rust-clippy/clippy_lints/src/unused_self.rs

105 lines
3.3 KiB
Rust

use if_chain::if_chain;
use rustc_hir::def::Res;
use rustc_hir::intravisit::{walk_path, NestedVisitorMap, Visitor};
use rustc_hir::{HirId, Impl, ImplItem, ImplItemKind, ItemKind, Path};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::hir::map::Map;
use rustc_session::{declare_lint_pass, declare_tool_lint};
use crate::utils::span_lint_and_help;
declare_clippy_lint! {
/// **What it does:** Checks methods that contain a `self` argument but don't use it
///
/// **Why is this bad?** It may be clearer to define the method as an associated function instead
/// of an instance method if it doesn't require `self`.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust,ignore
/// struct A;
/// impl A {
/// fn method(&self) {}
/// }
/// ```
///
/// Could be written:
///
/// ```rust,ignore
/// struct A;
/// impl A {
/// fn method() {}
/// }
/// ```
pub UNUSED_SELF,
pedantic,
"methods that contain a `self` argument but don't use it"
}
declare_lint_pass!(UnusedSelf => [UNUSED_SELF]);
impl<'tcx> LateLintPass<'tcx> for UnusedSelf {
fn check_impl_item(&mut self, cx: &LateContext<'tcx>, impl_item: &ImplItem<'_>) {
if impl_item.span.from_expansion() {
return;
}
let parent = cx.tcx.hir().get_parent_item(impl_item.hir_id);
let parent_item = cx.tcx.hir().expect_item(parent);
let def_id = cx.tcx.hir().local_def_id(impl_item.hir_id);
let assoc_item = cx.tcx.associated_item(def_id);
if_chain! {
if let ItemKind::Impl(Impl { of_trait: None, .. }) = parent_item.kind;
if assoc_item.fn_has_self_parameter;
if let ImplItemKind::Fn(.., body_id) = &impl_item.kind;
let body = cx.tcx.hir().body(*body_id);
if !body.params.is_empty();
then {
let self_param = &body.params[0];
let self_hir_id = self_param.pat.hir_id;
let mut visitor = UnusedSelfVisitor {
cx,
uses_self: false,
self_hir_id: &self_hir_id,
};
visitor.visit_body(body);
if !visitor.uses_self {
span_lint_and_help(
cx,
UNUSED_SELF,
self_param.span,
"unused `self` argument",
None,
"consider refactoring to a associated function",
);
return;
}
}
}
}
}
struct UnusedSelfVisitor<'a, 'tcx> {
cx: &'a LateContext<'tcx>,
uses_self: bool,
self_hir_id: &'a HirId,
}
impl<'a, 'tcx> Visitor<'tcx> for UnusedSelfVisitor<'a, 'tcx> {
type Map = Map<'tcx>;
fn visit_path(&mut self, path: &'tcx Path<'_>, _id: HirId) {
if self.uses_self {
// This function already uses `self`
return;
}
if let Res::Local(hir_id) = &path.res {
self.uses_self = self.self_hir_id == hir_id
}
walk_path(self, path);
}
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
}
}