Also consider transmute with the invalid_reference_casting lint

compiler/rustc_lint/src/reference_casting.rs

@@ -98,6 +98,7 @@ fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
 fn is_cast_from_const_to_mut<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'tcx>) -> bool {
     let e = e.peel_blocks();
 
+    fn from_casts<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'tcx>) -> Option<&'tcx Expr<'tcx>> {
         // <expr> as *mut ...
         let e = if let ExprKind::Cast(e, t) = e.kind
             && let ty::RawPtr(TypeAndMut { mutbl: Mutability::Mut, .. }) = cx.typeck_results().node_type(t.hir_id).kind() {
@@ -108,7 +109,7 @@ fn is_cast_from_const_to_mut<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'tcx>)
             && cx.tcx.is_diagnostic_item(sym::ptr_cast_mut, def_id) {
             expr
         } else {
-        return false;
+            return None;
         };
 
         let e = e.peel_blocks();
@@ -124,6 +125,29 @@ fn is_cast_from_const_to_mut<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'tcx>)
             && cx.tcx.is_diagnostic_item(sym::ptr_from_ref, def_id) {
             arg
         } else {
+            return None;
+        };
+
+        Some(e)
+    }
+
+    fn from_transmute<'tcx>(
+        cx: &LateContext<'tcx>,
+        e: &'tcx Expr<'tcx>,
+    ) -> Option<&'tcx Expr<'tcx>> {
+        // mem::transmute::<_, *mut _>(<expr>)
+        if let ExprKind::Call(path, [arg]) = e.kind
+            && let ExprKind::Path(ref qpath) = path.kind
+            && let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id()
+            && cx.tcx.is_diagnostic_item(sym::transmute, def_id)
+            && let ty::RawPtr(TypeAndMut { mutbl: Mutability::Mut, .. }) = cx.typeck_results().node_type(e.hir_id).kind() {
+            Some(arg)
+        } else {
+            None
+        }
+    }
+
+    let Some(e) = from_casts(cx, e).or_else(|| from_transmute(cx, e)) else {
         return false;
     };
 

tests/ui/lint/reference_casting.rs

@@ -24,6 +24,8 @@ unsafe fn ref_to_mut() {
     //~^ ERROR casting `&T` to `&mut T` is undefined behavior
     let _num = &mut *(std::ptr::from_ref({ num }) as *mut i32);
     //~^ ERROR casting `&T` to `&mut T` is undefined behavior
+    let _num = &mut *std::mem::transmute::<_, *mut i32>(num);
+    //~^ ERROR casting `&T` to `&mut T` is undefined behavior
 
     let deferred = num as *const i32 as *mut i32;
     let _num = &mut *deferred;
@@ -47,6 +49,9 @@ unsafe fn assign_to_ref() {
     //~^ ERROR assigning to `&T` is undefined behavior
     *(std::ptr::from_ref({ num }) as *mut i32) += 1;
     //~^ ERROR assigning to `&T` is undefined behavior
+    *std::mem::transmute::<_, *mut i32>(num) += 1;
+    //~^ ERROR assigning to `&T` is undefined behavior
+
     let value = num as *const i32 as *mut i32;
     *value = 1;
     //~^ ERROR assigning to `&T` is undefined behavior

tests/ui/lint/reference_casting.stderr

@@ -37,7 +37,13 @@ LL |     let _num = &mut *(std::ptr::from_ref({ num }) as *mut i32);
    |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
-  --> $DIR/reference_casting.rs:29:16
+  --> $DIR/reference_casting.rs:27:16
+   |
+LL |     let _num = &mut *std::mem::transmute::<_, *mut i32>(num);
+   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
+  --> $DIR/reference_casting.rs:31:16
    |
 LL |     let deferred = num as *const i32 as *mut i32;
    |                    ----------------------------- casting happend here
@@ -45,48 +51,54 @@ LL |     let _num = &mut *deferred;
    |                ^^^^^^^^^^^^^^
 
 error: assigning to `&T` is undefined behavior, consider using an `UnsafeCell`
-  --> $DIR/reference_casting.rs:38:5
+  --> $DIR/reference_casting.rs:40:5
    |
 LL |     *(a as *const _ as *mut _) = String::from("Replaced");
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: assigning to `&T` is undefined behavior, consider using an `UnsafeCell`
-  --> $DIR/reference_casting.rs:40:5
+  --> $DIR/reference_casting.rs:42:5
    |
 LL |     *(a as *const _ as *mut String) += " world";
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: assigning to `&T` is undefined behavior, consider using an `UnsafeCell`
-  --> $DIR/reference_casting.rs:42:5
+  --> $DIR/reference_casting.rs:44:5
    |
 LL |     *std::ptr::from_ref(num).cast_mut() += 1;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: assigning to `&T` is undefined behavior, consider using an `UnsafeCell`
-  --> $DIR/reference_casting.rs:44:5
+  --> $DIR/reference_casting.rs:46:5
    |
 LL |     *std::ptr::from_ref({ num }).cast_mut() += 1;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: assigning to `&T` is undefined behavior, consider using an `UnsafeCell`
-  --> $DIR/reference_casting.rs:46:5
+  --> $DIR/reference_casting.rs:48:5
    |
 LL |     *{ std::ptr::from_ref(num) }.cast_mut() += 1;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: assigning to `&T` is undefined behavior, consider using an `UnsafeCell`
-  --> $DIR/reference_casting.rs:48:5
+  --> $DIR/reference_casting.rs:50:5
    |
 LL |     *(std::ptr::from_ref({ num }) as *mut i32) += 1;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: assigning to `&T` is undefined behavior, consider using an `UnsafeCell`
-  --> $DIR/reference_casting.rs:51:5
+  --> $DIR/reference_casting.rs:52:5
+   |
+LL |     *std::mem::transmute::<_, *mut i32>(num) += 1;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: assigning to `&T` is undefined behavior, consider using an `UnsafeCell`
+  --> $DIR/reference_casting.rs:56:5
    |
 LL |     let value = num as *const i32 as *mut i32;
    |                 ----------------------------- casting happend here
 LL |     *value = 1;
    |     ^^^^^^^^^^
 
-error: aborting due to 14 previous errors
+error: aborting due to 16 previous errors