clippy_lints/src/map_clone.rs

   1 use rustc::lint::*;
   2 use rustc::hir::*;
   3 use rustc::ty;
   4 use syntax::ast;
   5 use utils::{get_arg_name, is_adjusted, iter_input_pats, match_qpath, match_trait_method, match_type,
   6             paths, remove_blocks, snippet, span_help_and_lint, walk_ptrs_ty, walk_ptrs_ty_depth};
   7
   8 /// **What it does:** Checks for mapping `clone()` over an iterator.
   9 ///
  10 /// **Why is this bad?** It makes the code less readable than using the
  11 /// `.cloned()` adapter.
  12 ///
  13 /// **Known problems:** Sometimes `.cloned()` requires stricter trait
  14 /// bound than `.map(|e| e.clone())` (which works because of the coercion).
  15 /// See [#498](https://github.com/rust-lang-nursery/rust-clippy/issues/498).
  16 ///
  17 /// **Example:**
  18 /// ```rust
  19 /// x.map(|e| e.clone());
  20 /// ```
  21 declare_clippy_lint! {
  22     pub MAP_CLONE,
  23     style,
  24     "using `.map(|x| x.clone())` to clone an iterator or option's contents"
  25 }
  26
  27 #[derive(Copy, Clone)]
  28 pub struct Pass;
  29
  30 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
  31     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  32         // call to .map()
  33         if let ExprMethodCall(ref method, _, ref args) = expr.node {
  34             if method.name == "map" && args.len() == 2 {
  35                 match args[1].node {
  36                     ExprClosure(_, ref decl, closure_eid, _, _) => {
  37                         let body = cx.tcx.hir.body(closure_eid);
  38                         let closure_expr = remove_blocks(&body.value);
  39                         let ty = cx.tables.pat_ty(&body.arguments[0].pat);
  40                         if_chain! {
  41                             // nothing special in the argument, besides reference bindings
  42                             // (e.g. .map(|&x| x) )
  43                             if let Some(first_arg) = iter_input_pats(decl, body).next();
  44                             if let Some(arg_ident) = get_arg_name(&first_arg.pat);
  45                             // the method is being called on a known type (option or iterator)
  46                             if let Some(type_name) = get_type_name(cx, expr, &args[0]);
  47                             then {
  48                                 // look for derefs, for .map(|x| *x)
  49                                 if only_derefs(cx, &*closure_expr, arg_ident) &&
  50                                     // .cloned() only removes one level of indirection, don't lint on more
  51                                     walk_ptrs_ty_depth(cx.tables.pat_ty(&first_arg.pat)).1 == 1
  52                                 {
  53                                     // the argument is not an &mut T
  54                                     if let ty::TyRef(_, _, mutbl) = ty.sty {
  55                                         if mutbl == MutImmutable {
  56                                             span_help_and_lint(cx, MAP_CLONE, expr.span, &format!(
  57                                                 "you seem to be using .map() to clone the contents of an {}, consider \
  58                                                 using `.cloned()`", type_name),
  59                                                 &format!("try\n{}.cloned()", snippet(cx, args[0].span, "..")));
  60                                         }
  61                                     }
  62                                 }
  63                                 // explicit clone() calls ( .map(|x| x.clone()) )
  64                                 else if let ExprMethodCall(ref clone_call, _, ref clone_args) = closure_expr.node {
  65                                     if clone_call.name == "clone" &&
  66                                         clone_args.len() == 1 &&
  67                                         match_trait_method(cx, closure_expr, &paths::CLONE_TRAIT) &&
  68                                         expr_eq_name(&clone_args[0], arg_ident)
  69                                     {
  70                                         span_help_and_lint(cx, MAP_CLONE, expr.span, &format!(
  71                                             "you seem to be using .map() to clone the contents of an {}, consider \
  72                                             using `.cloned()`", type_name),
  73                                             &format!("try\n{}.cloned()", snippet(cx, args[0].span, "..")));
  74                                     }
  75                                 }
  76                             }
  77                         }
  78                     },
  79                     ExprPath(ref path) => if match_qpath(path, &paths::CLONE) {
  80                         let type_name = get_type_name(cx, expr, &args[0]).unwrap_or("_");
  81                         span_help_and_lint(
  82                             cx,
  83                             MAP_CLONE,
  84                             expr.span,
  85                             &format!(
  86                                 "you seem to be using .map() to clone the contents of an \
  87                                  {}, consider using `.cloned()`",
  88                                 type_name
  89                             ),
  90                             &format!("try\n{}.cloned()", snippet(cx, args[0].span, "..")),
  91                         );
  92                     },
  93                     _ => (),
  94                 }
  95             }
  96         }
  97     }
  98 }
  99
 100 fn expr_eq_name(expr: &Expr, id: ast::Name) -> bool {
 101     match expr.node {
 102         ExprPath(QPath::Resolved(None, ref path)) => {
 103             let arg_segment = [
 104                 PathSegment {
 105                     name: id,
 106                     parameters: None,
 107                     infer_types: true,
 108                 },
 109             ];
 110             !path.is_global() && path.segments[..] == arg_segment
 111         },
 112         _ => false,
 113     }
 114 }
 115
 116 fn get_type_name(cx: &LateContext, expr: &Expr, arg: &Expr) -> Option<&'static str> {
 117     if match_trait_method(cx, expr, &paths::ITERATOR) {
 118         Some("iterator")
 119     } else if match_type(cx, walk_ptrs_ty(cx.tables.expr_ty(arg)), &paths::OPTION) {
 120         Some("Option")
 121     } else {
 122         None
 123     }
 124 }
 125
 126 fn only_derefs(cx: &LateContext, expr: &Expr, id: ast::Name) -> bool {
 127     match expr.node {
 128         ExprUnary(UnDeref, ref subexpr) if !is_adjusted(cx, subexpr) => only_derefs(cx, subexpr, id),
 129         _ => expr_eq_name(expr, id),
 130     }
 131 }
 132
 133 impl LintPass for Pass {
 134     fn get_lints(&self) -> LintArray {
 135         lint_array!(MAP_CLONE)
 136     }
 137 }