1 use clippy_utils::consts::{constant_context, Constant};
2 use clippy_utils::diagnostics::span_lint;
3 use clippy_utils::is_expr_diagnostic_item;
4 use if_chain::if_chain;
5 use rustc_ast::LitKind;
6 use rustc_hir::{Expr, ExprKind};
7 use rustc_lint::{LateContext, LateLintPass, LintContext};
8 use rustc_middle::lint::in_external_macro;
9 use rustc_session::{declare_lint_pass, declare_tool_lint};
10 use rustc_span::symbol::sym;
12 declare_clippy_lint! {
14 /// Checks for transmute calls which would receive a null pointer.
16 /// ### Why is this bad?
17 /// Transmuting a null pointer is undefined behavior.
19 /// ### Known problems
20 /// Not all cases can be detected at the moment of this writing.
21 /// For example, variables which hold a null pointer and are then fed to a `transmute`
22 /// call, aren't detectable yet.
26 /// let null_ref: &u64 = unsafe { std::mem::transmute(0 as *const u64) };
30 "transmutes from a null pointer to a reference, which is undefined behavior"
33 declare_lint_pass!(TransmutingNull => [TRANSMUTING_NULL]);
35 const LINT_MSG: &str = "transmuting a known null pointer into a reference";
37 impl<'tcx> LateLintPass<'tcx> for TransmutingNull {
38 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
39 if in_external_macro(cx.sess(), expr.span) {
44 if let ExprKind::Call(func, [arg]) = expr.kind;
45 if is_expr_diagnostic_item(cx, func, sym::transmute);
48 // Catching transmute over constants that resolve to `null`.
49 let mut const_eval_context = constant_context(cx, cx.typeck_results());
51 if let ExprKind::Path(ref _qpath) = arg.kind;
52 if let Some(Constant::RawPtr(x)) = const_eval_context.expr(arg);
55 span_lint(cx, TRANSMUTING_NULL, expr.span, LINT_MSG)
60 // `std::mem::transmute(0 as *const i32)`
62 if let ExprKind::Cast(inner_expr, _cast_ty) = arg.kind;
63 if let ExprKind::Lit(ref lit) = inner_expr.kind;
64 if let LitKind::Int(0, _) = lit.node;
66 span_lint(cx, TRANSMUTING_NULL, expr.span, LINT_MSG)
71 // `std::mem::transmute(std::ptr::null::<i32>())`
73 if let ExprKind::Call(func1, []) = arg.kind;
74 if is_expr_diagnostic_item(cx, func1, sym::ptr_null);
76 span_lint(cx, TRANSMUTING_NULL, expr.span, LINT_MSG)
81 // Also catch transmutations of variables which are known nulls.
82 // To do this, MIR const propagation seems to be the better tool.
83 // Whenever MIR const prop routines are more developed, this will
84 // become available. As of this writing (25/03/19) it is not yet.