1 use clippy_utils::consts::{constant_context, Constant};
2 use clippy_utils::diagnostics::span_lint;
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;
9 use super::TRANSMUTING_NULL;
11 const LINT_MSG: &str = "transmuting a known null pointer into a reference";
13 pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, arg: &'tcx Expr<'_>, to_ty: Ty<'tcx>) -> bool {
18 // Catching transmute over constants that resolve to `null`.
19 let mut const_eval_context = constant_context(cx, cx.typeck_results());
20 if let ExprKind::Path(ref _qpath) = arg.kind &&
21 let Some(Constant::RawPtr(x)) = const_eval_context.expr(arg) &&
24 span_lint(cx, TRANSMUTING_NULL, expr.span, LINT_MSG);
29 // `std::mem::transmute(0 as *const i32)`
30 if let ExprKind::Cast(inner_expr, _cast_ty) = arg.kind && is_integer_literal(inner_expr, 0) {
31 span_lint(cx, TRANSMUTING_NULL, expr.span, LINT_MSG);
36 // `std::mem::transmute(std::ptr::null::<i32>())`
37 if let ExprKind::Call(func1, []) = arg.kind &&
38 is_path_diagnostic_item(cx, func1, sym::ptr_null)
40 span_lint(cx, TRANSMUTING_NULL, expr.span, LINT_MSG);
45 // Also catch transmutations of variables which are known nulls.
46 // To do this, MIR const propagation seems to be the better tool.
47 // Whenever MIR const prop routines are more developed, this will
48 // become available. As of this writing (25/03/19) it is not yet.