Auto merge of #119614 - RalfJung:const-refs-to-static, r=oli-obk

unstably allow constants to refer to statics and read from immutable statics

I am not aware of any fundamental reason why we cannot allow constants to mention statics. What we really need is that constants do not *read from* statics that can change their value:
- This would break the principle that "constants behave as-if their expression was inlined everywhere and executed at runtime". This is enforced by halting const-eval interpretation when a read from a mutable global occurs.
- When building a valtree we want to be sure that the constant and everything it refers to is truly immutable. This is enforced by aborting valtree construction when a read from a mutable global occurs.

r? `@oli-obk` -- if you are okay with experimenting with this feature, I will create a tracking issue.
Based on and blocked on rust-lang/rust#119044; only the last commit is new.

Author: bors

src/diagnostics.rs

@@ -290,7 +290,7 @@ pub fn report_error<'tcx, 'mir>(
                 ) =>
             {
                 ecx.handle_ice(); // print interpreter backtrace
-                bug!("This validation error should be impossible in Miri: {}", ecx.format_error(e));
+                bug!("This validation error should be impossible in Miri: {}", format_interp_error(ecx.tcx.dcx(), e));
             }
             UndefinedBehavior(_) => "Undefined Behavior",
             ResourceExhaustion(_) => "resource exhaustion",
@@ -304,7 +304,7 @@ pub fn report_error<'tcx, 'mir>(
             ) => "post-monomorphization error",
             _ => {
                 ecx.handle_ice(); // print interpreter backtrace
-                bug!("This error should be impossible in Miri: {}", ecx.format_error(e));
+                bug!("This error should be impossible in Miri: {}", format_interp_error(ecx.tcx.dcx(), e));
             }
         };
         #[rustfmt::skip]
@@ -370,7 +370,7 @@ pub fn report_error<'tcx, 'mir>(
         _ => {}
     }
 
-    msg.insert(0, ecx.format_error(e));
+    msg.insert(0, format_interp_error(ecx.tcx.dcx(), e));
 
     report_msg(
         DiagLevel::Error,