src/tools/clippy/clippy_lints/src/copy_iterator.rs

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