clippy_lints/src/map_clone.rs

   1 use rustc::lint::*;
   2 use rustc::hir::*;
   3 use rustc::ty;
   4 use syntax::ast;
   5 use crate::utils::{get_arg_ident, 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, SpanlessEq};
   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.ident.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                         if_chain! {
  40                             // nothing special in the argument, besides reference bindings
  41                             // (e.g. .map(|&x| x) )
  42                             if let Some(first_arg) = iter_input_pats(decl, body).next();
  43                             if let Some(arg_ident) = get_arg_ident(&first_arg.pat);
  44                             // the method is being called on a known type (option or iterator)
  45                             if let Some(type_name) = get_type_name(cx, expr, &args[0]);
  46                             then {
  47                                 // We know that body.arguments is not empty at this point
  48                                 let ty = cx.tables.pat_ty(&body.arguments[0].pat);
  49                                 // look for derefs, for .map(|x| *x)
  50                                 if only_derefs(cx, &*closure_expr, arg_ident) &&
  51                                     // .cloned() only removes one level of indirection, don't lint on more
  52                                     walk_ptrs_ty_depth(cx.tables.pat_ty(&first_arg.pat)).1 == 1
  53                                 {
  54                                     // the argument is not an &mut T
  55                                     if let ty::TyRef(_, _, mutbl) = ty.sty {
  56                                         if mutbl == MutImmutable {
  57                                             span_help_and_lint(cx, MAP_CLONE, expr.span, &format!(
  58                                                 "you seem to be using .map() to clone the contents of an {}, consider \
  59                                                 using `.cloned()`", type_name),
  60                                                 &format!("try\n{}.cloned()", snippet(cx, args[0].span, "..")));
  61                                         }
  62                                     }
  63                                 }
  64                                 // explicit clone() calls ( .map(|x| x.clone()) )
  65                                 else if let ExprMethodCall(ref clone_call, _, ref clone_args) = closure_expr.node {
  66                                     if clone_call.ident.name == "clone" &&
  67                                         clone_args.len() == 1 &&
  68                                         match_trait_method(cx, closure_expr, &paths::CLONE_TRAIT) &&
  69                                         expr_eq_name(cx, &clone_args[0], arg_ident)
  70                                     {
  71                                         span_help_and_lint(cx, MAP_CLONE, expr.span, &format!(
  72                                             "you seem to be using .map() to clone the contents of an {}, consider \
  73                                             using `.cloned()`", type_name),
  74                                             &format!("try\n{}.cloned()", snippet(cx, args[0].span, "..")));
  75                                     }
  76                                 }
  77                             }
  78                         }
  79                     },
  80                     ExprPath(ref path) => if match_qpath(path, &paths::CLONE) {
  81                         let type_name = get_type_name(cx, expr, &args[0]).unwrap_or("_");
  82                         span_help_and_lint(
  83                             cx,
  84                             MAP_CLONE,
  85                             expr.span,
  86                             &format!(
  87                                 "you seem to be using .map() to clone the contents of an \
  88                                  {}, consider using `.cloned()`",
  89                                 type_name
  90                             ),
  91                             &format!("try\n{}.cloned()", snippet(cx, args[0].span, "..")),
  92                         );
  93                     },
  94                     _ => (),
  95                 }
  96             }
  97         }
  98     }
  99 }
 100
 101 fn expr_eq_name(cx: &LateContext, expr: &Expr, id: ast::Ident) -> bool {
 102     match expr.node {
 103         ExprPath(QPath::Resolved(None, ref path)) => {
 104             let arg_segment = [
 105                 PathSegment {
 106                     ident: id,
 107                     args: None,
 108                     infer_types: true,
 109                 },
 110             ];
 111             !path.is_global() && SpanlessEq::new(cx).eq_path_segments(&path.segments[..], &arg_segment)
 112         },
 113         _ => false,
 114     }
 115 }
 116
 117 fn get_type_name(cx: &LateContext, expr: &Expr, arg: &Expr) -> Option<&'static str> {
 118     if match_trait_method(cx, expr, &paths::ITERATOR) {
 119         Some("iterator")
 120     } else if match_type(cx, walk_ptrs_ty(cx.tables.expr_ty(arg)), &paths::OPTION) {
 121         Some("Option")
 122     } else {
 123         None
 124     }
 125 }
 126
 127 fn only_derefs(cx: &LateContext, expr: &Expr, id: ast::Ident) -> bool {
 128     match expr.node {
 129         ExprUnary(UnDeref, ref subexpr) if !is_adjusted(cx, subexpr) => only_derefs(cx, subexpr, id),
 130         _ => expr_eq_name(cx, expr, id),
 131     }
 132 }
 133
 134 impl LintPass for Pass {
 135     fn get_lints(&self) -> LintArray {
 136         lint_array!(MAP_CLONE)
 137     }
 138 }