Add a lint about using clone on Copy types

README.md

@@ -6,7 +6,7 @@ A collection of lints to catch common mistakes and improve your Rust code.
 [Jump to usage instructions](#usage)
 
 ##Lints
-There are 107 lints included in this crate:
+There are 108 lints included in this crate:
 
 name                                                                                                           | default | meaning
 ---------------------------------------------------------------------------------------------------------------|---------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
@@ -22,6 +22,7 @@ name
 [cast_sign_loss](https://github.com/Manishearth/rust-clippy/wiki#cast_sign_loss)                               | allow   | casts from signed types to unsigned types, e.g `x as u32` where `x: i32`
 [char_lit_as_u8](https://github.com/Manishearth/rust-clippy/wiki#char_lit_as_u8)                               | warn    | Casting a character literal to u8
 [chars_next_cmp](https://github.com/Manishearth/rust-clippy/wiki#chars_next_cmp)                               | warn    | using `.chars().next()` to check if a string starts with a char
+[clone_on_copy](https://github.com/Manishearth/rust-clippy/wiki#clone_on_copy)                                 | warn    | using `clone` on a `Copy` type
 [cmp_nan](https://github.com/Manishearth/rust-clippy/wiki#cmp_nan)                                             | deny    | comparisons to NAN (which will always return false, which is probably not intended)
 [cmp_owned](https://github.com/Manishearth/rust-clippy/wiki#cmp_owned)                                         | warn    | creating owned instances for comparing with others, e.g. `x == "foo".to_string()`
 [collapsible_if](https://github.com/Manishearth/rust-clippy/wiki#collapsible_if)                               | warn    | two nested `if`-expressions can be collapsed into one, e.g. `if x { if y { foo() } }` can be written as `if x && y { foo() }` and an `else { if .. } expression can be collapsed to `else if`

src/lib.rs

@@ -214,6 +214,7 @@ pub fn plugin_registrar(reg: &mut Registry) {
         matches::MATCH_REF_PATS,
         matches::SINGLE_MATCH,
         methods::CHARS_NEXT_CMP,
+        methods::CLONE_ON_COPY,
         methods::EXTEND_FROM_SLICE,
         methods::FILTER_NEXT,
         methods::OK_EXPECT,

src/loops.rs

@@ -475,7 +475,7 @@ fn check_for_loop_explicit_counter(cx: &LateContext, arg: &Expr, body: &Expr, ex
                 let mut visitor2 = InitializeVisitor {
                     cx: cx,
                     end_expr: expr,
-                    var_id: id.clone(),
+                    var_id: *id,
                     state: VarState::IncrOnce,
                     name: None,
                     depth: 0,

src/methods.rs

@@ -219,6 +219,17 @@ declare_lint!(pub OR_FUN_CALL, Warn,
 declare_lint!(pub EXTEND_FROM_SLICE, Warn,
               "`.extend_from_slice(_)` is a faster way to extend a Vec by a slice");
 
+/// **What it does:** This lint warns on using `.clone()` on a `Copy` type.
+///
+/// **Why is this bad?** The only reason `Copy` types implement `Clone` is for generics, not for
+/// using the `clone` method on a concrete type.
+///
+/// **Known problems:** None.
+///
+/// **Example:** `42u64.clone()`
+declare_lint!(pub CLONE_ON_COPY, Warn,
+              "using `clone` on a `Copy` type");
+
 impl LintPass for MethodsPass {
     fn get_lints(&self) -> LintArray {
         lint_array!(EXTEND_FROM_SLICE,
@@ -233,7 +244,8 @@ impl LintPass for MethodsPass {
                     OPTION_MAP_UNWRAP_OR,
                     OPTION_MAP_UNWRAP_OR_ELSE,
                     OR_FUN_CALL,
-                    CHARS_NEXT_CMP)
+                    CHARS_NEXT_CMP,
+                    CLONE_ON_COPY)
     }
 }
 
