test that we check the layout constraints as early as we can

Author: RalfJung

tests/compile-fail/nonzero.rs

@@ -0,0 +1,11 @@
+#![feature(rustc_attrs)]
+#![allow(unused_attributes)]
+
+#[rustc_layout_scalar_valid_range_start(1)]
+#[repr(transparent)]
+pub(crate) struct NonZero<T>(pub(crate) T);
+
+fn main() {
+    // Make sure that we detect this even when no function call is happening along the way
+    let _x = Some(NonZero(0)); //~ ERROR encountered 0, but expected something greater or equal to 1
+}