clippy_lints/src/map_clone.rs

   1 use crate::utils::paths;
   2 use crate::utils::{
   3     is_copy, match_trait_method, match_type, remove_blocks, snippet_with_applicability, span_lint_and_sugg,
   4 };
   5 use if_chain::if_chain;
   6 use rustc::declare_lint_pass;
   7 use rustc::hir;
   8 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   9 use rustc::ty;
  10 use rustc_errors::Applicability;
  11 use rustc_session::declare_tool_lint;
  12 use syntax::ast::Ident;
  13 use syntax::source_map::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 match_type(cx, ty, &paths::OPTION) || 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, _) => 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) && !cx.tables.expr_ty(inner).is_box() {
  73                                     lint(cx, e.span, args[0].span, true);
  74                                 }
  75                             },
  76                             hir::ExprKind::MethodCall(ref method, _, ref obj) => {
  77                                 if ident_eq(name, &obj[0]) && method.ident.as_str() == "clone"
  78                                     && match_trait_method(cx, closure_expr, &paths::CLONE_TRAIT) {
  79
  80                                     let obj_ty = cx.tables.expr_ty(&obj[0]);
  81                                     if let ty::Ref(_, ty, _) = obj_ty.kind {
  82                                         let copy = is_copy(cx, ty);
  83                                         lint(cx, e.span, args[0].span, copy);
  84                                     } else {
  85                                         lint_needless_cloning(cx, e.span, args[0].span);
  86                                     }
  87                                 }
  88                             },
  89                             _ => {},
  90                         }
  91                     },
  92                     _ => {},
  93                 }
  94             }
  95         }
  96     }
  97 }
  98
  99 fn ident_eq(name: Ident, path: &hir::Expr) -> bool {
 100     if let hir::ExprKind::Path(hir::QPath::Resolved(None, ref path)) = path.kind {
 101         path.segments.len() == 1 && path.segments[0].ident == name
 102     } else {
 103         false
 104     }
 105 }
 106
 107 fn lint_needless_cloning(cx: &LateContext<'_, '_>, root: Span, receiver: Span) {
 108     span_lint_and_sugg(
 109         cx,
 110         MAP_CLONE,
 111         root.trim_start(receiver).unwrap(),
 112         "You are needlessly cloning iterator elements",
 113         "Remove the map call",
 114         String::new(),
 115         Applicability::MachineApplicable,
 116     )
 117 }
 118
 119 fn lint(cx: &LateContext<'_, '_>, replace: Span, root: Span, copied: bool) {
 120     let mut applicability = Applicability::MachineApplicable;
 121     if copied {
 122         span_lint_and_sugg(
 123             cx,
 124             MAP_CLONE,
 125             replace,
 126             "You are using an explicit closure for copying elements",
 127             "Consider calling the dedicated `copied` method",
 128             format!(
 129                 "{}.copied()",
 130                 snippet_with_applicability(cx, root, "..", &mut applicability)
 131             ),
 132             applicability,
 133         )
 134     } else {
 135         span_lint_and_sugg(
 136             cx,
 137             MAP_CLONE,
 138             replace,
 139             "You are using an explicit closure for cloning elements",
 140             "Consider calling the dedicated `cloned` method",
 141             format!(
 142                 "{}.cloned()",
 143                 snippet_with_applicability(cx, root, "..", &mut applicability)
 144             ),
 145             applicability,
 146         )
 147     }
 148 }