clippy_lints/src/copy_iterator.rs

   1 use crate::utils::{is_copy, match_path, paths, span_note_and_lint};
   2 use rustc::hir::{Item, ItemKind};
   3 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   4 use rustc::{declare_tool_lint, lint_array};
   5
   6 /// **What it does:** Checks for types that implement `Copy` as well as
   7 /// `Iterator`.
   8 ///
   9 /// **Why is this bad?** Implicit copies can be confusing when working with
  10 /// iterator combinators.
  11 ///
  12 /// **Known problems:** None.
  13 ///
  14 /// **Example:**
  15 /// ```rust
  16 /// #[derive(Copy, Clone)]
  17 /// struct Countdown(u8);
  18 ///
  19 /// impl Iterator for Countdown {
  20 ///     // ...
  21 /// }
  22 ///
  23 /// let a: Vec<_> = my_iterator.take(1).collect();
  24 /// let b: Vec<_> = my_iterator.collect();
  25 /// ```
  26 declare_clippy_lint! {
  27     pub COPY_ITERATOR,
  28     pedantic,
  29     "implementing `Iterator` on a `Copy` type"
  30 }
  31
  32 pub struct CopyIterator;
  33
  34 impl LintPass for CopyIterator {
  35     fn get_lints(&self) -> LintArray {
  36         lint_array![COPY_ITERATOR]
  37     }
  38
  39     fn name(&self) -> &'static str {
  40         "CopyIterator"
  41     }
  42 }
  43
  44 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for CopyIterator {
  45     fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) {
  46         if let ItemKind::Impl(_, _, _, _, Some(ref trait_ref), _, _) = item.node {
  47             let ty = cx.tcx.type_of(cx.tcx.hir().local_def_id(item.id));
  48
  49             if is_copy(cx, ty) && match_path(&trait_ref.path, &paths::ITERATOR) {
  50                 span_note_and_lint(
  51                     cx,
  52                     COPY_ITERATOR,
  53                     item.span,
  54                     "you are implementing `Iterator` on a `Copy` type",
  55                     item.span,
  56                     "consider implementing `IntoIterator` instead",
  57                 );
  58             }
  59         }
  60     }
  61 }