clippy_lints/src/map_clone.rs

   1 use crate::rustc::hir;
   2 use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   3 use crate::rustc::{declare_tool_lint, lint_array};
   4 use crate::syntax::source_map::Span;
   5 use crate::utils::paths;
   6 use crate::utils::{
   7     in_macro, match_trait_method, match_type,
   8     remove_blocks, snippet,
   9     span_lint_and_sugg,
  10 };
  11 use if_chain::if_chain;
  12 use crate::syntax::ast::Ident;
  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(hir::BindingAnnotation::Unannotated, _, name, None) = inner.node {
  69                         lint(cx, e.span, args[0].span, name, closure_expr);
  70                     },
  71                     hir::PatKind::Binding(hir::BindingAnnotation::Unannotated, _, name, None) => match closure_expr.node {
  72                         hir::ExprKind::Unary(hir::UnOp::UnDeref, ref inner) => lint(cx, e.span, args[0].span, name, inner),
  73                         hir::ExprKind::MethodCall(ref method, _, ref obj) => if method.ident.as_str() == "clone" && match_trait_method(cx, closure_expr, &paths::CLONE_TRAIT) {
  74                             lint(cx, e.span, args[0].span, name, &obj[0]);
  75                         }
  76                         _ => {},
  77                     },
  78                     _ => {},
  79                 }
  80             }
  81         }
  82     }
  83 }
  84
  85 fn lint(cx: &LateContext<'_, '_>, replace: Span, root: Span, name: Ident, path: &hir::Expr) {
  86     if let hir::ExprKind::Path(hir::QPath::Resolved(None, ref path)) = path.node {
  87         if path.segments.len() == 1 && path.segments[0].ident == name {
  88             span_lint_and_sugg(
  89                 cx,
  90                 MAP_CLONE,
  91                 replace,
  92                 "You are using an explicit closure for cloning elements",
  93                 "Consider calling the dedicated `cloned` method",
  94                 format!("{}.cloned()", snippet(cx, root, "..")),
  95             )
  96         }
  97     }
  98 }