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

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::is_trait_method;
   3 use clippy_utils::remove_blocks;
   4 use clippy_utils::source::snippet_with_applicability;
   5 use clippy_utils::ty::{is_copy, is_type_diagnostic_item};
   6 use if_chain::if_chain;
   7 use rustc_errors::Applicability;
   8 use rustc_hir as hir;
   9 use rustc_lint::{LateContext, LateLintPass};
  10 use rustc_middle::mir::Mutability;
  11 use rustc_middle::ty;
  12 use rustc_middle::ty::adjustment::Adjust;
  13 use rustc_session::{declare_lint_pass, declare_tool_lint};
  14 use rustc_span::symbol::Ident;
  15 use rustc_span::{sym, Span};
  16
  17 declare_clippy_lint! {
  18     /// ### What it does
  19     /// Checks for usage of `map(|x| x.clone())` or
  20     /// dereferencing closures for `Copy` types, on `Iterator` or `Option`,
  21     /// and suggests `cloned()` or `copied()` instead
  22     ///
  23     /// ### Why is this bad?
  24     /// Readability, this can be written more concisely
  25     ///
  26     /// ### Example
  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     #[clippy::version = "pre 1.29.0"]
  41     pub MAP_CLONE,
  42     style,
  43     "using `iterator.map(|x| x.clone())`, or dereferencing closures for `Copy` types"
  44 }
  45
  46 declare_lint_pass!(MapClone => [MAP_CLONE]);
  47
  48 impl<'tcx> LateLintPass<'tcx> for MapClone {
  49     fn check_expr(&mut self, cx: &LateContext<'_>, e: &hir::Expr<'_>) {
  50         if e.span.from_expansion() {
  51             return;
  52         }
  53
  54         if_chain! {
  55             if let hir::ExprKind::MethodCall(method, _, args, _) = e.kind;
  56             if args.len() == 2;
  57             if method.ident.name == sym::map;
  58             let ty = cx.typeck_results().expr_ty(&args[0]);
  59             if is_type_diagnostic_item(cx, ty, sym::Option) || is_trait_method(cx, e, sym::Iterator);
  60             if let hir::ExprKind::Closure(_, _, body_id, _, _) = args[1].kind;
  61             then {
  62                 let closure_body = cx.tcx.hir().body(body_id);
  63                 let closure_expr = remove_blocks(&closure_body.value);
  64                 match closure_body.params[0].pat.kind {
  65                     hir::PatKind::Ref(inner, hir::Mutability::Not) => if let hir::PatKind::Binding(
  66                         hir::BindingAnnotation::Unannotated, .., name, None
  67                     ) = inner.kind {
  68                         if ident_eq(name, closure_expr) {
  69                             lint(cx, e.span, args[0].span, true);
  70                         }
  71                     },
  72                     hir::PatKind::Binding(hir::BindingAnnotation::Unannotated, .., name, None) => {
  73                         match closure_expr.kind {
  74                             hir::ExprKind::Unary(hir::UnOp::Deref, inner) => {
  75                                 if ident_eq(name, inner) {
  76                                     if let ty::Ref(.., Mutability::Not) = cx.typeck_results().expr_ty(inner).kind() {
  77                                         lint(cx, e.span, args[0].span, true);
  78                                     }
  79                                 }
  80                             },
  81                             hir::ExprKind::MethodCall(method, _, [obj], _) => if_chain! {
  82                                 if ident_eq(name, obj) && method.ident.name == sym::clone;
  83                                 if let Some(fn_id) = cx.typeck_results().type_dependent_def_id(closure_expr.hir_id);
  84                                 if let Some(trait_id) = cx.tcx.trait_of_item(fn_id);
  85                                 if cx.tcx.lang_items().clone_trait().map_or(false, |id| id == trait_id);
  86                                 // no autoderefs
  87                                 if !cx.typeck_results().expr_adjustments(obj).iter()
  88                                     .any(|a| matches!(a.kind, Adjust::Deref(Some(..))));
  89                                 then {
  90                                     let obj_ty = cx.typeck_results().expr_ty(obj);
  91                                     if let ty::Ref(_, ty, mutability) = obj_ty.kind() {
  92                                         if matches!(mutability, Mutability::Not) {
  93                                             let copy = is_copy(cx, ty);
  94                                             lint(cx, e.span, args[0].span, copy);
  95                                         }
  96                                     } else {
  97                                         lint_needless_cloning(cx, e.span, args[0].span);
  98                                     }
  99                                 }
 100                             },
 101                             _ => {},
 102                         }
 103                     },
 104                     _ => {},
 105                 }
 106             }
 107         }
 108     }
 109 }
 110
 111 fn ident_eq(name: Ident, path: &hir::Expr<'_>) -> bool {
 112     if let hir::ExprKind::Path(hir::QPath::Resolved(None, path)) = path.kind {
 113         path.segments.len() == 1 && path.segments[0].ident == name
 114     } else {
 115         false
 116     }
 117 }
 118
 119 fn lint_needless_cloning(cx: &LateContext<'_>, root: Span, receiver: Span) {
 120     span_lint_and_sugg(
 121         cx,
 122         MAP_CLONE,
 123         root.trim_start(receiver).unwrap(),
 124         "you are needlessly cloning iterator elements",
 125         "remove the `map` call",
 126         String::new(),
 127         Applicability::MachineApplicable,
 128     );
 129 }
 130
 131 fn lint(cx: &LateContext<'_>, replace: Span, root: Span, copied: bool) {
 132     let mut applicability = Applicability::MachineApplicable;
 133     if copied {
 134         span_lint_and_sugg(
 135             cx,
 136             MAP_CLONE,
 137             replace,
 138             "you are using an explicit closure for copying elements",
 139             "consider calling the dedicated `copied` method",
 140             format!(
 141                 "{}.copied()",
 142                 snippet_with_applicability(cx, root, "..", &mut applicability)
 143             ),
 144             applicability,
 145         );
 146     } else {
 147         span_lint_and_sugg(
 148             cx,
 149             MAP_CLONE,
 150             replace,
 151             "you are using an explicit closure for cloning elements",
 152             "consider calling the dedicated `cloned` method",
 153             format!(
 154                 "{}.cloned()",
 155                 snippet_with_applicability(cx, root, "..", &mut applicability)
 156             ),
 157             applicability,
 158         );
 159     }
 160 }