clippy_lints/src/methods/suspicious_splitn.rs

   1 use clippy_utils::consts::{constant, Constant};
   2 use clippy_utils::diagnostics::span_lint_and_note;
   3 use if_chain::if_chain;
   4 use rustc_ast::LitKind;
   5 use rustc_hir::{Expr, ExprKind};
   6 use rustc_lint::LateContext;
   7 use rustc_span::source_map::Spanned;
   8
   9 use super::SUSPICIOUS_SPLITN;
  10
  11 pub(super) fn check(
  12     cx: &LateContext<'_>,
  13     method_name: &str,
  14     expr: &Expr<'_>,
  15     self_arg: &Expr<'_>,
  16     count_arg: &Expr<'_>,
  17 ) {
  18     if_chain! {
  19         if let Some((Constant::Int(count), _)) = constant(cx, cx.typeck_results(), count_arg);
  20         if count <= 1;
  21         if let Some(call_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
  22         if let Some(impl_id) = cx.tcx.impl_of_method(call_id);
  23         let lang_items = cx.tcx.lang_items();
  24         if lang_items.slice_impl() == Some(impl_id) || lang_items.str_impl() == Some(impl_id);
  25         then {
  26             // Ignore empty slice and string literals when used with a literal count.
  27             if (matches!(self_arg.kind, ExprKind::Array([]))
  28                 || matches!(self_arg.kind, ExprKind::Lit(Spanned { node: LitKind::Str(s, _), .. }) if s.is_empty())
  29             ) && matches!(count_arg.kind, ExprKind::Lit(_))
  30             {
  31                 return;
  32             }
  33
  34             let (msg, note_msg) = if count == 0 {
  35                 (format!("`{}` called with `0` splits", method_name),
  36                 "the resulting iterator will always return `None`")
  37             } else {
  38                 (format!("`{}` called with `1` split", method_name),
  39                 if lang_items.slice_impl() == Some(impl_id) {
  40                     "the resulting iterator will always return the entire slice followed by `None`"
  41                 } else {
  42                     "the resulting iterator will always return the entire string followed by `None`"
  43                 })
  44             };
  45
  46             span_lint_and_note(
  47                 cx,
  48                 SUSPICIOUS_SPLITN,
  49                 expr.span,
  50                 &msg,
  51                 None,
  52                 note_msg,
  53             );
  54         }
  55     }
  56 }