src/tools/clippy/clippy_lints/src/methods/get_last_with_len.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::source::snippet_with_applicability;
   3 use clippy_utils::SpanlessEq;
   4 use rustc_ast::LitKind;
   5 use rustc_errors::Applicability;
   6 use rustc_hir::{BinOpKind, Expr, ExprKind};
   7 use rustc_lint::LateContext;
   8 use rustc_middle::ty;
   9 use rustc_span::source_map::Spanned;
  10 use rustc_span::sym;
  11
  12 use super::GET_LAST_WITH_LEN;
  13
  14 pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, recv: &Expr<'_>, arg: &Expr<'_>) {
  15     // Argument to "get" is a subtraction
  16     if let ExprKind::Binary(
  17         Spanned {
  18             node: BinOpKind::Sub, ..
  19         },
  20         lhs,
  21         rhs,
  22     ) = arg.kind
  23
  24         // LHS of subtraction is "x.len()"
  25         && let ExprKind::MethodCall(lhs_path, lhs_recv, [], _) = &lhs.kind
  26         && lhs_path.ident.name == sym::len
  27
  28         // RHS of subtraction is 1
  29         && let ExprKind::Lit(rhs_lit) = &rhs.kind
  30         && let LitKind::Int(1, ..) = rhs_lit.node
  31
  32         // check that recv == lhs_recv `recv.get(lhs_recv.len() - 1)`
  33         && SpanlessEq::new(cx).eq_expr(recv, lhs_recv)
  34         && !recv.can_have_side_effects()
  35     {
  36         let method = match cx.typeck_results().expr_ty_adjusted(recv).peel_refs().kind() {
  37             ty::Adt(def, _) if cx.tcx.is_diagnostic_item(sym::VecDeque, def.did()) => "back",
  38             ty::Slice(_) => "last",
  39             _ => return,
  40         };
  41
  42         let mut applicability = Applicability::MachineApplicable;
  43         let recv_snippet = snippet_with_applicability(cx, recv.span, "_", &mut applicability);
  44
  45         span_lint_and_sugg(
  46             cx,
  47             GET_LAST_WITH_LEN,
  48             expr.span,
  49             &format!("accessing last element with `{recv_snippet}.get({recv_snippet}.len() - 1)`"),
  50             "try",
  51             format!("{recv_snippet}.{method}()"),
  52             applicability,
  53         );
  54     }
  55 }