src/tools/clippy/clippy_lints/src/casts/char_lit_as_u8.rs

   1 use clippy_utils::diagnostics::span_lint_and_then;
   2 use clippy_utils::source::snippet_with_applicability;
   3 use if_chain::if_chain;
   4 use rustc_ast::LitKind;
   5 use rustc_errors::Applicability;
   6 use rustc_hir::{Expr, ExprKind};
   7 use rustc_lint::LateContext;
   8 use rustc_middle::ty::{self, UintTy};
   9
  10 use super::CHAR_LIT_AS_U8;
  11
  12 pub(super) fn check(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  13     if_chain! {
  14         if let ExprKind::Cast(e, _) = &expr.kind;
  15         if let ExprKind::Lit(l) = &e.kind;
  16         if let LitKind::Char(c) = l.node;
  17         if ty::Uint(UintTy::U8) == *cx.typeck_results().expr_ty(expr).kind();
  18         then {
  19             let mut applicability = Applicability::MachineApplicable;
  20             let snippet = snippet_with_applicability(cx, e.span, "'x'", &mut applicability);
  21
  22             span_lint_and_then(
  23                 cx,
  24                 CHAR_LIT_AS_U8,
  25                 expr.span,
  26                 "casting a character literal to `u8` truncates",
  27                 |diag| {
  28                     diag.note("`char` is four bytes wide, but `u8` is a single byte");
  29
  30                     if c.is_ascii() {
  31                         diag.span_suggestion(
  32                             expr.span,
  33                             "use a byte literal instead",
  34                             format!("b{}", snippet),
  35                             applicability,
  36                         );
  37                     }
  38             });
  39         }
  40     }
  41 }