1 files changed, 122 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/methods/map_clone.rs b/src/tools/clippy/clippy_lints/src/methods/map_clone.rs
new file mode 100644
index 000000000..8261ef5e1
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/methods/map_clone.rs
@@ -0,0 +1,122 @@
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::source::snippet_with_applicability;
+use clippy_utils::ty::{is_copy, is_type_diagnostic_item};
+use clippy_utils::{is_diag_trait_item, meets_msrv, msrvs, peel_blocks};
+use if_chain::if_chain;
+use rustc_errors::Applicability;
+use rustc_hir as hir;
+use rustc_lint::LateContext;
+use rustc_middle::mir::Mutability;
+use rustc_middle::ty;
+use rustc_middle::ty::adjustment::Adjust;
+use rustc_semver::RustcVersion;
+use rustc_span::symbol::Ident;
+use rustc_span::{sym, Span};
+
+use super::MAP_CLONE;
+
+pub(super) fn check<'tcx>(
+    cx: &LateContext<'_>,
+    e: &hir::Expr<'_>,
+    recv: &hir::Expr<'_>,
+    arg: &'tcx hir::Expr<'_>,
+    msrv: Option<RustcVersion>,
+) {
+    if_chain! {
+        if let Some(method_id) = cx.typeck_results().type_dependent_def_id(e.hir_id);
+        if cx.tcx.impl_of_method(method_id)
+            .map_or(false, |id| is_type_diagnostic_item(cx, cx.tcx.type_of(id), sym::Option))
+            || is_diag_trait_item(cx, method_id, sym::Iterator);
+        if let hir::ExprKind::Closure(&hir::Closure{ body, .. }) = arg.kind;
+        then {
+            let closure_body = cx.tcx.hir().body(body);
+            let closure_expr = peel_blocks(closure_body.value);
+            match closure_body.params[0].pat.kind {
+                hir::PatKind::Ref(inner, hir::Mutability::Not) => if let hir::PatKind::Binding(
+                    hir::BindingAnnotation::NONE, .., name, None
+                ) = inner.kind {
+                    if ident_eq(name, closure_expr) {
+                        lint_explicit_closure(cx, e.span, recv.span, true, msrv);
+                    }
+                },
+                hir::PatKind::Binding(hir::BindingAnnotation::NONE, .., name, None) => {
+                    match closure_expr.kind {
+                        hir::ExprKind::Unary(hir::UnOp::Deref, inner) => {
+                            if ident_eq(name, inner) {
+                                if let ty::Ref(.., Mutability::Not) = cx.typeck_results().expr_ty(inner).kind() {
+                                    lint_explicit_closure(cx, e.span, recv.span, true, msrv);
+                                }
+                            }
+                        },
+                        hir::ExprKind::MethodCall(method, obj, [], _) => if_chain! {
+                            if ident_eq(name, obj) && method.ident.name == sym::clone;
+                            if let Some(fn_id) = cx.typeck_results().type_dependent_def_id(closure_expr.hir_id);
+                            if let Some(trait_id) = cx.tcx.trait_of_item(fn_id);
+                            if cx.tcx.lang_items().clone_trait().map_or(false, |id| id == trait_id);
+                            // no autoderefs
+                            if !cx.typeck_results().expr_adjustments(obj).iter()
+                                .any(|a| matches!(a.kind, Adjust::Deref(Some(..))));
+                            then {
+                                let obj_ty = cx.typeck_results().expr_ty(obj);
+                                if let ty::Ref(_, ty, mutability) = obj_ty.kind() {
+                                    if matches!(mutability, Mutability::Not) {
+                                        let copy = is_copy(cx, *ty);
+                                        lint_explicit_closure(cx, e.span, recv.span, copy, msrv);
+                                    }
+                                } else {
+                                    lint_needless_cloning(cx, e.span, recv.span);
+                                }
+                            }
+                        },
+                        _ => {},
+                    }
+                },
+                _ => {},
+            }
+        }
+    }
+}
+
+fn ident_eq(name: Ident, path: &hir::Expr<'_>) -> bool {
+    if let hir::ExprKind::Path(hir::QPath::Resolved(None, path)) = path.kind {
+        path.segments.len() == 1 && path.segments[0].ident == name
+    } else {
+        false
+    }
+}
+
+fn lint_needless_cloning(cx: &LateContext<'_>, root: Span, receiver: Span) {
+    span_lint_and_sugg(
+        cx,
+        MAP_CLONE,
+        root.trim_start(receiver).unwrap(),
+        "you are needlessly cloning iterator elements",
+        "remove the `map` call",
+        String::new(),
+        Applicability::MachineApplicable,
+    );
+}
+
+fn lint_explicit_closure(cx: &LateContext<'_>, replace: Span, root: Span, is_copy: bool, msrv: Option<RustcVersion>) {
+    let mut applicability = Applicability::MachineApplicable;
+
+    let (message, sugg_method) = if is_copy && meets_msrv(msrv, msrvs::ITERATOR_COPIED) {
+        ("you are using an explicit closure for copying elements", "copied")
+    } else {
+        ("you are using an explicit closure for cloning elements", "cloned")
+    };
+
+    span_lint_and_sugg(
+        cx,
+        MAP_CLONE,
+        replace,
+        message,
+        &format!("consider calling the dedicated `{}` method", sugg_method),
+        format!(
+            "{}.{}()",
+            snippet_with_applicability(cx, root, "..", &mut applicability),
+            sugg_method,
+        ),
+        applicability,
+    );
+}