clippy_lints/src/copy_iterator.rs

   1 use crate::utils::{is_copy, span_lint_and_note};
   2 use rustc_hir::{Impl, Item, ItemKind};
   3 use rustc_lint::{LateContext, LateLintPass};
   4 use rustc_session::{declare_lint_pass, declare_tool_lint};
   5 use rustc_span::sym;
   6
   7 use if_chain::if_chain;
   8
   9 declare_clippy_lint! {
  10     /// **What it does:** Checks for types that implement `Copy` as well as
  11     /// `Iterator`.
  12     ///
  13     /// **Why is this bad?** Implicit copies can be confusing when working with
  14     /// iterator combinators.
  15     ///
  16     /// **Known problems:** None.
  17     ///
  18     /// **Example:**
  19     /// ```rust,ignore
  20     /// #[derive(Copy, Clone)]
  21     /// struct Countdown(u8);
  22     ///
  23     /// impl Iterator for Countdown {
  24     ///     // ...
  25     /// }
  26     ///
  27     /// let a: Vec<_> = my_iterator.take(1).collect();
  28     /// let b: Vec<_> = my_iterator.collect();
  29     /// ```
  30     pub COPY_ITERATOR,
  31     pedantic,
  32     "implementing `Iterator` on a `Copy` type"
  33 }
  34
  35 declare_lint_pass!(CopyIterator => [COPY_ITERATOR]);
  36
  37 impl<'tcx> LateLintPass<'tcx> for CopyIterator {
  38     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
  39         if_chain! {
  40             if let ItemKind::Impl(Impl {
  41                 of_trait: Some(ref trait_ref),
  42                 ..
  43             }) = item.kind;
  44             let ty = cx.tcx.type_of(item.def_id);
  45             if is_copy(cx, ty);
  46             if let Some(trait_id) = trait_ref.trait_def_id();
  47             if cx.tcx.is_diagnostic_item(sym::Iterator, trait_id);
  48             then {
  49                 span_lint_and_note(
  50                     cx,
  51                     COPY_ITERATOR,
  52                     item.span,
  53                     "you are implementing `Iterator` on a `Copy` type",
  54                     None,
  55                     "consider implementing `IntoIterator` instead",
  56                 );
  57             }
  58         }
  59     }
  60 }