add test for sketchy vtable

Author: RalfJung

tests/compile-fail/issue-miri-1112.rs

@@ -0,0 +1,46 @@
+trait Empty {}
+
+#[repr(transparent)]
+pub struct FunnyPointer(dyn Empty);
+
+#[repr(C)]
+pub struct Meta {
+    drop_fn: fn(&mut ()),
+    size: usize,
+    align: usize,
+}
+
+impl Meta {
+    pub fn new() -> Self {
+        Meta {
+            drop_fn: |_| {},
+            size: 0,
+            align: 1,
+        }
+    }
+}
+
+#[repr(C)]
+pub struct FatPointer {
+    pub data: *const (),
+    pub vtable: *const (),
+}
+
+impl FunnyPointer {
+    pub unsafe fn from_data_ptr(data: &String, ptr: *const Meta) -> &Self {
+        let obj = FatPointer {
+            data: data as *const _ as *const (),
+            vtable: ptr as *const _ as *const (),
+        };
+        let obj = std::mem::transmute::<FatPointer, *mut FunnyPointer>(obj); //~ ERROR invalid drop fn in vtable
+        &*obj
+    }
+}
+
+fn main() {
+    unsafe {
+        let meta = Meta::new();
+        let hello = "hello".to_string();
+        let _raw: &FunnyPointer = FunnyPointer::from_data_ptr(&hello, &meta as *const _);
+    }
+}