clippy_lints/src/casts/cast_possible_truncation.rs

   1 use clippy_utils::ty::is_isize_or_usize;
   2 use rustc_hir::Expr;
   3 use rustc_lint::LateContext;
   4 use rustc_middle::ty::{self, FloatTy, Ty};
   5
   6 use crate::utils::span_lint;
   7
   8 use super::{utils, CAST_POSSIBLE_TRUNCATION};
   9
  10 pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
  11     let msg = match (cast_from.is_integral(), cast_to.is_integral()) {
  12         (true, true) => {
  13             let from_nbits = utils::int_ty_to_nbits(cast_from, cx.tcx);
  14             let to_nbits = utils::int_ty_to_nbits(cast_to, cx.tcx);
  15
  16             let (should_lint, suffix) = match (is_isize_or_usize(cast_from), is_isize_or_usize(cast_to)) {
  17                 (true, true) | (false, false) => (to_nbits < from_nbits, ""),
  18                 (true, false) => (
  19                     to_nbits <= 32,
  20                     if to_nbits == 32 {
  21                         " on targets with 64-bit wide pointers"
  22                     } else {
  23                         ""
  24                     },
  25                 ),
  26                 (false, true) => (from_nbits == 64, " on targets with 32-bit wide pointers"),
  27             };
  28
  29             if !should_lint {
  30                 return;
  31             }
  32
  33             format!(
  34                 "casting `{}` to `{}` may truncate the value{}",
  35                 cast_from, cast_to, suffix,
  36             )
  37         },
  38
  39         (false, true) => {
  40             format!("casting `{}` to `{}` may truncate the value", cast_from, cast_to)
  41         },
  42
  43         (_, _) => {
  44             if matches!(cast_from.kind(), &ty::Float(FloatTy::F64))
  45                 && matches!(cast_to.kind(), &ty::Float(FloatTy::F32))
  46             {
  47                 "casting `f64` to `f32` may truncate the value".to_string()
  48             } else {
  49                 return;
  50             }
  51         },
  52     };
  53
  54     span_lint(cx, CAST_POSSIBLE_TRUNCATION, expr.span, &msg);
  55 }