@@ -269,6 +281,7 @@ impl LateLintPass for MethodsPass {
                 }
 
                 lint_or_fun_call(cx, expr, &name.node.as_str(), &args);
+                lint_clone_on_copy(cx, expr, &name.node.as_str(), &args);
             }
             ExprBinary(op, ref lhs, ref rhs) if op.node == BiEq || op.node == BiNe => {
                 if !lint_chars_next(cx, expr, lhs, rhs, op.node == BiEq) {
@@ -439,6 +452,19 @@ fn lint_or_fun_call(cx: &LateContext, expr: &Expr, name: &str, args: &[P<Expr>])
     }
 }
 
+/// Checks for the `CLONE_ON_COPY` lint.
+fn lint_clone_on_copy(cx: &LateContext, expr: &Expr, name: &str, args: &[P<Expr>]) {
+    if args.len() == 1 && name == "clone" {
+        let ty = cx.tcx.expr_ty(expr);
+        let parent = cx.tcx.map.get_parent(expr.id);
+        let parameter_environment = ty::ParameterEnvironment::for_item(cx.tcx, parent);
+
+        if !ty.moves_by_default(&parameter_environment, expr.span) {
+            span_lint(cx, CLONE_ON_COPY, expr.span, "using `clone` on a `Copy` type");
+        }
+    }
+}
+
 fn lint_extend(cx: &LateContext, expr: &Expr, args: &MethodArgs) {
     let (obj_ty, _) = walk_ptrs_ty_depth(cx.tcx.expr_ty(&args[0]));
     if !match_type(cx, obj_ty, &VEC_PATH) {
@@ -701,7 +727,7 @@ fn lint_chars_next(cx: &LateContext, expr: &Expr, chain: &Expr, other: &Expr, eq
     false
 }
 
-// Given a `Result<T, E>` type, return its error type (`E`)
+/// Given a `Result<T, E>` type, return its error type (`E`).
 fn get_error_type<'a>(cx: &LateContext, ty: ty::Ty<'a>) -> Option<ty::Ty<'a>> {
     if !match_type(cx, ty, &RESULT_PATH) {
         return None;
@@ -714,9 +740,9 @@ fn get_error_type<'a>(cx: &LateContext, ty: ty::Ty<'a>) -> Option<ty::Ty<'a>> {
     None
 }
 
-// This checks whether a given type is known to implement Debug. It's
-// conservative, i.e. it should not return false positives, but will return
-// false negatives.
+/// This checks whether a given type is known to implement Debug. It's
+/// conservative, i.e. it should not return false positives, but will return
+/// false negatives.
 fn has_debug_impl<'a, 'b>(ty: ty::Ty<'a>, cx: &LateContext<'b, 'a>) -> bool {
     let no_ref_ty = walk_ptrs_ty(ty);
     let debug = match cx.tcx.lang_items.debug_trait() {

src/misc_early.rs

@@ -110,7 +110,7 @@ impl EarlyLintPass for MiscEarly {
                                            arg_name[1..].to_owned()));
                     }
                 } else {
-                    registered_names.insert(arg_name, arg.pat.span.clone());
+                    registered_names.insert(arg_name, arg.pat.span);
                 }
             }
         }

tests/compile-fail/map_clone.rs

@@ -3,7 +3,7 @@
 #![plugin(clippy)]
 #![deny(map_clone)]
 
-#![allow(unused)]
+#![allow(clone_on_copy, unused)]
 
 use std::ops::Deref;
 

tests/compile-fail/methods.rs

@@ -323,3 +323,14 @@ fn use_extend_from_slice() {
     //~| HELP try this
     //~| SUGGESTION v.extend_from_slice(&["But", "this"]);
 }
+
+fn clone_on_copy() {
+    42.clone(); //~ERROR using `clone` on a `Copy` type
+    vec![1].clone(); // ok, not a Copy type
+    Some(vec![1]).clone(); // ok, not a Copy type
+}
+
+fn clone_on_copy_generic<T: Copy>(t: T) {
+    t.clone(); //~ERROR using `clone` on a `Copy` type
+    Some(t).clone(); //~ERROR using `clone` on a `Copy` type
+}