clippy_lints/src/methods/iter_next_slice.rs

   1 use super::utils::derefs_to_slice;
   2 use clippy_utils::diagnostics::span_lint_and_sugg;
   3 use clippy_utils::source::snippet_with_applicability;
   4 use clippy_utils::ty::is_type_diagnostic_item;
   5 use clippy_utils::{get_parent_expr, higher};
   6 use if_chain::if_chain;
   7 use rustc_ast::ast;
   8 use rustc_errors::Applicability;
   9 use rustc_hir as hir;
  10 use rustc_lint::LateContext;
  11 use rustc_middle::ty;
  12 use rustc_span::symbol::sym;
  13
  14 use super::ITER_NEXT_SLICE;
  15
  16 pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>, caller_expr: &'tcx hir::Expr<'_>) {
  17     // Skip lint if the `iter().next()` expression is a for loop argument,
  18     // since it is already covered by `&loops::ITER_NEXT_LOOP`
  19     let mut parent_expr_opt = get_parent_expr(cx, expr);
  20     while let Some(parent_expr) = parent_expr_opt {
  21         if higher::for_loop(parent_expr).is_some() {
  22             return;
  23         }
  24         parent_expr_opt = get_parent_expr(cx, parent_expr);
  25     }
  26
  27     if derefs_to_slice(cx, caller_expr, cx.typeck_results().expr_ty(caller_expr)).is_some() {
  28         // caller is a Slice
  29         if_chain! {
  30             if let hir::ExprKind::Index(caller_var, index_expr) = &caller_expr.kind;
  31             if let Some(higher::Range { start: Some(start_expr), end: None, limits: ast::RangeLimits::HalfOpen })
  32                 = higher::range(index_expr);
  33             if let hir::ExprKind::Lit(ref start_lit) = &start_expr.kind;
  34             if let ast::LitKind::Int(start_idx, _) = start_lit.node;
  35             then {
  36                 let mut applicability = Applicability::MachineApplicable;
  37                 span_lint_and_sugg(
  38                     cx,
  39                     ITER_NEXT_SLICE,
  40                     expr.span,
  41                     "using `.iter().next()` on a Slice without end index",
  42                     "try calling",
  43                     format!("{}.get({})", snippet_with_applicability(cx, caller_var.span, "..", &mut applicability), start_idx),
  44                     applicability,
  45                 );
  46             }
  47         }
  48     } else if is_vec_or_array(cx, caller_expr) {
  49         // caller is a Vec or an Array
  50         let mut applicability = Applicability::MachineApplicable;
  51         span_lint_and_sugg(
  52             cx,
  53             ITER_NEXT_SLICE,
  54             expr.span,
  55             "using `.iter().next()` on an array",
  56             "try calling",
  57             format!(
  58                 "{}.get(0)",
  59                 snippet_with_applicability(cx, caller_expr.span, "..", &mut applicability)
  60             ),
  61             applicability,
  62         );
  63     }
  64 }
  65
  66 fn is_vec_or_array<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) -> bool {
  67     is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(expr), sym::vec_type)
  68         || matches!(&cx.typeck_results().expr_ty(expr).peel_refs().kind(), ty::Array(_, _))
  69 }