clippy_lints/src/map_clone.rs

   1 use crate::utils::is_trait_method;
   2 use crate::utils::{remove_blocks, snippet_with_applicability, span_lint_and_sugg};
   3 use clippy_utils::ty::{is_copy, is_type_diagnostic_item};
   4 use if_chain::if_chain;
   5 use rustc_errors::Applicability;
   6 use rustc_hir as hir;
   7 use rustc_lint::{LateContext, LateLintPass};
   8 use rustc_middle::mir::Mutability;
   9 use rustc_middle::ty;
  10 use rustc_middle::ty::adjustment::Adjust;
  11 use rustc_session::{declare_lint_pass, declare_tool_lint};
  12 use rustc_span::symbol::Ident;
  13 use rustc_span::{sym, Span};
  14
  15 declare_clippy_lint! {
  16     /// **What it does:** Checks for usage of `map(|x| x.clone())` or
  17     /// dereferencing closures for `Copy` types, on `Iterator` or `Option`,
  18     /// and suggests `cloned()` or `copied()` instead
  19     ///
  20     /// **Why is this bad?** Readability, this can be written more concisely
  21     ///
  22     /// **Known problems:** None
  23     ///
  24     /// **Example:**
  25     ///
  26     /// ```rust
  27     /// let x = vec![42, 43];
  28     /// let y = x.iter();
  29     /// let z = y.map(|i| *i);
  30     /// ```
  31     ///
  32     /// The correct use would be:
  33     ///
  34     /// ```rust
  35     /// let x = vec![42, 43];
  36     /// let y = x.iter();
  37     /// let z = y.cloned();
  38     /// ```
  39     pub MAP_CLONE,
  40     style,
  41     "using `iterator.map(|x| x.clone())`, or dereferencing closures for `Copy` types"
  42 }
  43
  44 declare_lint_pass!(MapClone => [MAP_CLONE]);
  45
  46 impl<'tcx> LateLintPass<'tcx> for MapClone {
  47     fn check_expr(&mut self, cx: &LateContext<'_>, e: &hir::Expr<'_>) {
  48         if e.span.from_expansion() {
  49             return;
  50         }
  51
  52         if_chain! {
  53             if let hir::ExprKind::MethodCall(ref method, _, ref args, _) = e.kind;
  54             if args.len() == 2;
  55             if method.ident.name == sym::map;
  56             let ty = cx.typeck_results().expr_ty(&args[0]);
  57             if is_type_diagnostic_item(cx, ty, sym::option_type) || is_trait_method(cx, e, sym::Iterator);
  58             if let hir::ExprKind::Closure(_, _, body_id, _, _) = args[1].kind;
  59             let closure_body = cx.tcx.hir().body(body_id);
  60             let closure_expr = remove_blocks(&closure_body.value);
  61             then {
  62                 match closure_body.params[0].pat.kind {
  63                     hir::PatKind::Ref(ref inner, hir::Mutability::Not) => if let hir::PatKind::Binding(
  64                         hir::BindingAnnotation::Unannotated, .., name, None
  65                     ) = inner.kind {
  66                         if ident_eq(name, closure_expr) {
  67                             lint(cx, e.span, args[0].span, true);
  68                         }
  69                     },
  70                     hir::PatKind::Binding(hir::BindingAnnotation::Unannotated, .., name, None) => {
  71                         match closure_expr.kind {
  72                             hir::ExprKind::Unary(hir::UnOp::Deref, ref inner) => {
  73                                 if ident_eq(name, inner) {
  74                                     if let ty::Ref(.., Mutability::Not) = cx.typeck_results().expr_ty(inner).kind() {
  75                                         lint(cx, e.span, args[0].span, true);
  76                                     }
  77                                 }
  78                             },
  79                             hir::ExprKind::MethodCall(ref method, _, [obj], _) => if_chain! {
  80                                 if ident_eq(name, obj) && method.ident.name == sym::clone;
  81                                 if let Some(fn_id) = cx.typeck_results().type_dependent_def_id(closure_expr.hir_id);
  82                                 if let Some(trait_id) = cx.tcx.trait_of_item(fn_id);
  83                                 if cx.tcx.lang_items().clone_trait().map_or(false, |id| id == trait_id);
  84                                 // no autoderefs
  85                                 if !cx.typeck_results().expr_adjustments(obj).iter()
  86                                     .any(|a| matches!(a.kind, Adjust::Deref(Some(..))));
  87                                 then {
  88                                     let obj_ty = cx.typeck_results().expr_ty(obj);
  89                                     if let ty::Ref(_, ty, mutability) = obj_ty.kind() {
  90                                         if matches!(mutability, Mutability::Not) {
  91                                             let copy = is_copy(cx, ty);
  92                                             lint(cx, e.span, args[0].span, copy);
  93                                         }
  94                                     } else {
  95                                         lint_needless_cloning(cx, e.span, args[0].span);
  96                                     }
  97                                 }
  98                             },
  99                             _ => {},
 100                         }
 101                     },
 102                     _ => {},
 103                 }
 104             }
 105         }
 106     }
 107 }
 108
 109 fn ident_eq(name: Ident, path: &hir::Expr<'_>) -> bool {
 110     if let hir::ExprKind::Path(hir::QPath::Resolved(None, ref path)) = path.kind {
 111         path.segments.len() == 1 && path.segments[0].ident == name
 112     } else {
 113         false
 114     }
 115 }
 116
 117 fn lint_needless_cloning(cx: &LateContext<'_>, root: Span, receiver: Span) {
 118     span_lint_and_sugg(
 119         cx,
 120         MAP_CLONE,
 121         root.trim_start(receiver).unwrap(),
 122         "you are needlessly cloning iterator elements",
 123         "remove the `map` call",
 124         String::new(),
 125         Applicability::MachineApplicable,
 126     )
 127 }
 128
 129 fn lint(cx: &LateContext<'_>, replace: Span, root: Span, copied: bool) {
 130     let mut applicability = Applicability::MachineApplicable;
 131     if copied {
 132         span_lint_and_sugg(
 133             cx,
 134             MAP_CLONE,
 135             replace,
 136             "you are using an explicit closure for copying elements",
 137             "consider calling the dedicated `copied` method",
 138             format!(
 139                 "{}.copied()",
 140                 snippet_with_applicability(cx, root, "..", &mut applicability)
 141             ),
 142             applicability,
 143         )
 144     } else {
 145         span_lint_and_sugg(
 146             cx,
 147             MAP_CLONE,
 148             replace,
 149             "you are using an explicit closure for cloning elements",
 150             "consider calling the dedicated `cloned` method",
 151             format!(
 152                 "{}.cloned()",
 153                 snippet_with_applicability(cx, root, "..", &mut applicability)
 154             ),
 155             applicability,
 156         )
 157     }
 158 }