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

   1 use clippy_utils::diagnostics::span_lint_and_note;
   2 use clippy_utils::ty::is_copy;
   3 use rustc_hir::{Impl, Item, ItemKind};
   4 use rustc_lint::{LateContext, LateLintPass};
   5 use rustc_session::{declare_lint_pass, declare_tool_lint};
   6 use rustc_span::sym;
   7
   8 use if_chain::if_chain;
   9
  10 declare_clippy_lint! {
  11     /// ### What it does
  12     /// Checks for types that implement `Copy` as well as
  13     /// `Iterator`.
  14     ///
  15     /// ### Why is this bad?
  16     /// Implicit copies can be confusing when working with
  17     /// iterator combinators.
  18     ///
  19     /// ### Example
  20     /// ```rust,ignore
  21     /// #[derive(Copy, Clone)]
  22     /// struct Countdown(u8);
  23     ///
  24     /// impl Iterator for Countdown {
  25     ///     // ...
  26     /// }
  27     ///
  28     /// let a: Vec<_> = my_iterator.take(1).collect();
  29     /// let b: Vec<_> = my_iterator.collect();
  30     /// ```
  31     pub COPY_ITERATOR,
  32     pedantic,
  33     "implementing `Iterator` on a `Copy` type"
  34 }
  35
  36 declare_lint_pass!(CopyIterator => [COPY_ITERATOR]);
  37
  38 impl<'tcx> LateLintPass<'tcx> for CopyIterator {
  39     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
  40         if_chain! {
  41             if let ItemKind::Impl(Impl {
  42                 of_trait: Some(ref trait_ref),
  43                 ..
  44             }) = item.kind;
  45             let ty = cx.tcx.type_of(item.def_id);
  46             if is_copy(cx, ty);
  47             if let Some(trait_id) = trait_ref.trait_def_id();
  48             if cx.tcx.is_diagnostic_item(sym::Iterator, trait_id);
  49             then {
  50                 span_lint_and_note(
  51                     cx,
  52                     COPY_ITERATOR,
  53                     item.span,
  54                     "you are implementing `Iterator` on a `Copy` type",
  55                     None,
  56                     "consider implementing `IntoIterator` instead",
  57                 );
  58             }
  59         }
  60     }
  61 }