            iter_overeager_cloned::Op::NeedlessMove(arg),
+                            false,
+                        ),
+                        Some(("chars", recv, _, _, _))
+                            if let ExprKind::Closure(arg) = arg.kind
+                                && let body = cx.tcx.hir().body(arg.body)
+                                && let [param] = body.params =>
+                        {
+                            string_lit_chars_any::check(cx, expr, recv, param, peel_blocks(body.value), &self.msrv);
+                        },
+                        _ => {},
+                    }
                 },
                 ("arg", [arg]) => {
                     suspicious_command_arg_space::check(cx, recv, arg, span);
@@ -4445,7 +4476,7 @@ impl Methods {
                 ("as_deref" | "as_deref_mut", []) => {
                     needless_option_as_deref::check(cx, expr, recv, name);
                 },
-                ("as_bytes" | "is_empty", []) => {
+                ("as_bytes", []) => {
                     if let Some(("as_str", recv, [], as_str_span, _)) = method_call(recv) {
                         redundant_as_str::check(cx, expr, recv, as_str_span, span);
                     }
@@ -4570,14 +4601,17 @@ impl Methods {
                     }
                 },
                 ("filter_map", [arg]) => {
+                    unused_enumerate_index::check(cx, expr, recv, arg);
                     unnecessary_filter_map::check(cx, expr, arg, name);
                     filter_map_bool_then::check(cx, expr, arg, call_span);
                     filter_map_identity::check(cx, expr, arg, span);
                 },
                 ("find_map", [arg]) => {
+                    unused_enumerate_index::check(cx, expr, recv, arg);
                     unnecessary_filter_map::check(cx, expr, arg, name);
                 },
                 ("flat_map", [arg]) => {
+                    unused_enumerate_index::check(cx, expr, recv, arg);
                     flat_map_identity::check(cx, expr, arg, span);
                     flat_map_option::check(cx, expr, arg, span);
                 },
@@ -4599,17 +4633,20 @@ impl Methods {
                     manual_try_fold::check(cx, expr, init, acc, call_span, &self.msrv);
                     unnecessary_fold::check(cx, expr, init, acc, span);
                 },
-                ("for_each", [arg]) => match method_call(recv) {
-                    Some(("inspect", _, [_], span2, _)) => inspect_for_each::check(cx, expr, span2),
-                    Some(("cloned", recv2, [], _, _)) => iter_overeager_cloned::check(
-                        cx,
-                        expr,
-                        recv,
-                        recv2,
-                        iter_overeager_cloned::Op::NeedlessMove(arg),
-                        false,
-                    ),
-                    _ => {},
+                ("for_each", [arg]) => {
+                    unused_enumerate_index::check(cx, expr, recv, arg);
+                    match method_call(recv) {
+                        Some(("inspect", _, [_], span2, _)) => inspect_for_each::check(cx, expr, span2),
+                        Some(("cloned", recv2, [], _, _)) => iter_overeager_cloned::check(
+                            cx,
+                            expr,
+                            recv,
+                            recv2,
+                            iter_overeager_cloned::Op::NeedlessMove(arg),
+                            false,
+                        ),
+                        _ => {},
+                    }
                 },
                 ("get", [arg]) => {
                     get_first::check(cx, expr, recv, arg);
@@ -4619,6 +4656,12 @@ impl Methods {
                 ("hash", [arg]) => {
                     unit_hash::check(cx, expr, recv, arg);
                 },
+                ("is_empty", []) => {
+                    if let Some(("as_str", recv, [], as_str_span, _)) = method_call(recv) {
+                        redundant_as_str::check(cx, expr, recv, as_str_span, span);
+                    }
+                    is_empty::check(cx, expr, recv);
+                },
                 ("is_file", []) => filetype_is_file::check(cx, expr, recv),
                 ("is_digit", [radix]) => is_digit_ascii_radix::check(cx, expr, recv, radix, &self.msrv),
