clippy_lints/src/casts/cast_possible_truncation.rs

   1 use rustc_hir::Expr;
   2 use rustc_lint::LateContext;
   3 use rustc_middle::ty::{self, FloatTy, Ty};
   4
   5 use crate::utils::{is_isize_or_usize, span_lint};
   6
   7 use super::{utils, CAST_POSSIBLE_TRUNCATION};
   8
   9 pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
  10     let msg = match (cast_from.is_integral(), cast_to.is_integral()) {
  11         (true, true) => {
  12             let from_nbits = utils::int_ty_to_nbits(cast_from, cx.tcx);
  13             let to_nbits = utils::int_ty_to_nbits(cast_to, cx.tcx);
  14
  15             let (should_lint, suffix) = match (is_isize_or_usize(cast_from), is_isize_or_usize(cast_to)) {
  16                 (true, true) | (false, false) => (to_nbits < from_nbits, ""),
  17                 (true, false) => (
  18                     to_nbits <= 32,
  19                     if to_nbits == 32 {
  20                         " on targets with 64-bit wide pointers"
  21                     } else {
  22                         ""
  23                     },
  24                 ),
  25                 (false, true) => (from_nbits == 64, " on targets with 32-bit wide pointers"),
  26             };
  27
  28             if !should_lint {
  29                 return;
  30             }
  31
  32             format!(
  33                 "casting `{}` to `{}` may truncate the value{}",
  34                 cast_from, cast_to, suffix,
  35             )
  36         },
  37
  38         (false, true) => {
  39             format!("casting `{}` to `{}` may truncate the value", cast_from, cast_to)
  40         },
  41
  42         (_, _) => {
  43             if matches!(cast_from.kind(), &ty::Float(FloatTy::F64))
  44                 && matches!(cast_to.kind(), &ty::Float(FloatTy::F32))
  45             {
  46                 "casting `f64` to `f32` may truncate the value".to_string()
  47             } else {
  48                 return;
  49             }
  50         },
  51     };
  52
  53     span_lint(cx, CAST_POSSIBLE_TRUNCATION, expr.span, &msg);
  54 }