make it possible for outside crates to inspect a mir::ConstValue with the interpreter

compiler/rustc_const_eval/src/util/caller_location.rs

@@ -6,7 +6,7 @@ use rustc_middle::ty::layout::LayoutOf;
 use rustc_span::symbol::Symbol;
 use rustc_type_ir::Mutability;
 
-use crate::const_eval::{mk_eval_cx, CanAccessMutGlobal, CompileTimeEvalContext};
+use crate::const_eval::{mk_eval_cx_to_read_const_val, CanAccessMutGlobal, CompileTimeEvalContext};
 use crate::interpret::*;
 
 /// Allocate a `const core::panic::Location` with the provided filename and line/column numbers.
@@ -57,7 +57,12 @@ pub(crate) fn const_caller_location_provider(
     col: u32,
 ) -> mir::ConstValue<'_> {
     trace!("const_caller_location: {}:{}:{}", file, line, col);
-    let mut ecx = mk_eval_cx(tcx.tcx, tcx.span, ty::ParamEnv::reveal_all(), CanAccessMutGlobal::No);
+    let mut ecx = mk_eval_cx_to_read_const_val(
+        tcx.tcx,
+        tcx.span,
+        ty::ParamEnv::reveal_all(),
+        CanAccessMutGlobal::No,
+    );
 
     let loc_place = alloc_caller_location(&mut ecx, file, line, col);
     if intern_const_alloc_recursive(&mut ecx, InternKind::Constant, &loc_place).is_err() {