Don't emit null pointer lint for raw ref of null deref

Author: compiler-errors

compiler/rustc_lint/src/builtin.rs

@@ -2679,8 +2679,8 @@ declare_lint! {
     ///
     /// ### Explanation
     ///
-    /// Dereferencing a null pointer causes [undefined behavior] even as a place expression,
-    /// like `&*(0 as *const i32)` or `addr_of!(*(0 as *const i32))`.
+    /// Dereferencing a null pointer causes [undefined behavior] if it is accessed
+    /// (loaded from or stored to).
     ///
     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
     pub DEREF_NULLPTR,
@@ -2695,14 +2695,14 @@ impl<'tcx> LateLintPass<'tcx> for DerefNullPtr {
         /// test if expression is a null ptr
         fn is_null_ptr(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> bool {
             match &expr.kind {
-                rustc_hir::ExprKind::Cast(expr, ty) => {
-                    if let rustc_hir::TyKind::Ptr(_) = ty.kind {
+                hir::ExprKind::Cast(expr, ty) => {
+                    if let hir::TyKind::Ptr(_) = ty.kind {
                         return is_zero(expr) || is_null_ptr(cx, expr);
                     }
                 }
                 // check for call to `core::ptr::null` or `core::ptr::null_mut`
-                rustc_hir::ExprKind::Call(path, _) => {
-                    if let rustc_hir::ExprKind::Path(ref qpath) = path.kind {
+                hir::ExprKind::Call(path, _) => {
+                    if let hir::ExprKind::Path(ref qpath) = path.kind {
                         if let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id() {
                             return matches!(
                                 cx.tcx.get_diagnostic_name(def_id),
@@ -2719,7 +2719,7 @@ impl<'tcx> LateLintPass<'tcx> for DerefNullPtr {
         /// test if expression is the literal `0`
         fn is_zero(expr: &hir::Expr<'_>) -> bool {
             match &expr.kind {
-                rustc_hir::ExprKind::Lit(lit) => {
+                hir::ExprKind::Lit(lit) => {
                     if let LitKind::Int(a, _) = lit.node {
                         return a == 0;
                     }
@@ -2729,8 +2729,16 @@ impl<'tcx> LateLintPass<'tcx> for DerefNullPtr {
             false
         }
 
-        if let rustc_hir::ExprKind::Unary(rustc_hir::UnOp::Deref, expr_deref) = expr.kind {
-            if is_null_ptr(cx, expr_deref) {
+        if let hir::ExprKind::Unary(hir::UnOp::Deref, expr_deref) = expr.kind
+            && is_null_ptr(cx, expr_deref)
+        {
+            if let hir::Node::Expr(hir::Expr {
+                kind: hir::ExprKind::AddrOf(hir::BorrowKind::Raw, ..),
+                ..
+            }) = cx.tcx.parent_hir_node(expr.hir_id)
+            {
+                // `&raw *NULL` is ok.
+            } else {
                 cx.emit_span_lint(
                     DEREF_NULLPTR,
                     expr.span,

tests/ui/lint/lint-deref-nullptr.rs

@@ -27,9 +27,9 @@ fn f() {
         let ub = &*ptr::null_mut::<i32>();
         //~^ ERROR dereferencing a null pointer
         ptr::addr_of!(*ptr::null::<i32>());
-        //~^ ERROR dereferencing a null pointer
+        // ^^ OKAY
         ptr::addr_of_mut!(*ptr::null_mut::<i32>());
-        //~^ ERROR dereferencing a null pointer
+        // ^^ OKAY
         let offset = ptr::addr_of!((*ptr::null::<Struct>()).field);
         //~^ ERROR dereferencing a null pointer
     }

tests/ui/lint/lint-deref-nullptr.stderr

@@ -46,23 +46,11 @@ error: dereferencing a null pointer
 LL |         let ub = &*ptr::null_mut::<i32>();
    |                   ^^^^^^^^^^^^^^^^^^^^^^^ this code causes undefined behavior when executed
 
-error: dereferencing a null pointer
-  --> $DIR/lint-deref-nullptr.rs:29:23
-   |
-LL |         ptr::addr_of!(*ptr::null::<i32>());
-   |                       ^^^^^^^^^^^^^^^^^^^ this code causes undefined behavior when executed
-
-error: dereferencing a null pointer
-  --> $DIR/lint-deref-nullptr.rs:31:27
-   |
-LL |         ptr::addr_of_mut!(*ptr::null_mut::<i32>());
-   |                           ^^^^^^^^^^^^^^^^^^^^^^^ this code causes undefined behavior when executed
-
 error: dereferencing a null pointer
   --> $DIR/lint-deref-nullptr.rs:33:36
    |
 LL |         let offset = ptr::addr_of!((*ptr::null::<Struct>()).field);
    |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ this code causes undefined behavior when executed
 
-error: aborting due to 10 previous errors
+error: aborting due to 8 previous errors