Don't lint implicit_clone when the type doesn't implement clone

Author: Jarcho

clippy_lints/src/methods/implicit_clone.rs

@@ -1,6 +1,6 @@
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::source::snippet_with_context;
-use clippy_utils::ty::peel_mid_ty_refs;
+use clippy_utils::ty::{implements_trait, peel_mid_ty_refs};
 use clippy_utils::{is_diag_item_method, is_diag_trait_item};
 use if_chain::if_chain;
 use rustc_errors::Applicability;
@@ -19,6 +19,8 @@ pub fn check(cx: &LateContext<'_>, method_name: &str, expr: &hir::Expr<'_>, recv
         let (input_type, ref_count) = peel_mid_ty_refs(input_type);
         if let Some(ty_name) = input_type.ty_adt_def().map(|adt_def| cx.tcx.item_name(adt_def.did()));
         if return_type == input_type;
+        if let Some(clone_trait) = cx.tcx.lang_items().clone_trait();
+        if implements_trait(cx, return_type, clone_trait, &[]);
         then {
             let mut app = Applicability::MachineApplicable;
             let recv_snip = snippet_with_context(cx, recv.span, expr.span.ctxt(), "..", &mut app).0;

tests/ui/implicit_clone.fixed

@@ -115,4 +115,14 @@ fn main() {
     let pathbuf_ref = &pathbuf_ref;
     let _ = pathbuf_ref.to_owned(); // Don't lint. Returns `&&PathBuf`
     let _ = (**pathbuf_ref).clone();
+
+    struct NoClone;
+    impl ToOwned for NoClone {
+        type Owned = Self;
+        fn to_owned(&self) -> Self {
+            NoClone
+        }
+    }
+    let no_clone = &NoClone;
+    let _ = no_clone.to_owned();
 }

tests/ui/implicit_clone.rs

@@ -115,4 +115,14 @@ fn main() {
     let pathbuf_ref = &pathbuf_ref;
     let _ = pathbuf_ref.to_owned(); // Don't lint. Returns `&&PathBuf`
     let _ = pathbuf_ref.to_path_buf();
+
+    struct NoClone;
+    impl ToOwned for NoClone {
+        type Owned = Self;
+        fn to_owned(&self) -> Self {
+            NoClone
+        }
+    }
+    let no_clone = &NoClone;
+    let _ = no_clone.to_owned();
 }