clippy_lints/src/casts/char_lit_as_u8.rs

   1 use rustc_ast::LitKind;
   2 use rustc_errors::Applicability;
   3 use rustc_hir::{Expr, ExprKind};
   4 use rustc_lint::LateContext;
   5 use rustc_middle::ty::{self, UintTy};
   6
   7 use if_chain::if_chain;
   8
   9 use crate::utils::{snippet_with_applicability, span_lint_and_then};
  10
  11 use super::CHAR_LIT_AS_U8;
  12
  13 pub(super) fn check(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  14     if_chain! {
  15         if let ExprKind::Cast(e, _) = &expr.kind;
  16         if let ExprKind::Lit(l) = &e.kind;
  17         if let LitKind::Char(c) = l.node;
  18         if ty::Uint(UintTy::U8) == *cx.typeck_results().expr_ty(expr).kind();
  19         then {
  20             let mut applicability = Applicability::MachineApplicable;
  21             let snippet = snippet_with_applicability(cx, e.span, "'x'", &mut applicability);
  22
  23             span_lint_and_then(
  24                 cx,
  25                 CHAR_LIT_AS_U8,
  26                 expr.span,
  27                 "casting a character literal to `u8` truncates",
  28                 |diag| {
  29                     diag.note("`char` is four bytes wide, but `u8` is a single byte");
  30
  31                     if c.is_ascii() {
  32                         diag.span_suggestion(
  33                             expr.span,
  34                             "use a byte literal instead",
  35                             format!("b{}", snippet),
  36                             applicability,
  37                         );
  38                     }
  39             });
  40         }
  41     }
  42 }