src/tools/clippy/clippy_lints/src/transmute/transmute_null_to_fn.rs

   1 use clippy_utils::consts::{constant, Constant};
   2 use clippy_utils::diagnostics::span_lint_and_then;
   3 use clippy_utils::{is_integer_literal, is_path_diagnostic_item};
   4 use rustc_hir::{Expr, ExprKind};
   5 use rustc_lint::LateContext;
   6 use rustc_middle::ty::Ty;
   7 use rustc_span::symbol::sym;
   8
   9 use super::TRANSMUTE_NULL_TO_FN;
  10
  11 fn lint_expr(cx: &LateContext<'_>, expr: &Expr<'_>) {
  12     span_lint_and_then(
  13         cx,
  14         TRANSMUTE_NULL_TO_FN,
  15         expr.span,
  16         "transmuting a known null pointer into a function pointer",
  17         |diag| {
  18             diag.span_label(expr.span, "this transmute results in undefined behavior");
  19             diag.help(
  20                "try wrapping your function pointer type in `Option<T>` instead, and using `None` as a null pointer value"
  21             );
  22         },
  23     );
  24 }
  25
  26 pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, arg: &'tcx Expr<'_>, to_ty: Ty<'tcx>) -> bool {
  27     if !to_ty.is_fn() {
  28         return false;
  29     }
  30
  31     match arg.kind {
  32         // Catching:
  33         // transmute over constants that resolve to `null`.
  34         ExprKind::Path(ref _qpath)
  35             if matches!(constant(cx, cx.typeck_results(), arg), Some((Constant::RawPtr(0), _))) =>
  36         {
  37             lint_expr(cx, expr);
  38             true
  39         },
  40
  41         // Catching:
  42         // `std::mem::transmute(0 as *const i32)`
  43         ExprKind::Cast(inner_expr, _cast_ty) if is_integer_literal(inner_expr, 0) => {
  44             lint_expr(cx, expr);
  45             true
  46         },
  47
  48         // Catching:
  49         // `std::mem::transmute(std::ptr::null::<i32>())`
  50         ExprKind::Call(func1, []) if is_path_diagnostic_item(cx, func1, sym::ptr_null) => {
  51             lint_expr(cx, expr);
  52             true
  53         },
  54
  55         _ => {
  56             // FIXME:
  57             // Also catch transmutations of variables which are known nulls.
  58             // To do this, MIR const propagation seems to be the better tool.
  59             // Whenever MIR const prop routines are more developed, this will
  60             // become available. As of this writing (25/03/19) it is not yet.
  61             false
  62         },
  63     }
  64 }