Auto merge of #2039 - RalfJung:too-big, r=RalfJung

another test for too big type

The existing test covers "slice is bigger than largest supported object" but we had no test covering "total size is bigger than largest supported object", which happens when the unsized tail itself is okay in terms of size, but together with the sized prefix it becomes too big.

Cc rust-lang/rust#95334

Author: bors

tests/compile-fail/slice-too-big.rs renamed to tests/compile-fail/too-big-slice.rs

@@ -0,0 +1,18 @@
+use std::mem;
+
+#[allow(unused)]
+struct MySlice {
+    prefix: u64,
+    tail: [u8],
+}
+
+#[cfg(target_pointer_width = "64")]
+const TOO_BIG: usize = 1usize << 47;
+#[cfg(target_pointer_width = "32")]
+const TOO_BIG: usize = 1usize << 31;
+
+fn main() { unsafe {
+    let ptr = Box::into_raw(Box::new(0u8));
+    // The slice part is actually not "too big", but together with the `prefix` field it is.
+    let _x: &MySlice = mem::transmute((ptr, TOO_BIG-1)); //~ ERROR: invalid reference metadata: total size is bigger than largest supported object
+} }