1 files changed, 87 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/methods/iter_kv_map.rs b/src/tools/clippy/clippy_lints/src/methods/iter_kv_map.rs
new file mode 100644
index 000000000..2244ebfb1
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/methods/iter_kv_map.rs
@@ -0,0 +1,87 @@
+#![allow(unused_imports)]
+
+use super::ITER_KV_MAP;
+use clippy_utils::diagnostics::{multispan_sugg, span_lint_and_sugg, span_lint_and_then};
+use clippy_utils::source::{snippet, snippet_with_applicability};
+use clippy_utils::sugg;
+use clippy_utils::ty::is_type_diagnostic_item;
+use clippy_utils::visitors::is_local_used;
+use rustc_hir::{BindingAnnotation, Body, BorrowKind, Expr, ExprKind, Mutability, Pat, PatKind};
+use rustc_lint::{LateContext, LintContext};
+use rustc_middle::ty;
+use rustc_span::sym;
+use rustc_span::Span;
+
+/// lint use of:
+/// - `hashmap.iter().map(|(_, v)| v)`
+/// - `hashmap.into_iter().map(|(_, v)| v)`
+/// on `HashMaps` and `BTreeMaps` in std
+
+pub(super) fn check<'tcx>(
+    cx: &LateContext<'tcx>,
+    map_type: &'tcx str,     // iter / into_iter
+    expr: &'tcx Expr<'tcx>,  // .iter().map(|(_, v_| v))
+    recv: &'tcx Expr<'tcx>,  // hashmap
+    m_arg: &'tcx Expr<'tcx>, // |(_, v)| v
+) {
+    if_chain! {
+        if !expr.span.from_expansion();
+        if let ExprKind::Closure(c) = m_arg.kind;
+        if let Body {params: [p], value: body_expr, generator_kind: _ } = cx.tcx.hir().body(c.body);
+        if let PatKind::Tuple([key_pat, val_pat], _) = p.pat.kind;
+
+        let (replacement_kind, binded_ident) = match (&key_pat.kind, &val_pat.kind) {
+            (key, PatKind::Binding(_, _, value, _)) if pat_is_wild(cx, key, m_arg) => ("value", value),
+            (PatKind::Binding(_, _, key, _), value) if pat_is_wild(cx, value, m_arg) => ("key", key),
+            _ => return,
+        };
+
+        let ty = cx.typeck_results().expr_ty(recv);
+        if is_type_diagnostic_item(cx, ty, sym::HashMap) || is_type_diagnostic_item(cx, ty, sym::BTreeMap);
+
+        then {
+            let mut applicability = rustc_errors::Applicability::MachineApplicable;
+            let recv_snippet = snippet_with_applicability(cx, recv.span, "map", &mut applicability);
+            let into_prefix = if map_type == "into_iter" {"into_"} else {""};
+
+            if_chain! {
+                if let ExprKind::Path(rustc_hir::QPath::Resolved(_, path)) = body_expr.kind;
+                if let [local_ident] = path.segments;
+                if local_ident.ident.as_str() == binded_ident.as_str();
+
+                then {
+                    span_lint_and_sugg(
+                        cx,
+                        ITER_KV_MAP,
+                        expr.span,
+                        &format!("iterating on a map's {replacement_kind}s"),
+                        "try",
+                        format!("{recv_snippet}.{into_prefix}{replacement_kind}s()"),
+                        applicability,
+                    );
+                } else {
+                    span_lint_and_sugg(
+                        cx,
+                        ITER_KV_MAP,
+                        expr.span,
+                        &format!("iterating on a map's {replacement_kind}s"),
+                        "try",
+                        format!("{recv_snippet}.{into_prefix}{replacement_kind}s().map(|{binded_ident}| {})",
+                            snippet_with_applicability(cx, body_expr.span, "/* body */", &mut applicability)),
+                        applicability,
+                    );
+                }
+            }
+        }
+    }
+}
+
+/// Returns `true` if the pattern is a `PatWild`, or is an ident prefixed with `_`
+/// that is not locally used.
+fn pat_is_wild<'tcx>(cx: &LateContext<'tcx>, pat: &'tcx PatKind<'_>, body: &'tcx Expr<'_>) -> bool {
+    match *pat {
+        PatKind::Wild => true,
+        PatKind::Binding(_, id, ident, None) if ident.as_str().starts_with('_') => !is_local_used(cx, body, id),
+        _ => false,
+    }
+}