clippy_lints/src/map_clone.rs

   1 use crate::utils::paths;
   2 use crate::utils::{
   3     in_macro, match_trait_method, match_type, remove_blocks, snippet_with_applicability, span_lint_and_sugg,
   4 };
   5 use if_chain::if_chain;
   6 use rustc::hir;
   7 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   8 use rustc::ty;
   9 use rustc::{declare_tool_lint, lint_array};
  10 use rustc_errors::Applicability;
  11 use syntax::ast::Ident;
  12 use syntax::source_map::Span;
  13
  14 #[derive(Clone)]
  15 pub struct Pass;
  16
  17 /// **What it does:** Checks for usage of `iterator.map(|x| x.clone())` and suggests
  18 /// `iterator.cloned()` 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 declare_clippy_lint! {
  40     pub MAP_CLONE,
  41     style,
  42     "using `iterator.map(|x| x.clone())`, or dereferencing closures for `Copy` types"
  43 }
  44
  45 impl LintPass for Pass {
  46     fn get_lints(&self) -> LintArray {
  47         lint_array!(MAP_CLONE)
  48     }
  49 }
  50
  51 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
  52     fn check_expr(&mut self, cx: &LateContext<'_, '_>, e: &hir::Expr) {
  53         if in_macro(e.span) {
  54             return;
  55         }
  56
  57         if_chain! {
  58             if let hir::ExprKind::MethodCall(ref method, _, ref args) = e.node;
  59             if args.len() == 2;
  60             if method.ident.as_str() == "map";
  61             let ty = cx.tables.expr_ty(&args[0]);
  62             if match_type(cx, ty, &paths::OPTION) || match_trait_method(cx, e, &paths::ITERATOR);
  63             if let hir::ExprKind::Closure(_, _, body_id, _, _) = args[1].node;
  64             let closure_body = cx.tcx.hir().body(body_id);
  65             let closure_expr = remove_blocks(&closure_body.value);
  66             then {
  67                 match closure_body.arguments[0].pat.node {
  68                     hir::PatKind::Ref(ref inner, _) => if let hir::PatKind::Binding(
  69                         hir::BindingAnnotation::Unannotated, _, name, None
  70                     ) = inner.node {
  71                         if ident_eq(name, closure_expr) {
  72                             lint(cx, e.span, args[0].span);
  73                         }
  74                     },
  75                     hir::PatKind::Binding(hir::BindingAnnotation::Unannotated, _, name, None) => {
  76                         match closure_expr.node {
  77                             hir::ExprKind::Unary(hir::UnOp::UnDeref, ref inner) => {
  78                                 if ident_eq(name, inner) && !cx.tables.expr_ty(inner).is_box() {
  79                                     lint(cx, e.span, args[0].span);
  80                                 }
  81                             },
  82                             hir::ExprKind::MethodCall(ref method, _, ref obj) => {
  83                                 if ident_eq(name, &obj[0]) && method.ident.as_str() == "clone"
  84                                     && match_trait_method(cx, closure_expr, &paths::CLONE_TRAIT) {
  85
  86                                     let obj_ty = cx.tables.expr_ty(&obj[0]);
  87                                     if let ty::Ref(..) = obj_ty.sty {
  88                                         lint(cx, e.span, args[0].span);
  89                                     } else {
  90                                         lint_needless_cloning(cx, e.span, args[0].span);
  91                                     }
  92                                 }
  93                             },
  94                             _ => {},
  95                         }
  96                     },
  97                     _ => {},
  98                 }
  99             }
 100         }
 101     }
 102 }
 103
 104 fn ident_eq(name: Ident, path: &hir::Expr) -> bool {
 105     if let hir::ExprKind::Path(hir::QPath::Resolved(None, ref path)) = path.node {
 106         path.segments.len() == 1 && path.segments[0].ident == name
 107     } else {
 108         false
 109     }
 110 }
 111
 112 fn lint_needless_cloning(cx: &LateContext<'_, '_>, root: Span, receiver: Span) {
 113     span_lint_and_sugg(
 114         cx,
 115         MAP_CLONE,
 116         root.trim_start(receiver).unwrap(),
 117         "You are needlessly cloning iterator elements",
 118         "Remove the map call",
 119         String::new(),
 120         Applicability::MachineApplicable,
 121     )
 122 }
 123
 124 fn lint(cx: &LateContext<'_, '_>, replace: Span, root: Span) {
 125     let mut applicability = Applicability::MachineApplicable;
 126     span_lint_and_sugg(
 127         cx,
 128         MAP_CLONE,
 129         replace,
 130         "You are using an explicit closure for cloning elements",
 131         "Consider calling the dedicated `cloned` method",
 132         format!(
 133             "{}.cloned()",
 134             snippet_with_applicability(cx, root, "..", &mut applicability)
 135         ),
 136         applicability,
 137     )
 138 }