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use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::source::snippet_with_applicability;
use clippy_utils::SpanlessEq;
use rustc_ast::LitKind;
use rustc_errors::Applicability;
use rustc_hir::{BinOpKind, Expr, ExprKind};
use rustc_lint::LateContext;
use rustc_middle::ty;
use rustc_span::source_map::Spanned;
use rustc_span::sym;
use super::GET_LAST_WITH_LEN;
pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, recv: &Expr<'_>, arg: &Expr<'_>) {
// Argument to "get" is a subtraction
if let ExprKind::Binary(
Spanned {
node: BinOpKind::Sub, ..
},
lhs,
rhs,
) = arg.kind
// LHS of subtraction is "x.len()"
&& let ExprKind::MethodCall(lhs_path, [lhs_recv], _) = &lhs.kind
&& lhs_path.ident.name == sym::len
// RHS of subtraction is 1
&& let ExprKind::Lit(rhs_lit) = &rhs.kind
&& let LitKind::Int(1, ..) = rhs_lit.node
// check that recv == lhs_recv `recv.get(lhs_recv.len() - 1)`
&& SpanlessEq::new(cx).eq_expr(recv, lhs_recv)
&& !recv.can_have_side_effects()
{
let method = match cx.typeck_results().expr_ty_adjusted(recv).peel_refs().kind() {
ty::Adt(def, _) if cx.tcx.is_diagnostic_item(sym::VecDeque, def.did()) => "back",
ty::Slice(_) => "last",
_ => return,
};
let mut applicability = Applicability::MachineApplicable;
let recv_snippet = snippet_with_applicability(cx, recv.span, "_", &mut applicability);
span_lint_and_sugg(
cx,
GET_LAST_WITH_LEN,
expr.span,
&format!("accessing last element with `{recv_snippet}.get({recv_snippet}.len() - 1)`"),
"try",
format!("{recv_snippet}.{method}()"),
applicability,
);
}
}
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