clippy_lints/src/map_clone.rs

   1 use crate::utils::paths;
   2 use crate::utils::{
   3     in_macro, is_copy, match_trait_method, match_type, remove_blocks, snippet_with_applicability, span_lint_and_sugg,
   4 };
   5 use if_chain::if_chain;
   6 use rustc::hir;
   7 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   8 use rustc::ty;
   9 use rustc::{declare_tool_lint, lint_array};
  10 use rustc_errors::Applicability;
  11 use syntax::ast::Ident;
  12 use syntax::source_map::Span;
  13
  14 #[derive(Clone)]
  15 pub struct Pass;
  16
  17 declare_clippy_lint! {
  18     /// **What it does:** Checks for usage of `iterator.map(|x| x.clone())` and suggests
  19     /// `iterator.cloned()` instead
  20     ///
  21     /// **Why is this bad?** Readability, this can be written more concisely
  22     ///
  23     /// **Known problems:** None
  24     ///
  25     /// **Example:**
  26     ///
  27     /// ```rust
  28     /// let x = vec![42, 43];
  29     /// let y = x.iter();
  30     /// let z = y.map(|i| *i);
  31     /// ```
  32     ///
  33     /// The correct use would be:
  34     ///
  35     /// ```rust
  36     /// let x = vec![42, 43];
  37     /// let y = x.iter();
  38     /// let z = y.cloned();
  39     /// ```
  40     pub MAP_CLONE,
  41     style,
  42     "using `iterator.map(|x| x.clone())`, or dereferencing closures for `Copy` types"
  43 }
  44
  45 impl LintPass for Pass {
  46     fn get_lints(&self) -> LintArray {
  47         lint_array!(MAP_CLONE)
  48     }
  49
  50     fn name(&self) -> &'static str {
  51         "MapClone"
  52     }
  53 }
  54
  55 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
  56     fn check_expr(&mut self, cx: &LateContext<'_, '_>, e: &hir::Expr) {
  57         if in_macro(e.span) {
  58             return;
  59         }
  60
  61         if_chain! {
  62             if let hir::ExprKind::MethodCall(ref method, _, ref args) = e.node;
  63             if args.len() == 2;
  64             if method.ident.as_str() == "map";
  65             let ty = cx.tables.expr_ty(&args[0]);
  66             let is_option = match_type(cx, ty, &paths::OPTION);
  67             if is_option || match_trait_method(cx, e, &paths::ITERATOR);
  68             if let hir::ExprKind::Closure(_, _, body_id, _, _) = args[1].node;
  69             let closure_body = cx.tcx.hir().body(body_id);
  70             let closure_expr = remove_blocks(&closure_body.value);
  71             then {
  72                 match closure_body.arguments[0].pat.node {
  73                     hir::PatKind::Ref(ref inner, _) => if let hir::PatKind::Binding(
  74                         hir::BindingAnnotation::Unannotated, .., name, None
  75                     ) = inner.node {
  76                         if ident_eq(name, closure_expr) {
  77                             // FIXME When Iterator::copied() stabilizes we can remove is_option
  78                             // from here and the other lint() calls
  79                             lint(cx, e.span, args[0].span, is_option);
  80                         }
  81                     },
  82                     hir::PatKind::Binding(hir::BindingAnnotation::Unannotated, .., name, None) => {
  83                         match closure_expr.node {
  84                             hir::ExprKind::Unary(hir::UnOp::UnDeref, ref inner) => {
  85                                 if ident_eq(name, inner) && !cx.tables.expr_ty(inner).is_box() {
  86                                     lint(cx, e.span, args[0].span, is_option);
  87                                 }
  88                             },
  89                             hir::ExprKind::MethodCall(ref method, _, ref obj) => {
  90                                 if ident_eq(name, &obj[0]) && method.ident.as_str() == "clone"
  91                                     && match_trait_method(cx, closure_expr, &paths::CLONE_TRAIT) {
  92
  93                                     let obj_ty = cx.tables.expr_ty(&obj[0]);
  94                                     if let ty::Ref(_, ty, _) = obj_ty.sty {
  95                                         let copy = is_copy(cx, ty);
  96                                         lint(cx, e.span, args[0].span, is_option && copy);
  97                                     } else {
  98                                         lint_needless_cloning(cx, e.span, args[0].span);
  99                                     }
 100                                 }
 101                             },
 102                             _ => {},
 103                         }
 104                     },
 105                     _ => {},
 106                 }
 107             }
 108         }
 109     }
 110 }
 111
 112 fn ident_eq(name: Ident, path: &hir::Expr) -> bool {
 113     if let hir::ExprKind::Path(hir::QPath::Resolved(None, ref path)) = path.node {
 114         path.segments.len() == 1 && path.segments[0].ident == name
 115     } else {
 116         false
 117     }
 118 }
 119
 120 fn lint_needless_cloning(cx: &LateContext<'_, '_>, root: Span, receiver: Span) {
 121     span_lint_and_sugg(
 122         cx,
 123         MAP_CLONE,
 124         root.trim_start(receiver).unwrap(),
 125         "You are needlessly cloning iterator elements",
 126         "Remove the map call",
 127         String::new(),
 128         Applicability::MachineApplicable,
 129     )
 130 }
 131
 132 fn lint(cx: &LateContext<'_, '_>, replace: Span, root: Span, copied: bool) {
 133     let mut applicability = Applicability::MachineApplicable;
 134     if copied {
 135         span_lint_and_sugg(
 136             cx,
 137             MAP_CLONE,
 138             replace,
 139             "You are using an explicit closure for copying elements",
 140             "Consider calling the dedicated `copied` method",
 141             format!(
 142                 "{}.copied()",
 143                 snippet_with_applicability(cx, root, "..", &mut applicability)
 144             ),
 145             applicability,
 146         )
 147     } else {
 148         span_lint_and_sugg(
 149             cx,
 150             MAP_CLONE,
 151             replace,
 152             "You are using an explicit closure for cloning elements",
 153             "Consider calling the dedicated `cloned` method",
 154             format!(
 155                 "{}.cloned()",
 156                 snippet_with_applicability(cx, root, "..", &mut applicability)
 157             ),
 158             applicability,
 159         )
 160     }
 161 }