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

   1 use clippy_utils::diagnostics::span_lint_and_note;
   2 use if_chain::if_chain;
   3 use rustc_ast::LitKind;
   4 use rustc_hir::{Expr, ExprKind};
   5 use rustc_lint::LateContext;
   6 use rustc_span::source_map::Spanned;
   7
   8 use super::SUSPICIOUS_SPLITN;
   9
  10 pub(super) fn check(cx: &LateContext<'_>, method_name: &str, expr: &Expr<'_>, self_arg: &Expr<'_>, count: u128) {
  11     if_chain! {
  12         if count <= 1;
  13         if let Some(call_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
  14         if let Some(impl_id) = cx.tcx.impl_of_method(call_id);
  15         if cx.tcx.impl_trait_ref(impl_id).is_none();
  16         let self_ty = cx.tcx.type_of(impl_id);
  17         if self_ty.is_slice() || self_ty.is_str();
  18         then {
  19             // Ignore empty slice and string literals when used with a literal count.
  20             if matches!(self_arg.kind, ExprKind::Array([]))
  21                 || matches!(self_arg.kind, ExprKind::Lit(Spanned { node: LitKind::Str(s, _), .. }) if s.is_empty())
  22             {
  23                 return;
  24             }
  25
  26             let (msg, note_msg) = if count == 0 {
  27                 (format!("`{}` called with `0` splits", method_name),
  28                 "the resulting iterator will always return `None`")
  29             } else {
  30                 (format!("`{}` called with `1` split", method_name),
  31                 if self_ty.is_slice() {
  32                     "the resulting iterator will always return the entire slice followed by `None`"
  33                 } else {
  34                     "the resulting iterator will always return the entire string followed by `None`"
  35                 })
  36             };
  37
  38             span_lint_and_note(
  39                 cx,
  40                 SUSPICIOUS_SPLITN,
  41                 expr.span,
  42                 &msg,
  43                 None,
  44                 note_msg,
  45             );
  46         }
  47     }
  48 }