src/tools/clippy/clippy_lints/src/unused_self.rs

   1 use clippy_utils::diagnostics::span_lint_and_help;
   2 use clippy_utils::visitors::LocalUsedVisitor;
   3 use if_chain::if_chain;
   4 use rustc_hir::{Impl, ImplItem, ImplItemKind, ItemKind};
   5 use rustc_lint::{LateContext, LateLintPass};
   6 use rustc_session::{declare_lint_pass, declare_tool_lint};
   7
   8 declare_clippy_lint! {
   9     /// **What it does:** Checks methods that contain a `self` argument but don't use it
  10     ///
  11     /// **Why is this bad?** It may be clearer to define the method as an associated function instead
  12     /// of an instance method if it doesn't require `self`.
  13     ///
  14     /// **Known problems:** None.
  15     ///
  16     /// **Example:**
  17     /// ```rust,ignore
  18     /// struct A;
  19     /// impl A {
  20     ///     fn method(&self) {}
  21     /// }
  22     /// ```
  23     ///
  24     /// Could be written:
  25     ///
  26     /// ```rust,ignore
  27     /// struct A;
  28     /// impl A {
  29     ///     fn method() {}
  30     /// }
  31     /// ```
  32     pub UNUSED_SELF,
  33     pedantic,
  34     "methods that contain a `self` argument but don't use it"
  35 }
  36
  37 declare_lint_pass!(UnusedSelf => [UNUSED_SELF]);
  38
  39 impl<'tcx> LateLintPass<'tcx> for UnusedSelf {
  40     fn check_impl_item(&mut self, cx: &LateContext<'tcx>, impl_item: &ImplItem<'_>) {
  41         if impl_item.span.from_expansion() {
  42             return;
  43         }
  44         let parent = cx.tcx.hir().get_parent_item(impl_item.hir_id());
  45         let parent_item = cx.tcx.hir().expect_item(parent);
  46         let assoc_item = cx.tcx.associated_item(impl_item.def_id);
  47         if_chain! {
  48             if let ItemKind::Impl(Impl { of_trait: None, .. }) = parent_item.kind;
  49             if assoc_item.fn_has_self_parameter;
  50             if let ImplItemKind::Fn(.., body_id) = &impl_item.kind;
  51             let body = cx.tcx.hir().body(*body_id);
  52             if let [self_param, ..] = body.params;
  53             let self_hir_id = self_param.pat.hir_id;
  54             if !LocalUsedVisitor::new(cx, self_hir_id).check_body(body);
  55             then {
  56                 span_lint_and_help(
  57                     cx,
  58                     UNUSED_SELF,
  59                     self_param.span,
  60                     "unused `self` argument",
  61                     None,
  62                     "consider refactoring to a associated function",
  63                 );
  64             }
  65         }
  66     }
  67 }