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use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::source::snippet_with_applicability;
use clippy_utils::ty::walk_ptrs_ty_depth;
use clippy_utils::{get_parent_expr, is_trait_method};
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir as hir;
use rustc_lint::LateContext;
use rustc_span::sym;
use super::USELESS_ASREF;
/// Checks for the `USELESS_ASREF` lint.
pub(super) fn check(cx: &LateContext<'_>, expr: &hir::Expr<'_>, call_name: &str, recvr: &hir::Expr<'_>) {
// when we get here, we've already checked that the call name is "as_ref" or "as_mut"
// check if the call is to the actual `AsRef` or `AsMut` trait
if is_trait_method(cx, expr, sym::AsRef) || is_trait_method(cx, expr, sym::AsMut) {
// check if the type after `as_ref` or `as_mut` is the same as before
let rcv_ty = cx.typeck_results().expr_ty(recvr);
let res_ty = cx.typeck_results().expr_ty(expr);
let (base_res_ty, res_depth) = walk_ptrs_ty_depth(res_ty);
let (base_rcv_ty, rcv_depth) = walk_ptrs_ty_depth(rcv_ty);
if base_rcv_ty == base_res_ty && rcv_depth >= res_depth {
// allow the `as_ref` or `as_mut` if it is followed by another method call
if_chain! {
if let Some(parent) = get_parent_expr(cx, expr);
if let hir::ExprKind::MethodCall(segment, ..) = parent.kind;
if segment.ident.span != expr.span;
then {
return;
}
}
let mut applicability = Applicability::MachineApplicable;
span_lint_and_sugg(
cx,
USELESS_ASREF,
expr.span,
&format!("this call to `{call_name}` does nothing"),
"try this",
snippet_with_applicability(cx, recvr.span, "..", &mut applicability).to_string(),
applicability,
);
}
}
}
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