                 ("is_none", []) => check_is_some_is_none(cx, expr, recv, call_span, false),
@@ -4650,6 +4693,7 @@ impl Methods {
                 },
                 (name @ ("map" | "map_err"), [m_arg]) => {
                     if name == "map" {
+                        unused_enumerate_index::check(cx, expr, recv, m_arg);
                         map_clone::check(cx, expr, recv, m_arg, &self.msrv);
                         match method_call(recv) {
                             Some((map_name @ ("iter" | "into_iter"), recv2, _, _, _)) => {
@@ -4723,8 +4767,11 @@ impl Methods {
                         iter_overeager_cloned::Op::LaterCloned,
                         false,
                     ),
-                    Some(("iter", recv2, [], _, _)) => iter_nth::check(cx, expr, recv2, recv, n_arg, false),
-                    Some(("iter_mut", recv2, [], _, _)) => iter_nth::check(cx, expr, recv2, recv, n_arg, true),
+                    Some((iter_method @ ("iter" | "iter_mut"), iter_recv, [], iter_span, _)) => {
+                        if !iter_nth::check(cx, expr, iter_recv, iter_method, iter_span, span) {
+                            iter_nth_zero::check(cx, expr, recv, n_arg);
+                        }
+                    },
                     _ => iter_nth_zero::check(cx, expr, recv, n_arg),
                 },
                 ("ok_or_else", [arg]) => unnecessary_lazy_eval::check(cx, expr, recv, arg, "ok_or"),
diff --git a/clippy_lints/src/methods/no_effect_replace.rs b/clippy_lints/src/methods/no_effect_replace.rs
index 81df32bdee2..a301a5f7d65 100644
--- a/clippy_lints/src/methods/no_effect_replace.rs
+++ b/clippy_lints/src/methods/no_effect_replace.rs
@@ -25,6 +25,7 @@ pub(super) fn check<'tcx>(
         && param1 == param2.as_str()
     {
         span_lint(cx, NO_EFFECT_REPLACE, expr.span, "replacing text with itself");
+        return;
     }
 
     if SpanlessEq::new(cx).eq_expr(arg1, arg2) {
diff --git a/clippy_lints/src/methods/unnecessary_sort_by.rs b/clippy_lints/src/methods/unnecessary_sort_by.rs
index 6911da69b94..a92fe9e55a4 100644
--- a/clippy_lints/src/methods/unnecessary_sort_by.rs
+++ b/clippy_lints/src/methods/unnecessary_sort_by.rs
@@ -5,7 +5,8 @@ use clippy_utils::ty::implements_trait;
 use rustc_errors::Applicability;
 use rustc_hir::{Closure, Expr, ExprKind, Mutability, Param, Pat, PatKind, Path, PathSegment, QPath};
 use rustc_lint::LateContext;
-use rustc_middle::ty::{self, GenericArgKind};
+use rustc_middle::ty;
+use rustc_middle::ty::GenericArgKind;
 use rustc_span::sym;
 use rustc_span::symbol::Ident;
 use std::iter;
diff --git a/clippy_lints/src/methods/unused_enumerate_index.rs b/clippy_lints/src/methods/unused_enumerate_index.rs
new file mode 100644
index 00000000000..e5cc898612e
--- /dev/null
+++ b/clippy_lints/src/methods/unused_enumerate_index.rs
@@ -0,0 +1,135 @@
+use clippy_utils::diagnostics::{multispan_sugg_with_applicability, span_lint_hir_and_then};
+use clippy_utils::paths::{CORE_ITER_ENUMERATE_METHOD, CORE_ITER_ENUMERATE_STRUCT};
+use clippy_utils::source::{snippet, snippet_opt};
+use clippy_utils::{expr_or_init, is_trait_method, match_def_path, pat_is_wild};
+use rustc_errors::Applicability;
+use rustc_hir::{Expr, ExprKind, FnDecl, PatKind, TyKind};
+use rustc_lint::LateContext;
+use rustc_middle::ty::AdtDef;
+use rustc_span::{sym, Span};
+
+use crate::loops::UNUSED_ENUMERATE_INDEX;
+
+/// Check for the `UNUSED_ENUMERATE_INDEX` lint outside of loops.
+///
+/// The lint is declared in `clippy_lints/src/loops/mod.rs`. There, the following pattern is
+/// checked:
+/// ```ignore
+/// for (_, x) in some_iter.enumerate() {
+///     // Index is ignored
+/// }
+/// ```
+///
+/// This `check` function checks for chained method calls constructs where we can detect that the
+/// index is unused. Currently, this checks only for the following patterns:
+/// ```ignore
+/// some_iter.enumerate().map_function(|(_, x)| ..)
+/// let x = some_iter.enumerate();
+/// x.map_function(|(_, x)| ..)
+/// ```
+/// where `map_function` is one of `all`, `any`, `filter_map`, `find_map`, `flat_map`, `for_each` or
+/// `map`.
+///
+/// # Preconditions
+/// This function must be called not on the `enumerate` call expression itself, but on any of the
+/// map functions listed above. It will ensure that `recv` is a `std::iter::Enumerate` instance and
+/// that the method call is one of the `std::iter::Iterator` trait.
