1 files changed, 50 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/transmute/transmuting_null.rs b/src/tools/clippy/clippy_lints/src/transmute/transmuting_null.rs
new file mode 100644
index 000000000..19ce5ae72
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/transmute/transmuting_null.rs
@@ -0,0 +1,50 @@
+use clippy_utils::consts::{constant_context, Constant};
+use clippy_utils::diagnostics::span_lint;
+use clippy_utils::{is_integer_literal, is_path_diagnostic_item};
+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 let ExprKind::Path(ref _qpath) = arg.kind &&
+        let Some(Constant::RawPtr(x)) = const_eval_context.expr(arg) &&
+        x == 0
+    {
+        span_lint(cx, TRANSMUTING_NULL, expr.span, LINT_MSG);
+        return true;
+    }
+
+    // Catching:
+    // `std::mem::transmute(0 as *const i32)`
+    if let ExprKind::Cast(inner_expr, _cast_ty) = arg.kind && is_integer_literal(inner_expr, 0) {
+        span_lint(cx, TRANSMUTING_NULL, expr.span, LINT_MSG);
+        return true;
+    }
+
+    // Catching:
+    // `std::mem::transmute(std::ptr::null::<i32>())`
+    if let ExprKind::Call(func1, []) = arg.kind &&
+        is_path_diagnostic_item(cx, func1, sym::ptr_null)
+    {
+        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
+}