clippy_lints/src/casts/fn_to_numeric_cast_with_truncation.rs

   1 use rustc_errors::Applicability;
   2 use rustc_hir::Expr;
   3 use rustc_lint::LateContext;
   4 use rustc_middle::ty::{self, Ty};
   5
   6 use crate::utils::{snippet_with_applicability, span_lint_and_sugg};
   7
   8 use super::{utils, FN_TO_NUMERIC_CAST_WITH_TRUNCATION};
   9
  10 pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_expr: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
  11     // We only want to check casts to `ty::Uint` or `ty::Int`
  12     match cast_to.kind() {
  13         ty::Uint(_) | ty::Int(..) => { /* continue on */ },
  14         _ => return,
  15     }
  16     match cast_from.kind() {
  17         ty::FnDef(..) | ty::FnPtr(_) => {
  18             let mut applicability = Applicability::MaybeIncorrect;
  19             let from_snippet = snippet_with_applicability(cx, cast_expr.span, "x", &mut applicability);
  20
  21             let to_nbits = utils::int_ty_to_nbits(cast_to, cx.tcx);
  22             if to_nbits < cx.tcx.data_layout.pointer_size.bits() {
  23                 span_lint_and_sugg(
  24                     cx,
  25                     FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
  26                     expr.span,
  27                     &format!(
  28                         "casting function pointer `{}` to `{}`, which truncates the value",
  29                         from_snippet, cast_to
  30                     ),
  31                     "try",
  32                     format!("{} as usize", from_snippet),
  33                     applicability,
  34                 );
  35             }
  36         },
  37         _ => {},
  38     }
  39 }