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

   1 use clippy_utils::diagnostics::span_lint_and_help;
   2 use clippy_utils::macros::root_macro_call_first_node;
   3 use clippy_utils::visitors::is_local_used;
   4 use if_chain::if_chain;
   5 use rustc_hir::{Body, Impl, ImplItem, ImplItemKind, ItemKind};
   6 use rustc_lint::{LateContext, LateLintPass};
   7 use rustc_session::{declare_tool_lint, impl_lint_pass};
   8 use std::ops::ControlFlow;
   9
  10 declare_clippy_lint! {
  11     /// ### What it does
  12     /// Checks methods that contain a `self` argument but don't use it
  13     ///
  14     /// ### Why is this bad?
  15     /// It may be clearer to define the method as an associated function instead
  16     /// of an instance method if it doesn't require `self`.
  17     ///
  18     /// ### Example
  19     /// ```rust,ignore
  20     /// struct A;
  21     /// impl A {
  22     ///     fn method(&self) {}
  23     /// }
  24     /// ```
  25     ///
  26     /// Could be written:
  27     ///
  28     /// ```rust,ignore
  29     /// struct A;
  30     /// impl A {
  31     ///     fn method() {}
  32     /// }
  33     /// ```
  34     #[clippy::version = "1.40.0"]
  35     pub UNUSED_SELF,
  36     pedantic,
  37     "methods that contain a `self` argument but don't use it"
  38 }
  39
  40 pub struct UnusedSelf {
  41     avoid_breaking_exported_api: bool,
  42 }
  43
  44 impl_lint_pass!(UnusedSelf => [UNUSED_SELF]);
  45
  46 impl UnusedSelf {
  47     pub fn new(avoid_breaking_exported_api: bool) -> Self {
  48         Self {
  49             avoid_breaking_exported_api,
  50         }
  51     }
  52 }
  53
  54 impl<'tcx> LateLintPass<'tcx> for UnusedSelf {
  55     fn check_impl_item(&mut self, cx: &LateContext<'tcx>, impl_item: &ImplItem<'_>) {
  56         if impl_item.span.from_expansion() {
  57             return;
  58         }
  59         let parent = cx.tcx.hir().get_parent_item(impl_item.hir_id()).def_id;
  60         let parent_item = cx.tcx.hir().expect_item(parent);
  61         let assoc_item = cx.tcx.associated_item(impl_item.owner_id);
  62         let contains_todo = |cx, body: &'_ Body<'_>| -> bool {
  63             clippy_utils::visitors::for_each_expr(body.value, |e| {
  64                 if let Some(macro_call) = root_macro_call_first_node(cx, e) {
  65                     if cx.tcx.item_name(macro_call.def_id).as_str() == "todo" {
  66                         ControlFlow::Break(())
  67                     } else {
  68                         ControlFlow::Continue(())
  69                     }
  70                 } else {
  71                     ControlFlow::Continue(())
  72                 }
  73             })
  74             .is_some()
  75         };
  76         if_chain! {
  77             if let ItemKind::Impl(Impl { of_trait: None, .. }) = parent_item.kind;
  78             if assoc_item.fn_has_self_parameter;
  79             if let ImplItemKind::Fn(.., body_id) = &impl_item.kind;
  80             if !cx.effective_visibilities.is_exported(impl_item.owner_id.def_id) || !self.avoid_breaking_exported_api;
  81             let body = cx.tcx.hir().body(*body_id);
  82             if let [self_param, ..] = body.params;
  83             if !is_local_used(cx, body, self_param.pat.hir_id);
  84             if !contains_todo(cx, body);
  85             then {
  86                 span_lint_and_help(
  87                     cx,
  88                     UNUSED_SELF,
  89                     self_param.span,
  90                     "unused `self` argument",
  91                     None,
  92                     "consider refactoring to an associated function",
  93                 );
  94             }
  95         }
  96     }
  97 }