test fast path offset reporting

src/test/ui/consts/const-eval/ub-int-array.rs

@@ -0,0 +1,65 @@
+#![feature(const_transmute)]
+#![allow(const_err)] // make sure we cannot allow away the errors tested here
+
+//! Test the "array of int" fast path in validity checking, and in particular whether it
+//! points at the right array element.
+
+use std::mem;
+
+#[repr(C)]
+union MaybeUninit<T: Copy> {
+    uninit: (),
+    init: T,
+}
+
+const UNINIT_INT_0: [u32; 3] = unsafe {
+//~^ ERROR it is undefined behavior to use this value
+//~| type validation failed: encountered uninitialized bytes at [0]
+    [
+        MaybeUninit { uninit: () }.init,
+        1,
+        2,
+    ]
+};
+const UNINIT_INT_1: [u32; 3] = unsafe {
+//~^ ERROR it is undefined behavior to use this value
+//~| type validation failed: encountered uninitialized bytes at [1]
+    mem::transmute(
+        [
+            0u8,
+            0u8,
+            0u8,
+            0u8,
+            1u8,
+            MaybeUninit { uninit: () }.init,
+            1u8,
+            1u8,
+            2u8,
+            2u8,
+            MaybeUninit { uninit: () }.init,
+            2u8,
+        ]
+    )
+};
+const UNINIT_INT_2: [u32; 3] = unsafe {
+//~^ ERROR it is undefined behavior to use this value
+//~| type validation failed: encountered uninitialized bytes at [2]
+    mem::transmute(
+        [
+            0u8,
+            0u8,
+            0u8,
+            0u8,
+            1u8,
+            1u8,
+            1u8,
+            1u8,
+            2u8,
+            2u8,
+            2u8,
+            MaybeUninit { uninit: () }.init,
+        ]
+    )
+};
+
+fn main() {}