clippy_lints/src/map_clone.rs

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