Don't remove explicit cast to trait object pointer (#15145)

Fixes #15141

----

changelog: [`borrow_as_ptr`]: do not remove cast to trait object pointer

Author: llogiq

clippy_lints/src/casts/borrow_as_ptr.rs

@@ -18,7 +18,8 @@ pub(super) fn check<'tcx>(
     cast_to: &'tcx Ty<'_>,
     msrv: Msrv,
 ) -> bool {
-    if matches!(cast_to.kind, TyKind::Ptr(_))
+    if let TyKind::Ptr(target) = cast_to.kind
+        && !matches!(target.ty.kind, TyKind::TraitObject(..))
         && let ExprKind::AddrOf(BorrowKind::Ref, mutability, e) = cast_expr.kind
         && !is_lint_allowed(cx, BORROW_AS_PTR, expr.hir_id)
     {

tests/ui/borrow_as_ptr.fixed

@@ -47,3 +47,9 @@ fn implicit_cast() {
     // Do not lint references to temporaries
     core::ptr::eq(&0i32, &1i32);
 }
+
+fn issue_15141() {
+    let a = String::new();
+    // Don't lint cast to dyn trait pointers
+    let b = &a as *const dyn std::any::Any;
+}

tests/ui/borrow_as_ptr.rs

@@ -47,3 +47,9 @@ fn implicit_cast() {
     // Do not lint references to temporaries
     core::ptr::eq(&0i32, &1i32);
 }
+
+fn issue_15141() {
+    let a = String::new();
+    // Don't lint cast to dyn trait pointers
+    let b = &a as *const dyn std::any::Any;
+}