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