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

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::source::snippet_with_applicability;
   3 use rustc_errors::Applicability;
   4 use rustc_hir::Expr;
   5 use rustc_lint::LateContext;
   6 use rustc_middle::ty::{self, Ty};
   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!("casting function pointer `{from_snippet}` to `{cast_to}`, which truncates the value"),
  28                     "try",
  29                     format!("{from_snippet} as usize"),
  30                     applicability,
  31                 );
  32             }
  33         },
  34         _ => {},
  35     }
  36 }