src/tools/clippy/clippy_lints/src/map_clone.rs

   1 use crate::utils::paths;
   2 use crate::utils::{
   3     is_copy, is_type_diagnostic_item, match_trait_method, remove_blocks, snippet_with_applicability, span_lint_and_sugg,
   4 };
   5 use if_chain::if_chain;
   6 use rustc_errors::Applicability;
   7 use rustc_hir as hir;
   8 use rustc_lint::{LateContext, LateLintPass};
   9 use rustc_middle::mir::Mutability;
  10 use rustc_middle::ty;
  11 use rustc_session::{declare_lint_pass, declare_tool_lint};
  12 use rustc_span::symbol::Ident;
  13 use rustc_span::Span;
  14
  15 declare_clippy_lint! {
  16     /// **What it does:** Checks for usage of `iterator.map(|x| x.clone())` and suggests
  17     /// `iterator.cloned()` instead
  18     ///
  19     /// **Why is this bad?** Readability, this can be written more concisely
  20     ///
  21     /// **Known problems:** None
  22     ///
  23     /// **Example:**
  24     ///
  25     /// ```rust
  26     /// let x = vec![42, 43];
  27     /// let y = x.iter();
  28     /// let z = y.map(|i| *i);
  29     /// ```
  30     ///
  31     /// The correct use would be:
  32     ///
  33     /// ```rust
  34     /// let x = vec![42, 43];
  35     /// let y = x.iter();
  36     /// let z = y.cloned();
  37     /// ```
  38     pub MAP_CLONE,
  39     style,
  40     "using `iterator.map(|x| x.clone())`, or dereferencing closures for `Copy` types"
  41 }
  42
  43 declare_lint_pass!(MapClone => [MAP_CLONE]);
  44
  45 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MapClone {
  46     fn check_expr(&mut self, cx: &LateContext<'_, '_>, e: &hir::Expr<'_>) {
  47         if e.span.from_expansion() {
  48             return;
  49         }
  50
  51         if_chain! {
  52             if let hir::ExprKind::MethodCall(ref method, _, ref args, _) = e.kind;
  53             if args.len() == 2;
  54             if method.ident.as_str() == "map";
  55             let ty = cx.tables().expr_ty(&args[0]);
  56             if is_type_diagnostic_item(cx, ty, sym!(option_type)) || match_trait_method(cx, e, &paths::ITERATOR);
  57             if let hir::ExprKind::Closure(_, _, body_id, _, _) = args[1].kind;
  58             let closure_body = cx.tcx.hir().body(body_id);
  59             let closure_expr = remove_blocks(&closure_body.value);
  60             then {
  61                 match closure_body.params[0].pat.kind {
  62                     hir::PatKind::Ref(ref inner, hir::Mutability::Not) => if let hir::PatKind::Binding(
  63                         hir::BindingAnnotation::Unannotated, .., name, None
  64                     ) = inner.kind {
  65                         if ident_eq(name, closure_expr) {
  66                             lint(cx, e.span, args[0].span, true);
  67                         }
  68                     },
  69                     hir::PatKind::Binding(hir::BindingAnnotation::Unannotated, .., name, None) => {
  70                         match closure_expr.kind {
  71                             hir::ExprKind::Unary(hir::UnOp::UnDeref, ref inner) => {
  72                                 if ident_eq(name, inner) {
  73                                     if let ty::Ref(.., Mutability::Not) = cx.tables().expr_ty(inner).kind {
  74                                         lint(cx, e.span, args[0].span, true);
  75                                     }
  76                                 }
  77                             },
  78                             hir::ExprKind::MethodCall(ref method, _, ref obj, _) => {
  79                                 if ident_eq(name, &obj[0]) && method.ident.as_str() == "clone"
  80                                     && match_trait_method(cx, closure_expr, &paths::CLONE_TRAIT) {
  81
  82                                     let obj_ty = cx.tables().expr_ty(&obj[0]);
  83                                     if let ty::Ref(_, ty, _) = obj_ty.kind {
  84                                         let copy = is_copy(cx, ty);
  85                                         lint(cx, e.span, args[0].span, copy);
  86                                     } else {
  87                                         lint_needless_cloning(cx, e.span, args[0].span);
  88                                     }
  89                                 }
  90                             },
  91                             _ => {},
  92                         }
  93                     },
  94                     _ => {},
  95                 }
  96             }
  97         }
  98     }
  99 }
 100
 101 fn ident_eq(name: Ident, path: &hir::Expr<'_>) -> bool {
 102     if let hir::ExprKind::Path(hir::QPath::Resolved(None, ref path)) = path.kind {
 103         path.segments.len() == 1 && path.segments[0].ident == name
 104     } else {
 105         false
 106     }
 107 }
 108
 109 fn lint_needless_cloning(cx: &LateContext<'_, '_>, root: Span, receiver: Span) {
 110     span_lint_and_sugg(
 111         cx,
 112         MAP_CLONE,
 113         root.trim_start(receiver).unwrap(),
 114         "You are needlessly cloning iterator elements",
 115         "Remove the `map` call",
 116         String::new(),
 117         Applicability::MachineApplicable,
 118     )
 119 }
 120
 121 fn lint(cx: &LateContext<'_, '_>, replace: Span, root: Span, copied: bool) {
 122     let mut applicability = Applicability::MachineApplicable;
 123     if copied {
 124         span_lint_and_sugg(
 125             cx,
 126             MAP_CLONE,
 127             replace,
 128             "You are using an explicit closure for copying elements",
 129             "Consider calling the dedicated `copied` method",
 130             format!(
 131                 "{}.copied()",
 132                 snippet_with_applicability(cx, root, "..", &mut applicability)
 133             ),
 134             applicability,
 135         )
 136     } else {
 137         span_lint_and_sugg(
 138             cx,
 139             MAP_CLONE,
 140             replace,
 141             "You are using an explicit closure for cloning elements",
 142             "Consider calling the dedicated `cloned` method",
 143             format!(
 144                 "{}.cloned()",
 145                 snippet_with_applicability(cx, root, "..", &mut applicability)
 146             ),
 147             applicability,
 148         )
 149     }
 150 }