use clippy_config::Conf;

use clippy_utils::diagnostics::span_lint_and_help;

use clippy_utils::usage::is_todo_unimplemented_stub;

use clippy_utils::visitors::is_local_used;

use rustc_hir::{Impl, ImplItem, ImplItemKind, ItemKind};

use rustc_lint::{LateContext, LateLintPass};

use rustc_session::impl_lint_pass;

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`.

///

/// ### Example

/// ```rust,ignore

/// struct A;

/// impl A {

/// fn method(&self) {}

/// }

/// ```

///

/// Could be written:

///

/// ```rust,ignore

/// struct A;

/// impl A {

/// fn method() {}

/// }

/// ```

#[clippy::version = "1.40.0"]

pub UNUSED_SELF,

pedantic,

"methods that contain a `self` argument but don't use it"

}

impl_lint_pass!(UnusedSelf => [UNUSED_SELF]);

pub struct UnusedSelf {

avoid_breaking_exported_api: bool,

}

impl UnusedSelf {

pub fn new(conf: &'static Conf) -> Self {

Self {

avoid_breaking_exported_api: conf.avoid_breaking_exported_api,

}

}

}

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()).def_id;

let parent_item = cx.tcx.hir_expect_item(parent);

let assoc_item = cx.tcx.associated_item(impl_item.owner_id);

if let ItemKind::Impl(Impl { of_trait: None, .. }) = parent_item.kind

&& assoc_item.is_method()

&& let ImplItemKind::Fn(.., body_id) = &impl_item.kind

&& (!cx.effective_visibilities.is_exported(impl_item.owner_id.def_id) || !self.avoid_breaking_exported_api)

&& let body = cx.tcx.hir_body(*body_id)

&& let [self_param, ..] = body.params

&& !is_local_used(cx, body, self_param.pat.hir_id)

&& !is_todo_unimplemented_stub(cx, body.value)

{

span_lint_and_help(

cx,

UNUSED_SELF,

self_param.span,

"unused `self` argument",

None,

"consider refactoring to an associated function",

);

}

}

}