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

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::source::snippet_with_applicability;
   3 use clippy_utils::ty::{is_copy, is_type_diagnostic_item};
   4 use clippy_utils::{is_trait_method, meets_msrv, msrvs, peel_blocks};
   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_semver::RustcVersion;
  13 use rustc_session::{declare_tool_lint, impl_lint_pass};
  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 pub struct MapClone {
  47     msrv: Option<RustcVersion>,
  48 }
  49
  50 impl_lint_pass!(MapClone => [MAP_CLONE]);
  51
  52 impl MapClone {
  53     pub fn new(msrv: Option<RustcVersion>) -> Self {
  54         Self { msrv }
  55     }
  56 }
  57
  58 impl<'tcx> LateLintPass<'tcx> for MapClone {
  59     fn check_expr(&mut self, cx: &LateContext<'_>, e: &hir::Expr<'_>) {
  60         if e.span.from_expansion() {
  61             return;
  62         }
  63
  64         if_chain! {
  65             if let hir::ExprKind::MethodCall(method, args, _) = e.kind;
  66             if args.len() == 2;
  67             if method.ident.name == sym::map;
  68             let ty = cx.typeck_results().expr_ty(&args[0]);
  69             if is_type_diagnostic_item(cx, ty, sym::Option) || is_trait_method(cx, e, sym::Iterator);
  70             if let hir::ExprKind::Closure(_, _, body_id, _, _) = args[1].kind;
  71             then {
  72                 let closure_body = cx.tcx.hir().body(body_id);
  73                 let closure_expr = peel_blocks(&closure_body.value);
  74                 match closure_body.params[0].pat.kind {
  75                     hir::PatKind::Ref(inner, hir::Mutability::Not) => if let hir::PatKind::Binding(
  76                         hir::BindingAnnotation::Unannotated, .., name, None
  77                     ) = inner.kind {
  78                         if ident_eq(name, closure_expr) {
  79                             self.lint_explicit_closure(cx, e.span, args[0].span, true);
  80                         }
  81                     },
  82                     hir::PatKind::Binding(hir::BindingAnnotation::Unannotated, .., name, None) => {
  83                         match closure_expr.kind {
  84                             hir::ExprKind::Unary(hir::UnOp::Deref, inner) => {
  85                                 if ident_eq(name, inner) {
  86                                     if let ty::Ref(.., Mutability::Not) = cx.typeck_results().expr_ty(inner).kind() {
  87                                         self.lint_explicit_closure(cx, e.span, args[0].span, true);
  88                                     }
  89                                 }
  90                             },
  91                             hir::ExprKind::MethodCall(method, [obj], _) => if_chain! {
  92                                 if ident_eq(name, obj) && method.ident.name == sym::clone;
  93                                 if let Some(fn_id) = cx.typeck_results().type_dependent_def_id(closure_expr.hir_id);
  94                                 if let Some(trait_id) = cx.tcx.trait_of_item(fn_id);
  95                                 if cx.tcx.lang_items().clone_trait().map_or(false, |id| id == trait_id);
  96                                 // no autoderefs
  97                                 if !cx.typeck_results().expr_adjustments(obj).iter()
  98                                     .any(|a| matches!(a.kind, Adjust::Deref(Some(..))));
  99                                 then {
 100                                     let obj_ty = cx.typeck_results().expr_ty(obj);
 101                                     if let ty::Ref(_, ty, mutability) = obj_ty.kind() {
 102                                         if matches!(mutability, Mutability::Not) {
 103                                             let copy = is_copy(cx, *ty);
 104                                             self.lint_explicit_closure(cx, e.span, args[0].span, copy);
 105                                         }
 106                                     } else {
 107                                         lint_needless_cloning(cx, e.span, args[0].span);
 108                                     }
 109                                 }
 110                             },
 111                             _ => {},
 112                         }
 113                     },
 114                     _ => {},
 115                 }
 116             }
 117         }
 118     }
 119
 120     extract_msrv_attr!(LateContext);
 121 }
 122
 123 fn ident_eq(name: Ident, path: &hir::Expr<'_>) -> bool {
 124     if let hir::ExprKind::Path(hir::QPath::Resolved(None, path)) = path.kind {
 125         path.segments.len() == 1 && path.segments[0].ident == name
 126     } else {
 127         false
 128     }
 129 }
 130
 131 fn lint_needless_cloning(cx: &LateContext<'_>, root: Span, receiver: Span) {
 132     span_lint_and_sugg(
 133         cx,
 134         MAP_CLONE,
 135         root.trim_start(receiver).unwrap(),
 136         "you are needlessly cloning iterator elements",
 137         "remove the `map` call",
 138         String::new(),
 139         Applicability::MachineApplicable,
 140     );
 141 }
 142
 143 impl MapClone {
 144     fn lint_explicit_closure(&self, cx: &LateContext<'_>, replace: Span, root: Span, is_copy: bool) {
 145         let mut applicability = Applicability::MachineApplicable;
 146         let message = if is_copy {
 147             "you are using an explicit closure for copying elements"
 148         } else {
 149             "you are using an explicit closure for cloning elements"
 150         };
 151         let sugg_method = if is_copy && meets_msrv(self.msrv.as_ref(), &msrvs::ITERATOR_COPIED) {
 152             "copied"
 153         } else {
 154             "cloned"
 155         };
 156
 157         span_lint_and_sugg(
 158             cx,
 159             MAP_CLONE,
 160             replace,
 161             message,
 162             &format!("consider calling the dedicated `{}` method", sugg_method),
 163             format!(
 164                 "{}.{}()",
 165                 snippet_with_applicability(cx, root, "..", &mut applicability),
 166                 sugg_method,
 167             ),
 168             applicability,
 169         );
 170     }
 171 }