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use clippy_utils::consts::{constant_context, Constant};
use clippy_utils::diagnostics::span_lint;
use clippy_utils::is_path_diagnostic_item;
use if_chain::if_chain;
use rustc_ast::LitKind;
use rustc_hir::{Expr, ExprKind};
use rustc_lint::LateContext;
use rustc_middle::ty::Ty;
use rustc_span::symbol::sym;
use super::TRANSMUTING_NULL;
const LINT_MSG: &str = "transmuting a known null pointer into a reference";
pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, arg: &'tcx Expr<'_>, to_ty: Ty<'tcx>) -> bool {
if !to_ty.is_ref() {
return false;
}
// Catching transmute over constants that resolve to `null`.
let mut const_eval_context = constant_context(cx, cx.typeck_results());
if_chain! {
if let ExprKind::Path(ref _qpath) = arg.kind;
if let Some(Constant::RawPtr(x)) = const_eval_context.expr(arg);
if x == 0;
then {
span_lint(cx, TRANSMUTING_NULL, expr.span, LINT_MSG);
return true;
}
}
// Catching:
// `std::mem::transmute(0 as *const i32)`
if_chain! {
if let ExprKind::Cast(inner_expr, _cast_ty) = arg.kind;
if let ExprKind::Lit(ref lit) = inner_expr.kind;
if let LitKind::Int(0, _) = lit.node;
then {
span_lint(cx, TRANSMUTING_NULL, expr.span, LINT_MSG);
return true;
}
}
// Catching:
// `std::mem::transmute(std::ptr::null::<i32>())`
if_chain! {
if let ExprKind::Call(func1, []) = arg.kind;
if is_path_diagnostic_item(cx, func1, sym::ptr_null);
then {
span_lint(cx, TRANSMUTING_NULL, expr.span, LINT_MSG);
return true;
}
}
// FIXME:
// Also catch transmutations of variables which are known nulls.
// To do this, MIR const propagation seems to be the better tool.
// Whenever MIR const prop routines are more developed, this will
// become available. As of this writing (25/03/19) it is not yet.
false
}
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