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_middle::ty::adjustment::Adjust;
  12 use rustc_session::{declare_lint_pass, declare_tool_lint};
  13 use rustc_span::symbol::Ident;
  14 use rustc_span::{sym, Span};
  15
  16 declare_clippy_lint! {
  17     /// **What it does:** Checks for usage of `map(|x| x.clone())` or
  18     /// dereferencing closures for `Copy` types, on `Iterator` or `Option`,
  19     /// and suggests `cloned()` or `copied()` 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 declare_lint_pass!(MapClone => [MAP_CLONE]);
  46
  47 impl<'tcx> LateLintPass<'tcx> for MapClone {
  48     fn check_expr(&mut self, cx: &LateContext<'_>, e: &hir::Expr<'_>) {
  49         if e.span.from_expansion() {
  50             return;
  51         }
  52
  53         if_chain! {
  54             if let hir::ExprKind::MethodCall(ref method, _, ref args, _) = e.kind;
  55             if args.len() == 2;
  56             if method.ident.name == sym::map;
  57             let ty = cx.typeck_results().expr_ty(&args[0]);
  58             if is_type_diagnostic_item(cx, ty, sym::option_type) || match_trait_method(cx, e, &paths::ITERATOR);
  59             if let hir::ExprKind::Closure(_, _, body_id, _, _) = args[1].kind;
  60             let closure_body = cx.tcx.hir().body(body_id);
  61             let closure_expr = remove_blocks(&closure_body.value);
  62             then {
  63                 match closure_body.params[0].pat.kind {
  64                     hir::PatKind::Ref(ref inner, hir::Mutability::Not) => if let hir::PatKind::Binding(
  65                         hir::BindingAnnotation::Unannotated, .., name, None
  66                     ) = inner.kind {
  67                         if ident_eq(name, closure_expr) {
  68                             lint(cx, e.span, args[0].span, true);
  69                         }
  70                     },
  71                     hir::PatKind::Binding(hir::BindingAnnotation::Unannotated, .., name, None) => {
  72                         match closure_expr.kind {
  73                             hir::ExprKind::Unary(hir::UnOp::Deref, ref inner) => {
  74                                 if ident_eq(name, inner) {
  75                                     if let ty::Ref(.., Mutability::Not) = cx.typeck_results().expr_ty(inner).kind() {
  76                                         lint(cx, e.span, args[0].span, true);
  77                                     }
  78                                 }
  79                             },
  80                             hir::ExprKind::MethodCall(ref method, _, [obj], _) => if_chain! {
  81                                 if ident_eq(name, obj) && method.ident.name == sym::clone;
  82                                 if match_trait_method(cx, closure_expr, &paths::CLONE_TRAIT);
  83                                 // no autoderefs
  84                                 if !cx.typeck_results().expr_adjustments(obj).iter()
  85                                     .any(|a| matches!(a.kind, Adjust::Deref(Some(..))));
  86                                 then {
  87                                     let obj_ty = cx.typeck_results().expr_ty(obj);
  88                                     if let ty::Ref(_, ty, mutability) = obj_ty.kind() {
  89                                         if matches!(mutability, Mutability::Not) {
  90                                             let copy = is_copy(cx, ty);
  91                                             lint(cx, e.span, args[0].span, copy);
  92                                         }
  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.kind {
 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, copied: bool) {
 129     let mut applicability = Applicability::MachineApplicable;
 130     if copied {
 131         span_lint_and_sugg(
 132             cx,
 133             MAP_CLONE,
 134             replace,
 135             "you are using an explicit closure for copying elements",
 136             "consider calling the dedicated `copied` method",
 137             format!(
 138                 "{}.copied()",
 139                 snippet_with_applicability(cx, root, "..", &mut applicability)
 140             ),
 141             applicability,
 142         )
 143     } else {
 144         span_lint_and_sugg(
 145             cx,
 146             MAP_CLONE,
 147             replace,
 148             "you are using an explicit closure for cloning elements",
 149             "consider calling the dedicated `cloned` method",
 150             format!(
 151                 "{}.cloned()",
 152                 snippet_with_applicability(cx, root, "..", &mut applicability)
 153             ),
 154             applicability,
 155         )
 156     }
 157 }