Fix map_clone with deref and clone

Author: camsteffen

clippy_lints/src/map_clone.rs

@@ -8,6 +8,7 @@ use rustc_hir as hir;
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::mir::Mutability;
 use rustc_middle::ty;
+use rustc_middle::ty::adjustment::Adjust;
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::symbol::Ident;
 use rustc_span::{sym, Span};
@@ -75,11 +76,14 @@ impl<'tcx> LateLintPass<'tcx> for MapClone {
                                     }
                                 }
                             },
-                            hir::ExprKind::MethodCall(ref method, _, ref obj, _) => {
-                                if ident_eq(name, &obj[0]) && method.ident.as_str() == "clone"
-                                    && match_trait_method(cx, closure_expr, &paths::CLONE_TRAIT) {
-
-                                    let obj_ty = cx.typeck_results().expr_ty(&obj[0]);
+                            hir::ExprKind::MethodCall(ref method, _, [obj], _) => if_chain! {
+                                if ident_eq(name, obj) && method.ident.name == sym::clone;
+                                if match_trait_method(cx, closure_expr, &paths::CLONE_TRAIT);
+                                // no autoderefs
+                                if !cx.typeck_results().expr_adjustments(obj).iter()
+                                    .any(|a| matches!(a.kind, Adjust::Deref(Some(..))));
+                                let obj_ty = cx.typeck_results().expr_ty(obj);
+                                then {
                                     if let ty::Ref(_, ty, _) = obj_ty.kind() {
                                         let copy = is_copy(cx, ty);
                                         lint(cx, e.span, args[0].span, copy);

tests/ui/map_clone.fixed

@@ -44,4 +44,11 @@ fn main() {
         let v = vec![&mut d];
         let _: Vec<u32> = v.into_iter().map(|&mut x| x).collect();
     }
+
+    // Issue #6239 deref coercion and clone deref
+    {
+        use std::cell::RefCell;
+
+        let _ = Some(RefCell::new(String::new()).borrow()).map(|s| s.clone());
+    }
 }

tests/ui/map_clone.rs

@@ -44,4 +44,11 @@ fn main() {
         let v = vec![&mut d];
         let _: Vec<u32> = v.into_iter().map(|&mut x| x).collect();
     }
+
+    // Issue #6239 deref coercion and clone deref
+    {
+        use std::cell::RefCell;
+
+        let _ = Some(RefCell::new(String::new()).borrow()).map(|s| s.clone());
+    }
 }