Add cloned_instead_of_copied lint

clippy_lints/src/lib.rs

@@ -759,6 +759,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         methods::BYTES_NTH,
         methods::CHARS_LAST_CMP,
         methods::CHARS_NEXT_CMP,
+        methods::CLONED_INSTEAD_OF_COPIED,
         methods::CLONE_DOUBLE_REF,
         methods::CLONE_ON_COPY,
         methods::CLONE_ON_REF_PTR,
@@ -1380,6 +1381,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(matches::MATCH_WILDCARD_FOR_SINGLE_VARIANTS),
         LintId::of(matches::MATCH_WILD_ERR_ARM),
         LintId::of(matches::SINGLE_MATCH_ELSE),
+        LintId::of(methods::CLONED_INSTEAD_OF_COPIED),
         LintId::of(methods::FILTER_MAP_NEXT),
         LintId::of(methods::IMPLICIT_CLONE),
         LintId::of(methods::INEFFICIENT_TO_STRING),

clippy_lints/src/methods/cloned_instead_of_copied.rs

@@ -0,0 +1,38 @@
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::is_trait_method;
+use clippy_utils::ty::{get_iterator_item_ty, is_copy};
+use rustc_errors::Applicability;
+use rustc_hir::Expr;
+use rustc_lint::LateContext;
+use rustc_middle::ty;
+use rustc_span::{sym, Span};
+
+use super::CLONED_INSTEAD_OF_COPIED;
+
+pub fn check(cx: &LateContext<'_>, expr: &Expr<'_>, recv: &Expr<'_>, span: Span) {
+    let recv_ty = cx.typeck_results().expr_ty_adjusted(recv);
+    let inner_ty = match recv_ty.kind() {
+        // `Option<T>` -> `T`
+        ty::Adt(adt, subst) if cx.tcx.is_diagnostic_item(sym::option_type, adt.did) => subst.type_at(0),
+        _ if is_trait_method(cx, expr, sym::Iterator) => match get_iterator_item_ty(cx, recv_ty) {
+            // <T as Iterator>::Item
+            Some(ty) => ty,
+            _ => return,
+        },
+        _ => return,
+    };
+    match inner_ty.kind() {
+        // &T where T: Copy
+        ty::Ref(_, ty, _) if is_copy(cx, ty) => {},
+        _ => return,
+    };
+    span_lint_and_sugg(
+        cx,
+        CLONED_INSTEAD_OF_COPIED,
+        span,
+        "used `cloned` where `copied` could be used instead",
+        "try",
+        "copied".into(),
+        Applicability::MachineApplicable,
+    )
+}

clippy_lints/src/methods/mod.rs

@@ -8,6 +8,7 @@ mod chars_next_cmp;
 mod chars_next_cmp_with_unwrap;
 mod clone_on_copy;
 mod clone_on_ref_ptr;
+mod cloned_instead_of_copied;
 mod expect_fun_call;
 mod expect_used;
 mod filetype_is_file;
@@ -73,6 +74,29 @@ use rustc_span::symbol::SymbolStr;
 use rustc_span::{sym, Span};
 use rustc_typeck::hir_ty_to_ty;
 
+declare_clippy_lint! {
+    /// **What it does:** Checks for usages of `cloned()` on an `Iterator` or `Option` where
+    /// `copied()` could be used instead.
+    ///
+    /// **Why is this bad?** `copied()` is better because it guarantees that the type being cloned
+    /// implements `Copy`.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    ///
+    /// ```rust
+    /// [1, 2, 3].iter().cloned();
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// [1, 2, 3].iter().copied();
+    /// ```
+    pub CLONED_INSTEAD_OF_COPIED,
+    pedantic,
+    "used `cloned` where `copied` could be used instead"
+}
+
 declare_clippy_lint! {
     /// **What it does:** Checks for `.unwrap()` calls on `Option`s and on `Result`s.
     ///
@@ -1638,6 +1662,7 @@ impl_lint_pass!(Methods => [
     CLONE_ON_COPY,
     CLONE_ON_REF_PTR,
     CLONE_DOUBLE_REF,
+    CLONED_INSTEAD_OF_COPIED,
     INEFFICIENT_TO_STRING,
     NEW_RET_NO_SELF,
     SINGLE_CHAR_PATTERN,
@@ -1909,6 +1934,7 @@ fn check_methods<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, msrv: Optio
             ("as_mut", []) => useless_asref::check(cx, expr, "as_mut", recv),
             ("as_ref", []) => useless_asref::check(cx, expr, "as_ref", recv),
             ("assume_init", []) => uninit_assumed_init::check(cx, expr, recv),
+            ("cloned", []) => cloned_instead_of_copied::check(cx, expr, recv, span),
             ("collect", []) => match method_call!(recv) {
                 Some(("cloned", [recv2], _)) => iter_cloned_collect::check(cx, expr, recv2),
                 Some(("map", [m_recv, m_arg], _)) => {