Rollup merge of #109435 - oli-obk:🇨🇭🥚_copy_op, r=RalfJung

Detect uninhabited types early in const eval

r? `@RalfJung`

implements https://github.com/rust-lang/rust/pull/108442#discussion_r1143003840

this is a breaking change, as some UB during const eval is now detected instead of silently being ignored. Users can see this and other UB that may cause future breakage with `-Zextra-const-ub-checks` or just by running miri on their code, which sets that flag by default.

compiler/rustc_const_eval/src/const_eval/machine.rs

@@ -2,7 +2,7 @@ use rustc_hir::def::DefKind;
 use rustc_hir::{LangItem, CRATE_HIR_ID};
 use rustc_middle::mir;
 use rustc_middle::mir::interpret::PointerArithmetic;
-use rustc_middle::ty::layout::FnAbiOf;
+use rustc_middle::ty::layout::{FnAbiOf, TyAndLayout};
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_session::lint::builtin::INVALID_ALIGNMENT;
 use std::borrow::Borrow;
@@ -335,8 +335,8 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
     }
 
     #[inline(always)]
-    fn enforce_validity(ecx: &InterpCx<'mir, 'tcx, Self>) -> bool {
-        ecx.tcx.sess.opts.unstable_opts.extra_const_ub_checks
+    fn enforce_validity(ecx: &InterpCx<'mir, 'tcx, Self>, layout: TyAndLayout<'tcx>) -> bool {
+        ecx.tcx.sess.opts.unstable_opts.extra_const_ub_checks || layout.abi.is_uninhabited()
     }
 
     fn alignment_check_failed(