clippy_lints/src/map_clone.rs

   1 use crate::utils::paths;
   2 use crate::utils::{
   3     in_macro, 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             if match_type(cx, ty, &paths::OPTION) || match_trait_method(cx, e, &paths::ITERATOR);
  67             if let hir::ExprKind::Closure(_, _, body_id, _, _) = args[1].node;
  68             let closure_body = cx.tcx.hir().body(body_id);
  69             let closure_expr = remove_blocks(&closure_body.value);
  70             then {
  71                 match closure_body.arguments[0].pat.node {
  72                     hir::PatKind::Ref(ref inner, _) => if let hir::PatKind::Binding(
  73                         hir::BindingAnnotation::Unannotated, .., name, None
  74                     ) = inner.node {
  75                         if ident_eq(name, closure_expr) {
  76                             lint(cx, e.span, args[0].span);
  77                         }
  78                     },
  79                     hir::PatKind::Binding(hir::BindingAnnotation::Unannotated, .., name, None) => {
  80                         match closure_expr.node {
  81                             hir::ExprKind::Unary(hir::UnOp::UnDeref, ref inner) => {
  82                                 if ident_eq(name, inner) && !cx.tables.expr_ty(inner).is_box() {
  83                                     lint(cx, e.span, args[0].span);
  84                                 }
  85                             },
  86                             hir::ExprKind::MethodCall(ref method, _, ref obj) => {
  87                                 if ident_eq(name, &obj[0]) && method.ident.as_str() == "clone"
  88                                     && match_trait_method(cx, closure_expr, &paths::CLONE_TRAIT) {
  89
  90                                     let obj_ty = cx.tables.expr_ty(&obj[0]);
  91                                     if let ty::Ref(..) = obj_ty.sty {
  92                                         lint(cx, e.span, args[0].span);
  93                                     } else {
  94                                         lint_needless_cloning(cx, e.span, args[0].span);
  95                                     }
  96                                 }
  97                             },
  98                             _ => {},
  99                         }
 100                     },
 101                     _ => {},
 102                 }
 103             }
 104         }
 105     }
 106 }
 107
 108 fn ident_eq(name: Ident, path: &hir::Expr) -> bool {
 109     if let hir::ExprKind::Path(hir::QPath::Resolved(None, ref path)) = path.node {
 110         path.segments.len() == 1 && path.segments[0].ident == name
 111     } else {
 112         false
 113     }
 114 }
 115
 116 fn lint_needless_cloning(cx: &LateContext<'_, '_>, root: Span, receiver: Span) {
 117     span_lint_and_sugg(
 118         cx,
 119         MAP_CLONE,
 120         root.trim_start(receiver).unwrap(),
 121         "You are needlessly cloning iterator elements",
 122         "Remove the map call",
 123         String::new(),
 124         Applicability::MachineApplicable,
 125     )
 126 }
 127
 128 fn lint(cx: &LateContext<'_, '_>, replace: Span, root: Span) {
 129     let mut applicability = Applicability::MachineApplicable;
 130     span_lint_and_sugg(
 131         cx,
 132         MAP_CLONE,
 133         replace,
 134         "You are using an explicit closure for cloning elements",
 135         "Consider calling the dedicated `cloned` method",
 136         format!(
 137             "{}.cloned()",
 138             snippet_with_applicability(cx, root, "..", &mut applicability)
 139         ),
 140         applicability,
 141     )
 142 }