match .map(Clone::clone)

src/map_clone.rs

@@ -1,8 +1,8 @@
 use rustc::lint::*;
 use rustc_front::hir::*;
 use syntax::ast::Ident;
-use utils::OPTION_PATH;
+use utils::{CLONE_PATH, OPTION_PATH};
-use utils::{is_adjusted, match_trait_method, match_type, snippet, span_help_and_lint};
+use utils::{is_adjusted, match_path, match_trait_method, match_type, snippet, span_help_and_lint};
 use utils::{walk_ptrs_ty, walk_ptrs_ty_depth};
 
 declare_lint!(pub MAP_CLONE, Warn,
@@ -14,12 +14,13 @@ pub struct MapClonePass;
 
 impl LateLintPass for MapClonePass {
     fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
+        // call to .map()
+        if let ExprMethodCall(name, _, ref args) = expr.node {
+            if name.node.as_str() == "map" && args.len() == 2 {
+                match args[1].node {
+                    ExprClosure(_, ref decl, ref blk) => {
                         if_let_chain! {
                             [
-                // call to .map()
-                let ExprMethodCall(name, _, ref args) = expr.node,
-                name.node.as_str() == "map" && args.len() == 2,
-                let ExprClosure(_, ref decl, ref blk) = args[1].node,
                             // just one expression in the closure
                             blk.stmts.is_empty(),
                             let Some(ref closure_expr) = blk.expr,
@@ -54,6 +55,20 @@ impl LateLintPass for MapClonePass {
                                 }
                             }
                         }
+                    },
+                    ExprPath(_, ref path) => {
+                        if match_path(path, &CLONE_PATH) {
+                            let type_name = get_type_name(cx, expr, &args[0]).unwrap_or("_");
+                            span_help_and_lint(cx, MAP_CLONE, expr.span, &format!(
+                                "you seem to be using .map() to clone the contents of an {}, consider \
+                                using `.cloned()`", type_name),
+                                &format!("try\n{}.cloned()", snippet(cx, args[0].span, "..")));
+                        }
+                    }
+                    _ => (),
+                }
+            }
+        }
     }
 }
 

src/utils.rs

@@ -17,6 +17,7 @@ pub const VEC_PATH:    [&'static str; 3] = ["collections", "vec", "Vec"];
 pub const LL_PATH:     [&'static str; 3] = ["collections", "linked_list", "LinkedList"];
 pub const OPEN_OPTIONS_PATH: [&'static str; 3] = ["std", "fs", "OpenOptions"];
 pub const MUTEX_PATH:  [&'static str; 4] = ["std", "sync", "mutex", "Mutex"];
+pub const CLONE_PATH:  [&'static str; 2] = ["Clone", "clone"];
 
 /// Produce a nested chain of if-lets and ifs from the patterns:
 ///

tests/compile-fail/map_clone.rs

@@ -15,6 +15,8 @@ fn map_clone_iter() {
                           //~^ HELP try
     x.iter().map(|y| *y); //~ ERROR you seem to be using .map()
                           //~^ HELP try
+    x.iter().map(Clone::clone); //~ ERROR you seem to be using .map()
+                                //~^ HELP try
 }
 
 fn map_clone_option() {