src/tools/clippy/clippy_lints/src/partialeq_ne_impl.rs

   1 use rustc::lint::*;
   2 use rustc::hir::*;
   3 use utils::{is_automatically_derived, span_lint};
   4
   5 /// **What it does:** Checks for manual re-implementations of `PartialEq::ne`.
   6 ///
   7 /// **Why is this bad?** `PartialEq::ne` is required to always return the
   8 /// negated result of `PartialEq::eq`, which is exactly what the default
   9 /// implementation does. Therefore, there should never be any need to
  10 /// re-implement it.
  11 ///
  12 /// **Known problems:** None.
  13 ///
  14 /// **Example:**
  15 /// ```rust
  16 /// struct Foo;
  17 ///
  18 /// impl PartialEq for Foo {
  19 ///    fn eq(&self, other: &Foo) -> bool { ... }
  20 ///    fn ne(&self, other: &Foo) -> bool { !(self == other) }
  21 /// }
  22 /// ```
  23 declare_lint! {
  24     pub PARTIALEQ_NE_IMPL,
  25     Warn,
  26     "re-implementing `PartialEq::ne`"
  27 }
  28
  29 #[derive(Clone, Copy)]
  30 pub struct Pass;
  31
  32 impl LintPass for Pass {
  33     fn get_lints(&self) -> LintArray {
  34         lint_array!(PARTIALEQ_NE_IMPL)
  35     }
  36 }
  37
  38 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
  39     fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) {
  40         if_let_chain! {[
  41             let ItemImpl(_, _, _, _, Some(ref trait_ref), _, ref impl_items) = item.node,
  42             !is_automatically_derived(&*item.attrs),
  43             let Some(eq_trait) = cx.tcx.lang_items.eq_trait(),
  44             trait_ref.path.def.def_id() == eq_trait
  45         ], {
  46             for impl_item in impl_items {
  47                 if impl_item.name == "ne" {
  48                     span_lint(cx,
  49                               PARTIALEQ_NE_IMPL,
  50                               impl_item.span,
  51                               "re-implementing `PartialEq::ne` is unnecessary")
  52                 }
  53             }
  54         }};
  55     }
  56 }