Fix `clone_on_copy` not detecting derefs sometimes

clippy_lints/src/methods/mod.rs

@@ -1250,7 +1250,8 @@ fn lint_clone_on_copy(cx: &LateContext<'_, '_>, expr: &hir::Expr, arg: &hir::Exp
     if is_copy(cx, ty) {
         let snip;
         if let Some(snippet) = sugg::Sugg::hir_opt(cx, arg) {
-            if let ty::Ref(..) = cx.tables.expr_ty(arg).sty {
+            // x.clone() might have dereferenced x, possibly through a Deref impl
+            if cx.tables.expr_ty(arg) != ty {
                 let parent = cx.tcx.hir.get_parent_node(expr.id);
                 match cx.tcx.hir.get(parent) {
                     hir::Node::Expr(parent) => match parent.node {

tests/ui/unnecessary_clone.rs

@@ -13,6 +13,7 @@
 #![warn(clippy::clone_on_ref_ptr)]
 #![allow(unused)]
 
+use std::cell::RefCell;
 use std::collections::HashSet;
 use std::collections::VecDeque;
 use std::rc::{self, Rc};
@@ -30,6 +31,9 @@ fn clone_on_copy() {
     vec![1].clone(); // ok, not a Copy type
     Some(vec![1]).clone(); // ok, not a Copy type
     (&42).clone();
+
+    let rc = RefCell::new(0);
+    rc.borrow().clone();
 }
 
 fn clone_on_ref_ptr() {

tests/ui/unnecessary_clone.stderr

@@ -1,84 +1,90 @@
 error: using `clone` on a `Copy` type
-  --> $DIR/unnecessary_clone.rs:28:5
+  --> $DIR/unnecessary_clone.rs:29:5
    |
-28 |     42.clone();
+29 |     42.clone();
    |     ^^^^^^^^^^ help: try removing the `clone` call: `42`
    |
    = note: `-D clippy::clone-on-copy` implied by `-D warnings`
 
 error: using `clone` on a `Copy` type
-  --> $DIR/unnecessary_clone.rs:32:5
+  --> $DIR/unnecessary_clone.rs:33:5
    |
-32 |     (&42).clone();
+33 |     (&42).clone();
    |     ^^^^^^^^^^^^^ help: try dereferencing it: `*(&42)`
 
-error: using '.clone()' on a ref-counted pointer
-  --> $DIR/unnecessary_clone.rs:42:5
+error: using `clone` on a `Copy` type
+  --> $DIR/unnecessary_clone.rs:36:5
    |
-42 |     rc.clone();
+36 |     rc.borrow().clone();
+   |     ^^^^^^^^^^^^^^^^^^^ help: try dereferencing it: `*rc.borrow()`
+
+error: using '.clone()' on a ref-counted pointer
+  --> $DIR/unnecessary_clone.rs:46:5
+   |
+46 |     rc.clone();
    |     ^^^^^^^^^^ help: try this: `Rc::<bool>::clone(&rc)`
    |
    = note: `-D clippy::clone-on-ref-ptr` implied by `-D warnings`
 
 error: using '.clone()' on a ref-counted pointer
-  --> $DIR/unnecessary_clone.rs:45:5
+  --> $DIR/unnecessary_clone.rs:49:5
    |
-45 |     arc.clone();
+49 |     arc.clone();
    |     ^^^^^^^^^^^ help: try this: `Arc::<bool>::clone(&arc)`
 
 error: using '.clone()' on a ref-counted pointer
-  --> $DIR/unnecessary_clone.rs:48:5
+  --> $DIR/unnecessary_clone.rs:52:5
    |
-48 |     rcweak.clone();
+52 |     rcweak.clone();
    |     ^^^^^^^^^^^^^^ help: try this: `Weak::<bool>::clone(&rcweak)`
 
 error: using '.clone()' on a ref-counted pointer
-  --> $DIR/unnecessary_clone.rs:51:5
+  --> $DIR/unnecessary_clone.rs:55:5
    |
-51 |     arc_weak.clone();
+55 |     arc_weak.clone();
    |     ^^^^^^^^^^^^^^^^ help: try this: `Weak::<bool>::clone(&arc_weak)`
 
 error: using '.clone()' on a ref-counted pointer
-  --> $DIR/unnecessary_clone.rs:55:29
+  --> $DIR/unnecessary_clone.rs:59:29
    |
-55 |     let _: Arc<SomeTrait> = x.clone();
+59 |     let _: Arc<SomeTrait> = x.clone();
    |                             ^^^^^^^^^ help: try this: `Arc::<SomeImpl>::clone(&x)`
 
 error: using `clone` on a `Copy` type
-  --> $DIR/unnecessary_clone.rs:59:5
+  --> $DIR/unnecessary_clone.rs:63:5
    |
-59 |     t.clone();
+63 |     t.clone();
    |     ^^^^^^^^^ help: try removing the `clone` call: `t`
 
 error: using `clone` on a `Copy` type
-  --> $DIR/unnecessary_clone.rs:61:5
+  --> $DIR/unnecessary_clone.rs:65:5
    |
-61 |     Some(t).clone();
+65 |     Some(t).clone();
    |     ^^^^^^^^^^^^^^^ help: try removing the `clone` call: `Some(t)`
 
 error: using `clone` on a double-reference; this will copy the reference instead of cloning the inner type
-  --> $DIR/unnecessary_clone.rs:67:22
+  --> $DIR/unnecessary_clone.rs:71:22
    |
-67 |     let z: &Vec<_> = y.clone();
+71 |     let z: &Vec<_> = y.clone();
    |                      ^^^^^^^^^
    |
    = note: #[deny(clippy::clone_double_ref)] on by default
 help: try dereferencing it
    |
-67 |     let z: &Vec<_> = &(*y).clone();
+71 |     let z: &Vec<_> = &(*y).clone();
    |                      ^^^^^^^^^^^^^
 help: or try being explicit about what type to clone
    |
-67 |     let z: &Vec<_> = &std::vec::Vec<i32>::clone(y);
+71 |     let z: &Vec<_> = &std::vec::Vec<i32>::clone(y);
    |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: called `cloned().collect()` on a slice to create a `Vec`. Calling `to_vec()` is both faster and more readable
-  --> $DIR/unnecessary_clone.rs:74:27
+  --> $DIR/unnecessary_clone.rs:78:27
    |
-74 |     let v2 : Vec<isize> = v.iter().cloned().collect();
+78 |     let v2 : Vec<isize> = v.iter().cloned().collect();
    |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: `-D clippy::iter-cloned-collect` implied by `-D warnings`
 
-error: aborting due to 11 previous errors
+error: aborting due to 12 previous errors