+///
+/// * `call_expr`: The map function call expression
+/// * `recv`: The receiver of the call
+/// * `closure_arg`: The argument to the map function call containing the closure/function to apply
+pub(super) fn check(cx: &LateContext<'_>, call_expr: &Expr<'_>, recv: &Expr<'_>, closure_arg: &Expr<'_>) {
+    let recv_ty = cx.typeck_results().expr_ty(recv);
+    if let Some(recv_ty_defid) = recv_ty.ty_adt_def().map(AdtDef::did)
+        // If we call a method on a `std::iter::Enumerate` instance
+        && match_def_path(cx, recv_ty_defid, &CORE_ITER_ENUMERATE_STRUCT)
+        // If we are calling a method of the `Iterator` trait
+        && is_trait_method(cx, call_expr, sym::Iterator)
+        // And the map argument is a closure
+        && let ExprKind::Closure(closure) = closure_arg.kind
+        && let closure_body = cx.tcx.hir().body(closure.body)
+        // And that closure has one argument ...
+        && let [closure_param] = closure_body.params
+        // .. which is a tuple of 2 elements
+        && let PatKind::Tuple([index, elem], ..) = closure_param.pat.kind
+        // And that the first element (the index) is either `_` or unused in the body
+        && pat_is_wild(cx, &index.kind, closure_body)
+        // Try to find the initializer for `recv`. This is needed in case `recv` is a local_binding. In the
+        // first example below, `expr_or_init` would return `recv`.
+        // ```
+        // iter.enumerate().map(|(_, x)| x)
+        // ^^^^^^^^^^^^^^^^ `recv`, a call to `std::iter::Iterator::enumerate`
+        //
+        // let binding = iter.enumerate();
+        //               ^^^^^^^^^^^^^^^^ `recv_init_expr`
+        // binding.map(|(_, x)| x)
+        // ^^^^^^^ `recv`, not a call to `std::iter::Iterator::enumerate`
+        // ```
+        && let recv_init_expr = expr_or_init(cx, recv)
+        // Make sure the initializer is a method call. It may be that the `Enumerate` comes from something
+        // that we cannot control.
+        // This would for instance happen with:
+        // ```
+        // external_lib::some_function_returning_enumerate().map(|(_, x)| x)
+        // ```
+        && let ExprKind::MethodCall(_, enumerate_recv, _, enumerate_span) = recv_init_expr.kind
+        && let Some(enumerate_defid) = cx.typeck_results().type_dependent_def_id(recv_init_expr.hir_id)
+        // Make sure the method call is `std::iter::Iterator::enumerate`.
+        && match_def_path(cx, enumerate_defid, &CORE_ITER_ENUMERATE_METHOD)
+    {
+        // Check if the tuple type was explicit. It may be the type system _needs_ the type of the element
+        // that would be explicited in the closure.
+        let new_closure_param = match find_elem_explicit_type_span(closure.fn_decl) {
+            // We have an explicit type. Get its snippet, that of the binding name, and do `binding: ty`.
+            // Fallback to `..` if we fail getting either snippet.
+            Some(ty_span) => snippet_opt(cx, elem.span)
+                .and_then(|binding_name| snippet_opt(cx, ty_span).map(|ty_name| format!("{binding_name}: {ty_name}")))
+                .unwrap_or_else(|| "..".to_string()),
+            // Otherwise, we have no explicit type. We can replace with the binding name of the element.
+            None => snippet(cx, elem.span, "..").into_owned(),
+        };
+
+        // Suggest removing the tuple from the closure and the preceding call to `enumerate`, whose span we
+        // can get from the `MethodCall`.
+        span_lint_hir_and_then(
+            cx,
+            UNUSED_ENUMERATE_INDEX,
+            recv_init_expr.hir_id,
+            enumerate_span,
+            "you seem to use `.enumerate()` and immediately discard the index",
+            |diag| {
+                multispan_sugg_with_applicability(
+                    diag,
+                    "remove the `.enumerate()` call",
+                    Applicability::MachineApplicable,
+                    vec![
+                        (closure_param.span, new_closure_param),
+                        (
+                            enumerate_span.with_lo(enumerate_recv.span.source_callsite().hi()),
+                            String::new(),
+                        ),
+                    ],
+                );
+            },
+        );
+    }
+}
+
+/// Find the span of the explicit type of the element.
+///
+/// # Returns
+/// If the tuple argument:
+/// * Has no explicit type, returns `None`
+/// * Has an explicit tuple type with an implicit element type (`(usize, _)`), returns `None`
+/// * Has an explicit tuple type with an explicit element type (`(_, i32)`), returns the span for
+///   the element type.
+fn find_elem_explicit_type_span(fn_decl: &FnDecl<'_>) -> Option<Span> {
+    if let [tuple_ty] = fn_decl.inputs
+        && let TyKind::Tup([_idx_ty, elem_ty]) = tuple_ty.kind
+        && !matches!(elem_ty.kind, TyKind::Err(..) | TyKind::Infer)
+    {
+        Some(elem_ty.span)
+    } else {
+        None
+    }
+}